OXIDATION OF CO BY O2, NO, AND MIXTURES OF O2 AND NO OVER PD(100)

The rate Of CO2 formation in each of the three reactant mixtures, CO + O2, CO + NO, and CO + O2 + NO, was measured over Pd(100) at partial pressures of 1 Torr and temperatures in the range 430-580 K. The rate in both CO + O2 and CO + NO followed the Arrhenius behavior; in CO + NO, the rate was about 2 orders of magnitude lower than in CO + O2, whereas the apparent activation energy was about 30% lower. The rate in CO + O2 + NO, however, was the same as in CO + O2 at temperatures above 480 K and was even greater at temperatures below 480 K. This behavior may be contrasted with that in the case of Rh, where the addition of NO to CO + O2 drastically reduces the rate Of CO2 formation.