Oxidation of carbon monoxide with air on supported palladium catalysts: Effect of mass transfer limitation on the kinetics

The kinetics of oxidation of carbon monoxide on Pd-supported catalysts are determined at low temperature and under typical conditions of atmospheric p ollution (a few ppm of CO in air). The nature (silica, alumina, silica-alum ina) as well as the geometry (beads, fibers, powder) of the support were va ried, the latter to change the mass-transfer resistance. The nature of the support has no influence on the kinetics. With powder or fiber as the suppo rts, the catalyst operates without mass transfer limitation, and the kineti cs is of negative order with respect to CO, of positive order with respect to oxygen. The energy of activation is about 85 kJ/mol, This corresponds to the regime of GO-inhibition, never reported at so high O-2 to CO ratio (75 -10(4)). The surface is dominated by adsorbed carbon monoxide, and the reac tion rate is limited by oxygen adsorption, With beads as the support, the o rders in CO and in oxygen are both positive and the energy of activation is 42 kJ/mol, This kinetics law is attributed to mass transfer limitation.