Isobutane dehydrogenation over unimodal porous catalyst (part 2) - Role ofcatalyst components on Sn-Pt/ZnO/Al2O3

The role of catalyst components with a large ZnO/Al2O3 surface area on Sn-P t/ZnO/Al2O3 for dehydrogenation of isobutane was investigated by using the same gamma -alumina carrier having unimodal pore distribution. It was found that the activity of ZnO/Al2O3 was 40 times greater than that of Pt/Al2O3, moreover ZnO/Al2O3 had also shown high cracking activity simultaneously. P t played a role to promote the activity of ZnO/Al2O3 and suppress the catal yst deactivation. Possibly the effect of Pt addition was caused by reverse spillover. Sn suppressed the catalyst deactivation remarkably, since it imp roved both the activity and selectivity. The influence of the quantity of c omponents in Sn-Pt/ZnO/Al2O3 catalyst on such performances as activity, sel ectivity, deactivation rate was also investigated. It seemed that excess ad dition of Sn caused the poisoning of certain active sites on ZnO/Al2O3 sele ctively. The side reaction scheme was investigated and it was considered th at cracking and skeletal isomerization of isobutane occurred simultaneously in which cracking was predominant. When the quantity of the catalyst compo nents was changed, inverse first order relation resulted between selectivit y and deactivation rate constant. Possibly Sn had formed the Pt surface on the ZnO/Al2O3 bimetallic, and covered the cracking sites on ZnO/Al2O3.