Dual stimuli-responsive silver nanoparticles decorated SBA-15 hybrid catalyst for selective oxidation of alcohols under 'mild' conditions

Abstract

Herein, we develop an efficient and novel catalytic system, i.e. silver nanoparticles (AgNPs) incorporated mesoporous silica SBA-15/copolymer hybrid material, for selective oxidation of different alcohols to aldehydes or ketones under 'mild' conditions. The copolymer of N,-N-dimethylaminoethyl methacrylate and 2-hydroxyethyl acrylate (p(DMAEMA-co-HEA)) was used to graft the surface-modified SBA-15 (MS) using free radical polymerization method. Then AgNPs were decorated on the polymer grafted SBA-15. The dual (thermal and pH) responsive behaviors of the AgNPs/p(DMAEMA-co-HEA)/MS catalyst were investigated using the dynamic light scattering technique. The lower critical solution temperature (LCST) of the copolymer was found to be approximately 30-35 degrees C. The catalytic activity of AgNPs/p(DMAEMA-co-HEA)/MS was investigated for the selective oxidation of different alcohols to aldehydes or ketones. The conversion of catalytic products and selectivity were calculated using gas chromatographic techniques, whereas the molecular structure of products was determined using H-1 and C-13 nuclear magnetic resonance spectroscopy. The catalyst showed improved catalytic activity toward the oxidation of alcohols to aldehydes in aqueous medium below LCST and pKa value (7-7.5) of the copolymer. The selectivity toward the corresponding aldehyde was found to be significantly high (99%). The main advantages of the hybrid catalyst as compared to existing catalysts include outstanding alcohol conversion (up to 99%), short reaction time (1 h), small necessary amount of catalyst (6 mg), and performing the catalytic conversion at room temperature using water as a solvent, which are highly beneficial for organic conversion under mild reaction conditions.