Promotion of Pt/Al2O3 catalysts with chromium ions and investigation of the changes in their hydrogenating/dehydrogenating activity

Abstract Bimetallic Pt-Cr/Al 2 O 3 samples containing 4.75–7.90 wt.-% Cr 2 O 3 were obtained by modifying a laboratory aluminium-platinum (0.16 wt.-% Pt) catalyst with CrO 2 Cl 2 vapour or by impregnating it with aqueous solutions of (CrO 3 ) x' K 2 Cr 2 O 7 , (NH 4 ) 2 Cr 2 O 7 or their mixtures. The changes in the hydrogenating/dehydrogenating activity of the bimetallic catalysts obtained were studied with a flow apparatus and by gas chromatographic analysis of the products of model catalytic reactions such as hydrogenation of hex-1-ene and benzene, dehydrogenation of cyclohexane and conversion of cyclohexene and cyclopentene. Promotion with chromium ions was found to suppress the hydrogenating/dehydrogenating functions of metallic platinum and increase the stability and selectivity of the catalysts. The effects observed are ascribed to a reduced electron deficiency of the active sites as a result of the introduction of chromium as an electron donor, increasing the electron density of platinum, and to a change in the acidity of the support by the addition of potassium and chromium ions.