Mechanistic insights into the contribution of Lewis acidity to brominated VOCs combustion over titanium oxide supported Ru catalyst

CH3Br catalytic oxidation as the probe reaction was investigated over Ru supported on TiO2 with different crystalline phases. 1% Ru/anatase TiO2 (a-TiO2) exhibited superior stability at 240 °C after a 180 h time-on-stream run. And there was an induced activation for 1% Ru/a-TiO2 during the initial 60 h reaction. Then the activity sustained stable. To elucidate the intrinsic mechanism, a series of characterizations were performed such as XRD, CO-Pulse, H2-TPR, XPS and NH3-TPD etc. Results showed that the Ru particle size increased and the Ru0 content decreased as the reaction proceeded, which were not conductive to the reaction. It was assumed that the catalytic activity was strongly dependent on other factors. In combination with NH3-TPD and Py-FTIR measurements, it was confirmed that the enhanced activity and stability was strongly associated with the surface acidity, especially moderate strong Lewis acid (L acid). The increase of the acid amount and acidity strength was led by the generation and adsorption of HBr, Br2 and RuOxBry during the reaction, among which HBr and Br2 was easier to desorb at 250 °C. While moderate strong L acid was sourced from the formation of RuOxBry. The addition of transition metal (Ce, Co, Mn, Nb and Ni) further validated that the moderate strong L acid played a decisive role in the CH3Br catalytic oxidation.