WO2004103556A1

WO2004103556A1 - Mixed oxide catalysts containing manganese and cobalt and used for co oxidation

Info

Publication number: WO2004103556A1
Application number: PCT/EP2004/005503
Authority: WO
Inventors: Wilhelm Maier; Jens Saalfrank
Original assignee: Universität des Saarlandes
Priority date: 2003-05-22
Filing date: 2004-05-21
Publication date: 2004-12-02

Abstract

The invention relates to mixed oxide catalysts for the oxidation of carbon monoxide, said catalysts containing at least two of the elements Cu, Co, Mn and Ni and consisting of between 50 and 99.5 mol % of mixed oxides of said elements or mixtures of the oxides of said elements, excluding mixed oxides based on Cu and Co. The invention also relates to methods for producing said catalysts, to methods for oxidising carbon monoxide in the presence of said catalysts, and to the use of the inventive catalysts in fuel cells, breathing apparatus or exhaust air decontamination.

Description

Mixed oxide catalysts for CO oxidation

The present invention relates to mixed oxide catalysts for the oxidation of carbon monoxide containing at least two of the elements Cu, Co, Mn and Ni, processes for their preparation, processes for the oxidation of carbon monoxide in the presence of such catalysts and the use of the catalysts according to the invention in fuel cells, in breathing apparatus or in gas purification.

Mixed oxide catalysts for the oxidation of carbon monoxide (CO) are particularly suitable for applications in the field of respiratory protection, low-temperature fuel cells (PEM) and exhaust gas purification.

There are numerous publications and patents in the field of CO oxidation at low temperatures. Many of the catalysts examined here are precious metal catalysts on different oxide supports. However, there is still a great need for more efficient CO oxidation catalysts in the areas of the environment, energy and occupational safety.

This aspect plays a major role, especially when using methanol as an energy source for non-stationary membrane fuel cells (e.g. in motor vehicles). In these fuel cells, hydrogen is generated "on board" by methanol steam reforming. Small amounts (approx. 1%) of CO are produced which poison the anode of the fuel cell. For this reason, catalysts are required which selectively remove the CO in an H ₂ - Oxidize the atmosphere to CO ₂ without simultaneously consuming H ₂ .

Hopkalite ("CuMn ₂ O") is currently still used in respiratory masks for the oxidative removal of CO from contaminated breathing air (SH Taylor et al., Applied Catalysis A: General 166 (1998) 143; M. Katz, Advances Catalysis 5 (1953) 177).

The high activity of cobalt oxide and cobalt oxide on aluminum oxide for the catalytic oxidation of CO in air has also been known for a long time and has been intensively investigated. It has been observed that CO is oxidized on Co ₃ O or on CoOχ / Al ₂ O ₃ even at temperatures far below 0 ° C (DAH Cunningham et al., Catalysis Letters 25 (1994) 257; P. Thormahlen et al. , Journal of Catalysis 188 (1999) 300). In the case of the noble metal-containing cobalt catalysts, Au / Co ₃ O _{4 shows} high activity and stability far below 0 ° C (M. Haruta et al., Journal of Catalysis 115 (1989) 301; M. Haruta et al., Journal of Catalysis 144 (1993) 175). Furthermore, a CoMn ₂ O ₄ catalyst was reported which is active at temperatures above 200 ° C (AV Salker et al., Journal of Materials Science 35 (200) 4713) and an Ag Co-oxide catalyst which is used at temperatures below 100 ° C is active (E. Gulari et al., Applied Catalysis A: General 182 (1999) 147).

