In situ synthesis of MIL-101 on carboxyl-functionalized SBA-16: Preparation and catalytic performance in the Knoevenagel condensation reaction under mild conditions

The Knoevenagel reaction is one of the most significant reactions in the industrial synthesis of organic materials, pharmaceuticals, and biological compounds. In this study, 2-cyanoethyltriethoxysilane (CTES) was employed as a functionalizing agent to prepare carboxyl-functionalized silica (SBA-16-Cx) using a one-pot method. Subsequently, carboxyl groups served as anchoring points for Cr³⁺, and MOFs-modified SBA-16 (SBA-16-Cx@MIL) was obtained by in situ synthesis. The resulting materials were characterized using FT-IR, XPS, XRD, N 2 adsorption-desorption analysis, SEM, TEM, 13 C MAS NMR, and TG, which confirmed the successful synthesis of MIL-101 on the support. Meanwhile, the pore size of the composite was reduced from 5.1 nm (SBA-16) to 0.6 nm (SBA-16-C1.0@MIL). The condensation reaction of benzaldehyde with malononitrile was selected as a model reaction. The effects of various factors, including solvents, reactants molar ratios, temperature, catalyst dosage, and reaction time, on the reaction were studied. Under optimized conditions, the conversion rate of benzaldehyde reached 100 % and the catalyst demonstrated excellent stability for repeated use. The reaction follows second-order kinetics (R 2 >0.99), and the activation energy of the reaction was 17.18 kJ/mol. Finally, the mechanism of the catalytic process was proposed. This work provides a green catalytic route for the synthesis of α,β-unsaturated carbonyl compounds.