| CO2 capture-reduction (CCR) is a recently developed catalytic process that combines two critical functions of CO2 utilization path in one process, namely CO2 capture and subsequent transformation (e.g. reduction by H2) into chemical fuels or intermediates such as CO. A bifunctional catalyst material is needed and the two functions are activated by means of isothermal unsteady-state operation (i.e. gas switching). This work employs operando space- and time-resolved DRIFTS, XAFS, and XRD to elucidate the nature and functions of Cu and promoters using unpromoted and K/Ba-promoted Cu/Al2O3 and to clarify involved active surface species, which are varying along the catalyst bed. K promotor was found to uniquely facilitate efficient CO2 capture in the form of surface formates, dispersion of active metallic Cu and suppression of Cu oxidation. The high CO2 trapping efficiency of the K-promoted catalyst allows capturing most CO2 from a diluted-CO2 gas stream, gradually along the catalyst bed, creating large spatial and temporal gradients of surface chemical species. Understanding these features are of central importance to design efficient CCR catalysts. Furthermore, a completely different path for CO2 reduction was evidenced for the unpromoted and Ba-promoted catalysts where CO2 can directly react with metallic Cu and oxidize its outer surface, releasing CO. These insights provide important implications in the mechanism of reverse water-gas shift reaction and the roles of K and Ba promotors investigated widely.CO2 capture-reduction (CCR) is a recently developed catalytic process that combines two critical functions of CO2 utilization path in one process, namely CO2 capture and subsequent transformation (e.g. reduction by H2) into chemical fuels or intermediates such as CO. A bifunctional catalyst material is needed and the two functions are activated by means of isothermal unsteady-state operation (i.e. gas switching). This work employs operando space- and time-resolved DRIFTS, XAFS, and XRD to elucidate the nature and functions of Cu and promoters using unpromoted and K/Ba-promoted Cu/Al2O3 and to clarify involved active surface species, which are varying along the catalyst bed. K promotor was found to uniquely facilitate efficient CO2 capture in the form of surface formates, dispersion of active metallic Cu and suppression of Cu oxidation. The high CO2 trapping efficiency of the K-promoted catalyst allows capturing most CO2 from a diluted-CO2 gas stream, gradually along the catalyst bed, creating large spatial and temporal gradients of surface chemical species. Understanding these features are of central importance to design efficient CCR catalysts. Furthermore, a completely different path for CO2 reduction was evidenced for the unpromoted and Ba-promoted catalysts where CO2 can directly react with metallic Cu and oxidize its outer surface, releasing CO. These insights provide important implications in the mechanism of reverse water-gas shift reaction and the roles of K and Ba promotors investigated widely.CO2 capture-reduction (CCR) is a recently developed catalytic process that combines two critical functions of CO2 utilization path in one process, namely CO2 capture and subsequent transformation (e.g. reduction by H2) into chemical fuels or intermediates such as CO. A bifunctional catalyst material is needed and the two functions are activated by means of isothermal unsteady-state operation (i.e. gas switching). This work employs operando space- and time-resolved DRIFTS, XAFS, and XRD to elucidate the nature and functions of Cu and promoters using unpromoted and K/Ba-promoted Cu/Al2O3 and to clarify involved active surface species, which are varying along the catalyst bed. K promotor was found to uniquely facilitate efficient CO2 capture in the form of surface formates, dispersion of active metallic Cu and suppression of Cu oxidation. The high CO2 trapping efficiency of the K-promoted catalyst allows capturing most CO2 from a diluted-CO2 gas stream, gradually along the catalyst bed, creating large spatial and temporal gradients of surface chemical species. Understanding these features are of central importance to design efficient CCR catalysts. Furthermore, a completely different path for CO2 reduction was evidenced for the unpromoted and Ba-promoted catalysts where CO2 can directly react with metallic Cu and oxidize its outer surface, releasing CO. These insights provide important implications in the mechanism of reverse water-gas shift reaction and the roles of K and Ba promotors investigated widely.Space- and time-resolved operando DRIFTS, XAFS, and XRD uncovered the involved surface chemical species and active uncovered the involved surface chemical species and active CO2 capture-reduction process. |
