WO2008147013A2

WO2008147013A2 - Preparation methods for liquid hydrocarbons from syngas by using the zirconia-aluminum oxide-based fischer-tropsch catalysts

Info

Publication number: WO2008147013A2
Application number: PCT/KR2008/000547
Authority: WO
Inventors: Ki-Won Jun; Jong-Wook Bae; Seung-Moon Kim; Jong-Hyeok Oh
Original assignee: Korea Research Institute Of Chemical Technology; Daelim Industrial Co., Ltd.; Doosan Mecatec Co., Ltd.; Korea International Corporation; Hyundai Engineering Co., Ltd; Sk Energy Co., Ltd
Priority date: 2007-05-29
Filing date: 2008-01-30
Publication date: 2008-12-04
Also published as: KR100837377B1; EP2152413A2; WO2008147013A3

Abstract

The present invention relates to a cobalt/zirconia-alumina catalyst, in which cobalt is supported as an active ingredient on zirconia-alumina prepared by co-precipitation, having a bimodal pore structure with different pore sizes and maintaining a specific pore volume ratio and a method for preparing liquid hydrocarbons with high yield from the Fischer- Tropsch of a syngas (CO/H2/CO2 ) in the presence of the cobalt/zirconia-alumina catalyst.

Description

PREPARATION METHODS FOR LIQUID HYDROCARBONS

FROM SYNGAS BY USING THE ZIRCONIA-ALUMINUM

OXIDE-BASED FISCHER-TROPSCH CATALYSTS

Technical Field

[1] The present invention relates to a cobalt/zirconia- alumina catalyst, in which cobalt is supported as an active ingredient on zirconia- alumina prepared by co-precipitation. The catalysts show a bimodal pore structure with different pore sizes and maintaining a specific pore volume ratio and a method for preparing liquid hydrocarbons with high yield during the Fischer- Tropsch synthesis of syngas (CO/H₂/CO₂) in the presence of the cobalt/zirconia-alumina catalyst.

[2]

Background Art

[3] Recently, with the rapid increase of the international oil price, the method of producing synthetic petroleum products from synthesis gas resulting from the gasification of natural gas, coal or biomass becomes more and more important. In this regard, the preparation of liquid hydrocarbons by the gas-to-liquids (GTL) process can solve various problems as outlined below because the final product is in the liquid form.

[4] (1) The liquid product is easy to handle and can be transported across a long distance.

(2) The existing facilities can be utilized without the need of special transport, shipping and storing facilities. (3) High-price, clean products can be sold immediately after production. (4) Economical utilization of stranded/remote gases, or the medium- to-small scale gas resource distant from the demand site, becomes possible, without special transport facilities as in the case of LNG, if the reserve amounts to 1 trillion cubic feet.

[5] Since the Fischer-Tropsch (hereinafter referred to as F-T) was first developed in the

1920s, the GTL process has been refined and adjusted continuously. The GTL technology based on the F-T synthesis not only improves the environmental problem at the gas field, but also enables the production of clean synthetic fuels through processing of the flared gas. Further, the GTL products, which are clean liquid fuels with little sulfur content, may provide a better market value than those of the conventional petroleum products produced by refining a crude oil. In 2004, for instance, the US, Europe, Japan, etc., reduced the sulfur content in the diesel oil for cars from 500 ppm to 50 ppm and they are expected to further lower to below 10 ppm in the near future. [6] The F-T synthetic oil is a fuel that can effectively cope with the recently reinforced environmental regulations from developed countries, along with the recent regulations of the Kyoto Protocol. According to Sasol s LCA study, with little sulfur and aromatic compounds, the GTL synthetic fuel gives off less exhaust gas and nitrogen oxides and is capable of reducing the atmospheric acidification by more than 40 %. Further, the emission of particulate matters (PM) can be reduced by more than 40 % and the utilization of F-T synthetic oil in cars is expected to reduce the emission of greenhouse gas by at least 12 % through increased thermal efficiency.

[7] The F-T synthesis, the core process in the GTL technique, originates from the preparation of synthetic fuel from syngas by coal gasification invented by German chemists Fischer and Tropsch in 1923. The GTL process consists of the three major sub-processes of (1) reforming of natural gas, (2) F-T synthesis of syngas and (3) reforming of product. The F-T reaction which is performed at a reaction temperature of 200 to 350 ⁰C and a pressure of 10 to 30 atm using iron and cobalt as catalyst can be described by the following four key reactions.

[8] (a) Chain growth in F-T synthesis

[9] CO + 2H₂ → -CH₂- + H₂O ΔH(227 ⁰C) = -165 kJ/mol

[10] (b) Methanation

[11] CO + 3H₂ → CH₄ + H₂O ΔH(227 ⁰C) = -215 kJ/mol

[12] (c) Water gas shift reaction

[13] CO + H₂O <→ CO₂ + H₂ ΔH(227 ⁰C) = -40 kJ/mol

[14] (d) Boudouard reaction

[15] 2CO <→ C + CO₂ ΔH(227 ⁰C) = - 134 kJ/mol

[16] The mechanism by which the main product, or the straight-chain hydrocarbons, is produced is mainly explained by the Schulz-Flory polymerization kinetic scheme. In the F-T process, more than 60 % of the primary product has a boiling point higher than that of diesel oil. Thus, diesel oil can be produced by the following hydrocracking process and the wax component can be transformed into a high-quality lubricant base oil through the dewaxing process.

[17] In general, the current reforming process of atmospheric residue or vacuum residue used in the refinery plant is a reliable one owing to the improvement of catalysts and processing techniques. However, for the F-T synthetic oil, further development of an adequate hydrocarbon reforming process is required, because there is a big difference in compositions and physical properties from the source material used in the refinery plant. Examples of the processes for treating the primary product of the F-T reaction include hydrocracking, dewaxing, isomerization, allylation, and so forth. The major products of the F-T reaction include naphtha/gasoline, middle distillates with a high centane number, sulfur- and aromatic-free liquid hydrocarbons, α-olefins, oxygenates, waxes, and so forth.

[18] For the F-T reaction, mainly iron- and cobalt-based catalysts are used. The iron- based catalysts were preferred in the past for F-T reaction. But, recently, the cobalt catalysts are predominant in order to increase the production of liquid fuel or wax and to improve conversion. Iron-based catalysts are advaantageous for the F-T reaction as they are the most inexpensive F-T reaction catalysts producing less methane at high temperature and having high selectivity for olefins and the product can be utilized as source material in chemical industry as light olefin or α-olefin, as well as fuel. In addition, many byproducts, including alcohols, aldehydes, ketones, etc., are produced in addition to hydrocarbons. Furthermore, the iron-based catalyst mainly used in the low-temperature F-T reaction for wax production by Sasol comprises Cu and K components as cocatalyst and is produced by the precipitation using SiO₂ as a binder. The Sasol's high-temperature F-T catalyst is prepared by melting magnetite, K, alumina, MgO, etc.

[19]

Disclosure of Invention Technical Problem

[20] Cobalt-based catalysts are more expensive than Fe-based catalysts. But, they have higher activity, longer lifetime and higher yield of liquid paraffin-based hydrocarbon production with less CO₂ generation. However, they can be used only at low temperature because the excessive CH₄ is produced at high temperature. Further, with the usage of expensive cobalt, the catalysts are prepared by dispersing on a stable support with a large surface area, such as alumina, silica, titania, etc. A small amount of a precious metal cocatalyst such as Pt, Ru, Re, etc., is added as cocatalyst.

