The one-pot Prins–Friedel–Crafts reaction of aldehydes, a homoallylic alcohol and aromatics catalyzed by large-pore zeolites is an attractive environmentally friendly route towards valuable heterocyclic compounds co...The one-pot Prins–Friedel–Crafts reaction of aldehydes, a homoallylic alcohol and aromatics catalyzed by large-pore zeolites is an attractive environmentally friendly route towards valuable heterocyclic compounds containing a 4-aryltetrahydropyran moiety. Herein, the catalytic behavior of a set of MWW zeolite catalysts with tunable textural properties (e.g., three-dimensional MCM-22 and MCM-49, layered MCM-56 and MCM-36 materials) and variable chemical compositions was investigated in the Prins–Friedel–Crafts reaction involving either butyraldehyde or benzaldehyde and compared to that of a large pore beta zeolite. MWW zeolites differing in the concentration of acid sites 0.16–0.55 mmol g−1 and Brønsted-to-Lewis acid site ratios BAS/LAS=1.0–1.7 showed similar selectivities towards targeted 4-alkyltetrahydropyran-containing products (71–75% at 67% conversion of butyraldehyde), which exceed the value attained over a hierarchical beta zeolite (55–58% at the same conversion) with similar textural characteristics. While the conversion of relatively small butyraldehyde increased with the total concentration of acid sites in MWW catalysts, it was not affected by textural characteristics of MWW zeolites (98% and 100% over microporous MCM-22 and micro–mesoporous MCM-36, respectively). In contrast, not only a high concentration of acid sites but also their enhanced accessibility were the key factors, which provide the highest conversion (82%) and selectivity (50%) over micro–mesoporous MCM-36 using benzaldehyde as a substrate. Hierarchical MWW zeolite catalysts offered higher yields of targeted 4-aryltetrahydropyran in comparison with the conventional beta zeolites and previously reported hierarchical beta zeolites due to (1) the improved selectivity conditioned by lower strength of LAS and (2) maintaining high conversion due to the abundance of accessible acid sites on the well-exposed surface.展开更多
The assembly–disassembly–organisation–reassembly (ADOR) approach extends the synthesis of new zeolites. Understanding the disassembly and organisation mechanism is important to optimise the post-treatment process o...The assembly–disassembly–organisation–reassembly (ADOR) approach extends the synthesis of new zeolites. Understanding the disassembly and organisation mechanism is important to optimise the post-treatment process on germanosilicate zeolites. In situ synchrotron X-ray diffraction technique was applied to study the mechanism of these two steps in HCl vapour,which it is often unfeasible to capture using conventional ex situ characterisation. Three germanosilicate zeolites with different pore systems,i.e. UTL,UOV and IWR,were selected as models to compare the reaction behaviours. Three key steps,including fast hydrolysis of d4r units (ca. 1 min),further disassembly (ca. 3–5 min),and self-organisation after disassembly (ca. 2–3 min),were observed in the HCl acid vapour. An unusual lattice expansion of the intralayer was observed at the very beginning of the hydrolysis process in IWR,while the UTL and UOV showed continuous shrinkage. Owing to the diffusion differences related to the structural features,extra-large-pore UTL zeolite showed faster kinetics than the other two large-pore zeolites,although UTL zeolite has much larger crystals. These findings potentially guide further modification of the treatment parameters in the ADOR process to prepare new zeolites.展开更多
基金supporting this work through project 20-12099S(O.P.,J.L.,M.S,M.O.)and O.P.VVV“Excellent 2054 Research Teams”,project no.CZ.02.1.01/0.0/0.0/15_003/20550000417-CUCAM(M.O.,J.Č)support from the National Research Foundation of Ukraine through the project“New effective zeolite catalysts for environmentally friendly processes for the conversion of renewable raw materials into valuable organic compounds”(project number 2020.02/0335).
文摘The one-pot Prins–Friedel–Crafts reaction of aldehydes, a homoallylic alcohol and aromatics catalyzed by large-pore zeolites is an attractive environmentally friendly route towards valuable heterocyclic compounds containing a 4-aryltetrahydropyran moiety. Herein, the catalytic behavior of a set of MWW zeolite catalysts with tunable textural properties (e.g., three-dimensional MCM-22 and MCM-49, layered MCM-56 and MCM-36 materials) and variable chemical compositions was investigated in the Prins–Friedel–Crafts reaction involving either butyraldehyde or benzaldehyde and compared to that of a large pore beta zeolite. MWW zeolites differing in the concentration of acid sites 0.16–0.55 mmol g−1 and Brønsted-to-Lewis acid site ratios BAS/LAS=1.0–1.7 showed similar selectivities towards targeted 4-alkyltetrahydropyran-containing products (71–75% at 67% conversion of butyraldehyde), which exceed the value attained over a hierarchical beta zeolite (55–58% at the same conversion) with similar textural characteristics. While the conversion of relatively small butyraldehyde increased with the total concentration of acid sites in MWW catalysts, it was not affected by textural characteristics of MWW zeolites (98% and 100% over microporous MCM-22 and micro–mesoporous MCM-36, respectively). In contrast, not only a high concentration of acid sites but also their enhanced accessibility were the key factors, which provide the highest conversion (82%) and selectivity (50%) over micro–mesoporous MCM-36 using benzaldehyde as a substrate. Hierarchical MWW zeolite catalysts offered higher yields of targeted 4-aryltetrahydropyran in comparison with the conventional beta zeolites and previously reported hierarchical beta zeolites due to (1) the improved selectivity conditioned by lower strength of LAS and (2) maintaining high conversion due to the abundance of accessible acid sites on the well-exposed surface.
基金support from the BL14B station of the Shanghai Synchrotron Radiation Facility is sincerely acknowledged.This work was supported by the National Natural Science Foundation of China(no.12175235)supported by Charles University.M.O.acknowledges the Czech Science Foundation for supporting this work through project 20-12099S.
文摘The assembly–disassembly–organisation–reassembly (ADOR) approach extends the synthesis of new zeolites. Understanding the disassembly and organisation mechanism is important to optimise the post-treatment process on germanosilicate zeolites. In situ synchrotron X-ray diffraction technique was applied to study the mechanism of these two steps in HCl vapour,which it is often unfeasible to capture using conventional ex situ characterisation. Three germanosilicate zeolites with different pore systems,i.e. UTL,UOV and IWR,were selected as models to compare the reaction behaviours. Three key steps,including fast hydrolysis of d4r units (ca. 1 min),further disassembly (ca. 3–5 min),and self-organisation after disassembly (ca. 2–3 min),were observed in the HCl acid vapour. An unusual lattice expansion of the intralayer was observed at the very beginning of the hydrolysis process in IWR,while the UTL and UOV showed continuous shrinkage. Owing to the diffusion differences related to the structural features,extra-large-pore UTL zeolite showed faster kinetics than the other two large-pore zeolites,although UTL zeolite has much larger crystals. These findings potentially guide further modification of the treatment parameters in the ADOR process to prepare new zeolites.
