Microstructure characterization and propane oxidation over supported Ru nanoparticles synthesized by the microwave-polyol method

Ruthenium nanoparticles deposited on gamma-Al2O3 were prepared in one step by a microwave-polyol method and tested in the complete oxidation of propane. The oxidation reaction was carried out under oxygen rich-conditions over the as prepared colloidal 4.9 wt.% Ru/gamma-Al2O3 catalyst and heated in H-2 at 500 degrees C for 15 h. The as prepared catalyst contained Ru nanoparticles with mean size of 1.6 nm and narrow size distribution, while hydrogen treated metal particles with mean size of 6 nm. Before examining catalytic properties, the Ru nanoparticles were subjected to heat treatment in oxygen atmosphere to study their microstructure evolution. HRTEM, SAED, XRD, BET, XPS, as well as hydrogen chemisorption and O-2 uptake techniques were applied to characterize the supported Ru nanoparticles. It was established that catalyst with the 1.6 nm Ru nanoparticles exhibited slightly higher specific activity than the catalyst with the 6 nm Ru nanoparticles. The superior catalytic performance of the Ru nanoparticles could be correlated with a high metallic dispersion and low particle sizes. It was evidenced that the most active sites in the propane oxidation reaction, consist small RuxOy clusters without well-defined stoichiometry. Such surface species were formed at 100-200 degrees C, and as a result the as prepared Ru/gamma-Al2O3 catalyst reached 100% propane conversion below 200 degrees C. Moreover, the Ru nanoparticles under oxidative atmosphere up to 250 degrees C, both in oxygen and in reaction of propane oxidation, possesses good stability and the ruthenium phase was not agglomerated. In consequence, recycling of the supported Ru nanoparticles results only in an insignificant loss of the catalytic activity. The very good catalytic performances of supported Ru nanoparticles prepared under microwave-polyol conditions, preserved after consecutive runs, make them promising for practical application in the purification of environmental pollutions. (C) 2010 Elsevier B.V. All rights reserved.