[21] At present, there are four types of F-T synthesis reactors: circulating a fluidized bed reactor, a fluidized bed reactor, a multitubular fixed bed reactor and a slurry-phase reactor. The reactor should be adequately selected considering the syngas composition and the final product, because they have different reaction properties. The F-T process parameters are determined by the final product. Typically, the high-temperature F-T process for producing gasoline and olefin is carried out in the fluidized bed reactor and the low-temperature F-T process for producing wax and lubricant base oil is carried out in the multitubular fixed bed reactor (MTFBR) or in the slurry-phase reactor. Mostly, linear-chain paraffins are produced by the F-T synthesis reaction, but C_nH_2n compounds having double bonds, α-olefins or alcohols are obtained as the byproduct from side reactions.

[22] Typically, in order to disperse the highly expensive active components, cobalt or other activation substance is introduced to a support having a large surface area, such as alumina, silica, titania, etc., to prepare a catalyst. In the F-T reaction, a catalyst prepared by dispersing cobalt on a single-component or multi-component support is commercially utilized. However, if the particle size of cobalt included in the support is similar, the activity of the F-T reaction does not change much from the usage of one support to another [Applied Catalysis A 161 (1997) 59]. On the contrary, the activity of the F-T reaction is greatly affected by the dispersion and particle size of cobalt [ Journal of American Chemical Society, 128 (2006) 3956]. Accordingly, a lot of attempts are being made to improve the FTS activity and stability by modifying the surface property of the supports by pretreating them with different metal components.

[23] For instance, when cobalt-supported alumina is used, the surface characteristics of γ- alumina may be transformed into boehmite because of the water produced during the reaction. As a result, the catalyst may become deactivated or thermal stability may be reduced due to the increased oxidation rate of the cobalt component. In order to overcome this problem, there is a method for improving the stability of the catalyst by pretreating the surface of alumina using a silicon precursor [WO 2007/009680 Al].

[24] The other method of improving the activity of the F-T catalyst, there is a method of improving the stability of the catalyst by increasing the transfer rate of the compounds having a high boiling point produced during the F-T reaction, by preparing a silica- alumina catalyst having a bimodal pore structure is reported [US 2005/0107479 Al; Applied Catalysis A 292 (2005) 252]. However, the aforementioned methods are associated with the complicated processes of forming a support with a bimodal pore structure using a polymer substrate or physically mixing two alumina-silica gels prepared so as to have different pore sizes and then supporting cobalt or other active component.

[25] In case silica is used as a support, the decrease in reduction to cobalt metal and consequent reduction of activity is observed due to the strong interaction between cobalt and the support, as compared with the alumina support. It was reported that pretreating of the silica surface with zirconium or other metal is effective in overcoming this problem [EP 0167215 A2; Journal of Catalysis 185 (1999) 120].

[26] The aforesaid F-T catalysts show various specific surface areas, but the activity of the F-T reaction is known to be closely related with the particle size of the cobalt component, pore size distribution of the support and reducing tendency of the cobalt component. To improve these properties, a preparation method of the F-T catalyst by including the cobalt component through a well-known method on the support prepared through a complicated process is reported.

[27]

Technical Solution [28] The present inventors have demonstrated to develop a catalyst suitable for the

Fischer- Tropsch reaction with superior activity and heat- and matter-transfer performance in order to solve the aforementioned problems in an economical and efficient way.

[29] As a result, a catalyst having a bimodal pore structure was prepared on a zirconia- alumina support consisting of a predetermined proportion of ZrO₂ and Al₂O₃ prepared by the co-precipitation. The cobalt is supported by the co-precipitation to achieve uniform dispersion of cobalt on the support with a smaller pore size PSi and pores of a larger size PS₂. With the distribution of the larger and smaller pores maintained at a specific ratio, the catalyst exihibits better heat- and matter-transfer performance than the conventional unimodal catalyst. With the modification of alumina surface of the support by the zirconia component, the chemical properties such as the dispersion of the active component, electronic state, reducible properties, are improved. This enables the improvement of F-T reaction using the catalyst, one-pass yield of carbon monoxide and hydrogen and long-term stability of the catalyst.

[30] Accordingly, the objective of the present invention is to provide a cobalt/ zirconia- alumina catalyst having larger and smaller pores prepared by supporting cobalt on a zirconia-alumina support comprising ZrO₂ and Al₂O₃ and having a predetermined specific surface area obtained through co-precipitation as an active ingredient and a preparation method of liquid hydrocarbons from a syngas using the same.

[31]

Advantageous Effects

[32] In the development of the GTL technology, which is gaining spotlight as a solution to the abrupt increase of oil price of recent times, the improvement of the catalyst for the F-T synthesis is directly associated with the developement of the competitiveness of the GTL technology. In this regard, the cobalt/zirconia-alumina catalyst in accordance with the present invention offers advantages in the competitive design and development of a GTL process with significantly improved carbon efficiency. This enables the improvement of thermal efficiency and carbon efficiency in the GTL process, the systematic design of the F-T reaction process and reduced selectivity to methane and increased selectivity to liquid hydrocarbons having 5 or more carbon atoms.

[33]

Brief Description of the Drawings

[34] Figure 1 shows the conversion of carbon monoxide with reaction time after performing Fischer- Tropsch using the catalyst of the present invention (Example 1, 0.5 wt% Ru/20 wt% Co/5 wt% ZrO₂-Al₂O₃) and the catalyst prepared in Comparative Example 1 (20 wt% Co/80 wt% Al₂O₃).

[35] Figure 2 shows the pore distribution of the catalyst of the present invention (Example

1, 0.5 wt% Ru/20 wt% Co/5 wt% ZrO₂-Al₂O₃; Example 3, 20 wt% Co/5 wt% ZrO₂-Al₂ O₃), as compared with those of Comparative Example 1 (20 wt% Co/Al₂O₃) and Comparative Example 2 (0.5 wt% Ru/20 wt% Co/5 wt% Zr/Al₂O₃).

[36] Figure 3 shows the electron micrographs of the catalyst of the present invention

(Example 1, 0.5 wt% Ru/20 wt% Co/5 wt% ZrO₂-Al₂O₃) at (a) 20,000 and (b) X 100,000.

[37]

Mode for the Invention

[38] The present invention provides a catalyst for Fischer- Tropsch reaction in which cobalt is supported on a support as an active ingredient. The catalyst being a cobalt/ zirconia- alumina catalyst in which the cobalt is supported on a zirconia- alumina support comprising Al₂O₃ and ZrO₂ as an active ingredients with a bimodal pore structure with pores of a relatively smaller size PSi and of a larger size PS₂. The pore sizes PSi and PS₂ are in the range described below. The ZrO₂ being comprised in the amount of 1 to 30 wt% per 100 wt% of the Al₂O₃ and the cobalt being comprised in the amount of 5 to 40 wt% per 100 wt% of the support:

[40] 10 nm < PS₂ < 200 nm.

[41] Hereunder a detailed description of the present invention is given.

[42] Conventionally, in the F-T reaction for preparing liquid hydrocarbons from a syngas, a cobalt component or other active component is dispersed on a support having a large surface area, such as alumina, silica, titania, etc. If the only cobalt component is added, the dispersion and reducing property of the active component decreases as the pores may be clogged by the compounds having a high boiling point produced during the reaction, leads to accelerated deactivation of the catalyst. To overcome this problem, attempts are being made to improve the activity and stability of the Fischer- Tropsch synthesis (FTS) by modifying the properties of the support through the modification or pretreatment of the support with another metal oxide component.

