The reaction of dimethyl ether to olefin over HZSM-5/Al2O3 catalysts modified by Zr and Mg and stabilized by hydrothermal treatment has been studied. Regardless of the introduction method and the nature of the metal, the dependence of the key products selectivity on X(DME) over hydrothermally treated steady-state catalysts does not change, and the experimental points are described by the same curves. Metal introduction and the corresponding changes in the acid sites distribution do not change the ratio of main reaction rates, only the absolute values of the formation rate of the products are changed. Zr doping leads to the greatest activity in the DME conversion due to an equable decrease in the total acidity of the sample. On the other hand, the Mg-modified sample has a higher amount of weak acid sites, which reduces activity. At low DME conversion, methanol is one of the primary reaction products which formed from DME simultaneously with propylene in alkene cycle. At high DME conversion, the methanol acts as a main reagent which leads to ethylene formation in the arene cycle. Based on the results, the role of the metal in the reaction chemistry is considered and the mechanism of product formation from DME over steady-state catalyst is proposed, which describes both the participation of DME and the methanol produced.

The studies were focused on changes in the structure, texture and acid properties of the Mg-HZSM-5/Al2O3catalyst upon its treatment at different temperatures (400 and 500 °С) and times (6 and 12 h). Physicochemical techniques such as X-ray fluorescence analysis, XPS, solid-state27Al NMR, nitrogen adsorption, DRIFT spectroscopy, ammonia TPD were used for sample characterization. The catalytic activitites of the initial and treated samples were studied regarding conversion of dimethyl ether (DME) to lower olefins. It was shown that the initial activity of the Mg-containing zeolite catalyst was dependent of the total acidity of the surface and independent of the initial strength distribution of the acid sites, and the catalyst stability depended on the morphology.

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