US20160236176A1 - Method of making highly porous, stable aluminum oxides doped with silicon - Google Patents
Method of making highly porous, stable aluminum oxides doped with silicon Download PDFInfo
- Publication number
- US20160236176A1 US20160236176A1 US15/056,461 US201615056461A US2016236176A1 US 20160236176 A1 US20160236176 A1 US 20160236176A1 US 201615056461 A US201615056461 A US 201615056461A US 2016236176 A1 US2016236176 A1 US 2016236176A1
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- US
- United States
- Prior art keywords
- aluminum
- alumina
- silica
- organic silicon
- calcination
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
- Abandoned
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- PNEYBMLMFCGWSK-UHFFFAOYSA-N Alumina Chemical class [O-2].[O-2].[O-2].[Al+3].[Al+3] PNEYBMLMFCGWSK-UHFFFAOYSA-N 0.000 title claims abstract description 102
- 229910052710 silicon Inorganic materials 0.000 title abstract description 6
- 239000010703 silicon Substances 0.000 title abstract description 6
- 238000004519 manufacturing process Methods 0.000 title description 7
- 239000011148 porous material Substances 0.000 claims abstract description 61
- 238000000034 method Methods 0.000 claims abstract description 44
- 238000001354 calcination Methods 0.000 claims abstract description 36
- XLYOFNOQVPJJNP-UHFFFAOYSA-N water Substances O XLYOFNOQVPJJNP-UHFFFAOYSA-N 0.000 claims abstract description 27
- 150000003377 silicon compounds Chemical class 0.000 claims abstract description 21
- AZDRQVAHHNSJOQ-UHFFFAOYSA-N alumane Chemical class [AlH3] AZDRQVAHHNSJOQ-UHFFFAOYSA-N 0.000 claims abstract description 11
- TWNQGVIAIRXVLR-UHFFFAOYSA-N oxo(oxoalumanyloxy)alumane Chemical compound O=[Al]O[Al]=O TWNQGVIAIRXVLR-UHFFFAOYSA-N 0.000 claims abstract description 11
- 238000006243 chemical reaction Methods 0.000 claims abstract description 7
- VYPSYNLAJGMNEJ-UHFFFAOYSA-N Silicium dioxide Chemical compound O=[Si]=O VYPSYNLAJGMNEJ-UHFFFAOYSA-N 0.000 claims description 112
- 239000000377 silicon dioxide Substances 0.000 claims description 56
- BOTDANWDWHJENH-UHFFFAOYSA-N Tetraethyl orthosilicate Chemical compound CCO[Si](OCC)(OCC)OCC BOTDANWDWHJENH-UHFFFAOYSA-N 0.000 claims description 31
- 239000002243 precursor Substances 0.000 claims description 23
- SMZOGRDCAXLAAR-UHFFFAOYSA-N aluminium isopropoxide Chemical compound [Al+3].CC(C)[O-].CC(C)[O-].CC(C)[O-] SMZOGRDCAXLAAR-UHFFFAOYSA-N 0.000 claims description 18
- 235000013870 dimethyl polysiloxane Nutrition 0.000 claims description 17
- 239000004205 dimethyl polysiloxane Substances 0.000 claims description 17
- 229920000435 poly(dimethylsiloxane) Polymers 0.000 claims description 16
- 229910052782 aluminium Inorganic materials 0.000 claims description 13
- -1 aluminum alkoxide Chemical class 0.000 claims description 13
- ZQZCOBSUOFHDEE-UHFFFAOYSA-N tetrapropyl silicate Chemical compound CCCO[Si](OCCC)(OCCC)OCCC ZQZCOBSUOFHDEE-UHFFFAOYSA-N 0.000 claims description 13
- WOZZOSDBXABUFO-UHFFFAOYSA-N tri(butan-2-yloxy)alumane Chemical compound [Al+3].CCC(C)[O-].CCC(C)[O-].CCC(C)[O-] WOZZOSDBXABUFO-UHFFFAOYSA-N 0.000 claims description 13
- MDDPTCUZZASZIQ-UHFFFAOYSA-N tris[(2-methylpropan-2-yl)oxy]alumane Chemical compound [Al+3].CC(C)(C)[O-].CC(C)(C)[O-].CC(C)(C)[O-] MDDPTCUZZASZIQ-UHFFFAOYSA-N 0.000 claims description 13
- 239000000203 mixture Substances 0.000 claims description 11
- JPUHCPXFQIXLMW-UHFFFAOYSA-N aluminium triethoxide Chemical compound CCO[Al](OCC)OCC JPUHCPXFQIXLMW-UHFFFAOYSA-N 0.000 claims description 9
- 239000000047 product Substances 0.000 claims description 9
- OPSWAWSNPREEFQ-UHFFFAOYSA-K triphenoxyalumane Chemical compound [Al+3].[O-]C1=CC=CC=C1.[O-]C1=CC=CC=C1.[O-]C1=CC=CC=C1 OPSWAWSNPREEFQ-UHFFFAOYSA-K 0.000 claims description 9
- 239000012467 final product Substances 0.000 claims description 8
- 239000002105 nanoparticle Substances 0.000 claims description 8
- LFQSCWFLJHTTHZ-UHFFFAOYSA-N Ethanol Chemical compound CCO LFQSCWFLJHTTHZ-UHFFFAOYSA-N 0.000 claims description 7
- 238000002156 mixing Methods 0.000 claims description 7
- 125000004400 (C1-C12) alkyl group Chemical group 0.000 claims description 6
- 125000003118 aryl group Chemical group 0.000 claims description 5
- 239000003085 diluting agent Substances 0.000 claims description 5
- 239000000376 reactant Substances 0.000 claims description 5
- RTZKZFJDLAIYFH-UHFFFAOYSA-N Diethyl ether Chemical compound CCOCC RTZKZFJDLAIYFH-UHFFFAOYSA-N 0.000 claims description 4
- 150000001875 compounds Chemical class 0.000 claims description 3
- 150000002576 ketones Chemical class 0.000 claims description 2
- QFCVQKSWGFVMTB-UHFFFAOYSA-N trihexoxyalumane Chemical compound [Al+3].CCCCCC[O-].CCCCCC[O-].CCCCCC[O-] QFCVQKSWGFVMTB-UHFFFAOYSA-N 0.000 claims description 2
- CPUDPFPXCZDNGI-UHFFFAOYSA-N triethoxy(methyl)silane Chemical compound CCO[Si](C)(OCC)OCC CPUDPFPXCZDNGI-UHFFFAOYSA-N 0.000 claims 1
- 239000003054 catalyst Substances 0.000 abstract description 19
- 239000000463 material Substances 0.000 abstract description 18
- 239000002904 solvent Substances 0.000 abstract description 16
- 230000002950 deficient Effects 0.000 abstract description 12
- 238000006555 catalytic reaction Methods 0.000 abstract description 10
- 239000003153 chemical reaction reagent Substances 0.000 abstract description 7
- 238000005245 sintering Methods 0.000 abstract description 6
- 239000007787 solid Substances 0.000 abstract description 6
- XUIMIQQOPSSXEZ-UHFFFAOYSA-N Silicon Chemical compound [Si] XUIMIQQOPSSXEZ-UHFFFAOYSA-N 0.000 abstract description 5
- 239000002019 doping agent Substances 0.000 abstract description 4
- 150000004703 alkoxides Chemical class 0.000 abstract description 3
- 229910010293 ceramic material Inorganic materials 0.000 abstract description 3
- 230000000694 effects Effects 0.000 abstract 1
- 238000002441 X-ray diffraction Methods 0.000 description 22
- NKLYMYLJOXIVFB-UHFFFAOYSA-N triethoxymethylsilane Chemical compound CCOC([SiH3])(OCC)OCC NKLYMYLJOXIVFB-UHFFFAOYSA-N 0.000 description 14
- 230000000052 comparative effect Effects 0.000 description 11
- 238000010438 heat treatment Methods 0.000 description 10
- RMAQACBXLXPBSY-UHFFFAOYSA-N silicic acid Chemical compound O[Si](O)(O)O RMAQACBXLXPBSY-UHFFFAOYSA-N 0.000 description 10
- 235000012239 silicon dioxide Nutrition 0.000 description 10
- XAGFODPZIPBFFR-UHFFFAOYSA-N aluminium Chemical compound [Al] XAGFODPZIPBFFR-UHFFFAOYSA-N 0.000 description 8
- 238000001035 drying Methods 0.000 description 7
- 239000002002 slurry Substances 0.000 description 7
- 229910003158 γ-Al2O3 Inorganic materials 0.000 description 7
- 239000006227 byproduct Substances 0.000 description 6
- 230000007704 transition Effects 0.000 description 6
- BNGXYYYYKUGPPF-UHFFFAOYSA-M (3-methylphenyl)methyl-triphenylphosphanium;chloride Chemical compound [Cl-].CC1=CC=CC(C[P+](C=2C=CC=CC=2)(C=2C=CC=CC=2)C=2C=CC=CC=2)=C1 BNGXYYYYKUGPPF-UHFFFAOYSA-M 0.000 description 5
- 229910000525 Si/Al2O3 Inorganic materials 0.000 description 5
- 230000008901 benefit Effects 0.000 description 5
- FYDKNKUEBJQCCN-UHFFFAOYSA-N lanthanum(3+);trinitrate Chemical compound [La+3].[O-][N+]([O-])=O.[O-][N+]([O-])=O.[O-][N+]([O-])=O FYDKNKUEBJQCCN-UHFFFAOYSA-N 0.000 description 5
- UQMOLLPKNHFRAC-UHFFFAOYSA-N tetrabutyl silicate Chemical compound CCCCO[Si](OCCCC)(OCCCC)OCCCC UQMOLLPKNHFRAC-UHFFFAOYSA-N 0.000 description 5
- BLRPTPMANUNPDV-UHFFFAOYSA-N Silane Chemical compound [SiH4] BLRPTPMANUNPDV-UHFFFAOYSA-N 0.000 description 4
- 230000007423 decrease Effects 0.000 description 4
- 150000003839 salts Chemical class 0.000 description 4
- 229910000077 silane Inorganic materials 0.000 description 4
- 0 *O[Si](O*)(O*)O* Chemical compound *O[Si](O*)(O*)O* 0.000 description 3
- 230000009849 deactivation Effects 0.000 description 3
- 238000001704 evaporation Methods 0.000 description 3
- 230000008020 evaporation Effects 0.000 description 3
- 239000007788 liquid Substances 0.000 description 3
- ISWSIDIOOBJBQZ-UHFFFAOYSA-M phenolate Chemical compound [O-]C1=CC=CC=C1 ISWSIDIOOBJBQZ-UHFFFAOYSA-M 0.000 description 3
- 229910052594 sapphire Inorganic materials 0.000 description 3
- 238000001179 sorption measurement Methods 0.000 description 3
- 239000000126 substance Substances 0.000 description 3
- 238000003917 TEM image Methods 0.000 description 2
- MCMNRKCIXSYSNV-UHFFFAOYSA-N Zirconium dioxide Chemical compound O=[Zr]=O MCMNRKCIXSYSNV-UHFFFAOYSA-N 0.000 description 2
- WNROFYMDJYEPJX-UHFFFAOYSA-K aluminium hydroxide Chemical compound [OH-].[OH-].[OH-].[Al+3] WNROFYMDJYEPJX-UHFFFAOYSA-K 0.000 description 2
- VXAUWWUXCIMFIM-UHFFFAOYSA-M aluminum;oxygen(2-);hydroxide Chemical compound [OH-].[O-2].[Al+3] VXAUWWUXCIMFIM-UHFFFAOYSA-M 0.000 description 2
- 230000015572 biosynthetic process Effects 0.000 description 2
- 230000003197 catalytic effect Effects 0.000 description 2
- 229910052593 corundum Inorganic materials 0.000 description 2
- 238000003795 desorption Methods 0.000 description 2
- KZHJGOXRZJKJNY-UHFFFAOYSA-N dioxosilane;oxo(oxoalumanyloxy)alumane Chemical compound O=[Si]=O.O=[Si]=O.O=[Al]O[Al]=O.O=[Al]O[Al]=O.O=[Al]O[Al]=O KZHJGOXRZJKJNY-UHFFFAOYSA-N 0.000 description 2
- 239000006185 dispersion Substances 0.000 description 2
- 238000009826 distribution Methods 0.000 description 2
- 238000002474 experimental method Methods 0.000 description 2
- 238000001914 filtration Methods 0.000 description 2
- FAHBNUUHRFUEAI-UHFFFAOYSA-M hydroxidooxidoaluminium Chemical compound O[Al]=O FAHBNUUHRFUEAI-UHFFFAOYSA-M 0.000 description 2
- 238000011065 in-situ storage Methods 0.000 description 2
- 229910052746 lanthanum Inorganic materials 0.000 description 2
- 239000012528 membrane Substances 0.000 description 2
- 229910052751 metal Inorganic materials 0.000 description 2
- 239000002184 metal Substances 0.000 description 2
- 229910044991 metal oxide Inorganic materials 0.000 description 2
- 238000012986 modification Methods 0.000 description 2
- 230000004048 modification Effects 0.000 description 2
