Process for reducing the content of nitrogen oxides in a gaseous mixture containing the same

Claim 1

IN A PROCESS WHEREIN A MIXTURE CONTAINING AN EXHAUST GAS FROM AN INTERNAL COMBUSTION ENGINE THAT INCLUDES NITROGEN OXIDES CARBON MONOXIDE AND UNBURNED HYDROCARBONS AND ADDED OXYGEN IS PASSED OVER A FIRST CATALYST BED DURING THE INITIAL STAGES OF OPERATION OF SAID INTERNAL COMBUSTION ENGINE UNDER AN OXIDIZING ATMOSPHERE TO OXDIZE SAID CARBON MONOXIDE AND SAID UNBURNED HYDROCARBONS AND THE TREATED MIXTURE IS THEN PASSED OVER A SECOND CATALYST BED CONTAINING AN OXIDATION CATALYST, UPON CONTINUED OPERATION OF SAID INTERNAL COMBUSTION ENGINE SOLEY SAID EXHAUST GAS FROM SAID INTERNAL COMBUSTION ENGINE IS PASSED OVER SAID FIRST CATALYST BED UNDER A REDUCING ATMOSPHERE TO CONVERT SAID NITOGEN OXIDES TO NITROGEN AND THE LATTER TREATED MIXTURE AND ADDED OXYGEN ARE THEN PASSED OVER SAID CATALYST BED UNDER AN OXIDIZING ATMOSPHERE TO OXIDIZE SAID CARBON MONOXIDE AND UNBURNED HYDROCARBONS, THE IMPROVEMENT WHICH COMPRISES EMPLOYING AS CATALYST IN SAID FIRST CATALYST BED A METAL RUTHENATE SELECTED FROM THE GROUP CONSISTING OF LITHIUM, SODIUM, POTASSIUM, RUBIDIUM, CESIUM, CALCIUM, STRONTIUM AND BARIUM RUTHENATES, SAID METAL RUTHENATES EXHIBITING SUBSTANTIALLY NO VOLATILITY DURING SAID INITIAL STAGES OF OPERATION WHEN SAID BED IS UNDER AN OXIDIZING ATMOSPHERE.