ES2238172B1 - SELECTIVE OXIDATION METHOD OF CARBON MONOXIDE. - Google Patents

Abstract

Method of selective oxidation of carbon monoxide. The present invention relates to a method for selectively oxidizing carbon monoxide in a gas mixture characterized in that it comprises reacting the gas mixture with an oxidant in the presence of a catalyst comprising gold and nanocrystalline cerium oxide formed by particles with a diameter medium less than 10 nm; to the catalyst preparation process and to the catalyst comprising gold supported on nanocrystalline cerium oxide.

Description

Method of selective oxidation of monoxide carbon.

Technical field

This report is included in the field Pollution removal process technician. By way of particular refers to a monoxide oxidation process of carbon in the presence or absence of hydrogen in the middle of reaction.

Background

A procedure to convert chemical energy into electrical energy involves the use of cells or fuel cells. In these, H2 may be used as fuel. A contaminant from many sources of hydrogen is carbon monoxide that tends to poison the electrodes of the battery. Since CO2 does not poison the electrodes, it is of interest to oxidize the CO to CO2 in the stream of H2, although this should be done selectively without oxidizing the H2. Thus Haruta et al. (Journal of Catalysis, vol. 115, 301 (1989)) showed that catalysts formed by gold and a support are capable of selectively oxidizing CO to CO2. To do this, they deposited the gold on several supports observing great differences in the activity and selectivity of the catalyst, depending on the support used. Several authors found (M. Haruta, Cat Tech, vol. 6, 102 (2002); M. Haruta et al., Journal of Catalysis 144, 175 (1993); F. Boccuzzi et al., Catalysis Letters 29, 225 ( 1994); J. Guzmán and BC Gates, Angew. Chem. Int. Ed. 42, 690 (2003)) that the most suitable supports in the gold / support catalysts for the selective oxidation of CO to CO2 are: TiO2 (anatase), iron oxide, cobalt oxide, zinc oxide and magnesium oxide. In addition to the supports named above, others have been studied (see Bond and Thompson, Catalysis Review Sci. Eng., Vol. 41, 319 (1994)), and among them cerium oxide. Thus, different methods for supporting gold on a metal oxide have been described, such as: impregnation, coprecipitation, deposition-precipitation, ion exchange and chemical vapor deposition (Lee and Gavriilidis, Journal of Catalysis vol. 206, 305 (2002); Sánchez et al., Journal of Catalysis, vol. 168, 125 (1997); Chen and Yeh, Journal of Catalysis, vol. 200, 59 (2001); Wan and Kang, US Pat. 5550093 (1996). that when gold is supported on cerium oxide, the activity of the catalyst for the oxidation of CO to CO2 is low, with reaction temperatures above 100 ° C being required to achieve appreciable conversions (Bera and Hegde, Catalysis Letters, vol. 79, 75 (2002)) These results allow us to conclude that cerium oxide is not a suitable support for gold, at least as regards the selective oxidation of CO to CO2. patent catalyst finds a catalyst for selective oxidation d e CO in the presence of H2 which does not use cerium oxide as support but a mixture of cerium oxide and titanium oxide (B. Grigorova et al., WO 0059631) introducing in the composition tin as
promoter.

Even when existing posts showed  that gold catalysts on cerium oxide are not very active in the oxidation of CO to CO2, and its selectivity in the presence of H_ {2} is only moderate, it has been found that, surprisingly, when cerium oxide is prepared in the form of nanoparticles with an average size of less than 10 nm, and also if these nanoparticles are arranged forming a structure mesoporous, very supported supported gold catalysts are achieved active and selective. Indeed, as will be demonstrated throughout this memory, the catalysts formed by gold supported on the cerium oxide formed by unordered nanoparticles, as well as by mesostructured nanoparticles show very high activity for the oxidation of CO to CO2 at temperatures of 10 ° C and even  lower, being selective in the oxidation of CO in the presence of H2.