- 229910052863 mullite Inorganic materials 0.000 description 2
- 229910052763 palladium Inorganic materials 0.000 description 2
- 229910052697 platinum Inorganic materials 0.000 description 2
- 238000002360 preparation method Methods 0.000 description 2
- 239000011164 primary particle Substances 0.000 description 2
- 238000001228 spectrum Methods 0.000 description 2
- 238000003756 stirring Methods 0.000 description 2
- 239000004094 surface-active agent Substances 0.000 description 2
- 239000000725 suspension Substances 0.000 description 2
- 238000003786 synthesis reaction Methods 0.000 description 2
- OBROYCQXICMORW-UHFFFAOYSA-N tripropoxyalumane Chemical compound [Al+3].CCC[O-].CCC[O-].CCC[O-] OBROYCQXICMORW-UHFFFAOYSA-N 0.000 description 2
- 238000005406 washing Methods 0.000 description 2
- 229910001845 yogo sapphire Inorganic materials 0.000 description 2
- UQEAIHBTYFGYIE-UHFFFAOYSA-N C[Si](C)(C)O[Si](C)(C)C Chemical compound C[Si](C)(C)O[Si](C)(C)C UQEAIHBTYFGYIE-UHFFFAOYSA-N 0.000 description 1
- BPQQTUXANYXVAA-UHFFFAOYSA-N Orthosilicate Chemical compound [O-][Si]([O-])([O-])[O-] BPQQTUXANYXVAA-UHFFFAOYSA-N 0.000 description 1
- ISWSIDIOOBJBQZ-UHFFFAOYSA-N Phenol Chemical class OC1=CC=CC=C1 ISWSIDIOOBJBQZ-UHFFFAOYSA-N 0.000 description 1
- 229910008425 Si—Al2O3 Inorganic materials 0.000 description 1
- 239000004115 Sodium Silicate Substances 0.000 description 1
- UCKMPCXJQFINFW-UHFFFAOYSA-N Sulphide Chemical compound [S-2] UCKMPCXJQFINFW-UHFFFAOYSA-N 0.000 description 1
- 239000002253 acid Substances 0.000 description 1
- 239000003463 adsorbent Substances 0.000 description 1
- 230000002776 aggregation Effects 0.000 description 1
- 238000004220 aggregation Methods 0.000 description 1
- 150000001298 alcohols Chemical class 0.000 description 1
- 125000000217 alkyl group Chemical group 0.000 description 1
- DIZPMCHEQGEION-UHFFFAOYSA-H aluminium sulfate (anhydrous) Chemical compound [Al+3].[Al+3].[O-]S([O-])(=O)=O.[O-]S([O-])(=O)=O.[O-]S([O-])(=O)=O DIZPMCHEQGEION-UHFFFAOYSA-H 0.000 description 1
- 239000011959 amorphous silica alumina Substances 0.000 description 1
- 239000007864 aqueous solution Substances 0.000 description 1
- 230000002902 bimodal effect Effects 0.000 description 1
- 239000000919 ceramic Substances 0.000 description 1
- 239000002738 chelating agent Substances 0.000 description 1
- 239000003795 chemical substances by application Substances 0.000 description 1
- 238000000975 co-precipitation Methods 0.000 description 1
- 238000002485 combustion reaction Methods 0.000 description 1
- 238000002447 crystallographic data Methods 0.000 description 1
- 230000003247 decreasing effect Effects 0.000 description 1
- 230000006866 deterioration Effects 0.000 description 1
- 238000009792 diffusion process Methods 0.000 description 1
- 238000010790 dilution Methods 0.000 description 1
- 239000012895 dilution Substances 0.000 description 1
- XYIBRDXRRQCHLP-UHFFFAOYSA-N ethyl acetoacetate Chemical compound CCOC(=O)CC(C)=O XYIBRDXRRQCHLP-UHFFFAOYSA-N 0.000 description 1
- 239000000446 fuel Substances 0.000 description 1
- 238000001483 high-temperature X-ray diffraction Methods 0.000 description 1
- 238000005984 hydrogenation reaction Methods 0.000 description 1
- 238000005470 impregnation Methods 0.000 description 1
- 239000003999 initiator Substances 0.000 description 1
- 229910052742 iron Inorganic materials 0.000 description 1
- FZLIPJUXYLNCLC-UHFFFAOYSA-N lanthanum atom Chemical compound [La] FZLIPJUXYLNCLC-UHFFFAOYSA-N 0.000 description 1
- 238000011068 loading method Methods 0.000 description 1
- 229910000000 metal hydroxide Inorganic materials 0.000 description 1
- 150000004692 metal hydroxides Chemical class 0.000 description 1
- 150000004706 metal oxides Chemical class 0.000 description 1
- 125000001624 naphthyl group Chemical group 0.000 description 1
- 229910052759 nickel Inorganic materials 0.000 description 1
- 239000003960 organic solvent Substances 0.000 description 1
- 125000001997 phenyl group Chemical group [H]C1=C([H])C([H])=C(*)C([H])=C1[H] 0.000 description 1
- 230000001376 precipitating effect Effects 0.000 description 1
- 238000001556 precipitation Methods 0.000 description 1
- 230000008569 process Effects 0.000 description 1
- 238000000746 purification Methods 0.000 description 1
- 229910052761 rare earth metal Inorganic materials 0.000 description 1
- 239000011541 reaction mixture Substances 0.000 description 1
- 230000035484 reaction time Effects 0.000 description 1
- 229910052703 rhodium Inorganic materials 0.000 description 1
- 238000000926 separation method Methods 0.000 description 1
- 150000004756 silanes Chemical class 0.000 description 1
- 150000004760 silicates Chemical class 0.000 description 1
- LIVNPJMFVYWSIS-UHFFFAOYSA-N silicon monoxide Chemical class [Si-]#[O+] LIVNPJMFVYWSIS-UHFFFAOYSA-N 0.000 description 1
- 229910052814 silicon oxide Inorganic materials 0.000 description 1
- 125000005374 siloxide group Chemical group 0.000 description 1
- 238000002791 soaking Methods 0.000 description 1
- NTHWMYGWWRZVTN-UHFFFAOYSA-N sodium silicate Chemical compound [Na+].[Na+].[O-][Si]([O-])=O NTHWMYGWWRZVTN-UHFFFAOYSA-N 0.000 description 1
- 229910052911 sodium silicate Inorganic materials 0.000 description 1
- 239000007858 starting material Substances 0.000 description 1
- 238000001308 synthesis method Methods 0.000 description 1
- 230000002194 synthesizing effect Effects 0.000 description 1
- 230000009466 transformation Effects 0.000 description 1
- 230000001131 transforming effect Effects 0.000 description 1
- LIJDDOXRYWAXQG-UHFFFAOYSA-N tripentoxyalumane Chemical compound CCCCCO[Al](OCCCCC)OCCCCC LIJDDOXRYWAXQG-UHFFFAOYSA-N 0.000 description 1
- 239000010457 zeolite Substances 0.000 description 1
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- B01J21/00—Catalysts comprising the elements, oxides, or hydroxides of magnesium, boron, aluminium, carbon, silicon, titanium, zirconium, or hafnium
- B01J21/12—Silica and alumina
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- B01J20/02—Solid sorbent compositions or filter aid compositions; Sorbents for chromatography; Processes for preparing, regenerating or reactivating thereof comprising inorganic material
- B01J20/10—Solid sorbent compositions or filter aid compositions; Sorbents for chromatography; Processes for preparing, regenerating or reactivating thereof comprising inorganic material comprising silica or silicate
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- C01F7/02—Aluminium oxide; Aluminium hydroxide; Aluminates
- C01F7/34—Preparation of aluminium hydroxide by precipitation from solutions containing aluminium salts
- C01F7/36—Preparation of aluminium hydroxide by precipitation from solutions containing aluminium salts from organic aluminium salts
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- C04B35/01—Shaped ceramic products characterised by their composition; Ceramics compositions; Processing powders of inorganic compounds preparatory to the manufacturing of ceramic products based on oxide ceramics
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- C01P2006/12—Surface area
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- C—CHEMISTRY; METALLURGY
- C01—INORGANIC CHEMISTRY
- C01P—INDEXING SCHEME RELATING TO STRUCTURAL AND PHYSICAL ASPECTS OF SOLID INORGANIC COMPOUNDS
- C01P2006/00—Physical properties of inorganic compounds
- C01P2006/14—Pore volume
Definitions
- Alumina is the most common catalyst support used in industry and it has numerous applications as a ceramic material.
- Gamma alumina ( ⁇ -Al 2 O 3 ) is preferred for many catalyst systems including Pt, Pd, and Ni for hydrogenation reactions, for Pt, Rh and Pd catalysts for internal combustion engine emissions control (CO, NOx), for Co(Ni)—Mo(W) sulfide catalysts for fuel hydrodesulfurization, and for Co and Fe catalysts for Fischer-Tropsch synthesis (FTS).
- Alumina is prepared inexpensively with a wide range of surface areas and porosities, and is more thermally stable than other metal oxide supports. There are three important properties in selecting an appropriate catalyst support.
- WO 2007/009680 discloses treatment of alumina with an organic siloxide, i.e. Si(OR) 4-n R′n including TEOS.
- U.S. Pat. No. 6,977,273 discloses impregnating Sasol Puralox gamma-alumina with TEOS.
- (3) US 2003/0162849, WO 03/012008, and US Patent 2005/0245623 discloses addition of TEOS/ethanol or other organic silicon compounds in ethanol to an alumina support to improve mechanical and thermal/hydrothermal stabilities and resistance to sintering.
- U.S. Pat. No. 4,392,988 discloses that soaking alumina in polydimethyl-siloxane increases thermal stability of alumina.
- EPO 2,392,548 describes a method for the preparation of an amorphous silica-alumina with acid properties like zeolites, using silica to alumina weight ratio of 2. The method includes: co-precipitation of alumina and silica by adding a base precipitating agent to an aqueous solution of sodium silicate and aluminum sulfate in presence of a gelification initiator (bohemite) followed by filtration and drying. After calcination at 550° C.
- the surface area and a pore volume are 400 m 2 /g and 1.2 cm 3 /g, respectively.
- the silica content in such silica-alumina is high which may make it less stable at higher temperatures.
- the acidity of this support is also high which make it undesirable for some catalytic reactions such as Fischer-Tropsch.
- EPO Patent 1,701,787 discloses a silica-modified-alumina with 2-10% silica using a cogel method. After calcination at 648° C., the material has a surface area and pore volume of 318 m 2 /g and 0.46 cm 3 /g, respectively. There is no data available at higher temperatures.
- EPO Patent 0190883 discloses a stabilized 5.5% silica-alumina support produced by impregnating alumina with polyorgano silane. After calcination at 1100° C. and 1200° C., the surface area is 158.2 m 2 /g and 93 m 2 /g, respectively. No data are available for pore volume.
