Insight into the key factors governing the catalytic activity and stability of Ni/ZnO catalysts in CO2 hydrogenation†

Abstract

The requirements for industrial catalysts are not only high efficiency but also excellent stability. Therefore, understanding the crucial factors governing the catalytic performance and long-term stability is fundamental yet challenging due to the structural complexity of heterogeneous catalysts. Herein, ZnO-supported Ni catalysts with different ZnO morphologies were used for CO₂ hydrogenation. The results revealed that catalytic activity and stability were strongly related to weak basic sites and Ni–ZnO interactions, respectively. The Ni/r-ZnO (nanorod) catalyst, which possessed a higher amount of weak basic sites responsible for the adsorption and activation of CO₂, exhibited better catalytic activity. Nonetheless, r-ZnO, predominantly exposing nonpolar facets, was not conducive to Ni–r-ZnO interactions, which led to the agglomeration of supported Ni species during CO₂ hydrogenation and was the primary cause of the deactivation of the Ni/r-ZnO catalyst. Meanwhile, carbon deposition could be another minor factor affecting catalytic stability. Kinetic and in situ DRIFTS spectroscopy results demonstrated that the reaction proceeded through an H₂-assisted associated mechanism, with the adsorption and activation of CO₂ as the rate-determining step. These results not only deepen the fundamental understanding of Ni-/ZnO-catalyzed CO₂ hydrogenation but also provide potential insights for developing highly active and stable catalysts for CO₂ hydrogenation.