[43] As for the alumina support, the water produced during the reaction may cause the change of the surface property of the -alumina to that of boehmite, etc. Therefore, various methods of pre-treating with another component have been introduced to improve thermal stability of alumina. Besides, when silica is used as a support, a stronger interaction occurs between cobalt and the support than with an alumina support leads to the reducing tendency to cobalt metal and consequently decreases the activity. To overcome this problem, a method is proposed to pre-treat the silica surface with metal oxide as zirconium oxide. Especially, as an effective strategy, numerous attempts have been made to ensure long-term stability of the catalyst by improving the rate of transfer of compounds having a high boiling point and heat transfer, using a support having a bimodal pore structure.

[44] A support comprising zirconia and alumina and having a bimodal pore structure is disclosed in Korean Patent No. 10-388310. The pores of the support have sizes in the range of from 0.05 to 1 μm and from 1 to 10 μm. Each powder component of the support is mixed with each other and then the active component is supported on it in order to prepare a catalyst having a broad pore distribution.

[45] That is, the aforesaid patent relates to a catalyst prepared by supporting an active component on a zirconia-alumina support having a bimodal pore distribution. In contrast, in the present invention, cobalt is supported on a zirconia-alumina support with unimodal pores smaller than 10 nm to obtain a catalyst having a bimodal pore structure. Thus, the former relates to a support having a bimodal pore distribution, while the present invention relates to a catalyst having a bimodal pore structure. Such apparent difference leads to catalysts with totally different pore sizes, specific surface areas, and, consequently, to totally different applications. That is, the cited invention is for the conversion of hydrocarbons, while the present invention is for the Fischer- Tropsch reaction.

[46] In the field of catalysts, it will be understood that even if the same catalyst is used, the difference in application and active component leads to a totally differenct effect and activity. Although the component of the support is similar, the present invention is totally different from the cited invention in the structure of the support, pore size of the support, preparation method of the support, active component, application of the catalyst, etc. Therefore, the catalysts resulting from them are totally different.

[47] In conclusion, the present invention is characterized not by the support, but by performing the Fischer- Tropsch reaction using a cobalt/zirconia-alumina catalyst having a bimodal pore structure prepared by supporting cobalt as an active ingredient on a support having unimodal pores. Such a catalyst has never been utilized in the above field.

[48] The present invention provides a preparation method for a zirconia-alumina catalyst comprising cobalt and having a bimodal pore structure different from the conventional one.

[49] That is, according to the present invention, a catalyst having a bimodal pore structure is prepared by preparing a support comprising alumina and zirconia and then supporting cobalt, or the active component, on the support by co-precipitation. The co- precipitation method is commonly known in the related art, but, in the present invention, zirconia and aluminum precursor are co-precipitated using an adequate pre- cipitant under appropriate precipitation condition in order to form pores in the support smaller than 10 nm only. Then, using the resultant zirconia- alumina support with unimodal pores, the cobalt component is co-precipitated to prepare a catalyst having a bimodal pore structure. The methods of obtaining the porous support and preparing the F-T catalyst having a bimodal pore structure are not easily achievable from the conventional methods.

[50] When a catalyst is prepared by the known co-precipitation method, a support having a broad pore distribution is attained and a catalyst obtained by supporting a cobalt component on the support does not have superior activity. It is reported that a support having a too broad pore distribution results in a reduced dispersion of the cobalt component and consequent decrease in catalytic activity, while a support having a pore distribution within 10 nm offers superior F-T catalytic activity [Journal of Molecular Catalysis A 247 (2006) 206]. In the present invention, a zirconia-alumina support having pores of the size 10 nm or smaller on the first hand and then a cobalt component is co-precipitated to improve dispersion of the cobalt component and prevent clogging of the pores by the compounds having a high boiling point produced during the reaction. Accordingly, the cobalt/zirconia-alumina catalyst having a bimodal pore structure of the present invention, which is obtained by preparing a zirconia-alumina support having pores of the size 10 nm or smaller by co-precipitation and then supporting cobalt as an active ingredient on the support having unimodal pores by co-precipitation, offers the improved F-T catalytic activity.

[51] In general, a support comprising alumina has a broad pore distribution and is mainly prepared by sol-gel method or precipitation. In such a case, the unimodal pores are distributed over a large area and, when cobalt is supported on it the particle size distribution becomes non-uniform and the particle size tends to increase. If the F-T reaction is performed using such a catalyst, the compounds having a high boiling point produced during the reaction may clog the pores and, thereby, significantly reduces the activity of the catalyst. In contrast, the present invention provides a cobalt/ zirconia-alumina catalyst having a bimodal pore structure with relatively small-sized and large-sized pores prepared by the co-precipitation, ensures high yield of liquid hydrocarbons in the F-T reaction.

[52] The zirconia-alumina support of the catalyst for the F-T reaction is prepared by the co-precipitation and has pores with a pore size of 10 nm or smaller with a specific surface area in the range 150 to 400 m²/g. In the zirconia-alumina support, zirconium metal is comprised of 1 to 30 wt% per 100 wt% of alumina. If the content is smaller than 1 wt%, it does not improve much the dispersion and reducing property of the active component of cobalt. If it exceeds 30 wt%, specific surface area of the zirconia- alumina support decreases, which may result in the decrease of the dispersion of cobalt.

[53] The catalyst of the present invention may be prepared by the following two methods.

[54] The first method is a two-step process comprising: co-precipitating by adding a basic precipitant to an aqueous solution mixture including a zirconium precursor and an alumina precursor at pH 7 to 8, aging and baking at 300 to 900 ⁰C to prepare a zirconia- alumina support; and co-precipitating by adding an aqueous solution including a cobalt precursor and a basic precipitant to the prepared zirconia-alumina support at pH 7 to 8, aging and baking at 200 to 700 ⁰C to prepare a cobalt/ zirconia-alumina catalyst having a bimodal pore structure with a smaller pore size PSi and pores of a larger size PS₂.

[55] The second method is a three-step process comprising: co-precipitating by adding a basic precipitant to an aqueous solution including a zirconium precursor and an alumina precursor at pH 7 to 8 and aging to prepare a slurry-phase zirconia-alumina support; co-precipitating by adding a basic precipitant to an aqueous solution including a cobalt precursor at pH 7 to 8 and aging to prepare a cobalt slurry; and mixing the prepared slurry-phase zirconia-alumina support and the cobalt slurry, drying and baking at 200 to 700 ⁰C to prepare a cobalt/zirconia-alumina catalyst having a bimodal pore structure with a smaller pore size PSi and pores of a larger size PS₂.

[56] The zirconia-alumina support is prepared by co-precipitation. The co-precipitation is performed using a precipitant commonly used in the art. The precursors of the metals used in the preparation are those commonly used in the art and not particularly limited. Specifically, the alumina precursor may be aluminum nitrate (A1(NO₃)₃9H₂O) or aluminum isopropoxide (A1[OCH(CH₃)₂]₃) and the zirconium precursor may be zirconium nitrate (Zr(NO₃)₂2H₂O) or zirconium chloroxide (ZrCl₂O- 8H₂O). During the co-precipitation, a basic precipitant is used to maintain pH at 7 to 8. Specifically, sodium carbonate (Na₂CO₃), potassium carbonate (K₂CO₃), ammonium carbonate ((NH 4)₂CO₃), ammonia water, etc., may be used.

