Participation of Al/sub 2/O/sub 3/ hydroxyl-shell oxygen in the catalytic oxidation of carbon monoxide over Pd/Al/sub 2/O/sub 3/ and Pd. Cu/Al/sub 2/O/sub 3/ catalysts

This paper studies the mechanism of low temperature CO oxidation over catalysts of 0.003%-0.1 wt.% palladium supported on gamma-Al/sub 2/O/sub 3/, and over a solid solution of copper in gamma-Al/sub 2/O/sub 3/ (0.5-3.0 wt.% CuO). In order to obtain information about the reactive forms of oxygen in CO oxidation over these catalysts, the authors used tagged oxygen (ca 80 atom %) and secondary ion mass spectrometry. To confirm the effect of oxygen isotope exchange on the tracer content of the CO/sub 2/, CO oxidation was carried out with CO/sub 2/ freeze-out in the cycle. CO oxidation over supported palladium, under conditions of reduction or of catalysis, can go via reaction with OH oxygen atoms, but the temperature ranges of these conditions differ by more than 250 degrees. It is noted that over Pd.Cu/Al/sub 2/O/sub 3/ catalysts the mechanism represented is only partly realized. Along with OH oxygen, an adsorbed form of oxygen evidently also contributes to CO formation over these catalysts.