Description of the invention

The present invention relates to a method for  selectively oxidize carbon monoxide in a gas mixture characterized in that it comprises reacting the gas mixture with an oxidant in the presence of a catalyst comprising gold and nanocrystalline cerium oxide formed by particles with a mean diameter less than 10 nm.

Preferably the particle size of cerium oxide is 8 nm or less.

Carbon monoxide can be part of a any mixture of gases and in particular it can be a mixture reagent comprising hydrogen.

According to the method of the present invention the catalyst has a gold content between 0.5 and 6% in weight.

The oxidation reaction takes place at a temperature between 10 and 130 ° C.

According to a second embodiment of the method of present invention cerium oxide, CeO2, may be formed by mesostructured nanoparticles. In this case it obtain catalysts with a BET surface greater than 120 m 2 g -1. Cerium oxide nanoparticles have a average diameter less than or equal to 10 nm, and more preferably equal to or less than 8 nm.

According to this second embodiment of the method of present invention the catalyst has a gold content between 0.5 and 6% by weight.

In a particular embodiment of the method of present invention to selectively oxidize the CO to CO2 in a reactive mixture, for example a mixture containing H2, this mixture of gases is contacted with the catalyst at a temperature between 5 ° C and 200 ° C, preferably between 10ºC and 130ºC.

The present invention has as an additional object a process for preparing a catalyst comprising gold and a nanocrystalline cerium oxide support, said oxide support of cerium formed by particles with an average diameter of less than 10 nm, characterized in that said method comprises depositing the gold on cerium oxide nanoparticles with a size of diameter less than 10 nm.

According to the present procedure gold can be deposit on cerium oxide support by a method Anyone known in the art. A method is preferably used selected from impregnation, deposition-precipitation and chemical deposition of steam.

Even more preferably the procedure of The present invention comprises:

- prepare a gold solution with a higher pH to 2,

- modify the pH of the gold solution, up to obtain a gold solution with a basic pH, preferably a pH equal to 10,

- add the gold solution with a basic pH on a support of nanocrystalline cerium oxide, formed by particles with an average diameter of less than 10 nm,

- modify the pH of the gold solution to obtain a pH between 8 and 10, causing precipitation of gold on the stand and

- wash the support on which the  gold.

The nanocrystalline cerium oxide support is in the form of colloidal suspension.

The gold solution is preferably a aqueous solution of a gold salt, for example of HauCl 4. Water is preferably used to prepare this solution. deionized

In the step of modifying the pH of the solution gold is preferably used a basic aqueous solution, for example an aqueous solution of NaOH. The gold solution basic water and cerium oxide colloidal suspension are mixed under agitation

Optionally, the gold mixture on CeO2 is it can dry, and optionally it can be treated in the presence of air at a temperature below 200 ° C.

According to a particularly preferred embodiment the catalyst is prepared by contacting cerium oxide (CeO 2) formed by nanocrystals with a smaller average size 8 nm, with a gold solution that has a pH above 2.0, modifying the pH of the gold solution to a pH in the range of 8 to 10, thus causing the precipitation of gold on the support. TO then washed, being able to dry at a temperature between 20 and  100 ° C If desired the dry material can be calcined in the presence or absence of air at a temperature between 100 and 500 ° C, and preferably, between 100 and 300 ° C.

According to a further embodiment of the procedure  to prepare the catalyst, the cerium oxide support Nanocrystalline is mesostructured. Oxide particles mesostructured cerium preferably have a diameter size equal to or less than 10 nm, preferably equal to or less than 8 nm.

Cerium oxide particles can be mesostructure, following techniques described in the art.

The mesostructured cerium oxide support is preferably prepared by mixing a colloidal oxide solution of cerium with particles of average diameter equal to or less than 8 nm, and an aqueous solution containing a structuring agent, which serves as a "composite template" in order to sort the nanoparticles and mesostructure them. As a structuring agent, preferably use surfactants. As an example of surfactant neutral surfactants are used as block polymers of poly (alkene oxides), such as E20 PO_ {70} EO20 pluronic P 123 from BASF.