[57] The alumina and zirconium precursors are co-precipitated in an aqueous solution of pH 7 to 8 using the aforesaid precipitant and aged at 40 to 90 ⁰C. Then, the precipitate is filtrated and washed. The zirconia-alumina support is prepared so as to comprise 1 to 30 wt% of zirconium oxide and 70 to 99 wt% of Al₂O₃. If the aging temperature is below 40 ⁰C, it is difficult to obtain a zirconia-alumina support having unimodal pores adequate for the F-T reaction. And, if it exceeds 90 ⁰C, the particle size of the support increases and, thus, the specific surface area decreases. The aging is performed for 0.1 to 15 hours, preferably for 0.5 to 10 hours, in order to form a structure advantageous to the activity. If the aging time is shorter than 0.1 hour, the structure of the zirconia- alumina support does not develop sufficiently. And, if it exceeds 15 hours, particle size increases and, thus the activity decreases and the synthesis time increases. [58] The resultant precipitate is washed and dried for about a day in an oven of 100 ⁰C or higher. Then, a cobalt component is supported on the precipitate and baking is performed to apply for the F-T reaction. Alternatively, the cobalt component may be supported after baking the zirconia-alumina support.

[59] To be specific, the active component of cobalt may be included in the zirconia- alumina support by the following two methods.

[60] First, a slurry solution is prepared using the prepared powdery zirconia-alumina support. Then, a cobalt precursor is co-precipitated in an aqueous solution at pH 7 to 8 using a co-precipitant. After aging at 40 to 90 ⁰C, the precipitate is filtrated and washed for use. The F-T catalyst is prepared such that the cobalt component is comprised in the amount of 5 to 40 wt% per 100 wt% of the zirconia-alumina support. If the content of cobalt is less than 5 wt%, the shortage of the active component required for the F-T reaction may result in the reduction of conversion and decrease in the production of the compounds having a high boiling point. And, if it exceeds 40 wt%, the use of the expensive cobalt component results in increased cost and the decrease of the dispersion of the cobalt component leads to a minimal increase in activity. Hence, the aforesaid range is preferable.

[61] During the co-precipitation, a basic precipitant is used to maintain pH at 7 to 8, as described earlier. The aging is performed at 40 to 90 ⁰C, preferably at 50 to 80 ⁰C. If the temperature of aging the catalyst is below 40 ⁰C, it is difficult to attain cobalt with uniform particle size and shape, which makes the supporting of the cobalt component difficult. If it exceeds 90 ⁰C, the particle size of cobalt increases due to coagulation, which results in the decrease of specific surface area and reaction activity. The aging time is maintained for 0.1 to 15 hours, preferably for 0.5 to 10 hours, since the aging time in the recommended range is advantageous in the formation of a cobalt-supported zirconia-alumina catalyst with superior activity. An aging time shorter than 0.1 hour is unfavorable with regard to the F-T reaction because of reduced dispersion of cobalt. And, if the aging time exceeds 15 hours, the number of active sites decreases and the synthesis time increases because of increased particle size of cobalt.

[62] The resultant precipitate is washed and dried at 100 ⁰C or above, specifically for about a day in an oven of 100 to 150 ⁰C. Such prepared precipitate may be directly used for the synthesis of the F-T reaction catalyst or may be baked after supporting a second precious metal catalyst component.

[63] The zirconia-alumina catalyst on which cobalt has been supported is baked at 200 to

700 ⁰C, preferably at 300 to 600 ⁰C. If the baking temperature is below 200 ⁰C, interaction between cobalt and the support may be inadequate and particle size may increase during the reaction. And, if it exceeds 700 ⁰C, dispersion and catalytic activity may decrease because of the increased particle size of the cobalt component. Hence, the aforesaid range is preferable.

[64] The F-T catalyst may also be prepared using the powdery zirconia-alumina support, as follows. A cobalt precursor is co-precipitated in an aqueous solution of pH 7 to 8 and is aged at 40 to 90 ⁰C. Then, the precipitate is baked at 300 to 900 ⁰C, preferably at 400 to 800 ⁰C, to prepare a zirconia-alumina support.

[65] If the baking temperature is below 300 ⁰C, γ-alumina is not formed adequately and activity may decrease because of the phase transition of the support caused by the water produced during the F-T reaction. And, if it exceeds 900 ⁰C, dispersion of cobalt may become inappropriate due to the decrease of the specific surface area of the zirconia-alumina support.

[66] Subsequently, the cobalt/zirconia-alumina catalyst is prepared by supporting the cobalt component. The use of basic precipitant during the co-precipitation and the process of aging, washing and drying of the catalyst are the same as described above.

[67] After washing and drying, the prepared cobalt component is mixed with the zirconia- alumina support prepared by baking in water or an alcohol solution while stirring to prepare the wanted cobalt-supported zirconia-alumina catalyst. Such prepared precipitate may be directly used for the synthesis of the F-T reaction catalyst after washing and drying for about a day in an oven of 100 ⁰C or higher or may be baked after supporting a second precious metal catalyst component.

[68] The resultant cobalt-supported zirconia-alumina catalyst for F-T reaction has a bimodal pore structure, the final specific surface area ranging from 100 to 300 m²/g and having pores of smaller size ranging from 2 to 10 nm and pores of larger size ranging from 10 to 200 nm. And, the proportion of the volume PVi of the smaller pores of 2 to 10 nm to the volume PV₂ of the larger pores of 10 to 200 nm, or PVi/PV₂, is maintained in the range of from 0.5 to 2.0. If the ratio is smaller than 0.5, specific surface area of the cobalt component decreases because of the increase of larger pores and, resultantly, activity may decrease. If it exceeds 2.0, the dispersion decreases because of the increase of smaller pores and, resultantly, activity may decrease.

[69] In addition, a precious metal component may be used to improve reducing property of the cobalt active component and inhibit oxidation of the cobalt active component by water. Specifically, a precursor such as ruthenium, rhenium, platinum, etc., may be used in the form of nitrate salt, acetate salt or chloride salt. The precious metal component is used in 0.05 to 1 wt% per 100 wt% of the zirconium precursor. If it is used less than 0.05 wt%, the effect is insignificant. If in excess of 1 wt%, the catalyst manufacture cost increases and selectivity for methane increases.

[70] As compared with the conventional alumina, titania or silica support pre-treated with various metal components, the support of the present invention facilitates the transfer of the compounds having a high boiling point produced during the reaction while further improving dispersion and reducing property of the cobalt and other active components. Consequently, it reduces the production of methane and improves the selectivity for liquid hydrocarbons via improved FT reactivity.

[71] The present invention further provides a preparation method for liquid hydrocarbons using the catalyst from a syngas by the Fischer- Tropsch reaction. The F-T reaction may be performed as commonly carried out in the art and is not particularly limited. In the present invention, the F-T reaction is performed using the catalyst in a fixed bed, a fluidized bed or slurry reactor, in the temperature range of from 200 to 700 ⁰C, after reducing under hydrogen atmosphere. Using the reduced F-T reaction catalyst, F-T reaction is performed in a standard condition, specifically at a temperature of 300 to 500 ⁰C, at a pressure of 30 to 60 kg/cm² and at a space velocity of 1000 to 10000 h \ although not limited thereto.

