GB2279583A

GB2279583A - Catalyst for the reduction of carbon dioxide

Info

Publication number: GB2279583A
Application number: GB9412673A
Authority: GB
Inventors: Hikoichi Iwanani; Takashi Yoshizawa; Takashi Suzuki
Original assignee: COSMO SOGO KENKYUSHO KK; Cosmo Oil Co Ltd; Cosmo Research Institute
Current assignee: COSMO SOGO KENKYUSHO KK; Cosmo Oil Co Ltd; Cosmo Research Institute
Priority date: 1993-06-25
Filing date: 1994-06-23
Publication date: 1995-01-11
Anticipated expiration: 2014-06-23
Also published as: JPH0768171A; JP2847018B2; DE4422227A1; GB2279583B; GB9412673D0; DE4422227C2; CA2126502A1; CA2126502C

Description

2279583 CATALYST FOR REDUCTION OF CARBON DIOXIDE The present invention

relates to a catalyst for promoting the chemical reduction of carbon dioxide using hydrogen to produce carbon monoxide. The catalyst can be employed even when a sulf ur compound, such as H2S and/or a large amount of carbon monoxide, is present in the raw material gas.

The hydrogenation reaction of carbon dioxide by hydrogen is known and has been industrialized as a method f or the production of a hydrocarbon using a precious metal (e.g., Ru or Rh) type catalyst or a Ni type catalyst, as shown in the following reaction formula:

C02 + 4H2 CH4 + 2H20 According to this reaction, methane can be readily produced with high selectivity, with hardly any Co being produced.

On the other hand, carbon monoxide alone or mixed with hydrogen in an equimolar amount (called oxo, gas) is useful as a raw material for methanol synthesis, acrylic acid synthesis, formic acid synthesis, fatty acid synthesis, acetic acid synthesis, ox0 synthesis (hydroformylation), and carbonyl synthesis, etc.

In general, carbon monoxide is produced by the steam reforming process of a light hydrocarbon. In the steam reforming process, a light hydrocarbon (e.g., methane), water and carbon dioxide are reacted in the presence of a catalyst to change the reactants to a gas containing H2/C021CO, then the C02 in the gas is absorbed by an amine solution or the like, whereby a mixed gas of H2 with CO is obtained, which may be further deeply cooled to separate CO.

Recently, there has been active research to solidify and utilize C02 produced in the production of carbon monoxide, from the standpoint of global environmental protection. In this connection, research has been conducted to develop a catalyst which is capable of producing CO with high selectivity by the reduction of carbon dioxide, as the raw material, using hydrogen, as shown in the following reaction formula:

C02 + H2 CO + H20 This reaction selectively produces CO without forming a hydrocarbon.

A catalyst used in this reaction is required to have an activity which will provide a high degree of conversion relative to the equilibrium degree of conversion, and high selectivity, so such a catalyst is very difficult to design. Accordingly, if any sulfur compound such as HS is present in the raw material gas, the catalyst may be instantly poisoned by the sulfur compound.

As an improved catalyst for this purpose, JP-A-4-363142 discloses a tungsten sulfide catalyst and a molybdenum sulf ide catalyst. (The term IIJP-AII as used herein means an "unexamined published Japanese patent application".) These catalysts are prepared by previously treating ammonium tetrathiotungstate [ (NH4) 2WS43 or ammonium tetrathiomolybdate I (NH4)2MOS43 under an H2 stream at 300 to 4000 to prepare WS2 or MOS2.

Also,, there are catalysts, such as MoS2/TiO2 and MOS2/'71"20,, which are prepared by dipping a carrier, such as TiO2., A1203 or SiO2, in the abovementioned aqueous ammonium sulfide solution to which an aqueous ammonia is added for support, followed by drying and pretreatment. These catalysts are not poisoned by a sulfur compound, since a metal sulfide is used as the active component of the catalyst.

Moreover, it is known that these catalysts are capable of producing CO by the reduction reaction of carbon dioxide using a mixed gas of carbon dioxide and hydrogen with high selectivity and without forming a hydrocarbon.

