Boosting Low-Temperature CO<sub>2</sub> Methanation Activity on Ru/Anatase-TiO<sub>2</sub> Via Mn Doping: Revealing the Crucial Role of CO<sub>2</sub> Dissociation
Shaorong Deng, Zijian Qian, Chen Zhu, Boxing Cheng, Xiaowei Wang, Xiuzhong Fang, Xianglan Xu, Xiang Wang
Abstract
A series of Ru/Ti 1– x Mn x O 2 catalysts with varying Mn/(Ti + Mn) molar ratios ( x = 0.10–0.25) were synthesized to investigate the CO 2 methanation mechanism on anatase TiO 2 -supported Ru catalysts (Ru/a-TiO 2 ) and develop high-performance catalysts at low temperatures. Among these catalysts, the Ru/Ti 0.8 Mn 0.2 O 2 exhibited the highest activity, achieving approximately 65% CO 2 conversion at 230 °C, which is markedly superior to the unmodified Ru/a-TiO 2 catalyst yielding only about 15% CO 2 conversion. The majority of Mn cations were incorporated into the lattice of a-TiO 2 as Mn 3+ cations, forming a solid solution structure in the Ti 0.8 Mn 0.2 O 2 support. This modification resulted in a higher specific surface area, improved reducibility, and increased oxygen vacancy compared with pure a-TiO 2 . Consequently, Ru dispersion and electronic metal–support interactions were enhanced in Ru/Ti 0.8 Mn 0.2 O 2 compared to those in Ru/a-TiO 2 . In-situ diffuse reflectance infrared Fourier transform spectroscopy combined with temperature-programmed surface reaction experiments revealed that CO 2 methanation predominantly proceeded via the CO* route on the Ru/a-TiO 2 . The CO 2 adsorption in the presence of decomposed H 2 led to dissociation to linear CO*, followed by CO methanation where CO 2 dissociation to CO* was identified as the rate-determining step (RDS). Mn cation doping induced the formation of oxygen vacancies, significantly enhancing CO 2 dissociation on Ru/Ti 0.8 Mn 0.2 O 2, thereby shifting the RDS to CO methanation. This mechanism explains the superior activity of Ru/Ti 0.8 Mn 0.2 O 2 at low temperatures for CO 2 methanation compared to the Ru/a-TiO 2 .