The Rise of Calcination Temperature Enhances the Performance of Cu Catalysts: Contributions of Support

To develop the high-performance supported metal catalyst for industrial processes, it is highly desirable to elucidate and fully utilize the indispensable support part. Herein, the relationship between catalytic performance and the structure of support ZrO2 was elucidated by comprehensive analysis of the progressive calcination experiments, tests over model catalysts, and various characterizations of catalyst structures. We demonstrated that combination of Cu and tetragonal ZrO2 makes a highly active, selective, and especially stable catalyst for the hydrogenation of dimethyl oxalate to ethylene glycol. To obtain stable Cu particles, the catalyst was annealed at high temperatures (e.g., from 450 to 850 degrees C). The stable large Cu particles were formed, and the number of exposed Cu sites decreased. Fortunately, support ZrO2 was motivated into the tetragonal phase, compensating for and even improving the activity. Thus, the yield of ethylene glycol was greatly improved from similar to 26 to 99%, and a stable performance was achieved (life span of >600 h). The strategy alleviated the dependence of hydrogenation on highly dispersed metal sites and provided an alternative way to enhance the catalytic stability. This simple way simultaneously improved the efficiency and reduced the level of irreversible deactivation due to sintering, which has great potential for industrial applications. Tetragonal ZrO2 also proved to be effective for a series of carbonyl hydrogenations (e.g., esters, aldehydes, ketones, and acids), indicating a general promotion of these reactions by ZrO2.