Tuning CO adsorption states via enhanced metal-support interaction for boosting CO2 methanation activity of Ru/rutile-TiO2

Abstract

Understanding the correlation between metal–support interactions (MSIs) and the adsorption states of reaction intermediates is critical for developing heterogeneous catalysts. To modulate MSIs and CO adsorption states, various Ru/Ti1-xCrxO2 catalysts were prepared by Cr3+ cation doping and used for CO2 methanation compared to the rutile TiO2-supported Ru catalyst (Ru/r-TiO2). The activity followed the order: Ru/Ti0.95Cr0.05O2 > Ru/Ti0.97Cr0.03O2 > Ru/Ti0.87Cr0.13O2 ≫ Ru/r-TiO2. The best Ru/Ti0.95Cr0.05O2 catalyst possessed CO2 turnover frequency (TOF) value at 200 °C 10.2 times higher than that on the Ru/r-TiO2. Cr3+ doping in the lattice of r-TiO2 support led to the Ru/Ti0.95Cr0.05O2 with higher dispersion of Ru and enhanced MSIs. A linear-CO*-II intermediate formed on the Ru/Ti0.95Cr0.05O2 with higher C-O vibrational frequency (2003 cm−1) than the linear-CO*-I at 1972 cm−1 on the Ru/r-TiO2, and the blue-shifted CO possessed higher activity for CO hydrogenation to CH4. The higher activity of the linear-CO* were accounting for the much higher TOF value of the Ru/Ti0.95Cr0.05O2. The strength of MSIs was proved to be highly correlated with CO adsorpton states including the balance of the strength of Ru-C and C-O bonds, which were found to be a crucial factor for the activity of supported Ru-based catalysts for CO hydrogenation.