Recently, the research team led by Profs. LIUZhongmin and WEIYingxu (from National Engineering Laboratory for Methanol to Olefins,Dalian Institute of Chemical Physics(DICP), Chinese Academy of Sciences (CAS) ) cooperated with the teamled by Prof.ZHENG Anmin(from Innovation Academy for PrecisionMeasurement Science and Technology, CAS) and the teamled by Prof.XIAO Jianping (from State Key Laboratory of Catalysis, DICP, CAS)have made a new progress in the reaction mechanism of methanol-to-olefin process.They revealed the full and dynamic autocatalytic molecular routes of MTH process.This result,entitled “Molecular routes of dynamic autocatalysis for methanol-to-hydrocarbons (MTH) reaction”,was published onJournal of the American Chemical Society(143 (31):12038-12052, 2021).
The well-known methanol-to-hydrocarbons (MTH) processover zeolite and zeotype catalystsis not only the most successful non-petroleum route for producing light olefins and gasoline, but also an important reaction in C1 chemistry, and has been attracted a greatdeal of attention from both industry and academia.The research team led by Profs. LIUZhongmin and WEIYingxuhas been dedicated to the study of reaction mechanism of methanol conversion for many years.Many researchprogresses have been made in the indirect mechanisms (J. Am. Chem. Soc., 2012;Angew. Chem. Int. Ed., 2017;ACS Catal., 2015;ACS Catal., 2018;ACS Catal., 2018;ACS Catal., 2019;ACS Catal., 2020), direct mechanism (Angew. Chem. Int. Ed., 2017;Chem, 2021;ACS Cent. Sci., 2021), and deactivation (J. Catal., 2018;Nat. Commun., 2020).Autocatalysis, a particularcase of catalysis, refers to a process in which a reaction product acts as the catalyst, exponentially accelerating the reaction by producing more of itself. The MTH reaction, conducting in the confined space of the molecular sieve, is driven and sustained by autocatalysis in adynamic and complex manner. However, the complete molecular routes and the chemical nature of its autocatalytic reaction network have not been well understood.
In this work, we build a multi-technique approach by integrating kinetics,electronic states analysis, PDOS electronic interaction analysis with AIMD simulations and multiplein situandoperandospectroscopic analyses.By virtue of this, we successfully map the full-spectrum molecular routes of dynamic autocatalysis from initiating to decaying, and uncover the chemical genesis of induction period of autocatalysis.The full-spectrum molecular routes of methanol conversion are an ensemble of chain reactions comprising a cascade of catalytic and autocatalytic events. The reaction sequence runs from the initiation to decay like domino, including three stages: I) initiating stage.The higher energy increase of the highest electronic states below Fermi-levelfor adsorbed DME than methanol exerted by the constrained environments of zeolite suggests a marked pre-activation of DME than methanol.The more reactive DME is plausible to react with the surface methoxy species (SMS) to generate initial olefins toinitiate autocatalysis, followed by the speciation of methylcyclopentenyl (MCP) and aromatic cyclic active species.Concurrently, the active sites are dynamically evolved from acidic protons to the SMS, and then to organic-inorganic hybrid, microenvironment-involved supramolecular active centers; II) sustaining stage.The olefins- and cyclic species-guided catalytic cycles are interdependently linked to forge a previously unidentified hypercycle, being composed of one ‘selfish’ autocatalytic cycle (i.e., olefins-based cycle with lighter olefins as autocatalysts for catalyzing the formation of olefins) and three cross-catalysis cycles (with olefinic, MCP and aromatic species as autocatalysts for catalyzing each other’s formation).; III) decaying stage.The active aromatic species gradually decay and age into inactive polycyclic aromatic hydrocarbons, terminating autocatalysis.Furthermore, we also discussed the effect of zeolite confined space, acidity and reaction conditions on the dynamic evolution of autocatalytic hypercycle.
This work was supported by Chinese Academy of Sciences, the National Natural Science Foundation of China,DICP, the High Level Talents Innovative SupportPlan of Dalian, the Key Research Program ofFrontier Sciences, Chinese Academy of Sciences, and the International Partnership Program ofChinese Academy of Sciences. (Text and picture by LINShanfanand ZHIYuchun)
Molecular Routes of Dynamic Autocatalysis for Methanol-to-Hydrocarbons Reaction. Shanfan Lin, YuchunZhi, Wei Chen, Huan Li, Wenna Zhang, Caiyi Lou, Xinqiang Wu, Shu Zeng, Shutao Xu, Jianping Xiao*, Anmin Zheng*, Yingxu Wei*, and Zhongmin Liu*, Journal of the American Chemical Society, 143 (31):12038-12052, 2021
