Dynamic response and poisoning studies of a liquid-solid catalytic reaction: Effects of metal content on adsorption and surface reaction rates

Abstract

Individual adsorption equilibrium, adsorption rate, and surface reaction rate coefficients were determined for three supported-metal ( Pd Al 2O 3 ) catalysts of 0.050, 0.150, and 0.450 wt% palladium content. The data were obtained by a hydrogen-gas, pulse response technique in a well-mixed, three-phase slurry reactor at 25, 38, and 50 °C and atmospheric pressure. The reaction, hydrogenation of α-methyl styrene to cumene in pure methyl styrene, is first-order in H 2 and zero-order in methyl styrene. Adsorption equilibrium coefficients for hydrogen on Pd increased with Pd content. The heat of adsorption, 13.7 kJ/mole, was the same for the three catalysts. Adsorption and surface reaction rate coefficients based on mass of catalyst also increase, while those based on mass of Pd decrease with Pd content. The energy of activation increases for adsorption and decreases for the surface reaction rate as Pd content increases, but remains constant for the overall rate constant. The number of active sites on the catalyst surface for these metal loadings was estimated from experimental data of CS 2 poisoning. The number of active sites per gram of catalyst increases, and the number per gram of Pd decreases with Pd content. Adsorption equilibrium, adsorption rate, and surface reaction coefficients increase with number of active sites for unpoisoned catalyst. The results suggest that the dynamic response technique combined with poisoning studies is a useful tool in the study of heterogeneous catalysis.