- Huang et al. U.S. provisional Patent application 61/340,762 corresponding to application Ser. No. 13/069,317 filed Mar. 22, 2011 previously disclosed a simple method of preparing ⁇ -Al 2 O 3 supports which have high surface areas (>350 m 2 /g) and pore volumes (>1.7 cm 3 /g); and in which the pore diameters can be controlled over a large range (3 to 55 nm) made by an inexpensive, solvent deficient method without the use of templates or surfactants.
- pore volume and surface area decrease sharply to about 60 m 2 /g at approximately 1000° C. due to the ⁇ to ⁇ -Al 2 O 3 transition.
- Doping with 3% La increases the thermal stability somewhat to achieve a surface area of 139 m 2 /g and pore volume of 0.22 cm 3 /g at 1100° C.
- these supports tend to collapse in the presence of water or steam.
- alumina catalyst supports with improved stability at high temperatures (e.g., above 1100° C.) in the presence of water/steam, i.e., materials which maintain high surface area, large pore volume medium to large mesopore diameter, under these demanding conditions.
- Such catalyst supports can be used to facilitate higher catalyst loading and dispersion with attendant increases in catalytic activity, selectivity, productivity, and lifetime at these operating temperatures. It is also desirable to produce such materials using simple manufacturing methods with associated low costs of manufacturing.
- This invention comprises a method for preparation of a silica doped alumina which maintains high surface areas, large pore volumes and large pore diameters at elevated temperatures, such as about 1200° C. in the presence or absence of water (or steam).
- the method produces silica-stabilized alumina nanoparticles highly resistant to sintering or fusing with consequent grain growth and conversion of the ⁇ to the ⁇ crystalline lattice structure, thus maintaining optimal surface area and pore structure s.
- the silica-doped alumina is produced by a unique solid-state, solvent-deficient synthesis method combined with a novel method of doping with an organic silicon reagent to produce products of superior thermal and hydrothermal stability and pore characteristics.
- the invention may be practiced by either of two alternative methods as a “One Step” or “Two Step” method:
- An organic silicon compound such as tetraethyl orthosilicate (TEOS) is mixed with an organic aluminum salt such as aluminum isopropoxide and a small amount of water in a solvent deficient environment to produce doped alumina precursor nanoparticles.
- the organic silicon compound used may vary in concentration to yield from about 1% to about 30% by weight of silica in the final product.
- the aluminum alkoxide and the organic silicon compound form a precursor in the form of a solid suspension or slurry. Upon further stirring, the slurry may thicken to a slightly-wet solid.
- the precursor (with or without drying to remove the water and by-product volatile alcohols) is dried at 25-200° C. and calcined by heating to 500-800° C. (e.g., to 700° C. for 2 hrs., ramp rate, 5 hrs.) to form a stable silica-doped aluminum oxide (“SDA” herein) with evaporation of all byproducts.
- SDA silica
- An organic aluminum salt such as aluminum isopropoxide and a small amount of water are mixed in a solvent deficient environment to produce an alumina nanoparticle precursor in the form of a slurry.
- the alumina precursor (with or without drying to remove the water and by-product volatile alcohol) is calcined (e.g., at 700° C. for 2 hrs., ramp rate, 5 hrs.) to form aluminum oxide with evaporation of all byproducts.
- An organic silicon compound such as TEOS is mixed with the alumina produced in step a) and with a small amount of water sufficient to hydrolyze the TEOS.
- the organic silicon compound may vary in concentration to yield from about 1% to about 30% by weight of silica in the final product.
- the mixture is calcined (e.g., at 700° C. for 2 hrs., ramp rate, 5 hrs.) to form the stable silica doped aluminum oxide (SDA) with evaporation of all byproducts.
- SDA silic
- organic aluminum salts include, but are not limited to aluminum isopropoxide, aluminum phenoxide, aluminum sec-butoxide, aluminum tert-butoxide, aluminum ethoxide, and aluminum hexoxide.
- organic silicon compounds include, but are not limited to: teraethyl ortho silicate, tetra-n-butoxysilane, tetra n-propoxy silane, polydimethyl siloxane, and triethoxy methyl silane.
- FIG. 1A shows XRD patterns of 5% silica doped alumina (SDA) from Example 1 ( FIG. 1A ) calcined at different temperatures for 2 hrs.
- SDA silica doped alumina
- FIG. 1B shows a commercially available alumina, Sasol 5% silica doped alumina, “SIRAL-5” (from Example 4) calcined at different temperatures.
- FIGS. 1A and 1B also show XRD patterns for standard alumina phases including “Mullite” (3:1 weight % alumina/silica, also designated as “Alumina silica” in FIG. 1A and other Examples) as well as alpha, theta, and gamma phases.
- XRD standard patterns described in this and other Examples to follow were compared to an XRD standard pattern for alpha, gamma, theta and mullite phases in the International Centre for Diffraction Data (ICDD) database software.
- ICDD International Centre for Diffraction Data
- FIG. 2 shows XRD patterns of a 5% doped alumina from Example 2 calcined at different temperatures from 700-1200° C. and stability of the sample over this range.
- FIGS. 3A and 3B show TEM micrographs of 5% silica doped alumina calcined at 700° C. ( FIG. 3A ), and 5% silica doped alumina calcined at 1100° C. ( FIG. 3B ).
- the SDA's were prepared as described in Example 3.
- FIG. 4A shows XRD patterns of an SDA (Example 5) 5% doped alumina calcined at different temperatures for 24 hrs.
- FIG. 4B shows XRD patterns for “Sasol” 5% doped alumina (Example 6, “SIRAL-5”) calcined at different temperatures for 24 h. The standards for various alumina phases as described in Example 1 are also shown.
- FIGS. 5A-5D show XRD patterns of different aluminas calcined at different temperatures for 2 hr.
- FIG. 5A Example 7, 0% silica
- FIG. 5B 5% doped alumina, Example 1
- FIG. 5C 15% doped alumina
- Example 8 Example 8
- FIG. 5D 27% doped alumina
- the standards for various alumina phases as described in Example 1 are also shown.
- FIG. 6 shows XRD patterns of silica doped alumina (Examples 10-13) from different organic silicons after calcining at 1200° for 2 hrs. The standards for various alumina phases as described in Example 1 are shown.
- FIGS. 7A and 7B show XRD patterns of silica doped aluminas from Examples 16 ( FIG. 7A ) and Example 18 ( FIG. 7B .) Standards for alumina phases as described in Example 1 are shown.
- FIG. 8 shows XRD patterns of 5% silica doped alumina (Example 19) hydrothermally treated with water for 24 hours at different temperatures. Standards for alumina phases as described in Example 1 are shown.
- FIG. 9 shows XRD patterns of 5% silica doped alumina (Example 20) calcined using the Two Step method at different temperatures for 2 hrs. Standards for alumina phases as described in Example 1 are shown.
- FIG. 10 shows XRD patterns of commercial aluminas (Examples 30-33) after adding TEOS and calcining at different temperatures for 2 hrs and one sample prepared by the two step method of Example 20 (“SDA”.) Standards for alumina phases as described in Example 1 are shown.
- FIG. 11 shows XRD patterns of commercial aluminas with no dopant (Example 34) after calcining at 1200° C. for 2 hrs. Standards for alumina phases as described in Example 1 are shown.
- the present invention employs the use of a solvent deficient method of making small nanoparticles with tight size distributions to enable the production of high quality aluminum oxide materials stable at high temperatures in the presence or absence of water and/or steam and with high surface area and large mesopore volume.
- the invention also provides a means of manipulating the secondary structure or aggregation of the nanoparticles to systematically control the surface properties and pore structure of said materials as determined by the BET surface area, pore volume, and pore size from N 2 adsorption. Pore size of the aluminum oxide products can vary from small to large mesopores.
- the basic method of making alumina materials includes mixing a dry powdered (but can be hydrated) organic aluminum salt, preferably an alkoxide or phenoxide (or a mixture of such), an organic silicon compound (hereinafter described) and a small amount of water (in the event a non-hydrated salt is used) to form what is opined to be a complex metal hydroxide/metal-oxide hydroxide precursor material and a byproduct salt.
- the organic silicon compound may be added in an amount to provide up to about 1% to about 30 weight % of silica in the final product.
- the reaction is solvent deficient and the reaction mixture consists of a solid suspension or slurry.
- solvent deficient or “no solvent added” in that the small amount of water is sufficient to react with (hydrolyze) the aluminum alkoxide and the organic silicon compound, but not sufficient to solubilize the reactants.
- water may be provided in an amount to provide a molar ratio to aluminum of at least 3:1 and to silicon of at least 2:1. Larger amounts may be employed but not in sufficient quantities to solubilize the reactants.
- the slurry may thicken to a slightly-wet solid depending upon the reagents used.
- the entire mixing method to produce the precursor can be carried out at room temperature within 10-30 minutes to bring the reaction to completion. Reaction temperatures from 25 to 90° C. may be used.
- the intermediate so produced is opined to contain an aluminum hydroxide and/or aluminum oxide hydroxide.
- the precursor thus formed may optionally be air dried at room temperature or heated to a temperature sufficient to dehydrate the precursor. In one embodiment drying is carried out prior to calcination by heating at a temperature greater than 50° C., 80° C., or 100° C., less than 200° C., or 120° C., or a range constructed from any of the foregoing temperatures.
- the precursor is calcined. Calcination produces thermally, stable silica doped aluminas.
- the calcination can be carried out at a temperature equal to or greater than 300° C., 350° C., or 400° C., and equal to or less than 1200° C., 800° C., 600° C., 400° C., or a range constructed from any of the foregoing temperatures. Calcination at 500-1200° C. is preferred.
- the calcination can be carried out for a period of time greater than 10 minutes, 30 minutes, 1 hour, 2 hours, or 5 hours and various ramp rates may be used such as 0.5-10° C./min. Ramp rates of 0.5 to 3° C. are preferred.
- Calcination at preferred conditions produces highly thermally stable silica-doped aluminas in mostly the gamma phase.
- the drying and calcination can be carried out as separate discrete steps in the same or different heating vessels or as a single step (i.e., the drying step may be a single step that transitions to calcination).
- the method may also be modified by washing the precursor material prior to calcination, or the alumina may be washed after calcination.
- an organic aluminum salt typically an aluminum alkoxide or phenoxide or mixtures thereof, is mixed with a small amount of water to provide sufficient water for the reaction as described above to produce a nanoparticle precursor opined to contain aluminum hydroxide and/or aluminum oxide hydroxide which form a slurry.
- This precursor (with or without the drying step as described above) is calcined to form aluminum oxide nanoparticles.
- the calcination can be carried out at a temperature greater than 300° C., 350° C., or 400° C., and less than 1200° C., 800° C., 600° C., 400° C., or a range constructed from any of the foregoing temperatures.
- the calcination can be carried out for a period of time greater than 10 minutes 30 minutes, 1 hour, 2 hours, or 5 hours and various ramp rates may be used such as 0.5-10° C./min.
- the aluminum oxide so formed is then mixed with an organic silicon compound (described hereafter) and a small amount of water sufficient to hydrolyze the organic silicon compound.
- the silicon added may vary in concentration, but is typically employed in an amount to provide from about 1% to about 30% by weight of silica in the final product.
- the mixture of the organic silicon compound and aluminum oxide is then calcined under the conditions, temperatures, times, and heating rates as the calcination described above for Step 1. Calcination under preferred conditions produces highly thermally stable silica doped aluminas. Additional details regarding methods for making a solvent deficient precursor mixture and the reagents that can be used to make solvent deficient precursor mixtures are disclosed in the co-pending U.S. Provisional Patent Application No. 61/340,762 corresponding to application Ser. No. 13/069,317, filed Mar. 22, 2011 which is hereby incorporated herein by reference in its entirety.
