Oxygen vacancy engineering in ZnO/ZrO2 composite catalysts for highly enhanced hydrogen production by methanol steam reforming

The ZnO/ZrO 2 binary catalyst system has been an emerging and promising catalyst for efficient production of H 2 through methanol steam reforming (MSR). Herein, ZrO 2 supports with different crystalline phases were prepared by the oxygen vacancy engineering strategy of Li doping, and then ZnO/ZrO 2 catalysts were prepared by the isovolumic impregnation method. The different quantities of doped Li have been found to have a significant impact on dominant crystal phase of ZrO 2 supports, which dictates the interaction between ZnO and ZrO 2 and the number of oxygen vacancies. In comparison with ZnO/ZrO 2 -20Li and ZnO/ZrO 2 -40Li catalysts with predominate tetragonal and monoclinic crystal phase, ZnO/ZrO 2 -3Li with a mixed crystalline phase exhibits higher catalytic activity for methanol conversion ( X CH 3 OH ) and CO selectivity (S CO ). Complete methanol conversion of the best performing ZnO/ZrO 2 -3Li catalyst was observed at a very low CO selectivity of 3.1 % at 375 ℃. The XRD, UV, and XPS characterization results indicate that the strong interaction between ZrO 2 and ZnO leads to the appearance of large amount of oxygen vacancies at the ZnO/ZrO 2 interface, which greatly improves the performance of the catalyst. ZnO/ZrO 2 catalyst showed remarkable stability without obvious deactivation after 32 hours of continuous testing. This work highlights the effectiveness of oxygen vacancy engineering of the ZnO/ZrO 2 catalysts for applications in methanol steam reforming and other heterogeneous catalytic systems.