Vapour phase methylation of phenol over nanocrystalline ZnFe_2-xAl_xO₄(x= 0, 0.25, 0.5, 0.75 and 1.0) ferrospinel system

Abstract

The alkylation of phenol with methanol was carried out over ZnFe_2-xAl_xO₄(x₌ 0, 0.25, 0.5, 0.75 and 1.0) type spinel systems in a fixed bed, down flow reactor. The influence of surface acidity, cation distribution in the spinel lattice and various reaction parameters are discussed. A maximum yield of 70.9 and 22.9% with selectivity of 73.5 and 23.3% was obtained for 2,6-xylenol and <i style="">o</i>-cresol respectively, giving a total ortho selectivity of 96.8% over ZnFeAlO₄ at 350^oC, methanol to phenol molar ratio of 5 and WHSV of 0.6 h^–1. Catalyst characterization was made by XRD, Mössbauer spectroscopy, ammonia desorption and BET surface area measurements. Mössbauer spectroscopy reveals isomorphic substitution of Fe³⁺by smaller Al³⁺into the octahedral sites leading to lattice distortion, unsymmetrical charge distribution and charge transfer from iron to oxygen making it more basic and proton attracting. This helps vertical adsorption of phenol and formation of 2,6-xylenol. It has been concluded that catalyst acidity plays major role in the reaction as compared to surface area.