- Suitable organic aluminum starting reagents used in this invention are generally aluminum organic salts such as alkoxides and phenoxides. Examples are aluminum isopropoxide (ATP), aluminum sec butoxide (Abu), aluminum tert butoxide (ATB), aluminum ethoxide (AEt), aluminum propoxide (ApO), aluminum pentoxide, and aluminum phenoxide (Aph). They may generally be represented by the formula Al(O—R) 3 where R is C 1 -C 12 alkyl, C 5 -C 12 cycloalkyl, aryl or combinations thereof.
- organic silicon compounds used as reagents in this invention are a broad class of compositions generally characterized as silicon oxides. They may also be characterized as silanes (silane derivatives) and silicates. They may be generally represented by the following formula:
- R is alkyl or aryl and can be about C1-C12 alkyl, C5-C12 cycloalkyl, phenyl, naphthyl and the like.
- R may also be a polyalkyl siloxane radical represented by the following structure:
- TEOS tetraethyl orthosilicate
- TNBS tetera-n-butoxysilane
- TNPS tetra n-propoxy silane
- PDMS polydimethyl siloxane
- TOMS triethoxy methyl silane
- TEOS is a preferred compound.
- the organic silicon compound is typically employed in an amount to provide from about 1% to about 30%, and preferably about 5-10% by weight of silica in the final product in both One Step and Two Step Methods including any amount within these ranges.
- the pore structure of the aluminas can also be controlled by dilution of the starting materials with a liquid.
- the addition of small amounts of liquids to the solvent deficient slurry will result in substantial changes in the porous characteristics of the product.
- the diluent may be water, an alcohol, ketone, ether, or other liquids that are generally useful as solvents when dissolving metal salts. However, when used in the present invention, the diluent is added in concentrations that do not dissolve the aluminum salts in the precursor mixture.
- the diluent may be included in the precursor mixture in molar ratios of diluent to aluminum alkoxide or phenoxide in a range from 1:0.5 to 1:10 or any number or range between.
- the pore diameter can be varied by three fold and the pore volume by four fold with the addition of small amounts of water (but still maintaining the ⁇ solvent deficient environment.)
- the pore structure can also be controlled by rinsing the precursor material prior to calcination with various solvents.
- the pore diameter can be varied by almost seven fold by rinsing the precursor with various organic solvents.
- the aluminas produced by this invention are highly thermally stable and can have higher surface areas, larger pore volumes, and generally have larger mesopores following treatment at elevated temperatures than aluminas reported in the prior art, with only a few exceptions, in which case the thermal stability and pore volume are generally comparable.
- the methods of the present invention are also relatively simple, scalable, and designed to be commercially economical compared to methods reported in prior art processes. For example, after calcination temperatures of 1200° C. the silica-doped alumina maintains surface areas of >100 m 2 /g, pore volumes >0.5 cm 3 /g. and pore diameters >20 nm.
- Ceramic silica-alumina porous membranes prepared from the silica-aluminas of this invention can also be used in aggressive media, steam, or high temperature applications. They are preferred over polymeric membranes due to their long life, ecological benefits, and their chemical and thermal stability. They also can be used in gas separation and purification and in numerous filtration applications. Importantly, the silica-aluminas of this invention remain in the gamma phase at high temperature.
- ⁇ -Aluminas produced by methods in the current art often exhibit substantial grain growth and loss of surface area as they are exposed to higher temperatures, and all reported examples transition to the ⁇ or ⁇ -phases at temperatures from 1100° C. to 1200° C. The ⁇ -phase is characterized by excessive grain growth and collapse of the porous structure.
- the silica doped aluminas of the present invention may also be subject to grain growth and loss of surface area, but to a lesser extent, and they remain in the ⁇ -phase with conserved pore structure up to 1200° C. to 1250° C.
- the silica-doped aluminas of this invention have significant benefits in the properties mentioned over similar materials reported in the prior art.
- water is added to aluminum isopropoxide (AIP) in a 1:5 mole ratio, immediately followed by adding the equivalent of 5 wt. % silica in the form of TEOS.
- AIP aluminum isopropoxide
- the reagents are mixed for 30 minutes by a Bosch kitchen mixer to form the precursor and the precursor is calcined at 700° C. for 2 hrs (ramp rate 2° C./min) to produce the thermally stable silica doped alumina (SDA).
- SDA thermally stable silica doped alumina
- Table 2 includes BET data for 5 wt. % SDA thermally treated at 700° C., 900° C., 1100° C. and 1200° C. for 2 hrs (ramp rate 2° C./min). Following calcination at 1100° C.
- FIGS. 1A and 5B show that the principal phase of the SDA treated at 1250° C. is ⁇ -Al 2 O 3 . Peaks attributed to ⁇ -Al 2 O 3 are not observed until the sample is calcined at 1300° C.
- Example 1 which had been previously air-calcined at 700° C. was loaded in an in situ XRD cell, ramped to 700° C. in air, and held for 30 minutes; the XRD spectrum was scanned and the temperature was ramped to 800° C. and held for 30 minutes, then scanned, etc. up through 1200° C.
- FIG. 2 shows in situ high-temperature XRD patterns in air. It is evident that the ⁇ -Al 2 O 3 phase in 5% SDA is stable to 1200° C. without transforming to either theta ( ⁇ ) or ⁇ -alumina.
- FIG. 3A A sample from Example 1 calcined at 700° C. was studied by TEM.
- TEM images FIG. 3A ) show that primary particles of 5% SDA are plate-like, having an average length of 20 nm, an average width of 15 nm; and a thickness of about 5 nm based on XRD calculations using the Scherrer formula.
- FIG. 3B At higher temperatures, i.e. 1100° C., ( FIG. 3B ), the shape and size of the 5% SDA primary particle remains relatively small, no significant grain growth due to sintering from gamma to alpha phase transition is observed.
- FIG. 1 B shows the XRD patterns where the SIRAL transitioned from the ⁇ to ⁇ phase at 1100° C., while the 5% silica doped alumina of this invention remains in ⁇ phase to 1200° C. as shown in FIG. 1A ).
- FIG. 4B shows the XRD patterns where the SIRAL transitions from the ⁇ to ⁇ phase at 1100° C. while the 5% silica doped alumina of this invention remains in ⁇ phase to 1200° C. as shown in FIG. 1A .
- Example 1 For comparative purposes, Example 1 was repeated except no dopant was used. It was thermally treated for 2 hrs (ramp rate 5 hrs) at the same temperatures. Table 2 includes surface area and porosity data for the 0 wt. % silica batch which show significant deterioration of the surface area and pore structure with increasing temperatures as it transitioned to the alpha crystalline phase ( FIG. 5A ).
- Example 1 was repeated except 15 wt. % silica based on alumina in the final product was used. It was thermally treated for 2 hrs (ramp rate 5 hrs) at the same temperatures.
- Table 2 includes surface area and porosity data for the 15 wt. % silica batch.
- FIG. 5C shows XRD patterns of the 15% silica batch which remains in ⁇ -Al 2 O 3 phase at 1200° C.
- Example 1 was repeated except 27 wt. % silica based on the weight of alumina in the final sample was used. It was thermally treated for 2 hrs (ramp rate 5 hrs) at the same temperatures. Table 2 includes surface area and porosity data. Alpha peaks are observed at 1100° C. ( FIG. 5 d ). Table 2 shows that 5 wt. % has the highest surface area and largest porosity at higher temperatures compared to others, but all of the TEOS doped samples were significantly better thermally stabilized than the control.
- Example 2 A sample was made according to Example 1 except 5 wt % tetra-n-butoxysilane (TNBS) was substituted for the 5 wt % TEOS. Surface area and porosity remained high after calcination at 1200° C. for 2 hours (Table 4). XRD shows ( FIG. 6 ) alpha and gamma at 1200° C.
- TNBS tetra-n-butoxysilane
- Example 2 A sample was made according to Example 1 except 5 wt % tetra n-propoxy silane (TNPS) was substituted for the 5 wt % TEOS. The surface area, pore volume, and pore diameter were still adequately high after calcination at 1200° C. for 2 hours (Table 4). XRD shows ( FIG. 6 ) that the SDA is stable with theta and gamma phases at 1200° C.
- TNPS wt % tetra n-propoxy silane
- Example 2 A sample was made according to Example 1 except 5 wt % polydimethyl siloxane (PDMS) was substituted for the 5 wt % TEOS. The surface area, pore volume, and pore diameter were still adequately high after calcination at 1200° C. for 2 hours (Table 4). XRD shows ( FIG. 6 ) that the sample contained some alpha with the gamma phase at 1200° C.
- PDMS polydimethyl siloxane
- Example 2 A sample was made according to Example 1 except 5 wt % triethoxy methyl silane (TEOMS) was substituted for the 5 wt % TEOS. Surface area, pore volume, and pore diameter were still adequately high after calcination at 1200° C. for 2 hours (Table 4). XRD shows ( FIG. 6 ) that the SDA is stable with theta and gamma phases at 1200° C.
- TEOMS triethoxy methyl silane
- Example 4 For comparative purposes a sample was made according to Example 1 except 5 wt % Lanthanum nitrate (LaN) was substituted for 5 wt % TEOS. Substantial decreases in surface area and porosity (Table 4) show that the sample was not stabilized and XRD shows that it is in the alpha phase at 1200° C.
- LaN Lanthanum nitrate
- Example 4 For comparative purposes, a sample was made according to Example 1 except 5 wt % silicic acid (SA) was substituted for the 5 wt % TEOS. Substantial decreases in surface area and porosity (Table 4) show that the sample was not stabilized and XRD shows that it is in the alpha phase at 1200° C.
- SA silicic acid
- Table 4 Substantial decreases in surface area and porosity
- Example 2 A sample was made according to Example 1 except aluminum sec butoxide (ABu) was substituted for the aluminum isopropoxide. Surface area, pore volume, and pore diameter listed in Table 5 differ from those for the SDA derived from aluminum isopropoxide, but it is also thermally stabilized. The XRD spectra indicate that aluminum sec-butoxide derived SDA is mostly gamma at 1200° C. ( FIG. 7A ).
- a sample was made according to Example 1 except aluminum tert butoxide (ATB) was substituted for the aluminum isopropoxide.
- Table 5 shows that the SDA is mostly gamma at 1200° C.
- Example 2 For comparative purposes, a sample was made according to Example 1 except aluminum nitrate (AN) was substituted for the aluminum isopropoxide. Relatively low values of surface area, pore volume, and pore diameter listed n in Table 5 indicate that this inorganic aluminum source does not produce a thermally stabilized product. The XRD spectra indicate that the SDA is not stable and it is in the alpha phase at 1200° C. and ( FIG. 7B ).
- Sample from example 1 was thermally treated in presence of water (0.16 ml/min) for 24 hr at temperatures from 800° C. to 1200° C.
- Table 6 shows that surface area and porosity are also stable up to 1200° C. in the presence of steam
- FIG. 8A shows that the alumina of this Example is mostly in gamma phase at 1100° C.
- Two-Step Water and aluminum isopropoxide ere mixed in a 1:5 mole ratio for 15 min and calcined to 700° C. for 2 hrs (ramp rate 5 hrs) to produce pure alumina.
- TEOS was added to the alumina to give a final concentration of 5% wt/wt silica/alumina and mixed for 30 minutes in Bosch kitchen mixer, then calcined at 700° C., 900° C., 1100° C. and 1200° C. for 2 hrs (ramp rate 5 hrs).
- Surface area and porosity data indicate that this two-step method also produces a thermally stable alumina product (Table 7).
- the XRD spectrum indicates it is ⁇ -alumina with a trace of 0 at 1200° C. ( FIGS. 9 and 10 , “SDA in FIG. 10 ).
- TNBS tetra-n-butoxysilane
- TNPS tetra n-propoxy silane
- a sample was made according to Example 20 except 5 wt % polydimethyl siloxane (PDMS) was substituted for the 5 wt % TEOS.
- XRD shows (Table 8) that the PDMS sample transformed to alpha at 1200° C.
