Hydroconversion of n-alkanes over carbided Rh/molybdena zirconia catalysts

A low loading of Rh (0.5 wt%) was added to a MoO3/ZrO2 sample with the objective of lowering the temperature at which the molybdena phase could be transformed in the presence of CH4/H-2 to produce an active carbide phase for the hydroisomerisation reaction of linear alkanes. The presence of Rh reduced the reduction temperature of the supported molybdena in hydrogen alone and reduced the temperature required for the onset of carburisation in hydrogen/methane. Pre-treatment cycles of reduction and oxidation further enhanced the extent of rhodium-molybdena interactions and further lowered the temperature required to form the carbidic phase. Although the presence of rhodium facilitated the formation of an active molybdenum carbide phase, the products formed in the hydroisomerisation reactions of both hexane and octane were mainly hydrogenolysis products due to the high activity of rhodium for these reactions under the conditions employed. The distribution of the fragments were different for sample carbided after calcination and sample carbided after a reduction-oxidation cycle suggesting a surface composition which was significantly different for the samples prepared by the two different routes.