Furthermore, since these catalysts are not poisoned by sulfur compounds as discussed above,, they are also advantageous in that no removal of H2S is required. However, in cases where a large amount of CO is contained in the raw material gas, it is known, as shown by the following reaction formulae, that they promote the formation of hydrocarbons and/or deposition of carbon in a remarkable manner; and that these catalysts are deactivated by CO:

CO + (m/2n + 1)H2 _> 1/n x CnHm + H2 (formation of a hydrocarbon) 2CO -> C02 + Cj (deposition of a carbon) In addition, in cases where no, or only a small amount of, sulfur compound is contained in the raw material gas, a metal sulfide catalyst active component is reduced by hydrogen to form H2S in the reaction of carbon dioxide with hydrogen, and the H2S is transferred to the reaction product in the C02-H2 system; as a result, the catalyst is deactivated.

Furthermore, regardless of the presence or absence of a sulfur compound, such as H2S, in the raw material gas, a post-treatment for removing H2S is required due to the transferred H2S in the reaction product.

In the process of forming an oxo gas (CO/H2 = 1) by the steam reforming process and subsequently separating CO by deeply cooling the resulting oxo gas, the reaction gas is condensed and circulated after separation of a great amount of unreacted C02. Accordingly, when a sulfur compound such as H2S is introduced into the f ormed gas by the reduction of a catalyst, the sulfur compound is simultaneously condensed in the course of the C02 separation and C02 condensation steps, and the condensed sulfur compound is introduced into the reforming reactor, the reforming catalyst is thus deleteriously poisoned, which is observed when using a sulfide catalyst. In this process, it is important to decrease the amount of unreacted C02 to save costs. For this purpose, it is essentially required to conduct the reverse shift reaction of a reforming gas containing CO, C02 and H2 to decrease the amount of C02 in the gas. Generally, in cases where CO is present, it brings about remarkable catalyst poisoning, carbon deposition, and hydrocarbon formation.

The present invention is based on the following findings which were obtained in research and development relating to a carbon dioxide reduction catalyst for obtaining carbon monoxide by the reduction of carbon dioxide with hydrogen; specifically,, in the use of a catalyst carrying a transition metal on zinc oxide alone or on a composite formed of zinc oxide and a metal oxide selected from either Group IIIb or Group IVa or both in the Periodic Table, including such catalysts as have been developed for the deep desulfurization of a middle or light distillate oil:- (1) Even though a sulf ur compound such as H2S is present in the raw material gas, these catalysts are not poisoned by it; their catalytic life is prolonged; and the final product is not contaminated with H.S. so that no HS removal treatment is required; and (2) in particular, in cases where a composite of a zinc oxide, a titanium oxide and an aluminum oxide is used as a carrier, even though CO is contained in an amount similar to that of the Co. in the raw material gas, the hydrogenation reaction of CO. to CO proceeds selectively without any accompanying side reaction such as the poisoning of the catalyst, the deposition of carbon or the formation of hydrocarbons.

An object of the present invention is to provide a catalyst for the reduction of carbon dioxide which is capable of selectively reducing Co. to CO with hydrogen., even when using a mixed gas of C02 and H. in which a large amount of CO is contained in the raw material system (for example, one produced by the steam-reforming process), and which is resistant to poisoning by sulfur or sulfur compounds.

More specifically, the present invention provides a catalyst for the reduction of carbon dioxide characterized by supporting a transition metal on zinc oxide alone or on a composite containing zinc oxide and at least one oxide of a metal selected from metals in Group IIIb and Group IVa in the Periodic Table.

In a preferred embodiment, the metal oxide selected from oxides of metals in Group IIIb and Group IVa in the Periodic Table includes oxides of Al. Ga, Ti or Zr or a composite thereof; and the transition metal includes metals belonging to Group VIII and Group VIa in the Periodic Table, and more preferably, it includes Ni, Fe, Co, Ru, Rh, Pt, Pd, Mo and W.