[72] Such prepared catalyst provides an F-T reaction conversion of 10 to 50 mol% and a selectivity for hydrocarbons with five carbon atoms or more, specifically naphtha, diesel, middle distillate, heavy oil, wax, etc., of 83 mol% or higher.

[73]

[74] Hereinafter, the present invention is described in detail through examples. However, the following examples do not limit the present invention.

[75]

[76] Example 1

[77] A solution in which 10.8 g of zirconium nitrate (ZrO(NO₃)₂2H₂O; Kanto Chem.), a zirconium precursor, and 55.2 g of aluminum nitrate (A1(NO₃)₃9H₂O; Samchun Chem.), an alumina precursor, are dissolved in 600 mL of deionized water and a solution in which 71.4 g of potassium carbonate (K₂CO₃), a precipitant, is dissolved in 600 mL of deionized water were simultaneously added dropwise into a 2000 mL flask holding 200 mL of deionized water at 70 ⁰C at a rate of 5 mL/min, while stirring and maintaining pH at 7 to 8. The slurry solution was stirred and aged for about 3 hours at 70 ⁰C. The precipitant was removed by washing with 1800 mL of deionized water and filtering. Subsequently, after drying at 100 ⁰C for 12 hours, a 5 wt% powdery zirconia- alumina support was prepared by baking for 5 hours under air atmosphere at 500 ⁰C. The prepared support had pores of 10 nm or smaller only and the specific surface area was 299 m²/g and the pore volume was 0.47 cmVg.

[78] An aqueous cobalt precursor solution in which 8.5 g of cobalt acetate (Co(CH₃COO)₂

4H₂O), a cobalt precursor, is dissolved in 300 mL of deionized water and a potassium carbonate precursor aqueous solution in which 10.8 g of potassium carbonate (K₂CO₃), a precipitant, is dissolved in 300 mL of deionized water were prepared. The powdery 5 wt% zirconia- alumina support was prepared into a slurry phase in 200 mL of deionized water. The cobalt precursor aqueous solution, the potassium carbonate precursor aqueous solution and the 5 wt% zirconia- alumina support slurry were simultaneously added dropwise at a rate of 5 mL/min to a 2000 mL flask at 70 ⁰C, while stirring and maintaining pH at 7 to 8. The slurry solution was stirred and aged for about 1 hour at 70 ⁰C. The precipitant was removed by washing with 1800 mL of deionized water and filtering. Subsequently, after drying at 100 ⁰C for 12 hours or more, a 20 wt% Co/5 wt% ZrO₂-Al₂O₃ catalyst was prepared by baking for 5 hours under air atmosphere at 500 ⁰C.

[79] Subsequently, 0.5 wt% ruthenium nitrosyl nitrate (Ru(NO) (NO₃)₃) was supported on the 20 wt% Co/5 wt% ZrO₂-Al₂O₃ catalyst. After removing the solution using a rotary evaporator and drying, a 0.5 wt% Ru/20 wt% Co/5 wt% ZrO₂-Al₂O₃ catalyst was prepared by baking at 400 ⁰C for 5 hours under oxygen atmosphere. The prepared catalyst had a bimodal pore structure, the specific surface area being 245 m²/g and the pore volume being 0.80 cmVg, particularly the volume ratio of the smaller pores to the large pores PWPV₂ being 0.84.

[80] About 0.3 g of the prepared 0.5 wt% Ru/20 wt% Co/5 wt% ZrO₂-Al₂O₃ catalyst was placed in a 1/2-inch stainless steel fixed bed reactor and reduced for 12 hours under hydrogen atmosphere (5 vol% H₂/He) at 400 ⁰C before conducting a reaction. Subsequently, the reactants carbon monoxide, hydrogen, carbon dioxide and argon (internal standard) were supplied to the reactor at a fixed molar proportion of 28.4 : 57.3 : 9.3 : 5 under the condition of: reaction temperature = 220 ⁰C; reaction pressure = 20 kg/cm²; and space velocity = 2000 L/kg cat/hr. The contents of the product of the Fischer- Tropsch reaction are summarized in Table 1. The steady-state condition was obtained after around 60 hour operation and the averaged values for 10 hours at the steady-state were taken.

[81]

[82]

[83] Example 2

[84] A solution in which 10.8 g of zirconium nitrate (ZrO(NO₃)₂2H₂O; Kanto Chem.), a zirconium precursor, and 55.2 g of aluminum nitrate (A1(NO₃)₃9H₂O; Samchun Chem.), an alumina precursor, are dissolved in 600 mL of deionized water and a solution in which 71.4 g of potassium carbonate (K₂CO₃), a precipitant, is dissolved in 600 mL of deionized water were simultaneously added dropwise into a 2000 mL flask holding 200 mL of deionized water at 70 ⁰C at a rate of 5 mL/min, while stirring and maintaining pH at 7 to 8. The slurry solution was stirred and aged for about 3 hours at 70 ⁰C. The precipitant was removed by washing with 1800 mL of deionized water and filtering to prepare a 5 wt% zirconia- alumina precipitate in the form of cake.

[85] An aqueous cobalt precursor solution in which 8.5 g of cobalt acetate (Co(CH₃COO)₂

4H₂O), a cobalt precursor, is dissolved in 300 mL of deionized water and a potassium carbonate precursor aqueous solution in which 10.8 g of potassium carbonate (K₂CO₃), a precipitant, is dissolved in 300 rnL of deionized water were prepared. The solutions were simultaneously added dropwise at a rate of 5 mL/min to a 2000 mL flask holding 200 mL of deionized water at 70 ⁰C, while stirring and maintaining pH at 7 to 8. The slurry solution was stirred and aged for about 1 hour at 70 ⁰C. The precipitant was removed by washing with 1800 mL of deionized water and filtering to obtain cobalt precipitate in the form of cake.

[86] Each prepared zirconia- alumina precipitate and cobalt precipitate in the form of cake was stirred for over 1 hour in 200 mL of deionized water at room temperature to obtain a zirconia-alumina slurry containing cobalt. After filtering, the prepared slurry was dried in an oven at 100 ⁰C for over 12 hours and baked for 5 hours under air atmosphere at 500 ⁰C to prepare a 20 wt% Co/5 wt% ZrO₂-Al₂O₃ catalyst.

[87] Subsequently, 0.5 wt% ruthenium nitrosyl nitrate (Ru(NO) (NO₃)₃) was supported on the 20 wt% Co/5 wt% ZrO₂-Al₂O₃ catalyst. After removing the solution using a rotary evaporator and drying, a 0.5 wt% Ru/20 wt% Co/5 wt% ZrO₂-Al₂O₃ catalyst was prepared by baking at 400 ⁰C for 5 hours under oxygen atmosphere. The prepared catalyst had a bimodal pore structure, the specific surface area being 220 m²/g and the pore volume being 0.62 cmVg, particularly the volume ratio of the smaller pores to the large pores PVi/PV₂ being 1.27.

