Zirconia phase effect in Pd/ZrO2 catalyzed CO2 hydrogenation into formate

Abstract

© 2019 Elsevier B.V. In heterogeneous catalysis, transformation of CO2 into formate largely relies on supported palladium catalyst, in which the support and in particular the support basicity plays a critical role. In this study, we prepared a series of Pd catalysts loaded on ZrO2 bearing three different crystal phases, namely the tetragonal phase (ZrO2-T), the monoclinic phase (ZrO2-M), and the hybrid tetragonal and monoclinic phase (ZrO2-M&T). With the same metal loading, ZrO2-T supported Pd catalyst exhibited considerably higher intrinsic activity in CO2 hydrogenation into formate compared with the other two catalysts. Pd/ZrO2-T with 2 wt% Pd was the most active one in the series, affording a TOF of 2817 h−1 at 373 K. In situ DRIFTS spectroscopy, kinetic study and CO2-TPD analysis provided evidence that all Pd/ZrO2 catalysts follow a similar catalytic mechanism, and the origin of the superior activity for Pd/ZrO2-T is the higher density of weak basic sites on ZrO2-T, which facilitates the transformation of CO2 into the desirable surface adsorbed bicarbonate as the precursor for formate. This work highlights the importance of crystal-phase engineering of the support in tuning the catalytic activity of Pd based catalysts for CO2 hydrogenation.