Asymmetric Sites on the ZnZrO (x) Catalyst for Promoting Formate Formation and Transformation in CO2 Hydrogenation

摘要

The role of formate species for CO2 hydrogenation isstill under debate. Although formate has been frequently observedand commonly proposed as the possible intermediate, there is no definiteevidence for the reaction of formate species for methanol production.Here, formate formation and conversion over the ZnZrO (x) solid solution catalyst are investigated by in situ/operandodiffuse reflectance infrared Fourier transform spectroscopy-mass spectroscopy(DRIFTS-MS) coupled with density functional theory (DFT) calculations.Spectroscopic results show that bidentate carbonate formed from CO2 adsorption is hydrogenated to formate on Zn-O-Zrsites (asymmetric sites), where the Zn site is responsible for H-2 activation and the Zr site is beneficial for the stabilizationof reaction intermediates. The asymmetric Zn-O-Zr siteswith adjacent and inequivalent features on the ZnZrO (x) catalyst promote not only formate formation but also itstransformation. Both theoretical and experimental results demonstratethat the origin of the excellent performance of the ZnZrO (x) catalyst for methanol formation is associated withthe H-2 heterolytic cleavage promoted by the asymmetricZn and Zr sites.