In the selective CO oxidation in the presence of H ₂ , CoO shows a high activity in connection with a high selectivity and a wide temperature window (Y. Teng et al., International Journal of Hydrogen Energy 24 (1999) 355). However, the presence of H ₂ O has a negative effect on the activity of the catalyst. Under fuel cell conditions (76 ° C, 100% humidity), Ir / CoO _x -Al ₂ O ₃ / C shows almost 100% CO conversion and a selectivity of approx. 50% (JM Fenton et al., Journal Electrochemical Society 148 (2001 ) 10, AI 116). In addition, cobalt spinel oxides such as Zn _x Co _3-x O ₄ (x = 0-l), Al _x Co _3-x O (x = 0-2.5) and Fe _x Co _3-x O ₄ (x = 0-2.5) was investigated for the selective CO oxidation. (K. Omata et al., Applied Catalysis A: General 146 (1996) 255). The good activity and selectivity of Pt / aluminum with and without promoters has been known for a long time and is still the subject of research (E. Gulari et al., Applied Catalysis B: Environmental 37 (2002) 17; R. Farrauto et al. , Catalysis Today 62 (2000) 249). In addition to platinum, catalysts containing Au (Au / MgO / Al ₂ O ₃ , Au / MnO _x / MgO / Al ₂ O ₃ ) have also been reported, which have CO ₂ selectivities of more than 90% at temperatures ≤ 100 ° C (BE Nieuwenhuys et al., Journal of Catalysis 199 (2001) 48).

In U.S. Pat. No. 5,258,340, catalysts with a layer structure are described, of which at least one layer must contain cobalt (II, III) oxide. The other layers are not required to contain manganese oxide. In addition, it is claimed that the high activity of these catalysts is due to the production process (sequential precipitation).

Since U.S. Pat. No. 6,168,772 Bl claims Pt, Ru, Pd, Co and PtRu zeolites for the selective CO oxidation in reforming gas.

Japanese patent JP2001149781 provides the use of Fe, Co and Cu in a Pt-containing catalyst for the selective CO oxidation in an H ₂ -containing gas at low temperatures.

Y. Teng et al., International Journal of Hydrogen Energy 24 (1999) 355 describes, among other things, the use of CoO, Co ₃ O ₄ , MnOOH, NiO and various MnO _x for the selective CO oxidation in H. At temperatures from 50 ° C to 150 ° C, catalysts that contain Co or Mn are the most active. RM Sinkevitch et al., Journal of Catalysis 142 (1993) 254 reports on the selective CO oxidation, inter alia, on Co / Cu / Al ₂ O ₃ and Ni / Co / Fe / Al O ₃ . These catalysts show a CO conversion of 50% only at temperatures around 200 ° C. The same applies to the spinel catalyst CoMn ₂ O (AV Salker et al., Journal of Materials Science 35 (200) 4713).

In principle and also in all of the literature examples mentioned above, the following problems still exist with known CO oxidation catalysts: moisture has a poisoning effect on the catalysts and in a hydrogen-containing atmosphere, H _{2 is also} oxidized in addition to CO. This is particularly disadvantageous for fuel cells in which there is an H ₂ -rich atmosphere and breathing apparatuses in which moist air can be present.

Starting from this prior art, it was an object of the present invention to provide catalysts which, at low temperatures, as are required in fuel cells and respiratory protective devices, also have high activity and selectivity in a humid atmosphere.

According to the invention, this object is achieved by mixed oxide catalysts for the oxidation of carbon monoxide containing at least two of the elements Cu, Co, Mn and Ni, the catalyst consisting of 50-99.5 mol% of mixed oxides of these elements or of mixtures of the oxides of the elements, mixed oxides based on Cu and Co are excluded.

Such catalysts have higher activities at lower temperatures than conventional catalysts. It has surprisingly been found that mixed oxide catalysts which contain at least two elements from the group Co, Mn, Cu and Ni oxidize CO with high selectivity and activity even at low temperatures.

The catalyst preferably consists of 60-98 mol% of mixed oxides of at least two of the elements Cu, Co, Mn and Ni, particularly preferably 70-95 mol%. The catalysts according to the invention can also contain more than two of the elements Cu, Co, Mn and Ni. Another metal can, for example, contain up to 2 mol%, preferably up to 3 mol%.

In a preferred embodiment, the present invention relates to a catalyst, the catalyst containing> 0% and <40% oxides of Mn and> 50% oxides of Cu. It is further preferred that the catalyst consists of> 0% and <40% oxides of Mn and> 50% of oxides of Cu, in particular> 10% and <40% of oxides of Mn and> 60% of oxides of Cu.

In an alternative embodiment, the present invention relates to a catalyst, the catalyst containing> 50% oxides of Co or Ni and> 0% and <49% oxides of Cu or Mn. A particularly preferred catalyst consists of> 50% of the oxides of Co or Ni and> 0% and <49% of oxides of Cu or Mn, for example> 60% of the oxides of Co or Ni and> 10% and <40% from oxides of Cu or Mn.