The catalyst according to the present invention is used in a reaction for obtaining carbon monoxide through the reduction of carbon dioxide by hydrogen. Even when a sulf ur compound such as H2S is present in a mixed gas of carbon dioxide and hydrogen, the catalyst according to the present invention can produce carbon monoxide with high selectivity and without being poisoned.

In the catalyst according to the present invention, exemplary carriers include zinc oxide alone, a zinc oxidecontaining metal oxide selected from Group IIIb and Group IVa in the Periodic Table (e.g., a metal oxide of Al, Ga, Ti, Zr) or a composite thereof (e.g., a composite of zinc oxide and aluminum oxide, a composite of zinc oxide, titanium oxide and aluminum oxide).

In particular, in the case of using a composite of zinc oxide and titanium oxide or aluminum oxide as a carrier, the catalyst according to the present invention is hardly poisoned at all by sulfur compounds and CO, even though a large amount of CO and sulfur compounds, such as H2S, are contained in the above- mentioned mixed gas.

The amount of zinc oxide in the carrier generally ranges from about 20 to 100 wt% based on the total amount of the catalyst in terms of the metal oxide. If the amount of zinc oxide is too small, the catalytic life is not sufficiently prolonged. Almost all the sulfur compounds, such as H2S, in a raw material gas are absorbed in the zinc oxide of the carrier, whereby the active component remains unpoisoned and the catalytic life is prolonged. Accordingly, where no zinc oxide is present, these effects cannot be obtained, which results in a short catalytic life.

Furthermore, when a composite is used, the mechanical strength of the catalyst is improved. In particular, in the case of using a composite containing titanium oxide and aluminum oxide, both the selectivity to carbon monoxide, and the resistance to CO poisoning and to coke formation are improved, as compared with zinc oxide alone, as demonstrated in the working Examples of the present invention.

If the proportions of these components of the carrier are too small, the resulting effects are insufficient; if too great, the amount of zinc oxide becomes relatively small and the H2 S absorption effect decreases. Accordingly, it is preferred that these components of the carrier are used in an amount of from about 40 to 80 wt%, based on the total amount of the catalyst in terms of the metal oxide.

In cases where titanium oxide and aluminum oxide are used together, their mixing ratio is not restricted, and it is acceptable that the total amount thereof is f rom about 40 to 80 wt%,, based on the total amount of the catalyst in terms of the metal oxide.

Any transition metal may be used as an active component, normally in the form of its oxide. In particular, it is preferred to use a metal belonging to Group VIII in the Periodic Table (especially Ni, Fe, Co. Ru, Rh, Pt or Pd) or a metal belonging to Group VIa in the Periodic Table (especially Mo or W). These transition metals may be used alone or in a mixture of two or more.

The supported amount of the transition metal (when two or more are used in a mixture, the total amount thereof) is not limited, but it generally ranges from about 5 to 20 wt% based on the total amount of the catalyst in terms of the metal oxide.

If the amount of the transition metal is too small, it is insufficient to produce carbon monoxide with high - 10 selectivity and insufficient to form a sulfur compound, such as H2 S, in the raw material gas which is capable of being easily absorbed on the zinc oxide. If the amount of transition metal is too great, these effects are not increased, thus there is no improved technical effect; moreover, an excess of transition metal is uneconomical.

The catalyst according to the present invention is obtained by i) preparing a carrier using a zinc compound alone or a zinc compound and either one or both of an aluminum compound and/or a titanium compound, i. e., a metal oxide selected from Group IIIb or Group IVa, then, ii) impregnating the resulting carrier with the transition metal in a conventional manner,, followed by drying and calcining.

The zinc compound and a metal oxide selected from Group III may be used in the form of a hydroxide, a chloride, an oxide, or the like of the selected element to be used.

The transition metal is introduced in the form of a hydroxide, a nitrate, an acetate, a chloride or the like of the transition metal.

In cases where zinc oxide alone is used as the carrier, it is prepared by, for example, calcining metalic zinc or by heat-decomposing an inorganic zinc salt (e.g., zinc nitrate or basic zinc carbonate) or an organic zinc (e.g., zinc benzoate, zinc citrate or zinc lactate).

