Correlations between the dispersion state of MgO and catalytic behavior of MgO/HZSM-5

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.