The significant volume of solvent required for the hydrothermal synthesis of zeolites remains the primary hurdle impeding industrial applications. With the benefits of reduced manufacturing costs, safety, and energy savings, reducing the use of solvents is one of the significant sought-after objectives. In this study, borosilicate zeolite B-MCM-22 is successfully obtained using a solvent-free synthesis method. The as-synthesized sample exhibits good long-range order, high crystallinity, and high silica utilization (ca. 95%). Furthermore, the B-MCM-22 precursor serves as a platform for introducing Co active sites via deboronization and impregnation processes. The resulting Co-MCM-22-DB catalyst provides a propylene selectivity of >90% with an initial propane conversion of 38% in the propane dehydrogenation reaction and shows a higher initial catalytic performance than the Co/ITQ-1 catalyst. The essential interplay between the metal–support interaction and catalytic performance is demonstrated by ultraviolet–visible (UV–vis), H2-TPR, and catalytic assessments, further elucidating that Co2+ species are the active sites for propane to propylene conversion. We anticipate that B-MCM-22 will be a versatile and ideal platform for catalyst design through structural manipulation.
Producing para-xylene (PX) by Diels–Alder (D–A) cycloaddition of 2,5-dimethylfuran (DMF) and acrylic acid (AA) was a potential renewable pathway. In this study, MCM-22 zeolites served as catalysts for the D–A cycloaddition reaction, exhibiting significantly higher activity compared to conventional Beta and ZSM-5 zeolites. The high activity was demonstrated to be derived mainly from the acid sites located within the pocket structures on the external surface of MCM-22. The rate-determining step for the formation of PX was the dehydration process of the B-acid-catalyzed cycloadduct. The external silanols at the pore entrance of the pocket structure could adsorb the reactants and promote the D–A cycloaddition reaction. The MCM-22(15) catalyst achieved 98% DMF conversion with 88% PX selectivity after 10 h at 190 ℃ in the D-A cycloaddition reaction.
Zijian Wang,Shuting Li,Jiashuo Zheng,Jiahan Li,Yanbing Tong,Ming Ke,Zhaozheng Song
MCM-22 zeolite synthesized by utilizing the hexamethyleneimine as the organic structure directing agent has a wide range of applications. For the growth mechanism of the typical sample, on the macro level, XRD, FT-IR, and SEM are used to confirm the epitaxial growth of the intercalation structure. On the micro level, eight different T sites of the zeolite are completely distinguished as well as the guidence of hexamethyleneimine on T 1 , T 2 , T 3 and T 5 sites has been demonstrated through DFT calculation and solid-state nuclear magnetic resonance. A series of MCM-22 zeolites display the good catalytic stability and dimerization selectivity. The synergy of hexamethyleneimine and amphiphilic organosilane optimizates the mesopore and acidity of the sample effectively, which makes the selectivity and yield of dimerization product exceed 94.8 % and 85.0 % after 12 hours respectively. At the same time, the carbon deposition decreases from 3.38 % to 3.13 %. This work provides a theoretical basis for the growth mechanism and application in olefin oligomerization of MCM-22 zeolite.
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