期刊
TOPICS IN CATALYSIS
卷 52, 期 9, 页码 1190-1202出版社
SPRINGER/PLENUM PUBLISHERS
DOI: 10.1007/s11244-009-9278-1
关键词
Desilication; Mesopores; MWW; Si-29 MAS-NMR; Toluene disproportionation and alkylation
资金
- EU FP6 INDENS [MRTNCT2004-005503]
- Grant Agency of the Czech Republic [203/08/0604]
- University of Oslo
Modification of HMCM-22 zeolite by alkaline treatment was investigated by various characterization techniques and in toluene disproportionation and alkylation with isopropyl alcohol. This 'desilication' process led for mild alkaline concentrations (similar to 0.10-0.20 M NaOH at 323 K for 45 min) to the partial destruction of the zeolite framework, but also to the formation of additional mesoporosity. Furthermore, the accessibility/availability of Lewis acid sites, investigated by d (3)-acetonitrile and pyridine adsorption using FTIR spectroscopy, increased for these mild alkaline treatments, while the Bronsted acidity decreased. Higher alkaline concentrations (up to 0.50 M NaOH) led to a too severe framework and pore destruction and a decrease of both the Lewis and Bronsted acid site concentration. Decomposition and deconvolution of Si-29 MAS-NMR spectra confirmed the Si extraction and partial framework destruction, since more Q(3) SiOH groups were formed at the expense of the Q(4) T-atoms in the framework. Furthermore, the T6 and T7 Si-atoms were preferentially extracted, which would indicate that an interconnection between the intralayer and the interlayer and/or outer surface is formed. The toluene conversion in its disproportionation reaction increased for the mildly treated sample, while the selectivity to xylene isomers (and cymene and n-propyltoluene isomers in the alkylation reaction with isopropyl alcohol) was similar to the thermodynamic equilibrium, suggesting that the reaction primarily occurs at outer surface cups of the HMCM-22 zeolite.
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