Another catalyst according to the invention contains a manganese / cobalt mixed oxide, the Co / Mn ratio being> 4. The catalyst preferably consists of manganese / cobalt mixed oxide, the Co / Mn ratio being> 4, preferably> 8.

It is also possible in the context of the present invention that the catalyst contains a nickel / manganese mixed oxide and the Ni / Mn ratio is between 1.5 and 4. It is preferred that the catalyst consists of nickel / manganese mixed oxide and the Ni / Mn ratio is between 1.5 and 4.

In a further embodiment, the present invention relates to a catalyst, the catalyst consisting of mixed copper oxide with Co, Mn or Ni, the Cu content being less than 45%, in particular <40%, for example <35%. The invention also relates to a catalyst which is present as a mixed oxide of> 40% Ni,> 0 and <50% Mn,> 0 and <5% Ag and> 0 and <5 Co, preferably> 60% Ni,> 0 and <40% Mn,> 0 and <5% Ag and> 0 and <5 Co.

The most active catalysts have a cobalt / manganese ratio of greater than 4, in particular greater than 8, particularly preferably greater than 10.

The activity of these materials can be further increased by adding small amounts of noble metals (e.g. Pt, Ag) and / or main group elements (e.g. AI, K). Therefore, catalysts are furthermore preferred according to the invention which contain at least one further component selected from noble metals or alkali metals or a component from the group of the elements aluminum, titanium, silicon, zirconium or mixtures of all. Aluminum is particularly preferred.

The catalyst preferably contains at least 0.5 mol%, particularly preferably at least 1.0 mol%, in particular 5.0 mol% of the further component. The noble metals are preferably Pt, Pd, Ir, Ru, Ag or Rh, Pt being preferred.

According to the invention, the alkali metals are preferably the oxides or carbonates of K, Cs or Rb.

According to the invention, it is preferred that the catalyst fulfills one of the following conditions:

(1) the molar ratio of Co and Mn relative to the platinum metal is> 95;

(2) the molar ratio of Co and Mn relative to the molar ratio of the alkali metal is> 90;

(3) the molar ratio of Co and Mn relative to the molar ratio of the element from the group aluminum, titanium, silicon, zirconium is> 90.

Such catalysts have particularly high activities and selectivities.

The oxide mixture has proven to be particularly active

proved. This catalyst has a high stability against air humidity at room temperature. At 25 ° C and a relative humidity of ≥ 85%, about 90% of the carbon monoxide present is oxidized after a reaction time of 60 minutes.

The catalysts of the invention can be used both in pure form and also applied to suitable support materials and moldings customary in heterogeneous catalysis, i.e. that the catalyst is present as a full catalyst or supported catalyst. Depending on the application, it may be necessary to adjust the pore size and porosity of the prior art catalysts by varying the production conditions. According to the invention, the catalyst can be crystalline or amorphous; the catalyst is preferably amorphous.

The present invention also relates to a production process for the mixed oxide catalysts according to the invention. According to the invention, the catalyst can be produced by precipitation, impregnation, sol-gel methods or powder synthesis. In a preferred embodiment, the present invention relates to a production process for a mixed oxide catalyst according to the invention comprising a sol-gel process and subsequent calcining.

In the oxidation of CO, the catalysts according to the invention have high activities and selectivities even at relatively low temperatures. The present invention therefore also relates to a process for the oxidation of CO in the presence of the mixed oxide catalysts according to the invention, which is carried out in a temperature range from -20 ° C. to + 200 ° C. The process is preferably carried out at temperatures from 0 to 120 ° C., in particular at 5 to 80 ° C., particularly preferably at 20 ° C. to 30 ° C., for example at 25 ° C.

The method according to the invention can also be operated with moist or dry air, in particular with moist air.

The catalyst according to the invention converts CO selectively both in oxidizing and in reducing medium. The process according to the invention is therefore suitable both for the selective oxidation of CO in reducing, hydrogen-rich gas mixtures and for the oxidation of CO in oxidizing, oxygen-rich gas mixtures.

