Cu Species Incorporated into Amorphous ZrO2 with High Activity and Selectivity in CO2-to-Methanol Hydrogenation

We prepared Cu/a-ZrO 2 (a-ZrO 2: amorphous ZrO 2 ), Cu/m-ZrO 2 (m-ZrO 2: monoclinic ZrO 2 ), Cu/a-ZrO 2 /KIT-6, and Cu/t-ZrO 2 /KIT-6 (t-ZrO 2: tetragonal ZrO 2 ) by a simple impregnation method and examined the effect of the ZrO 2 phase on CO 2 -to-methanol hydrogenation. We discovered a-ZrO 2 -containing catalysts with high activity and selectivity in CO 2 -to-methanol hydrogenation. Next, we focused on Cu species formation on the above-described catalysts. While pure CuO was observed on Cu/m-ZrO 2 and Cu/t-ZrO 2 /KIT-6, copper-zirconium mixed oxide (Cu x Zr y O z ), not pure CuO, was formed on Cu/a-ZrO 2 and Cu/a-ZrO 2 /KIT-6, as evidenced by X-ray absorption spectroscopy (XAS) and the powder color. After reducing a-ZrO 2 -containing catalysts with H 2 at 300 °C, we observed highly dispersed Cu nanoparticles in close contact with a-ZrO 2 (or Cu x Zr y O z ). In addition, methanol vapor sorption revealed that methanol adsorbed more weakly on a-ZrO 2 than on m-ZrO 2 . Therefore, the high dispersion of Cu species and weak adsorption of methanol led to high activity and selectivity in CO 2 -to-methanol hydrogenation.