Influence of Catalyst Pretreatments on Propane Oxidation Over Ru/γ-Al2O3

The influence of different treatments (in H-2 or in O-2 at 250 or 600 A degrees C) of alumina supported Ru catalysts on the total oxidation of propane was investigated. Ruthenium catalysts were prepared using RuCl3 as metal precursor and characterized by H-2 chemisorption, O-2 uptake, BET, XRD and TEM. The presence of chloride on the catalyst surface was found to exert an inhibiting effect on the activity of Ru. The reduced Ru/gamma-Al2O3 catalysts after partial removing chlorine ions were more active than the same samples oxidized at 250 A degrees C. The higher activity of the reduced Ru/gamma-Al2O3 catalysts was attributed to the presence of a large amount of active sites on small Ru (x) O (y) clusters without well defined stoichiometry or on a poorly ordered layer of a ruthenium oxide on the larger Ru particles. The formation of highly dispersed, but in some extent crystallized RuO2 phase in catalysts oxidized at 250 A degrees C, leads to slightly lower activity of the Ru phase. Strong decline of the activity was found for catalysts oxidized at 600 A degrees C. At this temperature, the Ru particles were completely oxidized to well-crystallized RuO2 oxide, and the mean crystallite size of the Ru oxide phase was much higher (9-25 nm) than that of after oxidation at 250 A degrees C (similar to 4 nm). The effect of the regeneration treatment in H-2 on the activity of the Ru/gamma-Al2O3 catalysts was also studied. The active ruthenium species for propane oxidation were discussed based on the catalytic and characterization data both before and after activity tests.