Ru nanoparticles on TiO2 with various anatase-to-rutile ratios tuned by selective chemical dissolution: Effect of support polymorph composition on selective benzene hydrogenation

Abstract

Using P25 TiO2 as the precursor, phase-pure anatase and rutile TiO2 as well as TiO2 with tunable anatase-to-rutile molar ratios (nA/nR) were prepared via a facile “selective chemical dissolution” approach. The Ru/TiO2 catalysts were then synthesized and comprehensively characterized by spectroscopic techniques and transmission electron microscopy. It is confirmed that these catalysts possessed similar physicochemical parameters and hydrophilicity, but different Ru sizes (2.3–4.5 nm). Ru nanoparticles (NPs) supported on TiO2 with nA/nR of 2.66 (Ru/TiO2-1.5%HF) exhibited moderate size of 3.4 nm and electron-deficient state, which was originated from the unique Ru-on-anatase/rutile junction structure. In selective benzene hydrogenation, the turnover frequencies of benzene of the mixed phase TiO2-supported Ru catalysts were similar irrespective of the nA/nR ratios and ranged between phase-pure anatase and rutile TiO2-supported Ru catalysts, which can be ascribed to the size effect of Ru. For the cyclohexene selectivity, Ru NPs supported on TiO2 with nA/nR of 0.88–2.66 exhibited higher S0 (92–95%) than Ru NPs on TiO2 with other nA/nR ratios, in which the Ru/TiO2-1.5%HF catalyst displayed a maximum of 95%. We demonstrated that in addition to the proper Ru size, the electron-deficiency of Ru on the Ru/TiO2-1.5%HF catalyst contributed greatly to the highest selectivity since it can promote the desorption of cyclohexene to avoid suffering over-hydrogenation.