CO2 methanation over Ru catalysts: Support engineering on the induction period via tuning metal-support interaction

Abstract

Support engineering on the induction period during CO₂ methanation over Ru catalysts were highlighted. The evaluation at 400 °C illustrated that the initial reaction rate over Ru/CeO₂ (52.3 $\mu mo{l}_{{\mathrm{CO}}_2}·g_{\mathrm{cat}}^{-1}·s^{-1}$) was the highest, whereas it showed an obvious proliferation over Ru/γ-Al₂O₃ and Ru/SiO₂ (from 33.0 and 46.3 to 59.9 and 51.8 $\mu mo{l}_{{\mathrm{CO}}_2}·g_{\mathrm{cat}}^{-1}·s^{-1}$, respectively). The above three catalysts exhibited high CH₄ selectivity (>96 %). However, Ru/TiO₂ showed the lowest reaction rate (14.0 $\mu mo{l}_{{\mathrm{CO}}_2}·g_{\mathrm{cat}}^{-1}·s^{-1}$) with 100 % CO selectivity. The comprehensive characterization demonstrated that the relatively strong metal-support interaction (MSI) led to the difficult-to-reduce Ru^χ+ (χ = 3 or 4) species, which were responsible for the occurrence of the induction period. TiO_x overlayer on Ru/TiO₂ due to the overly strong MSI resulted in the absence of Ru⁰ and weak CO bonding, accompanied by the inferior performance and no CH₄ product. The basic sites and oxygen-containing groups on the support were involved in the formation of the intermediates. Furthermore, we discussed the reaction mechanisms over Ru catalysts through in situ DRIFTS technique. This work clearly illustrated the correlation between the induction period and MSI modulated via support engineering, which could provide some meaningful references for the rational design of the highly efficient CO₂ hydrogenation catalysts.