In cases where a composite of zinc oxide and a metal oxide, selected from either Group IIIb or Group IVa or both, is employed, it is prepared, for example, by mixing titanium hydroxide or aluminum hydroxide or a mixture thereof with zinc hydroxide, or by adding alkali to a titanium compound or an aluminum compound other than the hydroxide or a mixture thereof for co-precipitation, followed by washing, molding and calcining, in a conventional manner.

In f orming a composite of zinc oxide and a metal oxide selected from either Group IIIb or Group IVa or both, the mixing order of each component (inclusive of the hydroxide) is not restricted. For instance, it may be prepared by mixing a mixture of a titanium compound and an aluminum compound with a zinc compound as described above, or by mixing a mixture of either a titanium compound or an aluminum compound and a zinc compound with the other nonmixed compound thereof.

Otherwise, a carrier having desired properties for the catalyst according to the present invention may be prepared by simply mixing a powder of the zinc oxide, titanium oxide, aluminum oxide, etc. in the selected amounts.

A transition metal may be applied onto the above- prepared carrier according to a conventional method, such as an impregnation method or a co-precipitation method.

As an example, in the case of applying Ni as a transition metal onto a carrier formed of zinc oxide alone, water is gradually added dropwise to the zinc oxide to effect water absorption into the body of the zinc oxide. It is preferred that the water absorption is conducted until the zinc oxide is saturated throughout. Next, the necessary amount of Ni is calculated from the amount of water absorbed at saturation and the amount of zinc oxide. Then, an aqueous Ni salt (e.g., a nitrate, acetate or chloride) solution which has been adjusted to an appropriate concentration based on the calculated Ni amount, is absorbed in the zinc oxide until saturation is reached, followed by washing, drying, molding, and calcining.

A similar procedure is followed in cases where two or more transition metals are supported on a composite carrier. For instance, i) water is absorbed into the body of the composite (preferably until it is saturated); ii) the necessary transition metal amounts (the total amount of two transition metals) are calculated from the water absorption amount at saturation and the zinc oxide amount in the composite; and iii) an aqueous transition metals solution which has been adjusted to an appropriate concentration based on the calculated amount of transition metals is absorbed until saturation is reached, followed by washing, etc., as mentioned above.

When the catalyst according to the present invention is used to obtain carbon monoxide by the reduction of carbon dioxide using hydrogen, acceptable carbon monoxide production can be achieved, even though a sulfur compound, such as H2S, is present in a raw material gas; or, in the case of using a composite of zinc oxide, titanium oxide/and aluminum oxide as a carrier, a large amount of CO is present in the raw material gas.

When using a catalyst according to the present invention, it is preferred to conduct the reaction at a temperature of about 4000C or higher, more preferably at about 500 to 5000C. under a pressure of about 20 kg/cm2 or less, more preferably atmospheric pressure to about 5 kg/cm2, and a GHSV of about 1000 to 30000 h'I.

As discussed above, the catalyst according to the present invention can provide the following effects:

(1) Even though a sulfur compound, such as H 2S, is present in the raw material gas for obtaining carbon monoxide by the reduction reaction of carbon dioxide using hydrogen, the catalyst according to the present invention is not poisoned, and the catalytic life is prolonged.

(2) Since the final product obtained by the 1 reduction reaction is not contaminated with H2S produced by the reduction of the catalystr no H2S removal treatment is required.

(3) In particular, in cases where a -composite of zinc oxide, titanium oxide and aluminum oxide is used as a carrier, even though CO is contained in an amount similar to that of the C02 in the raw material gas, the reduction reaction proceeds favorably with improved selectivity without any accompanying side reaction such as the poisoning of a catalyst, the deposition of carbon and the formation of light hydrocarbon(s).

(4) Accordingly, by conducting the above-mentioned reduction reaction, carbon monoxide can be produced with a high degree of conversion and high selectivity.

The catalyst according to the present invention is of great industrial value for obtaining an oxo, gas and the like.

The present invention will be further described in the following Examples, but the present invention should not be construed as being limited thereto.

