In-depth study on the good resistance to coke deposition of SAPO-34/ ZSM-5/quartz composite zeolite film with hierarchical structure in MTA reaction

In our previous research, SAPO-34/ZSM-5/quartz (SZ-F) composite zeolite was successfully prepared and used in MTA reaction, which greatly improved the selectivity of BTX. However, the anti-coking mechanism of SZ-F has not been subjected to further in-depth investigation. In this paper, the anti-coking performance of SZ-F in the MTA reaction was systematically investigated by comparing the pH value of the synthetic solution, the differences of cycling performance, the amount of coke deposition, and carbon deposition sites among SAPO-34, ZSM5, and SZ-F. The SZ-F was prepared to develop rich hierarchical pores by regulating the pH value of the synthetic solution, capable of transferring olefins from the SAPO-34 layer to the ZSM-5 layer, thereby shortening the MTA reaction path and enhancing the cyclic stability of SZ-F. Simultaneously, the prompt transfer of coke precursors generated in SAPO-34 to the ZSM-5 layer significantly prolonged the lifespan of the SAPO-34 layer. This mechanism primarily led to coke deposition covering the acidic sites within the mesopores of the ZSM-5 layer. Furthermore, the layered structure hindered the development of graphite-like carbon on the surface, allowing the soluble coke components to primarily comprise simple naphthalene and anthracene species. Coking activation energy showed that the SZ-F had the strongest resistance to coke deposition. This work can provide theoretical guidance for the wider application of composite zeolites.