Shape-selective methylation of aromatics with methanol over modified nanoscale-HZSM-5 catalysts

In this paper, nanoscale NaZSM-5 zeolite was synthesized by the hydrothermal crystallization from a gel consisting of sodium silicate, aluminium sulphate, butylamine, sulfuric acid and deionized water in a stainless steel autoclave at 100°C for 24 h, then 170°C for 48 h. The crystal size of the catalyst is 70-100 nm. Nanoscale HZSM-5 has more pore openings, more accessible acid sites, larger external surface area and the secondary pores which favor the diffusion of reactants and products further increase the reaction activity and the ability to resist coking during reactions. The nanoscale HZSM-5 zeolite modified with P-Mg-Si and further modified with Ni metal showed excellent stability and p-xylene selectivity in the alkylation of toluene with methanol. The selectivity for p-xylene of more than 98.3% with toluene conversion of about 25.0% was achieved during 500 h time on stream. Through changing the template and base treatment, nano-ZSM-5 and hollow ZSM-5 were obtained and their catalytic performances were compared in the shape-selective methylation of toluene. Moreover, the utilization of methanol is more than 80% by adjusting the ratio of toluene to methanol.