AgNPs Immobilized over Functionalized 2D Hexagonal SBA-15 for Catalytic C–H Oxidation of Hydrocarbons with Molecular Oxygen under Solvent-Free Conditions

Abstract

Activation of C–H bonds of hydrocarbons is one of the thrust areas of research over the years. Designing a robust catalyst, which can work efficiently under eco-friendly conditions for this reaction still remains a big challenge today. Highly dispersed aggregation-free silver nanoparticles (AgNPs) are immobilized over 2D hexagonally ordered functionalized mesoporous silica material via surface thioether functionalization, and the resulting supported AgNPs (AgMS) displayed environmentally benign selective oxidation of C–H bonds of the aliphatic and monocyclic hydrocarbons into their respective carbonyl compounds. AgNPs-supported mesoporous materials are characterized by powder X-ray diffraction, nitrogen adsorption–desorption, scanning electron microscopy, transmission electron microscopy, and X-ray photoelectron spectroscopy. The AgMS material retains mesoporosity with a narrow pore size distribution (D ∼ 5.7 nm) together with a high BET surface area of 844 m2g–1 after loading of AgNPs. The AgMS catalyst exhibited excellent activity toward liquid phase oxidation of C–H bonds under solvent-free and base-free neat conditions using molecular oxygen as the oxidant. This methodology was successfully applied for the oxidation of substituted toluene, benzylic C–H bonds, and cycloalkanes with very good conversion and selectivity. Moreover, the hydrocarbon conversion and selectivity for the carbonyl products in this partial oxidation reaction have been retained after six reaction cycles. Therefore, immobilization of AgNPs at the surface of ordered mesoporous silica offers a very efficient route in designing a readily separable, reusable, very robust, and promising catalyst for C–H bond activation under eco-friendly reaction conditions.