In a particular embodiment the oxide support of mesostructured cerium is obtained

- preparing an aqueous solution of a polymer of alkene oxides, such as polymer E_ {PO} {70} EO_ {pl} {P} {123}, which dissolves an aqueous colloidal acid solution of CeO2,

- evaporating the homogeneous solution and

- calcining the product obtained in air at temperatures above 300 ° C.

A mesostructured material is thus obtained whose  walls are formed by a monolayer of nanoparticles of CeO 2.

The surfactant occluded in the material Mesostructured can be removed by a medium selected from extraction and calcination.

In addition, the cerium oxide support mesostructured is prepared even more preferably introducing a functionalizing agent into the synthesis medium. He preparation procedure in this case consists of the assembly of functionalized individual CeO2 nanoparticles.

As functionalizing agents are used molecules that have at one end a terminal group that interacts with the nanoparticle, and at the other end a group terminal that interacts with the structuring agent. The agent Functionalizer is preferably an amino acid. An agent preferred functionalizer is for example acid 6-aminocaproic acid (H2N (CH 2) 5 CO 2 H).

In a particularly preferred embodiment of Mesostructured catalyst preparation, this is prepared starting from an acidic aqueous colloidal solution of nanoparticles of cerium oxide with an average diameter of less than 8 nm. The acidic aqueous colloidal solution of cerium oxide has a Ce concentration between 1.0 and 8.0 molar. Molar relationship [H +] / [CeO 2] is between 0.01 and 0.10. This solution is added, a functionalizing agent, such as the 6-aminocaproic acid, in a concentration amino acid / [CeO2] between 0.1 and 0.6. Dissolution CeO2 nanoparticle colloidal is added to a solution aqueous of a structuring agent that is poly (alkylene) oxide) E 20 PO 70 EO 20 pluronic P 123 from BASF. Taking this as a reference, the solution that contains the surfactant has a concentration of surfactant in H2O between 1 and 10% by weight, containing this solution also between 6 and 20% by weight of an aqueous HCl solution of 2M concentration. The weight ratio between the solutions of CeO2 colloidal and the solution containing the surfactant is between 0.015 and 0.060. The solution resulting from mixing these two can be aged at temperatures between 20 and 90 ° C for periods between 2 and 40 hours. The solid formed is filter, wash, and dry, calcining at higher temperatures at 300 ° C for at least 0.5 hours. The surfactant can be removed optionally by extraction following procedures known in the art.

On the calcined support, the gold is deposited, following the procedure described above, which comprises deposit gold on cerium oxide nanoparticles mesostructured with a diameter size of less than 10 nm.

Gold can be deposited on the support of mesostructured cerium oxide by any method known in the art. A method is preferably used selected from impregnation, deposition-precipitation and chemical deposition of steam.

Even more preferably the procedure understands:

- prepare a gold solution that has a pH greater than 2,

- modify the pH of the gold solution, up to obtain a gold solution with a basic pH, preferably a pH equal to 10,

- add the basic gold solution on a mesostructured nanocrystalline cerium oxide support, formed by particles with an average diameter of less than 10 nm,

- modify the pH of the gold solution to obtain a pH between 8 and 10, causing precipitation of gold on the stand and

- wash the support on which it has been deposited gold.

The final catalyst is treated in the same way as described above for the case of using as Unstructured cerium oxide nanoparticles support.

It is a further object of the present invention a catalyst for the selective oxidation of carbon monoxide, characterized in that it comprises gold supported on cerium oxide nanocrystalline, which has a lower average particle size at 10 nm.

The defined catalyst has a surface specific greater than 90 m 2 g -1.

The gold content on the oxide support of cerium formed by nanocrystals, is comprised between 0.5 and 6% in weight.

The use of gold as a support CeO2 nanocrystals with an average size of less than 10 nm and with a specific surface area greater than 90 m 2 g -1 allows to obtain more active supported gold catalysts for the selective oxidation of CO to CO2 than those obtained until moment using CeO_ {2} as support, and they are reached even larger activities if the size of rust nanocrystals of cerium is equal to or less than 8 nm. In addition The catalyst formed for gold on cerium oxide nanocrystals it is also active and selective if these nanocrystals are mesostructured forming a ordered mesoporous material. In this case they are obtained catalysts with a BET surface area greater than 120 m2 g <-1>.