According to the invention, it is preferred that the gas mixture used originates from a methanol reforming process. Gas mixtures derived from a methane or hydrocarbon reforming process can also be used. According to a further embodiment of the present invention, it is preferred that the gas mixture comes from the ambient air.

The process according to the invention can be carried out using a mixed oxide catalyst alone. However, it is also possible in the context of the present invention that the catalyst is used together with H ₂ O adsorbers, such as zeolites or superabsorbers.

The catalysts are suitable for removing CO from air or other gases, e.g. Hydrogen, in the temperature range from -10 to 200 ° C. The invention provides an application for the selective CO oxidation in the presence of hydrogen (fuel cells) and for the CO oxidation in air (breathing apparatus, exhaust gas purification) at low temperatures.

The catalysts of the invention are particularly suitable for use in fuel cells (selective removal of CO in a hydrogen-rich environment), in respiratory masks and respiratory protective devices (fire and mining, civil protection, occupational safety), in exhaust air purification from chemical production processes, in the exhaust air from internal combustion engines, e.g. in the cold start phase, in exhaust air purification in combustion power plants and domestic fire systems, in indoor air purification in closed units (submarine, aircraft, space technology, test laboratories), in CO ₂ laser devices The catalysts of the invention show high selectivity and activity even at low temperatures. This is particularly advantageous for use in fuel cells and breathing apparatus that are operated at temperatures around 20 ° C.

The present invention therefore also relates to the use of the mixed oxide catalysts according to the invention in fuel cells, in breathing apparatus and in that of exhaust air purification.

The present invention is to be explained in more detail below with the aid of examples.

EXAMPLES

CO oxidation

Example 1: CO oxidation in dry air

The investigations to determine the activity of the mixed oxide catalysts for CO oxidation were carried out in a flow tube reactor. The gases (CO, synthetic air, H ₂ ) were metered using mass flow controllers and the gas composition before and after the catalyst was determined using suitable gas sensors. At the same time, the gas composition of individual gas samples was checked using GC analysis. The reactor consisted of a glass reactor tube, which was surrounded by a heater for adjusting the measuring temperature. The catalyst was on a piece of glass wool in the reactor tube.

For the CO oxidation in dry air, 200 mg (100-200 μm sieve fraction) of the catalyst according to Example 7 were used and the measurement was carried out at 25 ° C. With a gas composition of 1 vol.% CO in synthetic air, the total volume flow was 50 mL / min. Under these reaction conditions, the mixed oxide _catalyst Ag _jl Mn _{33> 9} Co _{1; 6} Ni ₆ o _{> 4} O _x showed a CO conversion of 84% after 60 minutes.

Example 2: CO oxidation in humid air

The tests for CO oxidation in moist air were carried out using the same experimental setup as described in Example 1. In addition, the reaction gas (1 vol.% CO in synthetic air, 50 mL / min total volume flow) was saturated with water at room temperature by passing it through a water-filled one Washer bottle was directed. The measurement was carried out with 200 mg (100-200 μm sieve fraction) of the mixed oxide catalyst according to Example 8 at 25 ° C. and a relative atmospheric humidity of ≥ 85%. Under these reaction conditions, the mixed oxide catalyst Pto, 5AlιMn6, Co _{91; 8} O _x showed a CO conversion of 90% after 60 minutes.

Example 3: CO oxidation in a dry hydrogen atmosphere

The tests for CO oxidation in a dry hydrogen atmosphere were carried out using the same experimental setup as described in Example 1. The reaction gas consisted of 1 vol.% CO and 5 vol.% Synthetic air in H ₂ and was used with a total volume flow of 50 ml / min. The measurements were carried out with 200 mg (100

- 200 μm sieve fraction) of the catalyst according to Example 9 at 60, 80 and 100 ° C. After 60 minutes, the mixed oxide catalyst Mn _8.3 Co ι _> at 80 ° C had a CO conversion of 65% and a selectivity of 100%.

