Continuous CO2 capture and reduction in one process: CO2 methanation over unpromoted and promoted Ni/ZrO2

The recently demonstrated concept to combine CO2 capture and utilization in one process using isothermal unsteady-state operation, namely CO2 capture and reduction (CCR), was applied for CO2 methanation using unpromoted and K- or La-promoted Ni/ZrO2 catalysts. Both K and La promoters significantly improve CO2 capture capacity and also the selectivity of CO2 conversion to methane. The K-promoted catalyst (Ni-K/ZrO2) captures a larger amount of CO2 at high temperature but the capture capacity drops at low temperature due to incomplete catalyst regeneration during the cyclic unsteady-state reaction condition. In contrast, the La-promoted catalyst (Ni-La/ZrO2) shows temperature-independent CO2 capture capacity and rapid reduction of captured CO2, thus leading to stable CCR performance. The nature of the active sites and mechanistic details were gained by TPR, reductive CO2-TPD and space-and time-resolved operando DRIFTS, holistically elucidating the effects of the promoters and their impacts on CCR activity.