CeAlPO 5 molecular sieves for selective oxidation of organic compounds

Abstract

Catalytic oxidation is a key technology for converting petroleum based feedstocks to useful chemicals such as alcohols, carbonyl compounds and epoxides. Selective oxidations are pivotal transformations in organic synthesis. The present study reports the hydrothermal synthesis of CeAlPO-5 molecular sieves in fluoride medium, characterisation of the materials and their catalytic activity in the vapour phase oxidation of ethylbenzene, cyclohexane, diphenylmethane (DPM) and toluene in air. CeAlPO-5 molecular sieves were synthesised with Al/Ce ratios 25, 50, 75, 100 and 125 in fluoride medium. The DRS-UV-vis spectra of as-synthesised CeAlPO-5(Al/Ce = 25, 50, 75, 100 and 125) exhibited an intense broad absorption maximum close to 250 nm. This is assigned to O2- Ce3+ charge transfer transition. CeO2 exhibits absorption maximum around 370 nm for band gap excitation but such absorption maximum was absent in the spectrum. This analysis also established the incorporation of cerium entirely in the framework. The ESR spectrum of calcined CeAlPO-5(25) showed a broad envelope at g = 2.0. It is due to chemisorbed oxygen on cerium. The vapour phase oxidation of toluene was tested over CeAlPO-5 catalysts from 300 to 400 °C with an air flow rate of 10 mLmin-1 and feed rate 2 mLh-1. The conversion and product selectivity remained the same for the entire 6 h of time on stream. It confirmed the absence of coke formation over the active sites of the catalysts and the stability of the catalysts. Hence this study confirmed that CeAlPO-5 molecular sieves are suitable for selective oxidation of ethylbenzene, cyclohexane, diphenylmethane and toluene. As the catalysts did not exhibit leaching of cerium, they may find scope for industrial application in the future. The absence of coke formation is an additional advantage in this study as frequent regeneration of the catalyst is not required. newline