Mechanism of the oxidation of carbon monoxide on palladium?containing catalysts

Effect of platinum and palladium additives on the surface state and catalytic activity of vanadium oxides in the oxidation of carbon monoxide

“…At the same time, as seen from our kinetic data, the curve for r as a function of C CO in the intermediate temperature region features clockwise hysteresis, and the curve for r as a function of C O 2 features counter-clockwise hysteresis, i.e., steady state multiplicity (SSM) obtains. A number of authors [8][9][10][11][12] have observed SSM for platinum and palladium catalysts, especially, for alumina-support catalysts, in oxidation of CO. Spivak [8] and Kiperman [10] have interpreted this phenomenon using a two-pathway kinetic model combining the Langmuir-Hinshelwood and Eley-Rideal mechanisms. Ostapyuk [9] and Tsekhladze [11] have shown that the high-activity state is related to a heterogeneous homogeneous mechanism for the oxidation of CO. Pyatnitskii [13] has noted that the oxidation of CO in the high-activity state may proceed in parallel through a heterogeneous collision mechanism and a heterogeneous homogeneous mechanism; the author assigns 20% to the latter.…”

“…A number of authors [8][9][10][11][12] have observed SSM for platinum and palladium catalysts, especially, for alumina-support catalysts, in oxidation of CO. Spivak [8] and Kiperman [10] have interpreted this phenomenon using a two-pathway kinetic model combining the Langmuir-Hinshelwood and Eley-Rideal mechanisms. Ostapyuk [9] and Tsekhladze [11] have shown that the high-activity state is related to a heterogeneous homogeneous mechanism for the oxidation of CO. Pyatnitskii [13] has noted that the oxidation of CO in the high-activity state may proceed in parallel through a heterogeneous collision mechanism and a heterogeneous homogeneous mechanism; the author assigns 20% to the latter. Finally, we cannot exclude that an external diffusion process may be rate-limiting in the high-activity region for high conversions (for our samples with a small specific surface, an internal diffusion process may be neglected).…”