ALUMINA-SUPPORTED PLATINUM-RHENIUM DEHYDROGENATION CATALYSTS - INFLUENCE OF METAL RATION AND PRECURSORS ON CATALYTIC BEHAVIOR

Two series of Pt-Re/Al2O3 catalysts with 0.5 wt % loading were prepared by incipient wetness, with the ultimate goal of identifying catalysts that are highly selective for the dehydrogenation of methylcyclohexane to toluene. One series of dehydrogenation catalysts was prepared from H2PtCl6 and Re2O7 and had nominal Pt/Re atom ratios of 100/0, 75/25, 50/50, and 25/75. The second series of catalysts was prepared from H2Pt(OH)6 and Re2O7 and had nominal Pt/Re atom ratios of 100/0, 75/25, 50/50, 25/75, and 0/100. These Pt/Re catalysts were characterized by neutron activation analysis, by diffuse reflectance UV spectroscopy, and by model hydrocarbon dehydrogenation and hydrogenolysis activity tests which were conducted in a micropulse reactor. The characterization by diffuse UV/vis reflectance spectroscopy suggests the presence of Re(VI), Re(VII), and Pt(IV) in the freshly prepared and dried catalysts. Neutron activation analysis indicated a significant loss of rhenium after calcination for the catalysts prepared with H2Pt(OH)6. In the short-term catalyst screening and activity tests, the use of the chlorine-containing metal salt H2PtCl6 measurably increased the hydrogenolysis activity of the resulting catalysts. With respect to the dehydrogenation tests, virtually constant activity was observed on the 50/50, 75/25, and 100/0 Pt/Re catalysts for the conversion of cyclic C6 hydrocarbons whereas for the dehydrogenation of cyclic C5 hydrocarbons activity increased continuously with increasing Pt/Re ratio. The unchlorinated 75/25 and 50/50 Pt/Re on alumina catalysts show the most promise for the highly selective dehydrogenation of methylcyclohexane.