The single figure of the accompanying drawings relates to Comparative Example 3 and is a graph showing the change in the degree of C02 conversion and the change in the H2S concentration is a formed gas with reaction time when the catalyst of Comparative Example 3 was used.

In the following Examples, each reaction product (gas) was analyzed by means of a gas chromatograph equipped with a thermal conductive detector (TCD), by charging 60/80 mesh of an active carbon to a column (made of SUS) having I.D. (Inner Diameter) of 3mmO x 2m. H2S was detected by a gas indicator tube (Kitagawa type).

EXAMPLE 1

20g of a carrier obtained by mixing 9.8g of titanium oxide powder, 5.7g of zinc oxide powder and 4.5g of aluminum oxide powder was dipped in an aqueous solution of 9.91g of nickel(II) nitrate hexahydrate 1N'(N03),-6H. 0] in 20ml of water for 1 hour. After removal of the residual solution, the resulting product was dried at 1200C for 12 hours and calcined at 6000C for 3 hours. Then, a catalyst having NiO: 12.4 wt%, ZnO: 21.2 wt%, and balance: T'02 and A1203 was obtained.

8ml of the catalyst thus obtained was charged in a cylindrical reaction tube having an inner diameter of 16mmW and 50ml/min of H2 was passed thereto under normal pressure at 3500C for 6 hours.

Thereafter, using the catalyst, a reduction reaction of C02 by H2 was conducted with a mixed gas of H2: C02 (1: 1) as a raw material gas under normal pressure at 6000C and GHSV = 30OOh'1.

The results are shown in Table 1.

EXAMPLE 2

20g of a carrier which was prepared in the same manner as in Example 1 was dipped in an aqueous solution of 9.88g of cobalt(II) nitrate hexahydrate [Co(N03)2.6H20] dissolved in 20 ml of water. After removal of the residual solution, the resulting product was dried at 12CC for 12 hours and calcined at 6000C for 3 hours. Then, a catalyst having CoO: 12.7 wt%, ZnO:21.5 wt%, and balance: Ti02 and A1203 was obtained.

Using the catalyst thus obtained, a reduction reaction was conducted in the same manner as in Example 1.

The results are shown in Table 1. EXAMPLE 3 In an aqueous ammonium para-molybdate solution in which 5.2 g of ammonium para-molybdate tetrahydrate [ (NH4)6M07024.4H201 was dissolved in 20 ml of water and aqueous ammonia was dropwise added thereto was dipped 20 g of a carrier which was prepared in the same manner as in Example 1 for 1 hour. After removal of the residual solution, the resulting product was dried at 1200C to 12 hours and calcined at 6000C for 3 hours. Then, a catalyst having 14003: 15 wt%, ZnO: 21.3 wt%, balance: Ti02 and A1203 was obtained.

The results are shown in Table 1. EXAMPLE 4 A catalyst having NiO: 19.1 wt%, Zno: 70.0 wt% was prepared in the same manner as in Example 1, except that 20 g of a carrier made of zinc oxide alone (a molded product of "G7211 produced by Girdler Co.) and an aqueous solution of 19.86 g of nickel(II) nitrate hexahydrate [Ni(N03)26H20] dissolved in ml of water were used.

The results are shown in Table 1.

COMPARATIVE EXAMPLE 1 A catalyst having NiO: 12.4 wt% and balance: Ti02 and A1203 was prepared in the same manner as in Example 1, except that 20 g of a carrier made from a mixture of 10 g of titanium oxide powder and 10 g of aluminum oxide powder was used.

The results are shown in Table 1.

TABLE 1

Ex.1 Ex. 2 Ex. 3 Ex. 4 Comp. Ex. 1 Formed Gas Composition: (Vol%) H2 40.4 41.3 41.9 37.5 41.0 CO 21.0 20.2 18.5 22.0 20.8 C02 38.5 38.4 39.6 39.3 38.1 CH4 0.1 0.1 0.0 1.2 0.1 Degree of Conversion: 35.0 34.0 32.0 36.6 34.9 Selectivity: 99.5 99.5 100 94.8 99.5 Equilibrium Degree of Conversion: 38.5 38.5 38.5 38.5 38.5 19 - In the results of Table 1, the"degree of conversion" and the,,s electivity,are calculated from the following two equations, and the "equilibrium degree of conversion" means the theoretical degree of conversion.

