Structure Sensitivity of ZnZrO x Catalysts in CO 2 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 CO 2 hydrogenation to methanol. In this study, we investigated the impact of various synthesis conditions on the structural properties and catalytic activity of ZnO–ZrO 2 solid solution (ZnZrO x ) catalysts. By systematically adjusting the drying method, calcination temperature, postsynthesis ball-milling time, and use of additives, we synthesized a series of ZnZrO x 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 ZnZrO x catalysts is structure-sensitive and that area-normalized activity is positively correlated with the oxygen content on the catalyst surface. The surface lattice oxygen (O 2– ) 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 CO 2 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 ZnZrO x 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.