Selective Oxidation of Cyclopentene Over Amphiphilic Heteropolyacid Catalysts Loaded on Modified Activated Carbon

Abstract

The synthesis of glutaraldehyde and 1,2-cyclopentanediol has great industrial significance. However, the highly selective synthesis of these two compounds, and particularly of glutaraldehyde, is challenging. To improve the reaction rate and product selectivity of cyclopentene oxidation using green hydrogen peroxide (H₂O₂, 30 wt%) as an oxidant, activated carbon (AC)-supported amphiphilic vanadium-doped heteropolyacid (HPA) catalysts (AC-COIMI-C_n-HPA) were prepared by a series of modifications of AC, including acidification, imidazolylation, ammonium saltification, and HPAs loading. The structures and physicochemical properties of the catalysts were characterized by Fourier infrared spectroscopy, X-ray diffraction, thermogravimetric analysis, and nitrogen adsorption–desorption. The developed catalyst exhibits excellent catalytic properties and high selectivity toward glutaraldehyde. The AC carrier increases the number of effective active sites on the catalyst. The amphiphilicity of the catalyst increased the reaction rate. Vanadium doping of HPA enables fine-tuning of the oxidizability of the catalyst. The effects of the different active components of the catalyst, alkyl groups on the imidazole ring, solvent type and dosage, HPA loading on the catalyst, catalyst dosage, oxidant dosage, reaction temperature, and reaction time on the oxidation of cyclopentene were comprehensively examined. Finally, the optimized conditions were determined as follows: HPA doping by four V atoms (PW₈V₄), octyl (C₈) linked to the imidazole, 1 mL of acetonitrile, HPA loading of 35 wt%, 500 mg of the catalyst (AC-COIMI-C₈–35%PW₈V₄), n(H₂O₂):n (cyclopentene) = 2, reaction temperature and time of 40°C and 6 h, respectively. The conversion of cyclopentene was 98.8% and the total selectivity for glutaraldehyde and 1,2-cyclopentanediol was 91.6% (65.2% for glutaraldehyde and 26.4% for 1,2-cyclopentanediol). The catalyst was reused by centrifugation, and high cyclopentene conversion was maintained after three cycles.