In situ formation of the active sites in Pd-Au bimetallic nanocatalysts for CO oxidation: NAP (near ambient pressure) XPS and MS study

The model bimetallic Pd-Au/HOPG catalysts have been investigated in CO oxidation reaction using combination of NAP XPS and MS techniques. The samples have shown catalytic activity at temperatures above 150°C. The redistribution of Au and Pd on the surface depending on the reaction conditions has been demonstrated using NAP XPS. The Pd enrichment of the bimetallic particles surface under reaction gas mixture has been shown. Apparently, CO adsorption induces the Pd segregation on the surface. Heating the sample under reaction conditions above 150°C decomposes Pd-CO state due to CO desorption and reaction and simultaneous Pd-Au alloy formation on the surface takes place. Cooling down back to RT results in reversible Pd segregation due to Pd-CO formation and the sample becomes inactive. It has been shown that the in situ studies are necessary for the investigation of the active sites in Pd-Au bimetallic systems