Catalytic oxidation of propane over nanorod-like TiO₂ supported Ru catalysts: Structure-activity dependence and mechanistic insights

Nanorod-like titanium dioxide (TiO2-Rod) supported ruthenium catalysts with variable metal loadings (designated as x-Ru/TiO2-Rod, x = 0.1, 0.5, 1.0 and 1.5 wt.%) were prepared for the catalytic oxidation of propane. The unique nanorod-like structure and high specific surface area of TiO2-Rod support was favorable for the surface distribution of ruthenium nanoparticles, constructing highly active redox sites for propane oxidation. Light-off experimental results indicated that the x-Ru/TiO2-Rod catalysts exhibited diverse catalytic activities for propane oxidation, giving a volcanic sequence of 0.1-Ru/TiO2-Rod < 0.5-Ru/TiO2-Rod < 1.5-Ru/TiO2-Rod < 1.0-Ru/TiO2-Rod with the increasing ruthenium content. Additionally, the optimal 1.0-Ru/TiO2-Rod delivered adequate catalytic stability and CO2/water resistant ability under complex industrial conditions. Characterization results revealed that the metallic Ru-0 and the surface lattice oxygen species from the Ru-TiO(2 )interface were demonstrated to be the catalytic active components, which played an essential role in the reaction. In situ DRIFTs analysis verified the formation of acetate, acetone and formate species as the predominant organic intermediates in propane oxidation, which may result from two plausible reaction pathways depending on the activation of terminal methyl group (-CH3) and the central methylene (CH2) group in propane molecule. This work provides fundamental guidance for the development of Ru-based catalysts and the reaction mechanism understanding for light alkanes oxidation.