Enhancing ethylene selectivity in MTO reaction by incorporating metal species in the cavity of SAPO-34 catalysts

Abstract

The SAPO-34 catalysts were modified with metal cations by different processes (conventional ion exchange (CIE), template-assisted ion incorporation (TII) and alcoholic ion exchange (AIE)), systematically characterized by XRD, XRF, N2 adsorption-desorption, UV-VIS, H2-TPR, EPR, SEM, EDX, XPS, NH3-TPD, 1H NMR and IGA, and applied in MTO reaction. The metal cations incorporation introduces extra diffusion hindrance by metallic species located in the cavity of SAPO-34. In particular, the Zn cations-modified SAPO-34 catalysts exhibit core-shell like structure, with Si-rich and Zn-rich sublayer near the external surface, which favors the coke deposition at the beginning of MTO reaction, exerts marked impact on the diffusion of the generated products with relatively large molecular size (e.g. propylene), and significantly increases the selectivity to ethylene and the ratio of ethylene to propene in the MTO reaction.