Catalytic performance of SAPO-11/HZSM-5 composite supported Cr₂O₃ in the transformation of LPG to light olefins

HZSM-5(core)/SAPO-11(shell) composite molecular sieves were hydrothermally synthesized by crystallization of SAPO-11 outside HZSM-5 surface. After loading 10% Cr₂O₃, the pore distribution, acidity, and catalytic activity of the composite supported Cr₂O₃ in the transformation of liquefied petroleum gas (LPG) to ethene and propene were investigated. The results showed the HZSM-5 surface was coated with SAPO-11 microcrystalline of different thicknesses. With the increase of crystallization time, the shell thickness of the composite molecular sieves is increased; the mesoporosity and acidity can then be regulated by controlling the shell thickness. The composite supported Cr₂O₃ exhibits superior activity in the transformation of LPG to olefins than the single molecular sieves or mechanically mixed ones. The Cr₂O₃ catalyst supported on the composite by crystallization for 12 h gives the highest activity and selectivity to the target products; the feed conversion and the selectivity to ethene and propene are 42.63% and 65.89%, respectively, while the selectivities to CH₄ and C₅₊ are 6.32% and 15.48%, respectively.