The formation of polycyclic aromatic hydrocarbons (PAHs) is inevitable in catalysis processes,especially in industrially important petrochemical processes(catalytic cracking, isomerization, trans-alkylation of aromatics,etc.) and coal-based chemical processes (such as methanol-to-olefins(MTO) and syngas conversion).The deposition of theseextended aromatic hydrocarbons detrimentally induces catalystcoking and deactivation, necessitating regeneration operations,and posing challenges to practical process design.To alleviate oreven prevent catalyst deactivation, unambiguously unraveling ofthe structural motifs of PAHs, at a molecular scale, is necessary.Despite enormous endeavors,the cognition of coking behavior in zeolite or zeotype molecular sieves from literature could be summarized as simple fused-ring aromatic species confined in isolated molecular sieve cavities or graphitized carbon deposition generated on the outer surface of the molecular sieve crystal, and a full-molecular description of theprecise chemical structures of these PAHs is far from beingachieved.Yet, if a full-spectrum deciphering of such PAHs isrealized, it would become feasible to trace and uncover themolecular route of PAHs formation and evolution, and thus toobtain unprecedentedly detailed structural information of cokedeactivating the zeolite. This would, in turn, help in improvingindustrial processes.
Recently, a research team led by Prof. Liu Zhongmin and Prof. Wei Yingxu fromDalian Institute of Chemical Physics (DICP) of the Chinese Academy of Sciences (CAS) reporteda PAHs cage-passinggrowth mechanism which is later proved general onother cage-structured molecular sieves.The work was published in Nature Communications (https://www.nature.com/articles/s41467-020-14493-9).
In this work,researchers have demonstrated, through coupling the state-of-the-art matrix-assisted laser desorption/ionizationFourier-transform ion cyclotron resonance mass spectrometry (MALDI FT-ICR MS) with isotope labeling technique,the cage-passing growth concept (forming cross-linked multicorearomatics) by identifying the structural fingerprints of PAHs in anexemplary, industrially important SAPO-34-catalyzed methanolconversion reaction.These cage-crossing polycyclic aromatic hydrocarbon species severely impedes the molecular mass transfer and renders the catalyst to deactivation.The cage-passing growthmechanism was validated on other cage-structured zeolites, and isexpected to be a general C-C assembly mode for PAHs growth inzeolite- or molecular sieve-catalyzed reactions. Such a mechanisticmotif not only promotes the development of dynamic methanol conversion network, but also unveils the significance of host-guest chemistry in catalysisfield. In practical MTO industry,our well-built deactivation modelwouldserve as a solid basis for processdesign of both pre-cokingandpartial regeneration industrial technologies.
This paper is dedicated to the 70th anniversary of the Dalian Institute of ChemicalPhysics, Chinese Academy of Sciences. The authors thank the financial support from theNational Natural Science Foundation of China (Grant No. 21703239, 91745109,21972142 and 21991092), the Key Research Program of Frontier Sciences, ChineseAcademy of Sciences (QYZDY-SSW-JSC024), and International Partnership Program ofChinese Academy of Sciences (121421KYSB20180007). (Text by Wang Nan)
Molecular elucidating of an unusual growth mechanism for polycyclic aromatic hydrocarbons in confined space. Nan Wang, Yuchun Zhi, Yingxu Wei*, Wenna Zhang, Zhiqiang Liu, Jindou Huang, Tantan Sun, Shutao Xu, Shanfan Lin, Yanli He, Anmin Zheng, Zhongmin Liu*, Nature Communications, 11(1):10.1038/s41467-020-14493-9, 2020.
