Alkylation of toluene to mono-benzylated toluene over micro-mesoporous zeolite: effect of post-synthetic treatment and catalytic application

Abstract

Post-synthetic modification using acid (HNO3) and base (NaOH) are utilised to synthesize hierarchical micro-mesoporous zeolites with different pore structure. To investigate structural change in materials, X-ray diffraction (XRD), Scanning electron microscope (SEM), Inductive coupled plasma-optical emission spectrometry (ICP-OES), 29Si and 27Al MAS NMR, and N2 adsorption-desorption isotherms techniques were employed. Acid base titration, and ammonia-temperature programmed desorption (NH3-TPD) was performed to evaluate acidic characteristics of materials. As revealed by characterisation, the structure was well preserved after the modification. Hierarchical materials along with parent materials have been evaluated in the toluene alkylation with benzyl alcohol producing mono-benzylated toluene. All zeolite samples were proved to be catalytically active by their result in the alkylation reaction. Acid treated samples were compared with base treated and parent samples. The results indicate that, base modification significantly increases the mesoporous pore volume in all zeolite as compared to acid modification. Moreover, the highest benzyl alcohol conversion was found to be 98 % in the base modified Beta, with the highest mono-benzylated toluene selectivity (69 %). Reaction optimization was also studied by altering reaction duration, temperature, and catalyst amount. The reaction products were analysed using Gas Chromatography (GC) and confirmed using Gas chromatography mass spectrometry (GC-MS).