Example 4: CO oxidation in a humid hydrogen atmosphere

The investigations on CO oxidation in a moist hydrogen atmosphere were carried out using the same experimental setup as described in Example 1. At the same time, the reaction gas was saturated with water at room temperature by passing it through a wash bottle filled with water. The reaction gas was accordingly composed of 1% by volume of CO, 5% by volume of synthetic air and approximately 2.3% by volume of H ₂ O in H ₂ . The total volume flow was 50 mL / min. The measurements were carried out with 100 mg (100-200 μm sieve fraction) of the catalyst according to Example 8 at 60, 80, 100 and 120 ° C. After 30 minutes, the mixed oxide catalyst Pto, 5AlιMn6 _; Cθ _{91> 8} θ _x at 80 ° C a CO conversion of 75% and a selectivity of 82%.

Example 5: CO oxidation at low temperatures

The investigation of CO oxidation at low temperatures was carried out using the same experimental setup as described in Example 1. However, a Liebig glass cooler was used as the reactor tube and the heating was removed. To set temperatures <25 ° C in the reactor tube, a cryostat was connected, which was operated with a methanol-water mixture as the cooling medium. The measurements were carried out with a total volume flow of 50 mL / min and with 200 mg (100

- 200 μm sieve fraction) of the catalyst according to Example 10 at 20, 15, 10, 5 and 0 ° C. The reaction gas consisted of 1 vol .-% CO in synthetic air. After 30 minutes, the mixed oxide catalyst AlιMn _{6) 7} Co ₂ , ₃ θ _x at 5 ° C had a CO conversion of 70%. Example 6: Comparative example

As a comparative example, the commercially available CO oxidation catalyst hopkalite (“CuMn ₂ O ₄ ”) was measured in dry air and in moist air at 25 ° C. For this, the experimental set-up as described in Example 1 and Example 2 was used. The same was used After 60 minutes, Hopkalit showed a CO conversion of 66% in dry air. In moist air, the catalyst was completely deactivated after a measuring time of 60 minutes. The experimental set-up as described in Example 5 was used to investigate the activity at low temperatures Under the same reaction conditions, the CO conversion of hopkalite was 10% at 5 ° C. after 30 minutes.

The catalyst CuO-CeO ₂ (Matralis et al., Catalysis Today 75 (2002) 157) was investigated as a comparative example for CO oxidation in a dry and moist hydrogen atmosphere. For this purpose, the experimental set-up as described in Example 3 and Example 4 was used under the same reaction conditions. In a dry hydrogen atmosphere, CuO-CeO ₂ showed a CO conversion of 73% at 80 ° C after 30 minutes with a selectivity of 100%. In a humid hydrogen atmosphere at 80 ° C, the catalyst CuO-CeO _{2 was} poisoned by the H ₂ O and no conversion of CO was found.

Preparation of the catalyst

Example 7: Preparation of the catalyst

7.734 ml of ethanol and 1.872 ml of 4-hydroxy-4-methyl-2-pentanone were placed in a 20 ml rolled rim glass with a stirring fish. Then 3.02 mL (3.02 mmol) of a 1 M solution of Ni (II) propionate in methanol, 0.08 mL (0.08 mmol) of a 1 M solution of Co (II) propionate were added in succession with stirring in ethanol, 1.695 ml (1.695 mmol) of a 1 M solution of Mn (II) propionate in methanol and 2.05 ml (0.205 mmol) of a 0.1 M solution of AgNO ₃ in 2-propanol were added. This batch was stirred for 3 hours. The stir fish was then removed and the sol was placed in the hood for 5 days. After this drying time, the gel body was calcined at 300 ° C. (ramp: 1 ° C./min) for 5 hours.

Example 8: Preparation of the catalyst

0.06736 g (0.335 mmol) of Mn (II) propionate (M = 201.08 g mol) and 0.94557 g (4.615 mmol) of Co (II) propionate (M = 204.89 g mol) were mixed in one Weighed in 250 mL beaker. Then 4 mL propionic acid were added and the mixture was boiled on a hotplate with a stirring fish. While the batch was boiling, 0.5 mL (0.05 mmoL) of a 0.1 M solution of Al [C ₂ H ₅ CH (CH ₃ ) O] ₃ in 2- Propanol and then 0.25 mL (0.025 mmol) of a 0.1 M solution of Pt (NH ₃ ) ₄ (NO ₃ ) ₂ in distilled water were added. After approximately half of the propionic acid had evaporated, the solution was poured into a petri dish and placed in the fume cupboard for 2 days. A transparent red film was obtained, which was calcined at 300 ° C. for 5 hours (ramp: 1 ° C./min).

