Tuning CO2 Hydrogenation to Carbon Monoxide over Cu@SiO2: The Critical Role of Trace ZnO

Abstract

Selective CO2 hydrogenation to CO via reverse water–gas shift is severely restricted by competing methanol synthesis over Cu@SiO2 catalysts, owing to stable Cu–O–Si linkages that favor formate intermediates. Herein, trace ZnO introduction is proposed to precisely tune catalytic pathways. Characterizations verify trace ZnO disrupts Cu–O–Si bonds, generating highly dispersed metallic Cu0 sites. In-situ DRIFTS demonstrates suppressed formate accumulation and accelerated formate decomposition into CO after ZnO modification. The Cu-0.02ZnO@SiO2 catalyst achieves the optimal performance with 10.4% CO2 conversion, 85.5% CO selectivity and a CO space-time yield of 11.2 mmolCO·gcat–1·h–1. Excess ZnO may induce Cu agglomeration and probable Cu–ZnO interface formation, shifting product preference back to methanol. This study offers a simple strategy using minor metal oxide additives to regulate CO2 hydrogenation selectivity for CO production.