Selective catalytic reduction system and process for treating NOx emissions using a palladium and rhodium or ruthenium catalyst

1. A process for catalytic reduction of nitrogen oxides (NO x ) in a gas stream in the presence of H 2 comprising contacting the gas stream with a catalyst system comprising zirconia-silica washcoat particles, a pre-sulfated zirconia binder, and a catalyst combination comprising palladium and at least one of rhodium, ruthenium, or a mixture of rhodium and ruthenium.

2. The process according to claim 1 , wherein said catalyst combination comprises palladium and rhodium, and wherein a mass ratio of palladium to rhodium in the catalyst system is between 0.5 and 20.

3. The process according to claim 2 , wherein said mass ratio of palladium to rhodium in the catalyst system is between 7.5 and 15.

4. The process according to claim 1 , wherein said catalyst combination comprises palladium and ruthenium, and wherein a mass ratio of palladium to ruthenium in the catalyst system is between 0.5 and 20.

5. The process according to claim 4 , wherein said mass ratio of palladium to ruthenium in the catalyst system is between 7.5 and 15.

6. The process according to claim 1 , wherein said catalyst system comprises palladium and a mixture of rhodium and ruthenium, and wherein a mass ratio of palladium to the mixture of rhodium and ruthenium in said catalyst system is from 0.5:1 to 20:1.

7. The process according to claim 1 , wherein a loading of the palladium is from 0.01 to 2.0% by wt. of the catalyst system, and wherein the catalyst system further comprises a promoter.

8. The process according to claim 1 , wherein the sulfated zirconia washcoat particles comprise at least one of (ZrO 2 )SO 4 or (ZrO 2 —SiO 2 )SO 4 .

9. The process according to claim 1 , wherein a catalytic bed comprising the catalyst system is installed in a flow path of an exhaust gas stream of a gas turbine, and wherein the exhaust gas stream includes NO x , H 2 O, O 2 , and SO 2 .

10. The process according to claim 9 , wherein H 2 O and hydrogen are injected into the exhaust gas between the gas turbine and the catalytic bed, to a concentration of about 5-25 vol. % H 2 O and a molar ratio for H 2 /NO x in the range of 10 to 100 in the exhaust gas.

11. The process according to claim 9 , wherein the exhaust gas is passed over the catalytic bed at a temperature maintained in a range of 100-140° C.

12. The process according to claim 9 , wherein the catalytic bed is installed in the flow path of the exhaust gas of the gas turbine in an integrated gasification combined cycle (IGCC) power generation plant that synthesizes a hydrogen-containing fuel for the gas turbine, and further comprising:

diverting a portion of the hydrogen-containing fuel to supply the H 2 as a NO x reducing agent for the catalytic bed;

maintaining a water content in the exhaust gas to a concentration of about 15-25 vol. % and maintaining the diverted portion of the hydrogen-containing fuel into the exhaust gas between the gas turbine and the catalytic bed at a molar ratio for H 2 /NOx in the range of 10-100 in the exhaust gas; and

passing the exhaust gas over the catalytic bed at a temperature between 70-250° C. to remove an amount of NO x from the exhaust gas.

13. The process according to claim 12 , wherein the water content is maintained to a concentration of about 17-21 vol. %.

14. A system for implementing a process for selective catalytic reduction of nitrogen oxides (NO x ) in an exhaust gas from a gas turbine in an integrated gasification combined cycle power plant, comprising:

a fuel gas synthesizer that produces a fuel gas containing at least 10 vol. % H 2 and at least 10 vol. % nitrogen;

a gas turbine that burns a portion of the fuel gas, producing the exhaust gas;

a catalytic bed installed in a flow path of the exhaust gas, the catalytic bed comprising a catalyst system, the catalyst system comprising zirconia-silica washcoat particles, a pre-sulfated zirconia binder, and a catalyst combination comprising palladium and at least one of rhodium, ruthenium, or a mixture of rhodium and ruthenium;

a hydrogen injector that mixes a diverted portion of the fuel gas into the exhaust gas between the gas turbine and the catalytic bed;

an H 2 O injector that mixes H 2 O into the exhaust gas between the gas turbine and the catalytic bed; and

sensors and valves at control points in the system connected to a controller that maintains operational conditions in the exhaust gas at the catalytic bed, wherein the operational conditions comprise a temperature between 70-250° C., a molar ratio for H 2 /NO x in the range of 10-100, and H 2 O at a concentration of about 15-23 vol. %.

15. The system according to claim 14 , wherein said catalyst combination comprises palladium and rhodium, and wherein a mass ratio of palladium to rhodium in the catalyst system is between 0.5 and 20.

16. The system according to claim 15 , wherein said mass ratio of palladium to rhodium in the catalyst system is between 7.5 and 15.

17. The system according to claim 14 , wherein said catalyst combination comprises palladium and ruthenium, and wherein a mass ratio of palladium to ruthenium in the catalyst system is between 0.5 and 20.

18. The system according to claim 17 , wherein said mass ratio of palladium to ruthenium in the catalyst system is between 7.5 and 15.

19. The system according to claim 14 , wherein said catalyst combination comprises palladium and a mixture of rhodium and ruthenium, and wherein a mass ratio of palladium to the mixture of rhodium and ruthenium in said catalyst system is from 0.5:1 to 20:1.

20. The system according to claim 14 , wherein a loading of the palladium is from 0.01 to 2.0% by wt. of the catalyst system, and wherein the catalyst system further comprises a promoter.