Selective hydrogenation of isoprene over delta-alumina-supported eggshell Pd catalysts: Particle size effects

The effects of calcination temperature on the metal dispersion of delta-alumina-supported eggshell profile Pd catalyst and its catalytic performance in isoprene selective hydrogenation were investigated. The CO chemisorption results indicated that Pd particles grew with the elevation of calcination temperature. Catalytic tests showed that isoprene conversion increased with increasing Pd dispersion, while the selectivity to isopentenes decreased. Based on the results of CO chemisorption and isoprene temperature programmed desorption (TPD), the lower isoprene conversion of catalyst with lower Pd dispersion was attributed to fewer Pd sites for isoprene adsorption. The higher selectivity to isopentenes, however, was regarded as a consequence of both insufficient active sites for further hydrogenation of isopentenes to isopentane and lower electronic interaction between Pd and the alumina surface. Microscopic photo, electron probe microanalysis (EPMA), isoprene TPD, and catalysts test showed that coke was formed on both the Pd and on the alumina surface. The results also showed that, the higher the Pd dispersion the less is the coke formation on alumina.