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 ecofriendly 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 m 2 g −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.

Metal–Organic Framework-Derived Mn3O4/Co3O4/C/SiO2 Nanostructures for Catalytic Oxidation Reactions

“…Finally, based on the results obtained from the control reactions discussed above and the literature survey, a plausible mechanism route for the MCCO catalyzed oxidation reaction is outlined in Scheme using ethylbenzene as the model substrate . The oxidation reaction is anticipated to occur at the interfacial sites of Mn 3 O 4 –Co 3 O 4 because of the complementarity among them.…”

“…The direct and selective oxidation of C–H bonds, cycloalkanes, and alcohols to their oxygenated analogs has enticed ample interest in recent years because of their commercial viability, academic utility, and persistent application as intermediates for the manufacture of pharmaceuticals, agrochemicals, natural products, perfumes, dyes, and value-added chemicals. − Acetophenone, the oxidation product of ethylbenzene, is a widely utilized flavoring agent and intermediate in the manufacturing of perfumes, pharmaceuticals, soaps and detergents, plastics and resins, and so forth . Furthermore, cyclohexanone and cyclohexanol, the oxygenated products of cyclohexane, are used as intermediates for the production of nylon-6 or polycaprolactam polymer in textile and plastic industries …”

“…However, the toxic nature of these oxidants accompanied by the production of hazardous byproducts make them environmentally incompatible and hinder their commercial application. Moreover, these are noncatalytic methods that need renewal of reagents after each oxidation cycle. ,,− Hence, transition-metal-based homogeneous and heterogeneous catalysts capable of activating oxidizing agents like hydrogen peroxide and molecular oxygen were utilized, although noble metals have been more popular but are commercially restricted by their low availability and high cost. ,− Another challenge is the lack of recyclability in case of homogeneous catalysts despite their high activity, which constraints their academic and industrial relevance . Consequently, there is a need to develop catalytic procedures using earth-abundant transition metals and to heterogenize the catalytic systems for better stability, activity, selectivity, effortless recovery, and recyclability. ,− …”

Recent developments in metal-doped SBA-15 catalysts for heterogeneous catalysis and sustainable chemistry

“…Thus, it offers the atom economy and environmental compatibility. For example, converting benzyl alcohol, ethanol, glycerol, and propane to value-added products like benzaldehyde, acetaldehyde, carboxylic acids, and acrolein respectively, are very important as these chemicals are prepared via renewable resources and find extensive application [26][27][28][29] . Recently, these products have had high market demands.…”

Supported Metal Nanoparticles Assisted Catalysis: A Broad Concept in Functionalization of Ubiquitous C−H Bonds

“…In the recent year of 2020, Biswas et al. disclosed their work on silver NPs catalysed C−H oxidation of hydrocarbons with O 2 in neat condition [119] . The group has established the oxidation reaction of cyclic and benzylic ‐CH 2 in presence of silver NPs immobilized over functionalized mesoporous silica (SBA‐15) material (Ag@MS).…”