[88] About 0.3 g of the prepared 0.5 wt% Ru/20 wt% Co/5 wt% ZrO₂-Al₂O₃ catalyst was put in a 1/2-inch stainless steel fixed bed reactor and reduced for 12 hours under hydrogen atmosphere (5 vol% H₂/He) at 400 ⁰C before conducting a reaction. Subsequently, the reactants carbon monoxide, hydrogen, carbon dioxide and argon (internal standard) were supplied to the reactor at a fixed molar proportion of 28.4 : 57.3 : 9.3 : 5 under the condition of: reaction temperature = 220 ⁰C; reaction pressure = 20 kg/cm²; and space velocity = 2000 L/kg cat/hr. The contents of the product of the Fischer- Tropsch reaction are summarized in Table 1. The steady-state condition was obtained after around 60 hour operation and the averaged values for 10 hours at the steady-state were taken.

[89]

[90]

[91] Example 3

[92] A 20 wt% Co/5 wt% ZrO₂-Al₂O₃ catalyst was prepared in the same manner as in

Example 2, except for excluding ruthenium. The prepared catalyst had a bimodal pore structure, the specific surface area being 238 m²/g and the pore volume being 0.53 cm³ / g, particularly the volume ratio of the smaller pores to the large pores PVi/PV₂ being 1.43.

[93] Approximately 0.3 g of the prepared 0.5 wt% Ru/20 wt% Co/5 wt% ZrO₂-Al₂O₃ catalyst was put in a 1/2-inch stainless steel fixed bed reactor and reduced for 12 hours under hydrogen atmosphere (5 vol% H₂/He) at 400 ⁰C before conducting a reaction. Subsequently, the reactants carbon monoxide, hydrogen, carbon dioxide and argon (internal standard) were supplied to the reactor at a fixed molar proportion of 28.4 : 57.3 : 9.3 : 5 under the condition of: reaction temperature = 220 ⁰C; reaction pressure = 20 kg/cm²; and space velocity = 2000 L/kg cat/hr. The contents of the product of the Fischer- Tropsch reaction are summarized in Table 1. The steady-state condition was obtained after around 60 hour operation and the averaged values for 10 hours at the steady-state were taken.

[94]

[95] Example 4

[96] A 0.5 wt% Ru/20 wt% Co/5 wt% ZrO₂- Al₂O₃ catalyst was prepared in the same manner as in Example 1. The prepared catalyst was reduced with hydrogen at 400 ⁰C for 12 hours and introduced to a slurry reactor after sealing. 300 mL of squalane was added as solvent in the slurry reactor. After adding 5 g of the catalyst, another reduction was performed at 220 ⁰C for over 12 hours. The reactants carbon monoxide, hydrogen, carbon dioxide and argon (internal standard) were supplied to the reactor at a fixed molar proportion of 28.4 : 57.3 : 9.3 : 5 under the condition of: reaction temperature = 220 ⁰C; reaction pressure = 20 kg/cm²; space velocity = 2000 L/kg cat/hr; and stirring rate = 200 rpm. The contents of the product of the Fischer-Tropsch reaction are summarized in Table 1. The steady-state condition was obtained after around 60 hour operation and the averaged values for 10 hours at the steady- state were taken.

[97]

[98] Example 5

[99] Fischer-Tropsch reaction was performed in the same manner as in Example 4, except for changing the reaction temperature to 240 ⁰C. The contents of the product of the Fischer-Tropsch reaction are summarized in Table 1. The steady-state condition was obtained after around 60 hour operation and the averaged values for 10 hours at the steady-state were taken.

[100]

[101] Example 6

[102] A 0.5 wt% Ru/20 wt% Co/5 wt% ZrO₂-Al₂O₃ catalyst was prepared in the same manner as in Example 1, except for using cobalt nitrate (Co(NO₃)₂6H₂O) as cobalt precursor.

[103] Approximately 0.3 g of the prepared 0.5 wt% Ru/20 wt% Co/5 wt% ZrO₂-Al₂O₃ catalyst was loaded in a 1/2-inch stainless steel fixed bed reactor and reduced for 12 hours under hydrogen atmosphere (5 vol% H₂/He) at 400 ⁰C before conducting a reaction. Subsequently, the reactants carbon monoxide, hydrogen, carbon dioxide and argon (internal standard) were supplied to the reactor at a fixed molar proportion of 28.4 : 57.3 : 9.3 : 5 under the condition of: reaction temperature = 220 ⁰C; reaction pressure = 20 kg/cm²; and space velocity = 2000 L/kg cat/hr. The contents of the product of the Fischer- Tropsch reaction are summarized in Table 1. The steady-state condition was obtained after around 60 hour operation and the averaged values for 10 hours at the steady-state were taken.

[104]

[105] Example 7

[106] A 0.5 wt% Ru/20 wt% Co/5 wt% ZrO₂-Al₂O₃ catalyst was prepared in the same manner as in Example 1, except for stirring and aging for about 5 hours in slurry phase at 70 ⁰C while co-precipitating the cobalt component to the support. The prepared catalyst had a bimodal pore structure, the specific surface area being 256 m²/g and the pore volume being 0.85 cmVg, particularly the volume ratio of the smaller pores to the large pores PVi/PV₂ being 0.95.

[107] Approximately 0.3 g of the prepared 0.5 wt% Ru/20 wt% Co/5 wt% ZrO₂-Al₂O₃ catalyst was loaded in a 1/2-inch stainless steel fixed bed reactor and reduced for 12 hours under hydrogen atmosphere (5 vol% H₂/He) at 400 ⁰C before conducting a reaction. Subsequently, the reactants carbon monoxide, hydrogen, carbon dioxide and argon (internal standard) were supplied to the reactor at a fixed molar proportion of 28.4 : 57.3 : 9.3 : 5 under the condition of: reaction temperature = 220 ⁰C; reaction pressure = 20 kg/cm²; and space velocity = 2000 L/kg cat/hr. The contents of the product of the Fischer- Tropsch reaction are summarized in Table 1. The steady-state condition was obtained after around 60 hour operation and the averaged values for 10 hours at the steady-state were taken.

[108]

[109] Example 8

[110] A 0.5 wt% Ru/20 wt% Co/5 wt% ZrO₂-Al₂O₃ catalyst was prepared in the same manner as in Example 1, except for stirring and aging for about 10 hours in slurry phase at 70 ⁰C while co-precipitating the cobalt component to the support.

[I l l] Approximately 0.3 g of the prepared 0.5 wt% Ru/20 wt% Co/5 wt% ZrO₂-Al₂O₃ catalyst was put in a 1/2-inch stainless steel fixed bed reactor and reduced for 12 hours under hydrogen atmosphere (5 vol% H₂/He) at 400 ⁰C before conducting a reaction. Subsequently, the reactants carbon monoxide, hydrogen, carbon dioxide and argon (internal standard) were supplied to the reactor at a fixed molar proportion of 28.4 : 57.3 : 9.3 : 5 under the condition of: reaction temperature = 220 ⁰C; reaction pressure = 20 kg/cm²; and space velocity = 2000 L/kg cat/hr. The contents of the product of the Fischer- Tropsch reaction are summarized in Table 1. The steady-state condition was obtained after around 60 hour operation and the averaged values for 10 hours at the steady-state were taken.

[112]

[113]

[114] Example 9

[115] A 0.5 wt% Ru/20 wt% Co/2.5 wt% ZrO₂-Al₂O₃ catalyst was prepared in the same manner as in Example 1, except for using 5.4 g of zirconium nitrate (ZrO(NO₃)₂2H₂O; Kanto Chem.) as zirconium precursor.

