Acid-Base Bifunctional Catalysis of the Lewis Acidic Isolated Co(OH)₂ and Basic N Anion Generated from CeO₂ and 2-Cyanopyridine

Acid-base bifunctional catalysts, which have both acid and base sites that are arranged at an appropriate distance, are one of the effective catalyst categories and have been extensively studied as a simple and effective method for designing heterogeneous and homogeneous catalysts in both the laboratories and industry. Recently, we found that a heterogeneous-homogeneous hybrid strong base site of N^- was constructed only by mixing 2-cyanopyridine and CeO₂ in the solution, where the N^- site was formed by the covalent bonding between the lattice O atom of CeO₂ and the C atom of the CN group in 2-cyanopyridine. Herein, an effective acid-base bifunctional catalyst with proximal sites of the heterogeneous-homogeneous hybrid base site and metal species-derived Lewis acid site is presented. The introduction of Co species into CeO₂ forms isolated Co(OH)₂ on CeO₂, and further introduction of 2-cyanopyridine generates the heterogeneous-homogeneous hybrid base site of N^- near the Co(OH)₂ without the interference of these sites. The acid-base bifunctional sites work cooperatively to provide about 10-fold higher activity to the hydromethoxylation of acrylonitrile than the heterogeneous-homogeneous hybrid base site alone. Catalyst characterizations such as XRD, TEM, UV-vis, NO adsorption, XPS, Raman, XAS, NH₃-TPD and in situ XPS, DFT calculations, and kinetic studies show that acrylonitrile and methanol are activated by the Lewis acidic Co(OH)₂ and the hybrid base site, respectively, and the cooperative work results in the large rate enhancement.