- TEOMS triethoxy methyl silane
- Example 21 For comparison purposes, a sample was made according to Example 21 except 5 wt % silicic acid (SA) was substituted for the 5 wt % TEOS.
- SA silicic acid
- XRD shows (Table 8) that this sample transformed to alpha and gamma at 1200° C.
- Example 20 A sample was made according to Example 20 except aluminum sec butoxide (ABu) was substituted for the aluminum isopropoxide.
- Table 9 shows that SDA is thermally stable and mostly gamma at 1200° C.
- a sample was made according to Example 20 except aluminum tert butoxide (ATB) was substituted for the aluminum isopropoxide.
- Table 9 shows that SDA is thermally stable and mostly gamma at 1200° C.
- Example 20 A sample was made according to Example 20 except aluminum phenoxide (APh) was substituted for the aluminum isopropoxide.
- APIh aluminum phenoxide
- Table 9 shows that SDA is thermally stable and mostly gamma at 1200° C.
- Example 20 A sample was made according to Example 20 except aluminum ethoxide (AEt) was substituted for the aluminum isopropoxide.
- Table 9 shows that SDA is thermally stable and mostly gamma at 1200° C.
- CAPAL a commercial pure alumina material obtained from Sasol, Inc. was purchased. 5% TEOS was added to the alumina followed by mixing. Following calcination at 1200° C. for 2 hrs (ramp rate 5 hrs) the XRD pattern ( FIG. 10 ) indicates that CATAPAL transitions to ⁇ -alumina by 1200° C.
- “CATALOX”-SBa-90 a commercial gamma alumina obtained from Sasol, Inc. as calcined at 700° C. for 2 hrs (ramp rate 5 hrs) to produce ⁇ -alumina.
- 5% TEOS was added to the calcined alumina followed by mixing.
- the XRD pattern FIG. 10 indicates that it is not stable at 1200° C. and transforms to ⁇ -alumina.
- a “St.GOBAIN” moderately high pore volume gamma alumina as calcined at 700° C. for 2 hrs (ramp rate 5 hrs) to produce ⁇ -alumina.
- 5% TEOS was added to the calcined alumina followed by mixing.
- the XRD pattern FIG. 10 ) indicates that St. GOBAIN remains in gamma phase at 1200° C.
- ALPHA-Aesar 99.9% gamma alumina (stock#: 43832, lot#: E08T034) as calcined at 700° C. for 2 hrs (ramp rate 5 hrs) to produce ⁇ -alumina.
- 5% TEOS was added to the calcined alumina followed by mixing.
- the XRD pattern ( FIG. 10 ) indicates that ALPHA-Aesar is not stable at 1200° C. and transforms to ⁇ -alumina.
- FIG. 11 shows that several commercial aluminas are transformed to alpha alumina at 1200° C. without addition of an organic silicon compound.
Abstract
The present invention relates to a method for making high surface area and large pore volume thermally stable silica-doped alumina (aluminum oxide) catalyst support and ceramic materials. The ability of the silica-alumina to withstand high temperatures in presence or absence of water and prevent sintering allows it to maintain good activity over a long period of time in catalytic reactions. The method of preparing such materials includes adding organic silicon reagents to an organic aluminum salt such as an alkoxide in a controlled quantity as a doping agent in a solid state, solvent deficient reaction followed by calcination. Alternatively, the organic silicon compound may be added after calcination of the alumina, followed by another calcination step. This method is inexpensive and simple. The alumina catalyst support material prepared by the subject method maintains high pore volumes, pore diameters and surface areas at very high temperatures and in the presence of steam.
Description
- This application is a divisional of, and claims priority to and the benefit of, U.S. Non-Provisional patent application Ser. No. 14/201,538 filed on Mar. 7, 2014 and entitled “METHOD OF MAKING HIGHLY POROUS, STABLE ALUMINUM OXIDES DOPED WITH SILICON,” which claims the benefit of U.S. Provisional Patent Application Ser. No. 61/851,506 filed on Mar. 9, 2013 and entitled “A METHOD OF PRODUCING THERMALLY STABLE AND HIGH SURFACE AREA Al2O3 CATALYST SUPPORTS,” which applications are hereby expressly incorporated herein in their entirety by this reference.
- Alumina is the most common catalyst support used in industry and it has numerous applications as a ceramic material. Gamma alumina (γ-Al2O3) is preferred for many catalyst systems including Pt, Pd, and Ni for hydrogenation reactions, for Pt, Rh and Pd catalysts for internal combustion engine emissions control (CO, NOx), for Co(Ni)—Mo(W) sulfide catalysts for fuel hydrodesulfurization, and for Co and Fe catalysts for Fischer-Tropsch synthesis (FTS). Alumina is prepared inexpensively with a wide range of surface areas and porosities, and is more thermally stable than other metal oxide supports. There are three important properties in selecting an appropriate catalyst support. First, high surface area supports increase catalyst dispersion and catalytic reaction sites, which leads to decreased reaction times and catalyst usage. Second, optimal pore size is important in support materials since various catalytic systems require unique pore sizes for better diffusion and selectivity. Third, thermal stability is important since many catalytic reactions take place at elevated temperatures over long periods of time. However, at high temperatures and pressures, γ-Al2O3 is deactivated by sintering and a crystalline lattice phase transformation from γ to α-Al2O3 which causes a sharp decrease in surface area and pore size. And, the metal catalysts on such a support become occluded in the shrunken material, resulting in a loss of exposed catalyst surface area, or they are expelled from the support, resulting in a significant deactivation of the catalyst.
- In order to prevent sintering and suppress catalyst deactivation, methods to stabilize γ-Al2O3 supports against thermal deactivation have been developed by adding a dopant which may affect the porous structure and surface properties of the materials and improve their thermal stability. Thermal stability of alumina increases with silica, zirconia, rare earth elements such as lanthanum and chelating agents (ethyl acetoacetate). Several methods for synthesis of stable silica doped alumina have been reported, e.g., impregnation; precipitation/washing; and gel, areogel, and cryogol methods employing various solvents and/or surfactants and templates. These methods are costly and time consuming. Moreover, these supports, with few exceptions, do not maintain high surface areas and pore volumes at higher temperatures. Such materials are described in, e.g., J. W. Curley, M. J. Dreelan, O. E. Finlayson, Catalysis Today, 10 (1991) 401-404, in J. van de Loosdrecht, S. Barradas, E. A. Caricato, P. J. van Berge, and J. L. Visagie, Studies in Surface Science and Catalysis, 143 (2002) 587; in A. A. Shutilov, G. A. Zenkovets, S. v. Tsybulya, V. Y. Gavrilove, Kinetics and Catalysis, 53, (2012) 125-136; in A. W. Espie, J. C. Vickerman, Journal of the Chemical Society, Faraday Transactions 1: Physical Chemistry in Condensed Phases, 80(1984) 1903-1913, and in T. Fukui, M. Hori, Journal of Materials Science, 31 (1996) 3245-3248; in Beguin et al., Journal of Catalysis, 127 (1991) 595.
- WO 2007/009680 discloses treatment of alumina with an organic siloxide, i.e. Si(OR)4-nR′n including TEOS. U.S. Pat. No. 6,977,273 discloses impregnating Sasol Puralox gamma-alumina with TEOS. (3) US 2003/0162849, WO 03/012008, and US Patent 2005/0245623 discloses addition of TEOS/ethanol or other organic silicon compounds in ethanol to an alumina support to improve mechanical and thermal/hydrothermal stabilities and resistance to sintering.
- U.S. Pat. No. 4,392,988 discloses that soaking alumina in polydimethyl-siloxane increases thermal stability of alumina. EPO 2,392,548 describes a method for the preparation of an amorphous silica-alumina with acid properties like zeolites, using silica to alumina weight ratio of 2. The method includes: co-precipitation of alumina and silica by adding a base precipitating agent to an aqueous solution of sodium silicate and aluminum sulfate in presence of a gelification initiator (bohemite) followed by filtration and drying. After calcination at 550° C. the surface area and a pore volume are 400 m2/g and 1.2 cm3/g, respectively. But, the silica content in such silica-alumina is high which may make it less stable at higher temperatures. The acidity of this support is also high which make it undesirable for some catalytic reactions such as Fischer-Tropsch.
- EPO Patent 1,701,787 discloses a silica-modified-alumina with 2-10% silica using a cogel method. After calcination at 648° C., the material has a surface area and pore volume of 318 m2/g and 0.46 cm3/g, respectively. There is no data available at higher temperatures. EPO Patent 0190883 discloses a stabilized 5.5% silica-alumina support produced by impregnating alumina with polyorgano silane. After calcination at 1100° C. and 1200° C., the surface area is 158.2 m2/g and 93 m2/g, respectively. No data are available for pore volume.
- Huang et al. (U.S. provisional Patent application 61/340,762 corresponding to application Ser. No. 13/069,317 filed Mar. 22, 2011 previously disclosed a simple method of preparing γ-Al2O3 supports which have high surface areas (>350 m2/g) and pore volumes (>1.7 cm3/g); and in which the pore diameters can be controlled over a large range (3 to 55 nm) made by an inexpensive, solvent deficient method without the use of templates or surfactants. However, pore volume and surface area decrease sharply to about 60 m2/g at approximately 1000° C. due to the γ to α-Al2O3 transition. Doping with 3% La increases the thermal stability somewhat to achieve a surface area of 139 m2/g and pore volume of 0.22 cm3/g at 1100° C. Moreover, these supports tend to collapse in the presence of water or steam.
- Thus, the need is clear for development of methods for synthesizing alumina catalyst supports with improved stability at high temperatures (e.g., above 1100° C.) in the presence of water/steam, i.e., materials which maintain high surface area, large pore volume medium to large mesopore diameter, under these demanding conditions. Such catalyst supports can be used to facilitate higher catalyst loading and dispersion with attendant increases in catalytic activity, selectivity, productivity, and lifetime at these operating temperatures. It is also desirable to produce such materials using simple manufacturing methods with associated low costs of manufacturing.
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- Table 1 shows surface areas, pore diameters, and pore volumes for different Al2O3, and Si—Al2O3 supports available commercially and reported in the literature.
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BET surface area Mesopore volume PoreDiameter (m2/g) (cm3/g) (nm) Alumina phase Sample ID 700 1100 1200 700 1100 1200 700 1100 1200 1100 1200 5% Si/Al2O3 288 128 73 0.61 0.4 0.23 7.7 11.2 11.4 Gamma & Gamma & (SIRAL 5- Alpha Alpha Sasol)a 5% — 120 110 — 1.28 0.9 — 10.8 18.6 Theta Theta Si/Al2O3[1] b 10% — 100 47 — 0.2 0.1 — 3.5 3.5 Gamma Gamma Si/Al2O3[2] c 10% — — 150 — — 0.65 — — — — Alpha & Si/Al2O3[3]a Gamma a)5% 187 68 — 0.57 0.35 7.4 15.0 Alpha & — Si/Al2O3[4]d Theta Calcined for: a2 h, b1 h, c5 h, d4 h [1]T. Horiuchi, T. Osaki, T Sugiyama, H. Masuda, M. Horio, K. Suzuki, T. Mori, T. Sago, Journal of the Chemical Society, Faraday Transactions, 90 (1994) 2573-2578 [2]Osaki, T.; Nagashima, K.; Watari, K.; Tajiri, K., Journal of Non-Crystalline Solids 2007, 353, (24-25), 2436-2442. [3]J. B. Miller, E. I. Ko, Catalysis Today, 43) 1998) 51-67 [4]A. A. Shutilov, G. A. Zenkovets, S. V. Tsybulya, V. Y. Gavrilov, Kinetics and Catalysis, 53 125-136. - This invention comprises a method for preparation of a silica doped alumina which maintains high surface areas, large pore volumes and large pore diameters at elevated temperatures, such as about 1200° C. in the presence or absence of water (or steam). The method produces silica-stabilized alumina nanoparticles highly resistant to sintering or fusing with consequent grain growth and conversion of the γ to the α crystalline lattice structure, thus maintaining optimal surface area and pore structure s. The silica-doped alumina is produced by a unique solid-state, solvent-deficient synthesis method combined with a novel method of doping with an organic silicon reagent to produce products of superior thermal and hydrothermal stability and pore characteristics.
