Adsorption coupled metal/anion/oxide structure for synergistic synthesizing solketal from glycerol

Although homogeneous acid catalysts have been widely utilized in the production of solketal from glycerol, a significant aspect of the biodiesel industry, challenges remain, including the high corrosiveness of the catalysts and their excessive usage. In this study, a composite material of wCo(NO₃)₂/γ-Al₂O₃ was synthesized through an adsorption–desorption approach based on wet impregnation, achieving a Co(II) loading of only 1.8 wt%, which demonstrated a solketal yield of 84 % at 80 °C, significantly outperforming the catalytic activity of Co(NO₃)₂. Even when the amount of Co(NO₃)₂ was increased to 22-fold that of the Co(II) content in wCo(NO₃)₂/γ-Al₂O₃, the solketal yield only reached 67 %. Through systematic physicochemical characterization and theoretical calculations, it is revealed that Co(NO₃)₂ can be uniformly dispersed in an amorphous state on the surface of γ-Al₂O₃. Furthermore, γ-Al₂O₃ facilitates a reduction in the orbital binding energy of Co and N within Co(NO₃)₂. The synergistic effects of Co(II), NO₃⁻, and γ-Al₂O₃ contribute to decreasing the rate-determining energy of the ketalization reaction, thereby promoting the dehydration reactions of glycerol and acetone. Furthermore, this strategy is equally applicable to other soluble Co, Ni, and Cu salts, demonstrating universality. This method effectively reduces the usage of metal salts in the solketal synthesis process, enhancing the acid catalytic activity of the metal salts, providing an adsorption–desorption approach based on wet impregnation for the development of low-dose, highly active, and low-corrosive acid catalytic materials.