Hydroconversion of paraffinic wax over platinum and palladiumcatalysts supported on silica-alumina

Two bifunctional catalysts consisting of platinum or palladium supported on amorphous silica-alumina were prepared and tested in hydrocracking/hydroisomerization of paraffinic wax. The performance of both noble metals was studied at the following reaction conditions: P = 35 bar; T = 300-330oC;H2/wax = 0.1 wt/wt; WHSV = 1-4 h-1. The platinum sample was more active in hydrocracking of C22+compounds and more selective to middle distillates. On the other hand, the palladium-based catalyst resulted in a higher isomerization degree of the products and lower amounts of methane and ethane. The higher production of light compounds over platinum is attributed to a monofunctional hydrogenolysis mechanism, in addition to the classical bifunctional route. Characterization studies showed that both catalysts had comparable metal and acid site distributions. These observations would indicate that the different catalyst performance is due to the different nature of platinum and palladium as hydrogenation/dehydrogenation function.