High pH promoting the synthesis of V-Silicalite-1 with high vanadium content in the framework and its catalytic performance in selective oxidation of styrene

Abstract

It is difficult to synthesize a Silicalite-1 molecular sieve with a high vanadium content in the framework, because heteroatoms significantly affect the formation of V-Silicalite-1. Here, V-Silicalite-1 with a high vanadium content in the framework of the molecular sieve was successfully synthesized by controlling the pH at high levels. In the process of hydrothermal synthesis, OH⁻ ions effectively promoted the entry of vanadium atoms into the framework of the molecular sieve. Samples of V-Silicalite-1 with different vanadium contents were characterized by XRD, FTIR, UV-vis, XPS, EPR, ICP, FE-SEM, elemental mapping, N₂ adsorption–desorption, and TPR, which confirmed that vanadium atoms successfully replaced silicon atoms in the framework. V-Silicalite-1 exhibited good catalytic performance in the selective oxidation of styrene at different temperatures, with a styrene conversion of up to 84.89% and a selectivity of 91.04% for styrene oxide at 25 °C and a styrene conversion of 97.47% and a selectivity of 80.97% for benzaldehyde at 85 °C. This study provided a new idea for the synthesis of molecular sieves with high vanadium contents in the framework. Besides, it also enabled the direct application of vanadium-doped molecular sieves for the catalytic oxidation of styrene in industry.