RATE OF OXIDATION OF CO ON PD AT PRESSURE BETWEEN 10(-1) AND 10(2) MBAR

At 445 K, and equimolar ratio of reactants, the turnover rate for CO oxidation on unsupported and supported Pd is constant within experimental error between almost-equal-to 0.1 and 100 mbar. As first proposed in 1922 by Langmuir, the overall rate is the rate of adsorption on a surface almost saturated with CO. Thus the rate is proportional to the ratio of concentrations Of O2 and CO and is pressure independent. At quasi-saturation, the few vacant sites form an ideal dilute solution in the CO-Pd solvent. Adsorption on these sites is dominated by pressure invariant interactions with the solvent. Hence, the rate obeys Langmuir kinetics and the reaction is structure insensitive.