Effect of chlorine in the formation of PtRe alloys in [formula omitted] catalysts

Abstract

The role of chlorine and the thermal pretreatments of the samples in PtRe alloying during the reduction of Pt Al 2O 3 and PtRe Al 2O 3 systems have been examined by using the reaction of n-butane hydrogenolysis with the aid of temperature-programmed reduction (TPR) experiments. The presence of chlorine modifies only slightly the TPR profiles, and rhenium reduction is always catalyzed by the presence of platinum. This effect depends strongly on the hydration degree of the support, while it is almost independent of the chlorine content of the sample. However, chlorine greatly decreases the catalytic activity of both Pt and PtRe catalysts in n-butane hydrogenolysis. Selectivity to methane (measured as C 3 C 1 ratio) is close to 1 for the platinum samples, while in the PtRe systems it remains close to 0.5 for the chlorine-free catalyst after all the pretreatments, but changes from 0.5 to 1.0 when the chlorinated catalyst is predried at increasing temperatures, indicating differences in the degree of PtRe alloying. Chlorination/dechlorination experiments confirm the role of chlorine on the above results and point to the existence of oxychlorinated Pt and/or Re species that may strongly interact with the progressively dehydrated Al 2O 3 support, leading to higher metallic dispersions and lower PtRe alloying in the chlorinated catalysts after hydrogen reduction.