Abstract: Shape-selective alkylation of toluene (T) with methanol (M) was performed over Si-P-Mg-modified nano-scale HZSM-5 zeolite. The change of acidity and pore structure of the catalyst was studied by X-ray diffraction, NH₃ temperature-programmed desorption, Fourier transform infrared spectroscopy, and N₂ adsorption．The effects of temperature, space velocity (WHSV), and flow rate of N₂ carrier gas on the reaction were investigated in a continuous flow fixed-bed reactor. Under the optimized conditions (2 h^–1, 460 ^oC, n(T)/n(M) = n(H₂O)/n(HC) = n(N₂)/n(HC) = 8, where HC represents toluene and methanol), during 500 h on stream over the Si-P-Mg modified nano-scale HZSM-5 catalyst, the toluene conversion of about 10% and the selectivity to p-xylene of more than 97% were maintained, indicating that the catalyst exhibits high selectivity and good stability.

Key words: nano-scale HZSM-5 zeolite, silicon-phosphorus-magnesium modification, toluene, methanol, alkylation, p-xylene