Hydrogenation of 2-benzylpyridine over alumina-supported Ru catalysts: Use of Ru₃(CO)₁₂ as a Ru precursor

Abstract

Although Ru-3(CO)(12) becomes a popular precursor for supported Ru catalysts nowadays, the activities of the catalysts prepared by thermolysis of the supported Ru-3(CO)(12) under different atmospheres have been rarely compared. We herein report the preparation of alumina-supported Ru samples by thermal activation of Ru-3(CO)(12) in air, H-2 or N-2, followed by activity test in the hydrogenation of 2-benzylpyridine (BPy). When the supported Ru-3(CO)(12) was activated in air, RuO2 particles of 12-15 nm diameters were produced by complete oxidation of carbonyl groups. In contrast, thermal activation in H-2 and N-2 induced the formation of highly dispersed Ru particles of 1.4-2.3 nm diameters. In such activations methane was produced, suggesting that direct hydrogenation of CO coordinated to the Ru surface complex occurred in H-2 while the coordinated CO reacted with ruthenium hydride species in N-2. In the activity test for BPy hydrogenation, the samples prepared in H-2 and N-2 showed superior H-2 storage efficiencies and higher rate constants compared to those prepared in air (reduced before the reaction). Additionally, the former samples were examined to be relatively stable even though exposed to ambient air for 7 days. Therefore, H-2 and N-2 gases are recommended for thermal activation of alumina-supported Ru-3(CO)(12).