Degree of Conversion = Selectivity (C02 Mol. Number in Raw Material Gas) (C02 Mol. Number in Formed Gas) C02 Mol. Number in Raw Material Gas (CO Mol. Number in Formed Gas) (CO Mol. Number in Raw Material Gas) = ------------------------------------------- X 100 (C02 Mol. Number in Raw Material Gas) EXAMPLE 5 (C02 Mol. Number in Formed Gas) A reduction reaction was conducted in the same manner as in Example 1, except that a catalyst prepared in the same manner as in Example 4 was used and a mixed gas of H2: C02 (1: 1) containing 200 ppm of H2S was used as a raw material gas.

The results are shown in Table 2.

TABLE 2

Formed Gas Composition (Vol%):

Reaction Time Hr 100 Hr 150.Hr H2 37.4 37.5 37.5 CO 21.9 22.0 22.0 C02 39.5 39.5 39.5 CH4 1.2 1.1 1.1 Degree of Conversion (%): 36.5 36.5 36.5 Selectivity (%): 94.8 95.2 95.2 Outlet H2S Concentration (ppm): 0 0 0 COMPARATIVE EXAMPLE 2 A reduction reaction was conducted in the same manner as in Example 1, except for using a catalyst prepared in the same manner as in Comparative Example 1 and a mixed gas prepared in the same manner as in Example 5.

The results are shown in Table 3.

TABLE 3

Formed Gas Composition (Vol%):

Reaction Time Hr 100 Hr 150 Hr H2 47.1 48.4 49.3 CO 8.5 3.7 0.8 C02 44.4 47.9 49.9 CH4 0.0 0.0 0.0 Degree of Conversion 16.0 7.1 1.5 Selectivity (%): 100 100 100 Outlet H2S Concentration (ppm): 18 92 183 The results of Tables 1 to 3 support the following: regardless of the presence of zinc oxide inthe carrier of a catalyst, when a sulfur compound such as H2S was not present in a raw material gas, a high degree of conversion was achieved. However, when a sulfur compound, such as H2S. was present in a raw material gas, in cases using a catalyst containing no zinc oxide in a carrier, H2S was passed intotheformed gas or the catalyst was poisoned with a sulfur compound, such as H2S, whereby the degree of conversion was decreased and the catalytic life was shortened.

1 1 In cases using the catalysts according to the present invention, no H2S was observed inthe formed gas and, since the catalytic life was prolonged, the catalysts were not poisoned. COMPARATIVE EXAMPLE 3 8 ml of a commercially available molybdenum disulfide was charged to a cylindrical reaction tube having an inner diameter of 16 mmo. Using this, a reduction reaction of C02 by H2 was conducted with a mixed gas of H2CO2 (1:1) under normal pressure at 6000C and GHSV = 3000h-1. Then, a change of the degree of conversion and a change of the H2S concentration in a f ormed gas with the lapse of reaction time were determined.

From the drawing, it is apparent that when a metal sulf ide is used as a catalyst, the catalytic component sulfide is reduced by hydrogen to form H2S even though no sulfur compound, such as H2S. is present in a raw material gas, the formed H2S is transferred totheformed gas, whereby the catalytic activity is decreased.

EXAMPLE 6

Using the catalyst prepared in the same manner as in Example 1, a reduction of C02 was conducted continuously in the same manner as in Example 1, except that a mixed gas of H2 (49.7 vol%), CO (28.4 vol%), C02 (21.8 vol%) and CH4 (011 V01%) containing 200 ppm of H2S was used as a raw material gas.

The results with the lapse of 24 hours and the lapse of 200 hours are shown in Table 4.

