As the most significant groups in the class of porous materials,molecular sieves have extensively-used in the fields of petrochemistry, coal utilization, pollution abatement, energy conservation, household, electronics and pharmaceuticals. On the basis of artificial simulation of the natural zeolites formation process, molecular sieves have been successfully synthesized under hydrothermal condition with the participation of water at a certain temperature and pressure since 1940s. When molecular sieves are applied in industrial processes, they always confront the environment of water vapor atmosphere at elevated temperature, for instances, fluid-catalytic-cracking (FCC), methanol-to-olefins (MTO) and selective-catalytic-reduction of nitrogen oxides (SCR-DeNO_X), etc.However,due to the limitation of current experimental techniques, the effects of hydrothermal conditions on the molecular sieve framework, which are critical for a deeply understanding of the functions of water during catalytic reaction, have not yet been studied.

Recently, Prof. Yingxu Wei, Prof. Shutao Xu and Prof. Zhongmin Liufrom the Dalian Institute of Chemical Physics (DICP) of the Chinese Academy of Sciences provided new insights into the dynamic features of molecular sieves in the atmosphere of water.A water-induced structural dynamic and reversible breakage-bonding of T-O-T bonds in molecular sieves framework under mild hydrothermal conditions（100-300℃）is revealed.

This dynamic and reversible T-O-T bonds breakage-bonding process was directly confirmed by the incorporation of¹⁷O atoms from H₂¹⁷O vapor into the framework of an industrial MTO catalyst SAPO-34 molecular sieve. Considering the CHA topology of SAPO-34 has the distinctive feature that all the T atoms in tetrahedral coordination state are located on the 8-MR window of framework，the scientists realized the encapsulation of two kinds of bulky probe molecules，trimethylphosphine (TMP) and pyridine with kinetic diameters 5.5 Å and 5.3 Å respectively (much larger than the 8-MR pore size (3.8 Å) of SAPO-34,into CHA cavities by the dynamic and reversible breakage-bonding of T-O-T bonds under mild hydrothermal conditions. The successful ship-in-a-bottle strategy based on these findings also open new fields for fine acidity identification and give extra boost in shape selective catalysis. By the aid of encapsulated-TMP, four kinds of Br➢nsted acid sites, which are ascribed to the bridge hydroxyl groups with protons located on four nonequivalent O positions in SAPO-34 framework, are distinguished experimentally. TMP and pyridine modified SAPO-34 were applied in MTO reaction, and both exhibited very high light olefins selectivity particularly at initial reaction stage.

The study was supported by the National Natural Science Foundation of China, the Key Research Program of Frontier Sciences of CAS, the International Partnership Program of CAS, the Youth Innovation Promotion Association of CAS and Liaoning Revitalization Talents Program. (Text by Sun Tantan and Xu Shutao)

Water-Induced Structural Dynamic Process in Molecular Sieves under Mild Hydrothermal Conditions: Ship-in-a-Bottle Strategy for Acidity Identification and Catalyst Modification. Tantan Sun, Shutao Xu*, Dong Xiao, Zhiqiang Liu, Guangchao Li, Anmin Zheng, Wenjuan Liu, Zhaochao Xu, Yi Cao, Qiang Guo, Nan Wang, Yingxu Wei*,Zhongmin Liu*, Angewandte Chemie International Edition, 59(46):20672-20681, 2020