Methane oxidation catalyst, process to prepare the same and method of using the same
The invention provides a process for preparing a methane oxidation catalyst, a methane oxidation catalyst thus prepared and a method of oxidizing methane.
1. A process for preparing a methane oxidation catalyst comprising the following steps:
a.) calcining a non-modified zirconia precursor at a temperature in the range of from 675 to 1050° C. to prepare a calcined zirconia precursor comprising tetragonal zirconia, wherein the weight ratio of tetragonal zirconia to monoclinic zirconia, if any is present, is greater than 31:1;
b.) impregnating the zirconia obtained from step b.) with a noble metal precursor-comprising impregnation solution to generate a wet noble metal-impregnated zirconia;
c.) drying the wet noble metal-impregnated zirconia at a temperature of no more than 120° C. to generate a dried noble metal-impregnated zirconia; and
d.) calcining the dried noble metal-impregnated zirconia at a temperature in the range of from 400 to 650° C. to prepare a methane oxidation catalyst, wherein the weight ratio of tetragonal zirconia to monoclinic zirconia of the catalyst is in the range of from 1:1 to 31:1.
2. The process of claim 1 , wherein the weight ratio of tetragonal zirconia to monoclinic zirconia of the calcined zirconia precursor in step a.) is in the range of from 35:1 to 1000:1.
3. The process of claim 1 , wherein no detectable monoclinic zirconia is present after the calcination of step a.).
4. The process of claim 1 , further comprising depositing the dried noble metal-impregnated zirconia after calcination in step d.) in the form of a layer, film or coating on a ceramic or metallic monolith substrate.
5. The process of claim 1 , further comprising depositing the calined zirconia precursor obtained in step a.) in the form of a layer, film or coating on a ceramic or metallic monolith substrate and subsequently impregnating and treating the deposited calcined zirconia precursor according to steps (b) to (d).
6. The process of claim 1 , wherein the noble metal-impregnated zirconia obtained in step d.) or the calcined zirconia precursor obtained in step a.) is deposited on a ceramic or metallic monolith by a washcoating step.
7. The process of claim 1 , wherein the impregnation solution comprises a noble metal precursor selected from the group consisting of palladium compounds, platinum compounds, rhodium compounds and mixtures thereof.
8. The process of claim 1 , wherein the impregnation solution comprises at least one or more noble metal complexing or chelating compounds in a molar ratio of the complexing or chelating compounds to noble metal of from 1:1 to 5:1.
9. The process of claim 1 , wherein the calcination in step a.) is carried out at a temperature in the range of from 800 to 1025° C.
10. The process of claim 1 , wherein the non-modified zirconia precursor comprises tetragonal zirconia.
11. The process of claim 1 , wherein the non-modified zirconia precursor is not sulfated and not tungsten-modified.
12. The process of claim 1 , wherein the monoclinic zirconia is present as a dispersion of monoclinic zirconia in the tetragonal zirconia of step d.).
13. The process of claim 4 , wherein the methane oxidation catalyst is deposited on a ceramic or metallic monolith substrate comprising pore channels, defining an inner pore channel surface, and wherein the methane oxidation catalyst is deposited in the form of a coating, washcoat or a film of a thickness in the range of from 10 to 250 μm on the inner pore channel surface.
14. The process of claim 1 , wherein the dried noble metal-impregnated zirconia comprises in the range of from 0.5 to 15 wt % of total noble metals, based on the total weight of the noble metal(s) and tetragonal and monoclinic zirconia.
15. A methane oxidation catalyst prepared by the process according to claim 1 .
16. A method of oxidizing methane by contacting a gas stream comprising methane with a methane oxidation catalyst according to claim 15 in the presence of oxygen and oxidizing at least part of the methane in the gas stream to carbon dioxide and water.
17. A method according to claim 16 , wherein the stream comprising methane is an exhaust gas from a natural gas-fueled engine.