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

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 degrees 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.