Example 9: Preparation of the catalyst Mns, ₃ Co ₉₁₎ O _x

9.579 ml of ethanol and 1.872 ml of 4-hydroxy-4-methyl-2-pentanone were placed in a 20 ml rolled rim glass with a stirring fish. Then 4.585 mL (4.585 mmol) of a 1 M solution of Co (II) propionate in ethanol and 0.415 mL (0.415 mmol) of a 1 M solution of Mn (II) propionate in methanol were added with stirring. This batch was stirred for 3 hours. The stir fish was then removed and the sol was placed in the hood for 5 days. After this drying time, the gel body was calcined at 300 ° C. (ramp: 1 ° C./min) for 5 hours.

Example 10: Preparation of the catalyst AlιMn _{6) 7} Co _{92; 3} O _x

0.06736 g (0.335 mmol) of Mn (II) propionate (M = 201.08 g / mol) and 0.94557 g (4.615 mmol) of Co (II) propionate (M = 204.89 g / mol) were weighed into a 250 mL beaker. Then 4 mL propionic acid were added and the mixture was boiled on a hotplate with a stirring fish. While the batch was boiling, 0.5 mL (0.05 mmoL) of a 0.1 M solution of Al [C ₂ H5CH (CH ₃ ) O] ₃ in 2-propanol was added. After approximately half of the propionic acid had evaporated, the solution was poured into a petri dish and placed in the fume cupboard for 2 days. A transparent red film was obtained, which was calcined at 300 ° C. for 5 hours (ramp: 1 ° C./min).

Example 11: Preparation of the catalyst Mn _37> 8Ni _{62; 2} O _x

9.579 ml of ethanol and 1.872 ml of 4-hydroxy-4-methyl-2-pentanone were placed in a 20 ml rolled rim glass with a stirring fish. Then 3.11 mL (3.11 mmol) of a 1 M solution of Ni (II) propionate in methanol and 1.89 mL (1.89 mmol) of a 1 M solution of Mn (II) propionate were added in succession with stirring added in ethanol. This batch was stirred for 3 hours. The stir fish was then removed and the sol was placed in the hood for 5 days. After this drying time, the gel body was calcined at 300 ° C. (ramp: 1 ° C./min) for 5 hours.

Example 12: Preparation of the catalyst Mn ₃ 5 _{) 3} Coι ₎ Ni6 ₃ O _x

9.579 ml of ethanol and 1.872 ml of 4-hydroxy-4-methyl-2-pentanone were placed in a 20 ml rolled rim glass with a stirring fish. 3.15 ml (3.15 mmol) of a 1 M solution of Ni (II) propionate in methanol, 0.085 mL (0.085 mmol) of a 1 M solution of Co (IT) propionate in ethanol and 1.765 L (1.765 mmol) of a 1 M solution of Mn (II) ρropionate in methanol were added. This batch was stirred for 3 hours. The stir fish was then removed and the sol was placed in the hood for 5 days. After this drying time, the gel body was calcined at 300 ° C. (ramp: 1 ° C./min) for 5 hours.

Example 13: Preparation of the catalyst Agι, 5Cu _{23; 5} Co 5θ _x

2.35 mmol of Cu (IT) nitrate trihydrate and 7.5 mmol of Co (II) nitrate hexahydrate were weighed into a 25 ml beaker and dissolved in 10 ml of methanol with stirring. 0.15 mmol Ag (I) nitrate was weighed into a 10 ml beaker and dissolved in 3 ml methanol with stirring. The Ag-containing solution was then transferred to the 25 ml beaker. After adding 30 mmol of 4-hydroxy-4-methyl-2-pentanone, this mixture was stirred for a further 30 minutes and then transferred to a flat dish. This was covered for a period of 2 days and then kept open in the fume cupboard for a period of 5 days. A solid gel was formed, which was calcined at a temperature of 300 ° C. over a period of 5 hours.