- The invention may be practiced by either of two alternative methods as a “One Step” or “Two Step” method:
- One Step: An organic silicon compound such as tetraethyl orthosilicate (TEOS) is mixed with an organic aluminum salt such as aluminum isopropoxide and a small amount of water in a solvent deficient environment to produce doped alumina precursor nanoparticles. The organic silicon compound used may vary in concentration to yield from about 1% to about 30% by weight of silica in the final product. The aluminum alkoxide and the organic silicon compound form a precursor in the form of a solid suspension or slurry. Upon further stirring, the slurry may thicken to a slightly-wet solid. The precursor (with or without drying to remove the water and by-product volatile alcohols) is dried at 25-200° C. and calcined by heating to 500-800° C. (e.g., to 700° C. for 2 hrs., ramp rate, 5 hrs.) to form a stable silica-doped aluminum oxide (“SDA” herein) with evaporation of all byproducts.
- Two Step:
- a) An organic aluminum salt such as aluminum isopropoxide and a small amount of water are mixed in a solvent deficient environment to produce an alumina nanoparticle precursor in the form of a slurry. The alumina precursor (with or without drying to remove the water and by-product volatile alcohol) is calcined (e.g., at 700° C. for 2 hrs., ramp rate, 5 hrs.) to form aluminum oxide with evaporation of all byproducts.
b) An organic silicon compound such as TEOS is mixed with the alumina produced in step a) and with a small amount of water sufficient to hydrolyze the TEOS. The organic silicon compound may vary in concentration to yield from about 1% to about 30% by weight of silica in the final product. The mixture is calcined (e.g., at 700° C. for 2 hrs., ramp rate, 5 hrs.) to form the stable silica doped aluminum oxide (SDA) with evaporation of all byproducts. - Examples of appropriate organic aluminum salts include, but are not limited to aluminum isopropoxide, aluminum phenoxide, aluminum sec-butoxide, aluminum tert-butoxide, aluminum ethoxide, and aluminum hexoxide. Examples of organic silicon compounds include, but are not limited to: teraethyl ortho silicate, tetra-n-butoxysilane, tetra n-propoxy silane, polydimethyl siloxane, and triethoxy methyl silane.
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FIG. 1A shows XRD patterns of 5% silica doped alumina (SDA) from Example 1 (FIG. 1A ) calcined at different temperatures for 2 hrs. -
FIG. 1B shows a commercially available alumina,Sasol 5% silica doped alumina, “SIRAL-5” (from Example 4) calcined at different temperatures. -
FIGS. 1A and 1B also show XRD patterns for standard alumina phases including “Mullite” (3:1 weight % alumina/silica, also designated as “Alumina silica” inFIG. 1A and other Examples) as well as alpha, theta, and gamma phases. XRD standard patterns described in this and other Examples to follow were compared to an XRD standard pattern for alpha, gamma, theta and mullite phases in the International Centre for Diffraction Data (ICDD) database software. -
FIG. 2 shows XRD patterns of a 5% doped alumina from Example 2 calcined at different temperatures from 700-1200° C. and stability of the sample over this range. -
FIGS. 3A and 3B show TEM micrographs of 5% silica doped alumina calcined at 700° C. (FIG. 3A ), and 5% silica doped alumina calcined at 1100° C. (FIG. 3B ). The SDA's were prepared as described in Example 3. -
FIG. 4A shows XRD patterns of an SDA (Example 5) 5% doped alumina calcined at different temperatures for 24 hrs. -
FIG. 4B shows XRD patterns for “Sasol” 5% doped alumina (Example 6, “SIRAL-5”) calcined at different temperatures for 24 h. The standards for various alumina phases as described in Example 1 are also shown. -
FIGS. 5A-5D show XRD patterns of different aluminas calcined at different temperatures for 2 hr. (FIG. 5A , Example 7, 0% silica), (FIG. 5B , 5% doped alumina, Example 1),FIG. 5C , 15% doped alumina, Example 8, andFIG. 5D , 27% doped alumina, Example 9. The standards for various alumina phases as described in Example 1 are also shown. -
FIG. 6 shows XRD patterns of silica doped alumina (Examples 10-13) from different organic silicons after calcining at 1200° for 2 hrs. The standards for various alumina phases as described in Example 1 are shown. -
FIGS. 7A and 7B show XRD patterns of silica doped aluminas from Examples 16 (FIG. 7A ) and Example 18 (FIG. 7B .) Standards for alumina phases as described in Example 1 are shown. -
FIG. 8 shows XRD patterns of 5% silica doped alumina (Example 19) hydrothermally treated with water for 24 hours at different temperatures. Standards for alumina phases as described in Example 1 are shown. -
FIG. 9 shows XRD patterns of 5% silica doped alumina (Example 20) calcined using the Two Step method at different temperatures for 2 hrs. Standards for alumina phases as described in Example 1 are shown. -
FIG. 10 shows XRD patterns of commercial aluminas (Examples 30-33) after adding TEOS and calcining at different temperatures for 2 hrs and one sample prepared by the two step method of Example 20 (“SDA”.) Standards for alumina phases as described in Example 1 are shown. -
FIG. 11 shows XRD patterns of commercial aluminas with no dopant (Example 34) after calcining at 1200° C. for 2 hrs. Standards for alumina phases as described in Example 1 are shown. - The following descriptions and examples illustrate the preferred embodiments of the present invention in detail. Those of skill in the art will recognize that there are numerous variations and modifications of this invention that are encompassed by its scope. Accordingly, the description of the preferred embodiments should not be deemed to limit the scope of the present invention.
- It is an object of some embodiments of the present invention to provide a method for preparing nanoscale aluminum oxides stable at high temperatures in the presence or absence of water and/or steam and having high-surface area, large pore volume, and medium to large mesopores high mesoporosity-suitable as catalysts supports, ceramic materials and adsorbents.
- The present invention employs the use of a solvent deficient method of making small nanoparticles with tight size distributions to enable the production of high quality aluminum oxide materials stable at high temperatures in the presence or absence of water and/or steam and with high surface area and large mesopore volume. The invention also provides a means of manipulating the secondary structure or aggregation of the nanoparticles to systematically control the surface properties and pore structure of said materials as determined by the BET surface area, pore volume, and pore size from N2 adsorption. Pore size of the aluminum oxide products can vary from small to large mesopores.
- In one embodiment (referred to herein as the “One Step” method, the basic method of making alumina materials includes mixing a dry powdered (but can be hydrated) organic aluminum salt, preferably an alkoxide or phenoxide (or a mixture of such), an organic silicon compound (hereinafter described) and a small amount of water (in the event a non-hydrated salt is used) to form what is opined to be a complex metal hydroxide/metal-oxide hydroxide precursor material and a byproduct salt. The organic silicon compound may be added in an amount to provide up to about 1% to about 30 weight % of silica in the final product. The reaction is solvent deficient and the reaction mixture consists of a solid suspension or slurry. This condition is characterized as “solvent deficient” or “no solvent added” in that the small amount of water is sufficient to react with (hydrolyze) the aluminum alkoxide and the organic silicon compound, but not sufficient to solubilize the reactants. Typically, water may be provided in an amount to provide a molar ratio to aluminum of at least 3:1 and to silicon of at least 2:1. Larger amounts may be employed but not in sufficient quantities to solubilize the reactants. Upon further stirring, the slurry may thicken to a slightly-wet solid depending upon the reagents used. The entire mixing method to produce the precursor can be carried out at room temperature within 10-30 minutes to bring the reaction to completion. Reaction temperatures from 25 to 90° C. may be used. The intermediate so produced is opined to contain an aluminum hydroxide and/or aluminum oxide hydroxide. The precursor thus formed may optionally be air dried at room temperature or heated to a temperature sufficient to dehydrate the precursor. In one embodiment drying is carried out prior to calcination by heating at a temperature greater than 50° C., 80° C., or 100° C., less than 200° C., or 120° C., or a range constructed from any of the foregoing temperatures.
- Subsequently, the precursor is calcined. Calcination produces thermally, stable silica doped aluminas. The calcination can be carried out at a temperature equal to or greater than 300° C., 350° C., or 400° C., and equal to or less than 1200° C., 800° C., 600° C., 400° C., or a range constructed from any of the foregoing temperatures. Calcination at 500-1200° C. is preferred. The calcination can be carried out for a period of time greater than 10 minutes, 30 minutes, 1 hour, 2 hours, or 5 hours and various ramp rates may be used such as 0.5-10° C./min. Ramp rates of 0.5 to 3° C. are preferred. Calcination at preferred conditions produces highly thermally stable silica-doped aluminas in mostly the gamma phase.
- The drying and calcination can be carried out as separate discrete steps in the same or different heating vessels or as a single step (i.e., the drying step may be a single step that transitions to calcination).
- The method may also be modified by washing the precursor material prior to calcination, or the alumina may be washed after calcination.
- In another embodiment referred to herein as the “Two Step” method, in the first step an organic aluminum salt, typically an aluminum alkoxide or phenoxide or mixtures thereof, is mixed with a small amount of water to provide sufficient water for the reaction as described above to produce a nanoparticle precursor opined to contain aluminum hydroxide and/or aluminum oxide hydroxide which form a slurry. This precursor (with or without the drying step as described above) is calcined to form aluminum oxide nanoparticles. As above, the calcination can be carried out at a temperature greater than 300° C., 350° C., or 400° C., and less than 1200° C., 800° C., 600° C., 400° C., or a range constructed from any of the foregoing temperatures. The calcination can be carried out for a period of time greater than 10
minutes 30 minutes, 1 hour, 2 hours, or 5 hours and various ramp rates may be used such as 0.5-10° C./min. In the second step, the aluminum oxide so formed is then mixed with an organic silicon compound (described hereafter) and a small amount of water sufficient to hydrolyze the organic silicon compound. The silicon added may vary in concentration, but is typically employed in an amount to provide from about 1% to about 30% by weight of silica in the final product. The mixture of the organic silicon compound and aluminum oxide is then calcined under the conditions, temperatures, times, and heating rates as the calcination described above for Step 1. Calcination under preferred conditions produces highly thermally stable silica doped aluminas. Additional details regarding methods for making a solvent deficient precursor mixture and the reagents that can be used to make solvent deficient precursor mixtures are disclosed in the co-pending U.S. Provisional Patent Application No. 61/340,762 corresponding to application Ser. No. 13/069,317, filed Mar. 22, 2011 which is hereby incorporated herein by reference in its entirety. - Suitable organic aluminum starting reagents used in this invention are generally aluminum organic salts such as alkoxides and phenoxides. Examples are aluminum isopropoxide (ATP), aluminum sec butoxide (Abu), aluminum tert butoxide (ATB), aluminum ethoxide (AEt), aluminum propoxide (ApO), aluminum pentoxide, and aluminum phenoxide (Aph). They may generally be represented by the formula Al(O—R)3 where R is C1-C12 alkyl, C5-C12 cycloalkyl, aryl or combinations thereof.
- The organic silicon compounds used as reagents in this invention are a broad class of compositions generally characterized as silicon oxides. They may also be characterized as silanes (silane derivatives) and silicates. They may be generally represented by the following formula:
- Wherein R is alkyl or aryl and can be about C1-C12 alkyl, C5-C12 cycloalkyl, phenyl, naphthyl and the like. R may also be a polyalkyl siloxane radical represented by the following structure:
- Representative compounds are tetraethyl orthosilicate (TEOS), tetera-n-butoxysilane, (TNBS), tetra n-propoxy silane (TNPS), polydimethyl siloxane (PDMS), and triethoxy methyl silane (TEOMS). TEOS is a preferred compound. The organic silicon compound is typically employed in an amount to provide from about 1% to about 30%, and preferably about 5-10% by weight of silica in the final product in both One Step and Two Step Methods including any amount within these ranges.
