Coordination Environment Dependent Surface Cu State for CO2 Hydrogenation to Methanol

Catalytic conversion of CO2 with green hydrogenproducedfrom renewable sources into methanol is one of the promising waysto cycle waste CO2 for carbon neutralization. The activityof Cu-based catalysts for methanol synthesis is closely related tothe chemical environment of Cu species, which can be modulated bythe special structure of MOFs. It is desired to elucidate the relationshipbetween coordination environment of MOFs and chemical state of confinedactive metal (e.g., Cu). Herein, we regulate the surface Cu stateby changing the coordination environment of copper in MOF-derivedcatalysts (Cu@UiO-66 and Cu@UiO-66-NH2). It is found thatCu species in the fresh Cu@UiO-66 catalyst occupy defect sites coordinatedby carboxyl groups while being complexed by amino groups in Cu@UiO-66-NH2. Combined with XPS and in situ DRIFTS spectra,we find that the Cu@UiO-66 precursor facilitates the formation ofCu(+)-ZrO2 interfaces upon in situ activation, while Cu@UiO-66-NH2 favors the generationof metallic Cu sites. The catalytic results show that the methanolspace-time yield of Cu@UiO-66 reaches 2.86 g g(Cu) (-1) h(-1), which is 1.7 times that of Cu@UiO-66-NH2 and 6.0 times that of commercial Cu/ZnO/Al2O3 under the same conditions (260 & DEG;C, 1 MPa). The Cu@UiO-66catalyst also shows good stability for 100 h in a time-on-stream test.We believe that the superior activity of Cu@UiO-66 is attributed tothe formation of abundant Cu+-ZrO2 interfacialsites as active sites for methanol synthesis from CO2/H-2. The coordination environment of UiO-66regulates the chemicalstate of surface Cu for efficient CO2 hydrogenation tomethanol.