Example 14: Preparation of the catalyst JjιNiι ₉ Cu8oO _x

1.9 mmol of Ni (II) nitrate hexahydrate and 8 mmol of Cu (II) nitrate trihydrate were weighed into a 25 ml beaker and dissolved in 10 ml of ethylene glycol with stirring. 0.1 mmol of Ir (III) chloride were weighed into a 10 ml beaker and dissolved with stirring in a solution of 2 ml of methanol and 40 μl of nitric acid. The Ir-containing solution was then transferred to the 25 ml beaker. After adding 30 mmol of 4-hydroxy-4-methyl-2-pentanone, this mixture was stirred for a further 30 minutes and then transferred to a flat dish. This was kept for 3 days at night in a drying cabinet at a temperature of 60 ° C. and in the fume cupboard during the day. It was then kept open in an oven for a period of 5 days at a temperature of 65 ° C. and for a period of 2 days at a temperature of 80 ° C. An amorphous glass was formed, which was calcined at a temperature of 350 ° C. over a period of 5 hours.

Example 15: Preparation of the catalyst CeιoZnιoCu ₂ oMn ₆ oO _x

1 mmol Ce (III) nitrate hexahydrate, 1 mmol Zn (II) nitrate tetrahydrate, 2 mmol Cu (If) nitrate trihydrate and 6 mmol Mn (II) nitrate tetrahydrate were weighed into a 25 ml beaker and stirred in 10 ml of methanol dissolved. After adding 30 mmol of 4-hydroxy-4-methyl-2-pentanone, the mixture was stirred for a further 30 min. This batch was then transferred to a flat dish and kept open in the hood for a period of 7 days. A solid gel was formed, which was calcined at a temperature of 300 ° C. over a period of 5 hours.

Claims

claims

1. Mixed oxide catalyst for the oxidation of carbon monoxide containing at least two of the elements Cu, Co, Mn and Ni, the catalyst consisting of 50-99.5 mol% of mixed oxides of these elements or of mixtures of the oxides of the elements, mixed oxides based on Cu and Co are excluded.

2. Catalyst according to claim 1, characterized in that the catalyst contains> 0% and <40% oxides of Mn and> 50% oxides of Cu.

3. Catalyst according to claim 1, characterized in that the catalyst contains> 50% oxides of Co or Ni and> 0% and <49% oxides of Cu or Mn.

4. Catalyst according to claim 1 or 3, characterized in that the catalyst contains a manganese / cobalt mixed oxide, the Co / Mn ratio being> 4.

5. Catalyst according to one of the preceding claims, characterized in that the catalyst contains a nickel / manganese mixed oxide and the Ni / Mn ratio is between 1.5 and 4.

6. Catalyst according to one of the preceding claims, characterized in that it contains at least one further component selected from noble metals or alkali metals or a component from the group of the elements aluminum, titanium, silicon, zirconium or mixtures of all.

7. A catalyst according to claim 6, characterized in that the catalyst contains at least 0.5 mol% of the further component.

8. Catalyst according to one of claims 6 or 7, characterized in that the noble metals are Pt, Pd, Ir, Ru, Ag or Rh.

9. Catalyst according to one of claims 6 to 8, characterized in that the alkali metals are the oxides or carbonates of K, Cs or Rb.

10. Catalyst according to one of claims 6 to 9, characterized in that one of the following conditions is fulfilled:

(1) the molar ratio of Co and Mn relative to the platinum metal is> 95;

11. Catalyst according to one of the preceding claims, characterized in that it is amorphous.

12. A method for producing a mixed oxide catalyst according to any one of claims 1 to 11 comprising a sol-gel process and subsequent calcining.

13. A process for the oxidation of CO, characterized in that it is carried out in the presence of a catalyst according to any one of claims 1 to 11 in a temperature range from -20 ° C to + 200 ° C.

14. The method according to claim 13, characterized in that it is operated with moist air.

15. The method according to any one of claims 13 or 14, characterized in that CO is selectively oxidized in reducing, hydrogen-rich gas mixtures.

16. The method according to any one of claims 13 or 14, characterized in that CO is oxidized selectively in oxidizing, oxygen-rich gas mixtures.

17. Use of a mixed oxide catalyst according to one of claims 1 to 11 or a catalyst obtainable by a method according to claim 12 in fuel cells, in breathing apparatus or in exhaust air purification.