Abstract: Two series of MgO/HZSM-5 catalysts were prepared by impregnating HZSM-5 with solution of Mg(NO3)2 and Mg(CH3COO)2.The structures of the samples were characterized by XRD and XPS,and the acidity was determined by NH3-TPD.The catalytic behavior of MgO/HZSM-5 in the reaction of toluene methylation was investigated on a continuous flow micro-apparatus under atmospheric pressure.It was found that the dispersion of MgO was related to the precursor of MgO and had an important effect on the behavior of MgO/HZSM-5 catalyst.MgO disperses both on the internal surface and on the external surface of HZSM-5 in the catalysts prepared with Mg(NO3)2 as the precursor of MgO,therefore the para-selectivity of the catalyst is higher and the activity is lower.However MgO mainly deposits on the external surface of HZSM-5 in the catalysts prepared with Mg(CH3COO)2,and the activity of catalysts is higher and the para-selectivity is lower.By secondary impregnation and hydrothermal treatment MgO/HZSM-5 catalyst with relatively high activity and high para-selectivity was obtained.

Key words: Shape-selectivity, Surface modification, Toluene methylation, HZSM-5, MgO