Role of active sites in the reaction of methanol to olefin over modified ZSM-5 zeolite

ZSM-5 zeolites were modified with metals Mg, K, Ca, Ba and La by an incipient impregnation and characterized by X-ray diffraction, N/sub 2/ adsorption and temperature - programmed desorption of NH/sub 3/ and CO/sub 2/. The obtained samples were investigated for their selectivity and catalytic stability in the methanol-to-olefin (MTO) reaction. The catalytic performance was influenced by the properties of active sites on the catalyst, which was indicated by the changes of the light olefin selectivity and catalytic stability in the methanol conversion. Correlating the reaction evaluation with the catalyst characterization, it can be seen that the catalyst with too strong basic sites shows an inferior catalytic performance. In addition, steam treatment further increased the catalytic performance, especially for Ca modified ZSM-5. It may be concluded that basic sites must suitably match with acidic sites for a special ZSM-5 in the methanol conversion and the formed active sites were relative with the modification metal based on the obtained results. (author)