Hydrocracking of n-hexadecane on noble metal/silica–alumina catalysts

Bifunctional catalysts consisting of platinum or palladium on amorphous silica–alumina were prepared and tested in the hydrocracking of n-hexadecane (n-C16H34). Product selectivities toward mono-branched and multi-branched feed isomers and cracking products have been determined in a wide range of conversions, varying liquid hourly space velocity at constant operating parameters (pressure = 30 bar; temperature = 310 °C; H2/n-C16H34 feed molar ratio = 10). A simple kinetic study is presented, in which the reactions are approximated by a network of pseudo first order irreversible reaction steps. The reaction network model was fitted to the experimental data, and kinetic constants for the different reaction steps were obtained. It could be concluded that mono-branched feed isomers are primary products in the hydrocracking/hydroisomerization reaction network; multi-branched isomers are formed mainly from mono-branched as a secondary product. On the platinum catalyst cracking products were formed as primary products, and it proved to be slightly more active than the palladium based one, at the same metallic molar loading. It could be shown that the platinum catalyst yields cracking products both via a bifunctional metal/acid mechanism and by monofunctional (metal only) hydrogenolysis. This second mechanism accounted for the higher activity of the platinum catalyst.