An infrared and kinetic study of carbon monoxide oxidation on model silica-supported palladium catalysts from 10-9 to 15 Torr

Kinetic compensation effects observed during oxidation of carbon monoxide on γ‐alumina supported palladium, platinum, and rhodium metal catalysts: Toward a mechanistic explanation

“…10 of [30]). These conditions approach those of the present measurements, which are, therefore, identified as taking place with temperature variations of chemical characteristics and reactivities of the adsorbed precursors to CO oxidation [21,[26][27][28]30]. Moreover, as the temperature falls below 450 K, the total amounts of CO and oxygen retained on the metal surface increase [26][27][28], leading to crowding with consequent modifications of adsorption bonding energies [27], surface dispositions [26], and reactivities of adsorbed species.…”

“…(The apparent mean temperature of the total alumina/0.5% Pd mass is raised by about 10 K.) It is reasonable to suggest that in air (+1% CO) this local heating may cause further metal oxidation, with consequent catalyst deactivation [30] before a second or subsequent kinetic experiment. However, values of E a for reactions on oxidized Pd surfaces have been found to be similar to those on the clean metal, 100-140 kJ mol −1 [26][27][28]30]. We conclude that metal oxidation explains the relatively high E a values characteristic of second and further kinetic measurements.…”

“…We also note that during oxidation of CO on Pd at low pressures [26], (2-8) × 10 −5 Pa at 550-750 K, there were pronounced systematic variations in activation energy and enthalpy differences for the desorption and the oxidation of CO. This was not described as compensation [26] but there is a linear relationship between the listed values of H * and of S * .…”

“…Goodman and coworkers have reported detailed [26][27][28][29][30] kinetic and mechanistic investigations of the oxidation of CO on Pd across wide ranges of both pressures and temperatures. Much of the work is concerned with high (kPa) and with low (10 −5 Pa) pressure stoichiometric reactant mixtures above 450 K. The overall kinetic behavior is satisfactorily represented by a single Langmuir-Hinshelwood reaction model [26].…”

“…Much of the work is concerned with high (kPa) and with low (10 −5 Pa) pressure stoichiometric reactant mixtures above 450 K. The overall kinetic behavior is satisfactorily represented by a single Langmuir-Hinshelwood reaction model [26]. Reaction of a stoichiometric mixture above 450 K proceeds on an almost completely CO covered surface through oxygen adsorption at vacated surface sites.…”