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

Abstract

The ZnO/ZrO2 binary catalyst system has been an emerging and promising catalyst for efficient production of H2 through methanol steam reforming (MSR). Herein, ZrO2 supports with different crystalline phases were prepared by the oxygen vacancy engineering strategy of Li doping, and then ZnO/ZrO2 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 ZrO2 supports, which dictates the interaction between ZnO and ZrO2 and the number of oxygen vacancies. In comparison with ZnO/ZrO2-20Li and ZnO/ZrO2-40Li catalysts with predominate tetragonal and monoclinic crystal phase, ZnO/ZrO2-3Li with a mixed crystalline phase exhibits higher catalytic activity for methanol conversion (XCH3OH) and CO selectivity (SCO). Complete methanol conversion of the best performing ZnO/ZrO2-3Li 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 ZrO2 and ZnO leads to the appearance of large amount of oxygen vacancies at the ZnO/ZrO2 interface, which greatly improves the performance of the catalyst. ZnO/ZrO2 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/ZrO2 catalysts for applications in methanol steam reforming and other heterogeneous catalytic systems.