Synergistic Effect of Oxygen Vacancies and Ni Species on Tuning Selectivity of Ni/ZrO₂ Catalyst for Hydrogenation of Maleic Anhydride into Succinic Anhydride and γ-Butyrolacetone.

ZrO₂ nanoparticles, ZrO₂ (P) and ZrO₂ (H), with different tetragonal phase contents, were prepared. ZrO₂ (P) possessed higher tetragonal phase content than ZrO₂ (H). Ni/ZrO₂ catalysts (10% (/)), using ZrO₂ (P) and ZrO₂ (H) as supports, were prepared using an impregnation method, and were characterized using XRD, Raman, H₂-TPR, XPS, and H₂-TPD techniques. Their catalytic performance in maleic anhydride hydrogenation was tested. The Ni/ZrO₂ (P) catalyst exhibited stronger metal-support interactions than the Ni/ZrO₂ (H) catalyst because of its higher number of oxygen vacancies and the low-coordinated oxygen ions on its surface. Consequently, smaller Ni crystallites and a higher C=C hydrogenation activity for maleic anhydride to succinic anhydride were obtained over a Ni/ZrO₂ (P) catalyst. However, the C=O hydrogenation activity of Ni/ZrO₂ (P) catalyst was much lower than that of the Ni/ZrO₂ (H) catalyst. A 43.5% yield of γ-butyrolacetone was obtained over the Ni/ZrO₂ (H) catalyst at 210 °C and 5 MPa of H₂ pressure, while the yield of γ-butyrolactone was only 2.8% over the Ni/ZrO₂ (P) catalyst under the same reaction conditions. In situ FT-IR characterization demonstrated that the high C=O hydrogenation activity for the Ni/ZrO₂ (H) catalyst could be attributed to the surface synergy between active metallic nickel species and relatively electron-deficient oxygen vacancies.