The influence of pretreatment on the metal function of a commercial Pt-Re/Al2O3 catalyst

The metal function of a commercial 0.3-0.3 wt% Pt-Re/Al2O3 catalyst was characterized by temperature-programmed reduction, by H-2 and O-2 chemisorption, and by using methylcyclohexane dehydrogenation and n-heptane conversion as model reactions. Emphasis was put on investigating the influence of the drying conditions prior to reduction. The degree of hydration of the catalyst, as set by the drying temperature, strongly modifies the reducibility of rhenium and the extent of alloy formation in the reduced catalyst. Alloy formation affects the chemisorption characteristics and the hydrogenolysis activity of the catalyst. Platinum dispersion was not affected by air pretreatment at temperatures up to 680 degrees C, while in nitrogen, platinum oxide decomposition and sintering were observed from 400 degrees C and higher. The presence of water vapor during H-2 reduction was found to promote Pt sintering. (C) 1998 Academic Press.