AMORPHOUS NICKEL-BASE ALLOY CATALYSTS FOR OXIDATION OF CARBON-MONOXIDE BY OXYGEN AND NITROGEN MONOXIDE

Oxidation of carbon monoxide was carried out at low temperatures by using surface-activated amorphous nickel-niobium and nickel-tantalum alloys containing a few at.-% of platinum group elements. The surface activation treatment was carried out by immersion in hydrogen fluoride solution, and led to selective dissolution of nickel, niobium and tantalum with a consequent formation of microcrystalline surface alloys consisting of major platinum group elements and some nickel, niobium and tantalum in addition to surface roughening. The surface-activated amorphous alloys showed very high activities for oxidation of carbon monoxide even at low temperatures. Fatal concentrations of carbon monoxide can be converted to carbon dioxide at about 100-degrees-C. The high activities were not affected by changes of the platinum group elements contained in amorphous alloys except for the slightly lower activity of ruthenium-containing alloys for the carbon monoxide-oxygen reaction and of ruthenium- and palladium-containing alloys for the carbon monoxide-nitrogen monoxide reaction. The carbon monoxide-oxygen and carbon monoxide-nitrogen monoxide reactions took place on a few nm thick oxide films on the surface-activated amorphous alloys at temperatures lower than 200-degrees-C, while, when the surface activation treatment was not applied, the reactions occurred at higher temperatures on the nickel monoxide film grown on the alloys during the reactions.