[116] Approximately 0.3 g of the prepared 0.5 wt% Ru/20 wt% Co/2.5 wt% ZrO₂-Al₂O₃ catalyst was loaded in a 1/2-inch stainless steel fixed bed reactor and reduced for 12 hours under hydrogen atmosphere (5 vol% H₂/He) at 400 ⁰C before conducting a reaction. Subsequently, the reactants carbon monoxide, hydrogen, carbon dioxide and argon (internal standard) were supplied to the reactor at a fixed molar proportion of 28.4 : 57.3 : 9.3 : 5 under the condition of: reaction temperature = 220 ⁰C; reaction pressure = 20 kg/cm²; and space velocity = 2000 L/kg cat/hr. The contents of the product of the Fischer- Tropsch reaction are summarized in Table 1. The steady-state condition was obtained after around 60 hour operation and the averaged values for 10 hours at the steady-state were taken.

[117]

[118]

[119] Example 10

[120] A 0.5 wt% Ru/20 wt% Co/10 wt% ZrO₂-Al₂O₃ catalyst was prepared in the same manner as in Example 1, except for using 21.6 g of zirconium nitrate (ZrO(NO₃)₂2H₂ O; Kanto Chem.) as zirconium precursor.

[121] Approximately 0.3 g of the prepared 0.5 wt% Ru/20 wt% Co/10 wt% ZrO₂-Al₂O₃ catalyst was loaded in a 1/2-inch stainless steel fixed bed reactor and reduced for 12 hours under hydrogen atmosphere (5 vol% H₂/He) at 400 ⁰C before conducting a reaction. Subsequently, the reactants carbon monoxide, hydrogen, carbon dioxide and argon (internal standard) were supplied to the reactor at a fixed molar proportion of 28.4 : 57.3 : 9.3 : 5 under the condition of: reaction temperature = 220 ⁰C; reaction pressure = 20 kg/cm²; and space velocity = 2000 L/kg cat/hr. The contents of the product of the Fischer- Tropsch reaction are summarized in Table 1. The steady-state condition was obtained after around 60 hour operation and the averaged values for 10 hours at the steady-state were taken.

[122]

[123]

[124] Comparative Example 1

[125] A 20 wt% Co/ Al₂O₃ catalyst was prepared in the same manner as in Example 1, except for using alumina having a large surface area (specific surface area = 455 m²/g) as support, using cobalt nitrate (Co(NO₃)₂6H₂O) as cobalt precursor, stirring for over 5 hours at room temperature, (rotary evaporating at 70 ⁰C, drying in an oven of 100 ⁰C for 12 hours and baking at 400 ⁰C for 5 hours under air atmosphere. The prepared catalyst had a unimodal pore structure, the specific surface area being 227 m²/g and the pore volume being 0.68 cmVg.

[126] Approximately 0.3 g of the prepared 20 wt% Co/ Al₂O₃ catalyst was loaded in a

1/2-inch stainless steel fixed bed reactor and reduced for 12 hours under hydrogen atmosphere (5 vol% H₂/He) at 400 ⁰C before conducting a reaction. Subsequently, the reactants carbon monoxide, hydrogen, carbon dioxide and argon (internal standard) were supplied to the reactor at a fixed molar proportion of 28.4 : 57.3 : 9.3 : 5 under the condition of: reaction temperature = 220 ⁰C; reaction pressure = 20 kg/cm²; and space velocity = 2000 L/kg cat/hr. The contents of the product of the Fischer- Tropsch reaction are summarized in Table 1. The steady-state condition was obtained after around 60 hour operation and the averaged values for 10 hours at the steady- state were taken.

[127]

[128] Comparative Example 2

[129] A 0.5 wt% Ru/20 wt% Co/5 wt% Zr/ Al₂O₃ catalyst was prepared in the same manner as in Example 1, except for using zirconium oxychloride (ZrCl₂O 8H₂O), cobalt nitrate (Co(NO₃)₂6H₂O) and ruthenium nitrosyl nitrate (Ru(NO)(NO₃)₃) and supporting the components on an alumina support through impregnation. The prepared catalyst had a unimodal pore structure, the specific surface area being 187 m²/g and the pore volume being 0.23 cm³/g.

[130] Approximately 0.3 g of the prepared 0.5 wt% Ru/20 wt% Co/5 wt% Zr/Al₂O₃ catalyst was loaded in a 1/2-inch stainless steel fixed bed reactor and reduced for 12 hours under hydrogen atmosphere (5 vol% H₂/He) at 400 ⁰C before conducting a reaction. Subsequently, the reactants carbon monoxide, hydrogen, carbon dioxide and argon (internal standard) were supplied to the reactor at a fixed molar proportion of 28.4 : 57.3 : 9.3 : 5 under the condition of: reaction temperature = 220 ⁰C; reaction pressure = 20 kg/cm²; and space velocity = 2000 L/kg cat/hr. The contents of the product of the Fischer- Tropsch reaction are summarized in Table 1. The steady-state condition was obtained after around 60 hour operation and the averaged values for 10 hours at the steady-state were taken.

[131]

[132] Comparative Example 3

[133] A 0.5 wt% Ru/20 wt% Co/5 wt% Zr/ Al₂O₃ catalyst was prepared in the same manner as in Example 1, except for using zirconium nitrate (Zr(NO₃)₂2H₂O), cobalt acetate (Co(CH₃COOMH₂O) and ruthenium nitrosyl nitrate (Ru(NO) (NO₃)₃) and supporting the components on an alumina support through impregnation.

[134] Approximately 0.3 g of the prepared 0.5 wt% Ru/20 wt% Co/5 wt% Zr/Al₂O₃ catalyst was loaded in a 1/2-inch stainless steel fixed bed reactor and reduced for 12 hours under hydrogen atmosphere (5 vol% H₂/He) at 400 ⁰C before conducting a reaction. Subsequently, the reactants carbon monoxide, hydrogen, carbon dioxide and argon (internal standard) were supplied to the reactor at a fixed molar proportion of 28.4 : 57.3 : 9.3 : 5 under the condition of: reaction temperature = 220 ⁰C; reaction pressure = 20 kg/cm²; and space velocity = 2000 L/kg cat/hr. The contents of the product of the Fischer- Tropsch reaction are summarized in Table 1. The steady-state condition was obtained after around 60 hour operation and the averaged values for 10 hours at the steady-state were taken.

[135] [136] Table 1 [Table 1] [Table ]

[137] [138] As can be seen from Table 1, the cobalt/zirconia-alumina catalysts prepared in accordance with the present invention have a bimodal pore structure of larger and small pores.

[139] When compared with the catalysts of Comparative Examples 1 and 2 having a unimodal pore structure prepared by the conventional impregnation of a single component, matter- and heat-transfer performance is improved due to the presence of the larger pores and dispersion of cobalt becomes more uniform due to the use of the zirconia- alumina support having a uniform pore size. Therefore, clogging of the pores by the compounds having a high boiling point produced during the reaction could be reduced and more efficient Fischer- Tropsch reaction was possible due to reduced selectivity for methane.

[140] Especially, the method of Example 1 by which the cobalt component is introduced to the support slurry by co-precipitation increases the specific surface area and improves the selectivity for liquid hydrocarbons than the method of Example 2 by which the catalyst prepared simply by co-precipitation is mixed in slurry phase.