EXAMPLE 7 g of a carrier which was prepared in the same manner as in Example 1 was dipped in an aqueous solution of 26. 15 g of iron(III) nitrate nonahydrate [Fe(N03)39H20] dissolved in 20 ml of water for 1 hour. After removal of the residual solution, the resulting product was dried at 120C for 12 hours and calcined at 6000C for 3 hours. Then, a catalyst having Fe203: 20.5 wt%, ZnO: 21.2 wt%, and balance: Ti02 and A1203 was obtained.

Using the catalyst thus obtained, a reduction reaction was conducted in the same manner as in Example 6.

EXAMPLE-8

A reduction reaction was conducted in the same manner as in Example 6, except for using the catalyst which was prepared in the same manner as in Example 3.

TABLE 4

Example 6 Example 7 Example 8 24 200 24 200 24 200 Reaction Time (Hr) Formed Gas Composition: (Vol%) H2 45.7 46.0 46.1 46.5 44.8 44.7 CO 36.7 35.7 36.4 35.1 37.1 37.2 C02 17.3 17.9 17.3 18.1 17.9 17.9 CH4 0.3 0.4 0.2 0.3 0.2 0.2 Degree of Conversion: 27.2 24.5 26.9 23.4 25.8 26.0 Selectivity: 94.4 88.9 93.2 85.1 97.0 96.7 C-Balance: 99.7 99.3 99.4 98.8 99.8 99.8 In Table 4, the degree of conversion and the selectivity were calculated by the same equations described earlier in Table 1. The C-balance is a mass balance of a raw material system and a f ormed material system, and 6 lower Cbalance means the deposition of carbon on a catalyst.

As is apparent from Table 4, in cases using a catalyst according to the present invention, especially a catalyst using a composite of a zinc oxide, a titanium oxide and an aluminum oxide as a carrier, even though a great amount of CO is present in a raw material gas, the degree of conversion and the selectivity are not decreased with the lapse of time, and the catalyst is not poisoned with CO in the raw material gas, nor is the C- balance decreased.

Also. it is apparent that when a large amount of CO is present in a raw material gas, it is preferred to use a catalyst in which molybdenum oxide is supported on such a composite.

i

Claims

CLAIMS:

1. A catalyst for use in the production of carbon monoxide by the reduction of carbon dioxide using hydrogen, comprising a transition metal supported on a carrier of zinc oxide alone or on a composite containing zinc oxide and at least one oxide of a metal selected from metals in Groups IIIb and IVa of the Periodic Table.

2. A catalyst as claimed in claim 1, wherein the zinc oxide is present in an amount of 20 to 100 wt% based on the total amount of the carrier in terms of the metal oxide.

3. A catalyst as claimed in claim 1 or 2, wherein the metal oxide is selected from oxides of Al, Ga, Ti and Zr and composites thereof.

4. A catalyst as claimed in claim 3, wherein the transition metal is supported on a composite of zinc oxide and titanium oxide and/or aluminum oxide.

5. A catalyst as claimed in any preceding claim, wherein the metal oxide or the composite thereof is present in an amount of from 40 to 80 wt% based on the total amount of the carrier in terms of metal oxide.

6. A catalyst as claimed in any preceding claim, wherein the transition metal is at least one metal selected from those in Groups VIII and VI of the Periodic Table.

7. A catalyst as claimed in claim 6, wherein the transition metal is at least one metal selected from Ni, Fe, - 26 14.

Co, Ru, Rh, Pt, Pd, Mo and W.

8. A catalyst as claimed in any preceding claim, wherein the transition metal is present in an amount of from 5 to 20 wt% based on the total amount of the catalyst in terms of metal oxide.

9. A catalyst as claimed in any preceding claim, wherein the transition metal is present in the form of molybdenum oxide.

10. A catalyst as claimed in claim 1 and substantially as hereinbefore described.

11. A catalyst for use in the production of carbon monoxide by the reduction of carbon dioxide using hydrogen, substantially as herein described with reference to any one of Examples 1 to 8.

12. A process for producing carbon monoxide by the reduction of carbon dioxide with hydrogen using a catalyst as claimed in any preceding claim.

13. Carbon monoxide when produced by a process as claimed in claim 12.

The features herein described, or their equivalents, in any novel. patentable selection.

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