In the examples presented below, the method of preparation of the subject catalysts is described of this patent and its activity and oxidation selectivity selective from CO to CO2.

Examples Example 1 Preparation of a gold based oxidation catalyst on cerium oxide nanoparticles with an average size of 3.3 nm

An aqueous solution is prepared with 14 g of HauCl 4 in 2 liters of deionized water. They are added, subsequently, 750 g of an aqueous solution of NaOH (0.2 M). The resulting solution is added to a suspension of 126 g of cerium oxide nanoparticles with an average size of 3.3 nm in 2.5 g of deionized water, under stirring. Then it add 139 g of an aqueous solution of NaOH (0.2 M) and leave, under stirring, for 16 h. The suspension obtained is filtered and the resulting solid is washed with deionized water until elimination of chlorides. Finally, the solid is dried at 100 ° C for 16 h. He Final percentage by weight of gold in the catalyst was 2.8%.

Example 2 Preparation of a mesostructured cerium oxide

The mesostructured nanoparticle material of  CeO2 was prepared from a colloidal solution of CeO2 nanoparticles with an average diameter of 5 nm that are They used as building blocks. For the preparation of ordered mesoporous solid was split from a colloidal dispersion 4.0 Ce molar formed by nanoparticles, the pH of the solution being acid, and the ratio [H +] / [CeO 2] (referred to the nanoparticle concentration) of 0.024. Then, 10 g of poly (alkylene oxide) (E 20 PO 70 EO 20 pluronic P 123 of BASF) were dissolved in 35 cc of H2O and 38.0 cc of 2M HCl 4.88 cc of the colloidal solution of CeO2, before described, was added to the previous solution. Dissolution resulting is aged at 45 ° C for 16 hours, and then for 12 hours at 80 ° C. The solid formed was filtered, washed and calcined at 500 ° C for 6 hours The calcination temperature (500 ° C) was reached heating slowly, over a period of 6 hours.

Example 3 Preparation of a gold based oxidation catalyst on cerium oxide formed by 4 nm nanoparticles of medium diameter mesostructured

An aqueous solution is prepared with 14 g of HauCl 4 in 2 liters of deionized water. They are added, subsequently, 750 g of an aqueous solution of NaOH (0.2 M). The resulting solution is added to a suspension of 126 g of mesostructured cerium oxide nanoparticles, according to the Example 2, in 2.5 g of deionized water, under stirring. TO then 139 g of an aqueous solution of NaOH (0.2 M) and leave, under stirring at a pH of 10, for 16 h. The suspension obtained is filtered and the resulting solid is washed with deionized water until the removal of chlorides. Finally the solid is dried at 100 ° C for 16 h. The final weight percentage of Gold in the catalyst was 2.1%.

Example 4 Use of the catalyst of example 1 for monoxide oxidation carbon

0.5 g of the catalyst described in example 1 is  introduced into a fixed bed quartz reactor. The reaction is carried out using a mixture of gases A and B, with a ratio molar A / B = 2/8. Mix A is a gas mixture, with a ratio carbon monoxide molar: air = 1/99. Mix B is pure helium. TO a reaction temperature of 10 ° C and a total gas flow of 0.5 l / min, the analysis of reagents and products shows a 100% carbon monoxide conversion.

Example 5 Use of the catalyst of example 3 for the oxidation of monoxide carbon

0.5 g of the catalyst described in example 1 is  introduced into a fixed bed quartz reactor. The reaction is carried out using a mixture of gases A and B, with a ratio molar A / B = 2/8. The mixture A, is a mixture of gases with a ratio carbon monoxide molar: air = 1/99. Mix B is pure helium. TO a reaction temperature of 10 ° C and a total gas flow of 0.5 l / min, the analysis of reagents and products shows a 100% carbon monoxide conversion.

