Coordination Environment Dependent Surface Cu State for CO<sub>2</sub> Hydrogenation to Methanol
Mengyang Song, Tangkang Liu, Xinlin Hong, Guoliang Liu
Abstract
Catalytic conversion of CO 2 with green hydrogen produced from renewable sources into methanol is one of the promising ways to cycle waste CO 2 for carbon neutralization. The activity of Cu-based catalysts for methanol synthesis is closely related to the chemical environment of Cu species, which can be modulated by the special structure of MOFs. It is desired to elucidate the relationship between coordination environment of MOFs and chemical state of confined active metal (e.g., Cu). Herein, we regulate the surface Cu state by changing the coordination environment of copper in MOF-derived catalysts (Cu@UiO-66 and Cu@UiO-66-NH 2 ). It is found that Cu species in the fresh Cu@UiO-66 catalyst occupy defect sites coordinated by carboxyl groups while being complexed by amino groups in Cu@UiO-66-NH 2 . Combined with XPS and in situ DRIFTS spectra, we find that the Cu@UiO-66 precursor facilitates the formation of Cu + -ZrO 2 interfaces upon in situ activation, while Cu@UiO-66-NH 2 favors the generation of metallic Cu sites. The catalytic results show that the methanol space-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-NH 2 and 6.0 times that of commercial Cu/ZnO/Al 2 O 3 under the same conditions (260 °C, 1 MPa). The Cu@UiO-66 catalyst 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 to the formation of abundant Cu + -ZrO 2 interfacial sites as active sites for methanol synthesis from CO 2 /H 2 .