Liquid Phase Benzylation of O-Xylene on Nano Mesoporous Lanthanum Aluminates

Abstract

Nano lanthanum aluminates synthesized by sol-gel method were used for the liquid phase benzylation of o-xylene (oXyl) with benzyl chloride (BC) in a batch reactor at atmospheric pressure. Lanthanum aluminates were characterized in depth by Differential thermo gravimetric analysis (DTG), Differential scanning calorimetric analysis (DSC), X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), N2 sorpometry, transmission electron microscopy (TEM), temperatureprogrammed desorption using CO2/NH3 (CO2-TPD/NH3-TPD) and temperature-programmed reduction using H2 (H2-TPR) in order to relate its performances to the chemical and textural characteristics. Nano La10Al4O21 was detected for lower aluminum precursor concentration and stable nano mesoporous LaAlO3 becomes the major phase as the concentration increases. The band gap of LaAlO3 and La10Al4O21 was estimated from ultraviolet-visible (UV-Vis) spectrophotometry. Ac conductivity and dielectric measurement of lanthanum aluminates were also performed. The effect of catalyst concentration, reaction temperature, reaction time and o-Xyl/BC molar ratio on benzylation of o-Xyl was studied over stable nano mesoporous LaAlO3 and was extended to nano La10Al4O21 at the optimized conditions. LaAlO3 showed 92% and La10Al4O21 showed 51% BC conversion at the following reaction conditions (catalyst to BC (w/w) = 0.1, o-Xyl/BC molar ratio =1:1, 433K, 2h, 1 atm). The acidity and mesoporous structure of LaAlO3 appeared to be responsible for its good performance. Increase in catalyst concentration, reaction temperature and reaction time enhances the conversion of BC, whereas it decreases with the increase in o-Xyl/BC molar ratio. The Friedel-Crafts (FC) benzylation reaction mechanism involves the formation of an electrophile (C6H5CH2 + ) over an acidic lanthanum aluminate catalyst which attacks the O-Xyl ring resulting in the formation of 3,4 -dimethyl diphenyl methane.