Example 6 Use of the catalyst of example 1 for monoxide oxidation carbon in the presence of hydrogen

0.5 g of the catalyst described in example 1 is  introduced into a fixed bed quartz reactor. The reaction is carried out using a mixture of gases A and B, with a ratio molar A / B = 5/7. The mixture A, is a mixture of gases with a ratio carbon monoxide molar: oxygen: helium = 2/1/97. Mix B is pure hydrogen At a reaction temperature of 60 ° C and a flow rate total gas of 1.2 l / min, the analysis of reagents and products shows a conversion of carbon monoxide of 61%, with a 0.30% hydrogen conversion.

Example 7 Use of the catalyst of example 3 for the oxidation of monoxide carbon in the presence of hydrogen

0.5 g of the catalyst described in example 1 is  introduced into a fixed bed quartz reactor. The reaction is carried out using a mixture of gases A and B, with a ratio molar A / B = 5/7. The mixture A, is a mixture of gases with a ratio carbon monoxide molar: oxygen: helium = 2/1/97. The B mix is pure hydrogen At a reaction temperature of 60 ° C and a flow rate total gas of 1.2 l / min, the analysis of reagents and products shows a 56% carbon monoxide conversion with a 0.30% hydrogen conversion.

Example 8 Preparation of a gold based oxidation catalyst on cerium oxide that is not formed by defined nanoparticles, and precipitation prepared

An ammoniacal solution (25% by weight) is added  of ammonia in water) to a solution of cerium nitrate (25.0 g of cerium nitrate in 200 g of water) until reaching a pH of 9.0 and It is left under stirring for 1 hour. Then, the solid and be at 100 ° C for 16 hours. Finally he burns in air at 500 ° C for 4 hours, with a heating ramp of 5 ° C / min, obtaining a cerium oxide with a surface area of 69 m 2 g -1.

An aqueous solution is prepared with 1.0 g of HauCl 4 in 200 ml of deionized water. They are added, subsequently, an aqueous solution of NaOH (0.2 M) until reach a pH of 10. The resulting solution is added to a 9.0 g suspension of cerium oxide, described above, in 0.3 g of deionized water, under stirring. Then it add 139 g of an aqueous solution of NaOH (0.2 M) and leave, in  stirring, for 16 h. The suspension obtained is filtered and the resulting solid is washed with deionized water until elimination of chlorides. Finally, the solid is dried at 100 ° C for 16 h. He Final percentage by weight of gold in the catalyst was 2.09%.

Example 9 Use of the catalyst of Example 8 for the oxidation of monoxide carbon

0.5 g of the catalyst described in example 8 is  introduced into a fixed bed quartz reactor. The reaction is carried out using a mixture of gases A and B, with a ratio molar A / B = 2/8. The mixture A, is a mixture of gases with a ratio carbon monoxide molar: air = 1/99. Mix B is pure helium. TO a reaction temperature of 10 ° C and a total gas flow of 0.5 l / min, the analysis of reagents and products shows a 5.0% carbon monoxide conversion.

Example 10 Use of the catalyst of Example 8 for the oxidation of monoxide carbon in the presence of hydrogen

0.5 g of the catalyst described in example 8 is introduced into a fixed bed quartz reactor. The reaction is carried out using a mixture of gases A and B, with a ratio molar A / B = 5/7. The mixture A, is a mixture of gases with a ratio carbon monoxide molar: oxygen: helium = 2/1/97. The B mix is pure hydrogen At a reaction temperature of 60 ° C and a flow rate total gas of 1.2 l / min, the analysis of reagents and products shows a 27% carbon monoxide conversion with a 0.50% hydrogen conversion.

