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.