Characterization and catalytic performance of SAPO-11/Hβ composite molecular sieve compared with the mechanical mixture

SAPO-11/Hβ composite molecular sieve was synthesized with hydrothermal method. For comparing, the mechanical mixture of SAPO-11 and Hβ was also prepared by fully blending. The physicochemical properties of the composite and the mechanical mixture were comparatively characterized by using XRD, FT-IR, 27Al and 31P MAS NMR, SEM, N2 isothermal adsorption–desorption and Py-FTIR. In addition, the catalytic performance of the composite and the mechanical mixture in cracking of 2-butylene was also investigated, respectively. The results indicate that the properties and catalytic performance of the composite was quite different from those of the mechanical mixture, which was due to the occurrence of the strong interaction of SAPO-11 and Hβ in the composite. Such interaction resulted in the combination of the framework of SAPO-11 and Hβ by chemical bonds, the formation of defect structure in framework, extra-framework aluminum and new coordination structure of P. All that distinctly modified the acidity of the composite. The acidity of these samples was closely relative to their catalytic performance in the cracking of 2-butylene. The mechanical mixture had the higher density of total acid sites and higher density of L acid sites than the composite; therefore, the mechanical mixture exhibited higher specific conversion of 2-butylene and coke. The composite possessed the higher density of B acid sites and Btotal/Ltotal than the mechanical mixture, which was responsible for the higher specific selectivity of propylene and ethylene on the composites.