Qing Zhang,Yi Zhai,Fumin Wang,Xubin Zhang,Guojun Lv,Yongkui Liu,Mengyue Li,Mengyao Li
Hierarchical Fe-doped MFI/MCM-41 composites (Fe-HMZs) were one-pot hydrothermal synthesized by partial transformation strategy using conventional CTAB as a dual-functional template. The hierarchical Fe-doped MFI/MCM-41 composites possess ordered mesopores and crystallized MFI structure. The effect of addition amount of NaOH and CTAB as well as the type of the alkali source on the formation of hierarchical Fe-MFI/MCM-41 composites have been investigated in detail. In addition, the temperature-gradient treatment plays the vital roles in the formation of MFI and the possible formation mechanism has been proposed. The obtained hierarchical Fe-HMZ-40 sample exhibits outstanding catalytic performance for phenol hydroxylation and 48% of phenol conversion as well as 89% of dihydroxybenzene selectivity could be achieved, which are ascribed to the more accessible active sites endowed by the significant diffusion ability of ordered mesopores. Compared with Fe-MCM-41 sample, the hydrothermal stability is improved because of the presence of MFI structure.
Liu Xiaofang,Zeng Shangjing,Wang Runwei,Zhang Zongtao,Qiu Shilun
Hierarchical silicalite-1 zeolites were obtained from the direct conversion of a mixture of ground solid raw materials via a steam-assisted crystallization(SAC) method without involvement of any mesoscale template. Only a trace amount of water was necessary during the crystallization, implying that the amount of water can be dramatically reduced, which still offers easy separation and high yields. The simple procedure involved only grinding and heating, which not only saves resources and energy, but also significantly reduces the discharge of eco-friendly synthesis of zeolites for practical applications. Compared to conventional bulk silicalite-1, the nanosized hierarchical zeolites with MFI structure show enhanced removal capabilities for methylene blue owing to their hierarchical porosity.
Fu Tianyi,Ding He,Zhang Jingshuang,Bai Peng,Lyu Jiafei,Guo Xianghai
Abstract Hierarchical aluminosilicate zeolites with uniform mesoporosity were successfully synthesized by one-stage crystallization under constant temperature with a novel single-head quaternary ammonium salt ([C 18 H 37 –N + (CH 3 ) 2 –C 6 H 12 –N(CH 3 ) 2 ]Br − ) as mesoporogen and structure-directing agent (SDA). Through precisely controlling the molar ratio of Si/Al and synthetic time, the mesoporous 3D wormhole framework (MCM-48) and crystalline microporous MFI structure were simultaneously constructed, revealed by a series of in-depth characteristic studies. Combining the advantages of the significantly improved diffusion from the mesoporous MCM-48 and the strong framework acidity of the crystalline microporous MFI zeolite, the hierarchical aluminosilicate zeolites exhibited outstanding catalytic activity with good reusability towards bulky aldol condensation compared with the conventional meso- or microporous zeolites. Graphical abstract
Hierarchical aluminosilicate zeolites were simply synthesized by a temperature-gradient strategy using conventional CTAB as single structure directing agent. The as-synthesized zeolites were composed of an ordered two-dimensional hexagonal mesopores and crystallized MFI structure. Catalytic performance of the hierarchical aluminosilicate zeolites were explored by the Claisen-Schmidt condensation of bulky reactants (benzaldehyde and 2′-hydroxyacetophenone). The reaction results showed that the hierarchical zeolites exhibit outstanding catalytic performance with a conversion as high as 73%, which may be attributed to the combined advantage of framework acidity of zeolite and the significantly improved large molecule diffussion in mesoporosity. The higher hydrothermal stability and catalytic stability than those of MCM-41 samples were proved, which were ascribed to the presence of crystallized MFI structure.
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