[141] It was also confirmed that the catalyst of Example 1, in which zirconia was further supported to improve dispersion and reducing property of cobalt, showed better activity than that of Example 3, in which the zirconia component was not added. The catalytic performance resulting from the bimodal pore structure is more prominent in the slurry reactor, as seen in Examples 4 and 5, because the reactor type is more advantageous in matter- and heat transfer.

[142] When cobalt nitrate was used as cobalt precursor (Example 6), the conversion of carbon monoxide increased, but selectivity for liquid hydrocarbons decreased a little, when compared with cobalt acetate precursor.

[143] Further, when the aging time in the step of depositing the cobalt component in the zirconia- alumina support was 5 hours (Example 7), the conversion and selectivity for liquid hydrocarbons improved compared with the aging time was 1 hour (Example 1). But, when the aging time was 10 hours (Example 8), the conversion and the selectivity for liquid hydrocarbons decreased. However, selectivity for liquid hydrocarbons was superior to the unimodal catalysts of Comparative Examples 1, 2 and 3.

[144] Figure 1 shows the conversion of carbon monoxide with reaction time after performing Fischer- Tropsch using the catalyst of the present invention (Example 1, 0.5 wt% Ru/20 wt% Co/5 wt% ZrO₂-Al₂O₃) and the catalyst prepared in Comparative Example 1 (20 wt% Co/80 wt% Al₂O₃). It can be seen that initial conversion is superior and that, as also can be seen from Table 1, selectivity for liquid hydrocarbons is superior at similar conversion.

[145] Figure 2 shows the pore distribution of the catalyst of the present invention (Example 1, 0.5 wt% Ru/20 wt% Co/5 wt% ZrO₂-Al₂O₃; Example 3, 20 wt% Co/5 wt% ZrO₂-Al₂ O₃), as compared with those of Comparative Example 1 (20 wt% Co/Al₂O₃) and Comparative Example 2 (0.5 wt% Ru/20 wt% Co/5 wt% Zr/Al₂O₃). The catalysts of the Examples have a bimodal pore structure and thus provide superior selectivity for liquid hydrocarbons because of superior thermal- and matter transfer performance.

[146] Figure 3 shows the electron micrographs of the catalyst of the present invention

(Example 1, 0.5 wt% Ru/20 wt% Co/5 wt% ZrO₂-Al₂O₃). It can be seen that the nano- sized particulate cobalt component is uniformly distributed on the planar zirconia- alumina support.

[147] To conclude, the cobalt-supported zirconia- alumina catalyst having a bimodal pore structure provided by the present invention has improved the catalytic stability through improved transfer of compounds having a high boiling point and offers significantly improved Fischer- Tropsch reaction performance by minimizing transition to methane.

[148] While the catalyst of the present invention can be applied in any of the fixed bed reactor, fluidized bed reactor or slurry reactor to prepare liquid hydrocarbons from a syngas, the slurry reactor which is particularly advantageous in matter transfer offers the best result.

[149]

[150] It will be apparent to those skilled in the art that various modifications and variations can be made in the present invention without departing from the spirit or scope of the invention. Other embodiments of the invention will be apparent to those skilled in the art from consideration of the specification and practice of the invention disclosed herein. It is intended that the specification and examples be considered as exemplary only, with a true scope and spirit of the invention being indicated by the following claims.

[151]

Claims

[1] A catalyst for Fischer-Tropsch reaction in which cobalt is supported on a support as an active ingredient, wherein the catalyst is a cobalt/zirconia-alumina catalyst in which cobalt is supported on a zirconia- alumina support comprising Al₂O₃ and ZrO₂ as an active ingredient and having a bimodal pore structure with pores of a relatively smaller pore size PSi and pores of a larger size PS₂, the pore sizes PSi and PS₂ being in the range described below, the ZrO₂ being comprised in the amount of 1 to 30 wt% per 100 wt% of the Al₂O₃ and the cobalt being comprised in the amount of 5 to 40 wt% per 100 wt% of the support:

10 nm < PS₂ < 200 nm.

[2] The catalyst as claimed in claim 1, wherein the support has a specific surface area of 150 to 400 m²/g and the catalyst has a specific surface area of 100 to 300 m²/g.

[3] The catalyst as claimed in claim 1, wherein the proportion of the volume PVi of the smaller pores of 2 to 10 nm to the volume PV₂ of the larger pores of 10 to 200 nm, or PVi/PV₂, is maintained in the range of from 0.5 to 2.0.

[4] The catalyst as claimed in claim 1, wherein the catalyst comprises 0.05 to 1 wt% of a promoter selected from rhenium, ruthenium and platinum per 100 wt% of the catalyst.

[5] A method for preparing a catalyst for Fischer-Tropsch reaction comprising the steps of:

1) co-precipitating by adding a basic precipitant to an aqueous solution mixture including a zirconium precursor and an alumina precursor at pH 7 to 8, aging and baking at 300 to 900 ⁰C to prepare a zirconia- alumina support; and

2) co-precipitating by adding an aqueous solution including a cobalt precursor and a basic precipitant to the prepared zirconia- alumina support at pH 7 to 8, aging and baking at 200 to 700 ⁰C to prepare a cobalt/zirconia-alumina catalyst having a bimodal pore structure with a smaller pore size PSi and pores of a larger size PS₂, wherein

10 nm < PS₂ < 200 nm.

[6] A method for preparing a catalyst for Fischer-Tropsch reaction comprising the steps of:

1) co-precipitating by adding a basic precipitant to an aqueous solution including a zirconium precursor and an alumina precursor at pH 7 to 8 and aging to prepare a slurry-phase zirconia- alumina support;

2) co-precipitating by adding a basic precipitant to an aqueous solution including a cobalt precursor at pH 7 to 8 and aging to prepare a cobalt slurry; and

3) mixing the prepared slurry-phase zirconia- alumina support and the cobalt slurry, drying and baking at 200 to 700 ⁰C to prepare a cobalt/zirconia-alumina catalyst having a bimodal pore structure with a smaller pore size PSi and pores of a larger size PS₂, wherein

10 < nm PS₂ < 200 nm.

[7] The preparation method as claimed in claim 5 or claim 6, wherein each of the zirconium, alumina and cobalt precursors is a nitrate salt, halogenated salt or acetate salt of each metal or a mixture thereof.

[8] The preparation method as claimed in claim 5 or claim 6, wherein the zirconium precursor is used in 1 to 30 wt% per 100 wt% of the alumina precursor.

[9] The preparation method as claimed in claim 5 or claim 6, wherein the cobalt precursor is used in the ratio of 5 to 40 wt% per 100 wt% of the zirconia- alumina support.

[10] The preparation method as claimed in claim 5 or claim 6, wherein the basic precipitant is selected from sodium carbonate, potassium carbonate, ammonium carbonate and ammonia water. [11] The preparation method as claimed in claim 5 or claim 6, wherein the aging is performed at 40 to 90 ⁰C for 0.1 to 15 hours. [12] The preparation method as claimed in claim 5 or claim 6, wherein following the step 2), the step of adding 0.005 to 1 wt% of a ruthenium, rhenium and platinum precursors per 100 wt% of the zirconium precursor and baking at 100 to 600 ⁰C is further included. [13] A preparation method of liquid hydrocarbons from a syngas by Fischer-Tropsch reaction using the catalyst of any of claims 1 to 4. [14] The preparation method as claimed in claim 13, wherein the Fischer-Tropsch reaction is performed in a reactor selected from a fixed bed reactor, a fluidized bed reactor and a slurry reactor.