Structure Sensitivity of ZnZrOx Catalysts in CO2 Hydrogenation to Methanol: Significance of Surface Oxygen Content and Synthesis Strategy

Understanding the relationship between catalyst structure and activity is crucial to advancing catalytic processes such as CO2 hydrogenation to methanol. In this study, we investigated the impact of various synthesis conditions on the structural properties and catalytic activity of ZnO-ZrO2 solid solution (ZnZrOx) catalysts. By systematically adjusting the drying method, calcination temperature, postsynthesis ball-milling time, and use of additives, we synthesized a series of ZnZrOx catalysts with varying surface area (4.5-106 m(2) g(-1)) and surface oxygen content [O/(Zn + Zr) = 1.60-2.04] and similar surface Zn content [Zn/(Zn + Zr) = ca. 0.20]. Our experimental and computational studies revealed that methanol synthesis over ZnZrOx catalysts is structure-sensitive and that area-normalized activity is positively correlated with the oxygen content on the catalyst surface. The surface lattice oxygen (O2-) played a crucial role in H-2 activation, which is the rate-determining step for methanol formation; therefore, oxygen-rich regimes serve as the main active sites for CO2 hydrogenation to methanol. From a fundamental point of view, this study highlights the importance of surface oxygen content for catalytic activity, which has been previously overlooked. From an engineering standpoint, our investigations suggest that ZnZrOx catalysts bearing oxygen-rich surfaces combined with high surface areas can exhibit desirable catalytic activity, thus guiding the rational synthesis strategy to the development of oxide-based hydrogenation catalysts.