Electronic structure of chabazite zeolites H-SSZ-13 and H-SAPO-34

Abstract

H-SSZ-13 and H-SAPO-34 are chabazite (CHA) zeolites and successful methanol-to-olefins (MTO) catalysts. In order to understand their intrinsic origin of catalytic activity and compare their properties, the electronic structure of H-SSZ-13 and H-SAPO-34 referencing to neutral SiO2-CHA and AlPO4-CHA was studied in this work exhaustively. Based on the results, the following conclusions can be made. (1) The catalytic activity of acidic zeolites stems from that the electronic distribution of the valence band maximum (VBM) is highly localized in the acid catalytic center. (2) The acidity of H-SAPO-34 is weaker than that of H-SSZ-13 because the strength of H–O bond in H-SAPO-34 is stronger than that in H-SSZ-13. (3) From the Bader Charge analysis, the acidic center of H-SAPO-34 possesses stronger polarization ability than peripheral framework, while in H-SSZ-13 the polarization ability of the acidic center is almost equal with the outer framework. Thus, small gas molecules are easy to reach active centers and so H-SAPO-34 are more efficient for MTO process.