- The pore structure of the aluminas can also be controlled by dilution of the starting materials with a liquid. The addition of small amounts of liquids to the solvent deficient slurry will result in substantial changes in the porous characteristics of the product. The diluent may be water, an alcohol, ketone, ether, or other liquids that are generally useful as solvents when dissolving metal salts. However, when used in the present invention, the diluent is added in concentrations that do not dissolve the aluminum salts in the precursor mixture. The diluent may be included in the precursor mixture in molar ratios of diluent to aluminum alkoxide or phenoxide in a range from 1:0.5 to 1:10 or any number or range between. For example, with aluminas prepared from aluminum sec-butoxide, the pore diameter can be varied by three fold and the pore volume by four fold with the addition of small amounts of water (but still maintaining the ∞solvent deficient environment.) The pore structure can also be controlled by rinsing the precursor material prior to calcination with various solvents. For example, in the case of aluminas prepared from aluminum isopropoxide, the pore diameter can be varied by almost seven fold by rinsing the precursor with various organic solvents.
- The aluminas produced by this invention are highly thermally stable and can have higher surface areas, larger pore volumes, and generally have larger mesopores following treatment at elevated temperatures than aluminas reported in the prior art, with only a few exceptions, in which case the thermal stability and pore volume are generally comparable. The methods of the present invention are also relatively simple, scalable, and designed to be commercially economical compared to methods reported in prior art processes. For example, after calcination temperatures of 1200° C. the silica-doped alumina maintains surface areas of >100 m2/g, pore volumes >0.5 cm3/g. and pore diameters >20 nm. Ceramic silica-alumina porous membranes prepared from the silica-aluminas of this invention can also be used in aggressive media, steam, or high temperature applications. They are preferred over polymeric membranes due to their long life, ecological benefits, and their chemical and thermal stability. They also can be used in gas separation and purification and in numerous filtration applications. Importantly, the silica-aluminas of this invention remain in the gamma phase at high temperature. γ-Aluminas produced by methods in the current art often exhibit substantial grain growth and loss of surface area as they are exposed to higher temperatures, and all reported examples transition to the θ or α-phases at temperatures from 1100° C. to 1200° C. The α-phase is characterized by excessive grain growth and collapse of the porous structure. The silica doped aluminas of the present invention may also be subject to grain growth and loss of surface area, but to a lesser extent, and they remain in the γ-phase with conserved pore structure up to 1200° C. to 1250° C. Thus, the silica-doped aluminas of this invention have significant benefits in the properties mentioned over similar materials reported in the prior art.
- The following examples are presented to more completely describe the present invention, and comparison examples are also included to demonstrate the benefits of the invention. The examples are provided for illustrative purposes only. Various modifications or changes in light thereof will be obvious to persons skilled in the art and are to be included within the spirit and purview of this application. The invention can take other specific forms without departing from the spirit or essential attributes thereof. In all examples, BET surface area and mesopore volume were determined by N2 adsorption at 77 K and pore diameter was calculated from the hysteresis region of each isotherm using the improved slit pore geometry (SPG) model for large pore size using the desorption branch.
- In a preferred embodiment, water is added to aluminum isopropoxide (AIP) in a 1:5 mole ratio, immediately followed by adding the equivalent of 5 wt. % silica in the form of TEOS. The reagents are mixed for 30 minutes by a Bosch kitchen mixer to form the precursor and the precursor is calcined at 700° C. for 2 hrs (ramp rate 2° C./min) to produce the thermally stable silica doped alumina (SDA). Table 2 includes BET data for 5 wt. % SDA thermally treated at 700° C., 900° C., 1100° C. and 1200° C. for 2 hrs (ramp rate 2° C./min). Following calcination at 1100° C. a surface area of 160 m2/g, a pore volume of 0.99 cm3/g, and a bimodal pore size distribution with peaks at 23 and 52 nm are observed.
FIGS. 1A and 5B show that the principal phase of the SDA treated at 1250° C. is γ-Al2O3. Peaks attributed to α-Al2O3 are not observed until the sample is calcined at 1300° C. - A sample from Example 1 which had been previously air-calcined at 700° C. was loaded in an in situ XRD cell, ramped to 700° C. in air, and held for 30 minutes; the XRD spectrum was scanned and the temperature was ramped to 800° C. and held for 30 minutes, then scanned, etc. up through 1200° C.
FIG. 2 shows in situ high-temperature XRD patterns in air. It is evident that the γ-Al2O3 phase in 5% SDA is stable to 1200° C. without transforming to either theta (θ) or α-alumina. - A sample from Example 1 calcined at 700° C. was studied by TEM. TEM images (
FIG. 3A ) show that primary particles of 5% SDA are plate-like, having an average length of 20 nm, an average width of 15 nm; and a thickness of about 5 nm based on XRD calculations using the Scherrer formula. At higher temperatures, i.e. 1100° C., (FIG. 3B ), the shape and size of the 5% SDA primary particle remains relatively small, no significant grain growth due to sintering from gamma to alpha phase transition is observed. - In comparative experiments, a sample of commercial silica-doped alumina (“SIRAL”) from Sasol Inc. was calcined at 700° C., 900° C., 1100° C. and 1200° C. for 2 hrs. (
ramp rate 5 hrs.).FIG. 1 B shows the XRD patterns where the SIRAL transitioned from the γ to α phase at 1100° C., while the 5% silica doped alumina of this invention remains in γ phase to 1200° C. as shown inFIG. 1A ). -
TABLE 2 BET results of 0, 5, 15, 27% silica doped aluminas (SDAs) after heating at different temperatures for 2 hours BET surface Mesopore Pore Standard CalcinationT area volume diameter deviation Silica % (° C./2 hrs) (m2/g)a (cm3/g)a (nm)b (nm) 0% 700° C. 291 1.56 19.8 1.1 900° C. 208 1.12 25.5 1.2 1100° C. 119 0.77 26.7 1.6 1200° C. 15 0.05 0.00 — 5% 700° C. 378 1.83 14.7 and 35.0 1.8 900° C. 300 1.60 19.8 and 51.8 1.8 1100° C. 160 0.99 22.5 and 52.0 1.8 1200° C. 111 0.59 29.4 1.6 15% 700° C. 222 1.40 43.1 1.8 900° C. 180 1.10 39.2 1.8 1100° C. 146 0.96 33.6 1.6 1200° C. 100 0.66 31.1 1.6 27% 700° C. 195 1.0 51.6 1.5 900° C. 143 0.89 51.3 1.4 1100° C. 100 0.57 45.4 1.8 1200° C. 65 0.33 48.6 1.9 aDetermined by N2 adsorption at 77K. bDetermined by an improved slit pore geometry (SPG) model for large mesopore aluminas using the desorption branch. - Aliquots of SDA produced in Example 1, were thermally treated at 700° C., 900° C., 1100° C. and 1200° C. for 24 hrs (
ramp rate 5 hrs). Table 3 includes BET data andFIG. 4A shows XRD patterns which indicate that γ phase and trace of θ phase are seen at 1200° C. - For comparative experiments, commercial silica doped alumina (“SIRAL”) from Sasol Inc. was calcined at 700° C., 900° C., 1100° C. and 1200° C. for 24 hrs (
ramp rate 5 hrs). Table 2 includes surface area and porosity data andFIG. 4B shows the XRD patterns where the SIRAL transitions from the γ to α phase at 1100° C. while the 5% silica doped alumina of this invention remains in γ phase to 1200° C. as shown inFIG. 1A . -
TABLE 3 BET results of 5% silica doped aluminas (SDAs) and “SIRAL” 5 calcined at different temperature for 24 h BET Sample surface area (m2/g) Mesopore volume (cm3/g) Pore Diameter (nm) ID 700° C. 900° C. 1100° C. 1200° C. 700° C. 900° C. 1100° C. 1200° C. 700° C. 900° C. 1100° C. 1200° C. 5% 349 270 131 61 1.06 1.11 0.84 0.24 16.5 18.7 23.7 20.0 SDA and 51.3 Siral-5 262 203 90 28 0.61 0.56 0.33 0.13 8.8 10.5 12.4 18.6 5% SDA: 5% silica doped alumina. Siral-5: Sasol 5% silica doped alumina. - For comparative purposes, Example 1 was repeated except no dopant was used. It was thermally treated for 2 hrs (
ramp rate 5 hrs) at the same temperatures. Table 2 includes surface area and porosity data for the 0 wt. % silica batch which show significant deterioration of the surface area and pore structure with increasing temperatures as it transitioned to the alpha crystalline phase (FIG. 5A ). - Example 1 was repeated except 15 wt. % silica based on alumina in the final product was used. It was thermally treated for 2 hrs (
ramp rate 5 hrs) at the same temperatures. Table 2 includes surface area and porosity data for the 15 wt. % silica batch.FIG. 5C shows XRD patterns of the 15% silica batch which remains in γ-Al2O3 phase at 1200° C. - Example 1 was repeated except 27 wt. % silica based on the weight of alumina in the final sample was used. It was thermally treated for 2 hrs (
ramp rate 5 hrs) at the same temperatures. Table 2 includes surface area and porosity data. Alpha peaks are observed at 1100° C. (FIG. 5d ). Table 2 shows that 5 wt. % has the highest surface area and largest porosity at higher temperatures compared to others, but all of the TEOS doped samples were significantly better thermally stabilized than the control. - A sample was made according to Example 1 except 5 wt % tetra-n-butoxysilane (TNBS) was substituted for the 5 wt % TEOS. Surface area and porosity remained high after calcination at 1200° C. for 2 hours (Table 4). XRD shows (
FIG. 6 ) alpha and gamma at 1200° C. - A sample was made according to Example 1 except 5 wt % tetra n-propoxy silane (TNPS) was substituted for the 5 wt % TEOS. The surface area, pore volume, and pore diameter were still adequately high after calcination at 1200° C. for 2 hours (Table 4). XRD shows (
FIG. 6 ) that the SDA is stable with theta and gamma phases at 1200° C. - A sample was made according to Example 1 except 5 wt % polydimethyl siloxane (PDMS) was substituted for the 5 wt % TEOS. The surface area, pore volume, and pore diameter were still adequately high after calcination at 1200° C. for 2 hours (Table 4). XRD shows (
FIG. 6 ) that the sample contained some alpha with the gamma phase at 1200° C. - A sample was made according to Example 1 except 5 wt % triethoxy methyl silane (TEOMS) was substituted for the 5 wt % TEOS. Surface area, pore volume, and pore diameter were still adequately high after calcination at 1200° C. for 2 hours (Table 4). XRD shows (
FIG. 6 ) that the SDA is stable with theta and gamma phases at 1200° C. - For comparative purposes a sample was made according to Example 1 except 5 wt % Lanthanum nitrate (LaN) was substituted for 5 wt % TEOS. Substantial decreases in surface area and porosity (Table 4) show that the sample was not stabilized and XRD shows that it is in the alpha phase at 1200° C.
- For comparative purposes, a sample was made according to Example 1 except 5 wt % silicic acid (SA) was substituted for the 5 wt % TEOS. Substantial decreases in surface area and porosity (Table 4) show that the sample was not stabilized and XRD shows that it is in the alpha phase at 1200° C.
