Methylation of naphthalene on MTW-type zeolites. Influence of template origin and substitution of Al by Ga

Four ZSM-12 zeolites: Al-TEA, Al-MTEA, Ga/Al-MTEA and Ga-MTEA were investigated in the methylation of naphthalene. It was found that the catalysts exhibit drastically different properties regarding the production of dimethylnaphthalenes. Their distribution differs from that of thermodynamic equilibrium to a great extent in all cases, but the mode of this difference varies for each of the studied samples. This is mainly attributed to a presence of secondary mesopores in Al-TEA, Ga/Al-MTEA and Ga-MTEA zeolites. Two templates, methyltriethylammonium bromide (MTEA) and tetraethylammonium bromide (TEA) were used to synthesize aluminosilicate ZSM-12 zeolites. Additionally, zeolites isomorphously substituted (partially or totally) by gallium were prepared with MTEA. Various techniques including XRD, scanning electron microscopy (SEM), N 2 adsorption, NH 3-TPD, Fourier transform infrared (FTIR) spectroscopy and MAS NMR were used to monitor the physico-chemical properties of these solids. Catalytic properties of the prepared zeolites were studied in the methylation of naphthalene. Higher conversion of naphthalene, higher content of 2,6-DMN among total DMNs and higher 2,6-/2,7-DMN ratio were observed on Al-TEA sample and on Ga-containing zeolites compared to Al-MTEA. The specific morphology of zeolite crystals and the presence of secondary mesopores were identified to be responsible for remarkable catalytic performance of MTW-type zeolites.