Based on the previous coordination catalysis theory, the active site on the surface of transition metal oxides can activate the CO2 molecule. Ultrathin two-dimensional (2D) rutile TiO2 nanosheet with (110) crystal face as the main exposed surface has many active sites of Ti3+ and O vacancy, which have some synergistic effects to greatly reduce the dissociation energy of CO2. Following previous assumptions, four possible reduction processes of CO2 on rutile TiO2 (110) surface were systematically assessed by density functional theory (DFT) simulations. The reduction reactions of CO2 along I faces difficultly in proceeding due to the relatively weak interaction between CO2 and the active surface. Additionally, along III, the adsorption configuration of CO2 in the pristine state has huge distinctions with the model that suggests that the defined route is unlikely to occur on the rutile TiO2 (110) surface. However, through carefully comparing the energy differences as well as transition state searching, the reduction reaction along II has a high probability of finishing and finally generating HCOOH on the surface owing to the minimal energy differences and low activation barrier. Furthermore, the reduction reaction of CO2 to CH4 guided along IV is predicted to more easily take place with the assistance of O vacancy on the active surface. The synergistic action among Ti3+ site, O vacancy, and H+ can aid in fixing molecular CO2 by breaking the strong bond of C=O in CO2 and generating different fuels via coordination activation. This work will not only provide strong theoretical support to previous assumptions but can also lighten the routes to explore more active catalysis towards the reduction of CO2.

Xuemei Yang and Xiaohua Wang