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

The influence of different treatments (in H2 or in O2 at 250 or 600 °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 H2 chemisorption, O2 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/γ-Al2O3 catalysts after partial removing chlorine ions were more active than the same samples oxidized at 250 °C. The higher activity of the reduced Ru/γ-Al2O3 catalysts was attributed to the presence of a large amount of active sites on small RuxOy 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 °C, leads to slightly lower activity of the Ru phase. Strong decline of the activity was found for catalysts oxidized at 600 °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 °C (~4 nm). The effect of the regeneration treatment in H2 on the activity of the Ru/γ-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.