Vapour phase methylation of phenol over nanocrystalline ZnFe_(2-x) A1_XO_4 (x = 0, 0.25, 0.5, 0.75 and 1.0) ferrospinel system

摘要

The alkylation of phenol with methanol was carried out over ZnFc_(2-x)Al_xO_4 (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 arc discussed. A maximum yield of 70.9 and 22.9% with selectivity of 73.5 and 23.3% was obtained for 2,6-xylcnol and o-crcsol respectively, giving a total ortho selectivity of 96.8% over ZnFeAlO_4 at 350 deg C, methanol to phenol molar ratio of 5 and WHSV of 0.6 h~(-1). Catalyst characterization was made by XRD, Mossbauer spectroscopy, ammonia desorption and BET surface area measurements. Mossbauer spectroscopy reveals isomorphic substitution of Fe~(3+) by smaller Al~(3+) 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.