-
TABLE 4 BET results of silica doped alumina (SDA) using different silica sources after heating at different temperatures for 2 hours BET Mesopore Standard 5% different CalcinationT surface area volume Pore deviation silica sources (° C./2 hrs) (m2/g)a (cm3/g)a diameter (nm)b (nm) XRD phase PDMS* 700° C. 358 1.58 11.8, 52.8 2.1, 1.7 900° C. 272 1.54 16.2, 51.3 1.4, 1.7 1100° C. 145 0.84 40.88 2.6 1200° C. 80.5 0.44 42.24 2.2 Alpha + gamma TEOMS* 700° C. 291 1.54 18.5, 46.2 1.6, 1.7 900° C. 252 1.31 24.4 1.5 1100° C. 152 0.88 22.45 1.5 1200° C. 84.8 0.46 20.9 1.5 Theta + gamma TNBS* 700° C 305 1.76 18.3, 46.8 1.4, 1.7 900° C. 233 1.41 11.4, 54.7 6.9, 1.0 1100° C. 145 0.93 39.9 2 1200° C. 76.2 0.46 39.7 1.9 Alpha + gamma TNPS* 700° C. 320 1.88 19.8, 50.8 1.7, 1.6 900° C. 280 1.89 19.3, 49.0 1.9, 1.6 1100° C. 169 1.15 30.6 1.6 1200° C. 99.6 0.64 27.2 1.6 Theta + gamma SA* 1200° C. No stability Alpha LaN* 1200° C. No stability Alpha PDMS*: polydimethyl siloxane TEOMS*: Triethoxymethyl silane TNBS*: Tetra-n-butoxysilane TNPS*: Tetra n-proxy silane SA*: silicic acid LaN*: Lanthanum nitrate - A sample was made according to Example 1 except aluminum sec butoxide (ABu) was substituted for the aluminum isopropoxide. Surface area, pore volume, and pore diameter listed in Table 5 differ from those for the SDA derived from aluminum isopropoxide, but it is also thermally stabilized. The XRD spectra indicate that aluminum sec-butoxide derived SDA is mostly gamma at 1200° C. (
FIG. 7A ). - A sample was made according to Example 1 except aluminum tert butoxide (ATB) was substituted for the aluminum isopropoxide. Table 5 shows that the SDA is mostly gamma at 1200° C.
- For comparative purposes, a sample was made according to Example 1 except aluminum nitrate (AN) was substituted for the aluminum isopropoxide. Relatively low values of surface area, pore volume, and pore diameter listed n in Table 5 indicate that this inorganic aluminum source does not produce a thermally stabilized product. The XRD spectra indicate that the SDA is not stable and it is in the alpha phase at 1200° C. and (
FIG. 7B ). -
TABLE 5 BET results of silica doped alumina (SDA) using different aluminum sources after heating at different temperatures for 2 hours BET Mesopore Pore Standard Aluminum CalcinationT surface area Volume Diameter deviation source (° C./2 hrs) (m2/g)a (cm3/g)a (nm)b (nm) XRD phase ABu* 700° C. 392 1.13 17.1 1.44 900° C. 299 1.32 18.3 1.1 1100° C. 182 0.86 22.8 1.65 1200° C. 110 0.59 23. 6 1.35 Theta + trace alpha AN* 700° C. 252 0.31 3.5 2.24 900° C. 192 0.198 3.6 2.19 1100° C. 5 0.11 0.1 — 1200° C. 8 0.06 0 — Alpha ATB* 1200° C. 70 0.42 19.5 1.2 Gamma + alpha ABu*: Aluminum sec-butoxide AN*: Aluminum nitrate ATB*: Aluminum tert-butoxide - Sample from example 1 was thermally treated in presence of water (0.16 ml/min) for 24 hr at temperatures from 800° C. to 1200° C. Table 6 shows that surface area and porosity are also stable up to 1200° C. in the presence of steam, and
FIG. 8A shows that the alumina of this Example is mostly in gamma phase at 1100° C. -
TABLE 6 BET of 5% silica doped alumina (SDA) hydrothermally treated with water for 24 hours at different temperatures. BET Mesopore Pore surface area (m2/g)a volume (cm3/g)a Diameter (nm)b 700 900 1000 1100 1200 700 900 1000 1100 1200 700 900 1000 1100 1200 199 166 124 105 48 1.16 1.20 0.92 0.81 0.40 34.8 37.4 39.0 41.8 46.28 - Two-Step: Water and aluminum isopropoxide ere mixed in a 1:5 mole ratio for 15 min and calcined to 700° C. for 2 hrs (
ramp rate 5 hrs) to produce pure alumina. TEOS was added to the alumina to give a final concentration of 5% wt/wt silica/alumina and mixed for 30 minutes in Bosch kitchen mixer, then calcined at 700° C., 900° C., 1100° C. and 1200° C. for 2 hrs (ramp rate 5 hrs). Surface area and porosity data indicate that this two-step method also produces a thermally stable alumina product (Table 7). The XRD spectrum indicates it is γ-alumina with a trace of 0 at 1200° C. (FIGS. 9 and 10 , “SDA inFIG. 10 ). -
TABLE 7 BET results of 5% silica doped alumina (SDA) using 2-step method after heating at different temperatures for 2 hours BET surface Mesopore Pore Standard area volume diameter deviation Temperature (m2/g)a (cm3/g)a (nm)b (nm) 700 296.4 1.37 14.04 1.30 900 262.4 1.31 15.55 1.29 1100 180.5 0.87 14.48 1.22 1200 119.7 0.53 13.69 1.23 - A sample was made according to Example 20 except 5 wt % tetra-n-butoxysilane (TNBS) was substituted for the 5 wt % TEOS. XRD shows (Table 8) that the TNBS product transformed to alpha and gamma at 1200° C.
- A sample was made according to Example 20 except 5 wt % tetra n-propoxy silane (TNPS) was substituted for the 5 wt % TEOS. XRD shows (Table 8) that the TNPS product theta and gamma phases at 1200° C., indicating significant stability.
- A sample was made according to Example 20 except 5 wt % polydimethyl siloxane (PDMS) was substituted for the 5 wt % TEOS. XRD shows (Table 8) that the PDMS sample transformed to alpha at 1200° C.
- A sample was made according to Example 20 except 5 wt % triethoxy methyl silane (TEOMS) was substituted for the 5 wt % TEOS. XRD shows (Table 8) that the TEOMS product contains theta and gamma phases at 1200° C., indicating significant stability.
- For comparison purposes, a sample was made according to Example 21 except 5 wt % silicic acid (SA) was substituted for the 5 wt % TEOS. XRD shows (Table 8) that this sample transformed to alpha and gamma at 1200° C.
-
TABLE 8 XRD phase results of silica doped alumina (SDA) using different silica sources after heating at 1200° C. for 2 hours. Silica sources XRD phase at 5% 1200° C. SA* α + γ TEOMS* ⊖ + γ PDMS* α TNPS* ⊖ + γ TNBS* α + γ SA*: silicic acid TEOMS*: Triethoxymethyl silane PDMS*: polydimethyl siloxane TNPS*: Tetra n-proxy silane TNBS*: Tetra-n-butoxysilane - A sample was made according to Example 20 except aluminum sec butoxide (ABu) was substituted for the aluminum isopropoxide. Table 9 shows that SDA is thermally stable and mostly gamma at 1200° C.
- A sample was made according to Example 20 except aluminum tert butoxide (ATB) was substituted for the aluminum isopropoxide. Table 9 shows that SDA is thermally stable and mostly gamma at 1200° C.
- A sample was made according to Example 20 except aluminum phenoxide (APh) was substituted for the aluminum isopropoxide. Table 9 shows that SDA is thermally stable and mostly gamma at 1200° C.
- A sample was made according to Example 20 except aluminum ethoxide (AEt) was substituted for the aluminum isopropoxide. Table 9 shows that SDA is thermally stable and mostly gamma at 1200° C.
-
TABLE 9 XRD phase results of silica doped alumina (SDA) using different aluminum sources after heating at 1200° C. for 2 hours. Silica sources XRD phase at 5% 1200° C. A-Bu* Mostly gamma ATB* Mostly gamma APh* Mostly gamma AEt* Mostly gamma A-Bu*: Aluminum butoxide ATB*: Aluminum tert-Butoxide APh*: Aluminum phenoxide AEt*: Aluminum ethoxide - For comparative purposes, “CATAPAL”, a commercial pure alumina material obtained from Sasol, Inc. was purchased. 5% TEOS was added to the alumina followed by mixing. Following calcination at 1200° C. for 2 hrs (
ramp rate 5 hrs) the XRD pattern (FIG. 10 ) indicates that CATAPAL transitions to α-alumina by 1200° C. - For comparative purposes, “CATALOX”-SBa-90 a commercial gamma alumina obtained from Sasol, Inc. as calcined at 700° C. for 2 hrs (
ramp rate 5 hrs) to produce γ-alumina. 5% TEOS was added to the calcined alumina followed by mixing. Following calcination at 1200° C. for 2 hrs (ramp rate 5 hrs) the XRD pattern (FIG. 10 ) indicates that it is not stable at 1200° C. and transforms to α-alumina. - For comparative purposes, a “St.GOBAIN” moderately high pore volume gamma alumina as calcined at 700° C. for 2 hrs (
ramp rate 5 hrs) to produce γ-alumina. 5% TEOS was added to the calcined alumina followed by mixing. Following calcination at 1200° C. for 2 hrs (ramp rate 5 hrs) the XRD pattern (FIG. 10 ) indicates that St. GOBAIN remains in gamma phase at 1200° C. - For comparative purposes ALPHA-Aesar 99.9% gamma alumina (stock#: 43832, lot#: E08T034) as calcined at 700° C. for 2 hrs (
ramp rate 5 hrs) to produce γ-alumina. 5% TEOS was added to the calcined alumina followed by mixing. Following calcination at 1200° C. for 2 hrs (ramp time 5 hrs) the XRD pattern (FIG. 10 ) indicates that ALPHA-Aesar is not stable at 1200° C. and transforms to α-alumina. - For comparative purposes,
FIG. 11 shows that several commercial aluminas are transformed to alpha alumina at 1200° C. without addition of an organic silicon compound.
Claims (10)
1. A method for preparing a silicon-doped alumina comprising:
a) Bringing together as reactants at least one aluminum salt from the group consisting of an aluminum alkoxide, aluminum phenoxide and combinations thereof and water in an amount sufficient to hydrolyze without dissolving the reactants to produce an alumina nanoparticle precursor;
b) calcining the precursor of step a) at a temperature of from about 300-1200° C. to produce an aluminum oxide;
c) mixing the aluminum oxide of step b) with water and at least one of polydimethylsiloxane or an organic silicon compound of the structure
wherein R is selected from the group consisting of C1-C12 alkyl, C5-C12 cycloalkyl, aryl, a polyalkyl siloxane radical and combinations thereof, said water being present in an amount sufficient to hydrolyze without dissolving the reactants, and
d) calcining the product of step c) at a temperature of from about 300-1200° C.
2. The method of claim 1 wherein the aluminum salt is represented by the formula Al(O—R)3 wherein R is C1-C12 alkyl, C5-C12 cycloalkyl, aryl and combinations thereof.
3. The method of claim 1 wherein the aluminum salt is selected from the group consisting of aluminum isopropoxide, aluminum sec-butoxide, aluminum phenoxide, aluminum ethoxide, aluminum tert-butoxide, and aluminum hexoxide.
4. The method of claim 1 wherein the aluminum salt is aluminum isopropoxide.
6. The method of claim 5 wherein R is C1-C12 alkyl.
7. The method of claim 6 wherein the organic silicon compound is selected from the group consisting of tetraethyl ortho silicate, tetra-n-butyloxysilane, tetra n-propoxy silane, polydimethyl siloxane and triethoxy methyl silane and combinations thereof.
8. The method of claim 1 wherein the organic silicon compound is employed in a proportion to provide about 1%-30% silica by weight of the final product.
9. The method of claim 1 wherein the reaction of step a) is carried out in the presence of a diluent selected from the group consisting of an alcohol, a ketone, an ether or a combination thereof to adjust the pore characteristics of the final product.
10. An organic silicon-doped alumina composition having the following properties:
BET surface are at 1000° C. of >100 m2/g;
a mesopore volume at 1000° C. of at least 0.3 cm3/g; and
wherein said composition contains about 1-30 weight % silica and is substantially in the gamma form at a temperature of 1200°.
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2014
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2016
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US9289750B2 (en) | 2016-03-22 |
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