Catalytic and deactivated behavior of SAPO-34/ZSM-5 composite molecular sieve synthesized by in-situ two-step method

• Main Authors: Hong Wu, Fei Liu, Yun Yi, Jianxin Cao
• Format: Article
• Language: English
• Published: Elsevier 2021-11-01
• Series: Journal of Materials Research and Technology
• Subjects: In-situ two-step crystallization method; SAPO-34/ZSM-5 composite molecularsieve; Crystallization process; Reaction behavior; Deactivation
• Online Access: http://www.sciencedirect.com/science/article/pii/S2238785421009984

This work aims at revealing the reaction and carbon behavior of SAPO-34/ZSM-5 composite molecular sieve (SZ-TS) in MTO reaction, which is synthesized via in situ two-step crystallization method. Several tests are used to explore the structure–activity relationship of the SZ-TS. The results show that the strength of weak and medium-strong acid is suitable, the particle size of two-phase molecular sieve is decreased, the hierarchical pore structure with abundant mesoporous is formed. By using the SZ-TS in MTO reaction, the methanol conversion and light olefins selectivity are 98% and 92.7%, respectively. These results can be attributed to the interface phase effect produced by etching and dissociation on the skeleton of the nuclear phase SAPO-34. The result of in situ IR and analysis of carbon deactivation indicate that polymethylbenzene is generated as the active intermediate of MTO reaction.SZ-TS with appropriate acid sites and rich mesoporous distribution could alleviate the formation rate of methyl-substituted benzene and polycyclic aromatic hydrocarbons, smaller particle size can avoid the occurrence of secondary reactions of olefins, therefore displaying the excellent resistance to the carbon deposition inactivation, with a catalytic lifetime up to 1380 min.