Sandwich-structured CeO2@ZSM-5 hybrid composites for catalytic oxidation of 1, 2-dichloroethane: An integrated solution to coking and chlorine poisoning deactivation

Abstract Sandwich-structured CeO2@HZSM-5 core-shell hybrid composites were designed and prepared by an in situ two-step hydrothermal growth method under dynamic condition, and SEM indicated that CeO2 nanosheets were completely encapsulated by HZSM-5 particles which formed continuous and dense zeolite membranes (exposed HZSM-5). The catalytic total oxidation of 1, 2-dichloroethane (DCE) over CeO2@HZSM-5 was investigated, compared with CeO2/HZSM-5 (CeO2 dispersed on HZSM-5) and CeO2 + HZSM-5 (CeO2 mixed with HZSM-5) reference catalysts. Although the latter two showed a better catalytic activity due to the synergies of ceria and HZSM-5 zeolite, the formation of poly-chlorinated hydrocarbons (PCHs) by-products over CeO2@HZSM-5 was significantly inhibited since CeO2 with high activity for Deacon reaction was not directly exposed to DCE or HCl molecules. Moreover, CeO2@HZSM-5 also exhibited a better resistance to the coking and chlorine poisoning, because the formed non-activated coke species or polyaromatic species could be easier to be removed via in situ oxidation by the active oxygen species from CeO2, and the exposed HZSM-5 was tolerant to the chlorination of acid sites and avoided the direct adsorption of HCl on CeO2. Additionally, the presence of water and ethyl acetate (EA) dramatically inhibited the activity of CeO2@HZSM-5 for DCE oxidation, but water also completely suppressed the formation of PCHs by-products. The high Si/Al ratio could improve the water-resistance due to the increase of hydrophobicity, and the induction of trace Pd (0.1 wt%) further increased the CO2 selectivity.