Claims (25)

1. A catalyst for the selective oxidation of carbon monoxide in a gas mixture, characterized in that it comprises gold supported on nanocrystalline cerium oxide, wherein said cerium oxide is formed by particles with an average size of less than 10 nm. 2. A catalyst for the selective oxidation of carbon monoxide in a gas mixture according to claim 1, characterized in that said cerium oxide is formed by particles with an average size of less than 8 nm. 3. A catalyst for the selective oxidation of carbon monoxide in a gas mixture according to claim 1, characterized in that it comprises an amount of gold comprised between 0.5 and 6% by weight. 4. A catalyst for the selective oxidation of carbon monoxide in a gas mixture according to claim 1, characterized in that said catalyst has a specific surface area greater than 90 m 2 g -1. 5. A catalyst for the selective oxidation of carbon monoxide in a gas mixture according to any one of claims 1 to 4, characterized in that the nanocrystalline cerium oxide support is mesostructured. 6. A catalyst for the selective oxidation of carbon monoxide in a gas mixture according to claim 5, characterized in that said catalyst has a specific surface area greater than 120 m 2 g -1. 7. A process for preparing a catalyst comprising gold and a nanocrystalline cerium oxide support formed by particles with an average diameter of less than 10 nm characterized in that said process comprises depositing gold on cerium oxide nanoparticles with a diameter size less than 10 nm. 8. A process for preparing a catalyst according to claim 7 characterized in that the gold is deposited on the support by a method selected from impregnation, deposition-precipitation and chemical vapor deposition. 9. A process for preparing a catalyst according to claim 7 or 8, characterized in that it comprises: - prepare a gold solution that has a pH greater than 2, - modify the pH of the gold solution, up to get a gold solution with a basic pH, - add the gold solution with basic pH over a nanocrystalline cerium oxide support, formed by particles with an average diameter of less than 10 nm, - modify the pH of the gold solution to obtain a pH between 8 and 10, causing precipitation of gold on the stand and - wash the support on which the  gold. 10. A process for preparing a catalyst according to claim 9, characterized in that the nanocrystalline cerium oxide support is in the form of a colloidal suspension. 11. A process for preparing a catalyst according to claim 9, characterized in that the gold solution is an aqueous solution of a gold salt. 12. A process for preparing a catalyst according to one of claims 7 to 11, characterized in that the cerium oxide support is mesostructured. 13. A procedure in accordance with the claim 12, wherein the cerium oxide support Mesostructured is prepared by mixing a colloidal solution of cerium oxide particles having an equal average diameter or less than 10 nm with an aqueous solution containing an agent structuring 14. A procedure in accordance with the claim 13, wherein the structuring agent is a surfactant 15. A procedure in accordance with the claim 14 wherein the surfactant is an oxide polymer of alkenes. 16. A process according to claim 1 wherein the alkene oxide polymer is E20PO70
EO 20 pluronic P 123.

         \ newpage
      

17. A procedure in accordance with the claim 13, wherein the cerium oxide support Mesostructured is prepared: - mixing an acidic colloidal aqueous solution of  cerium oxide particles having an equal average diameter or less than 10 nm with an aqueous solution of an oxide polymer of alkenes, - evaporating the homogeneous solution and - calcining the product obtained in air temperatures above 300 ° C. 18. A procedure in accordance with the claim 12, wherein the cerium oxide support Mesostructured is prepared by entering the synthesis medium a functionalizing agent 19. A procedure in accordance with the claim 18, wherein the functionalizing agent is a amino acid 20. A procedure in accordance with the claim 14, wherein the surfactant occluded in the material mesostructured is removed by a means selected from extraction and calcination. 21. A method for selectively oxidizing carbon monoxide in a gas mixture characterized in that it comprises reacting the gas mixture with an oxidant in the presence of a catalyst comprising gold and nanocrystalline cerium oxide formed by particles with an average diameter of less than 10 nm. 22. A method according to claim 21, characterized in that it comprises reacting the gas mixture with an oxidant in the presence of a catalyst defined in any of claims 2 to 6. 23. A method according to claim 1 or 2, characterized in that said catalyst comprises a nanocrystalline cerium oxide support in which the cerium oxide nanoparticles have an average diameter less than or equal to 8 nm. 24. A method according to claim 21 or 22, in which the oxidant is oxygen. 25. A method according to claim 21, in which the oxidation takes place at a temperature between 10 and 130 ° C.