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Titolo:
Synthesis, structural characterization, and catalytic properties of tungsten-exchanged H-ZSM5
Autore:
Ding, WP; Meitzner, GD; Marler, DO; Iglesia, E;
Indirizzi:
Lawrence Berkeley Lab, Div Mat Sci, Berkeley, CA 94720 USA Lawrence Berkeley Lab Berkeley CA USA 94720 t Sci, Berkeley, CA 94720 USA Univ Calif Berkeley, Dept Chem Engn, Berkeley, CA 94720 USA Univ Calif Berkeley Berkeley CA USA 94720 em Engn, Berkeley, CA 94720 USA Nanjing Univ, Dept Chem, Nanjing 210093, Peoples R China Nanjing Univ Nanjing Peoples R China 210093 jing 210093, Peoples R China
Titolo Testata:
JOURNAL OF PHYSICAL CHEMISTRY B
fascicolo: 18, volume: 105, anno: 2001,
pagine: 3928 - 3936
SICI:
1520-6106(20010510)105:18<3928:SSCACP>2.0.ZU;2-W
Fonte:
ISI
Lingua:
ENG
Soggetto:
METHANE DEHYDRO-AROMATIZATION; MO-BASED CATALYSTS; NONOXIDATIVE AROMATIZATION; ELECTRONIC-STRUCTURE; ZEOLITE CATALYSTS; BENZENE; CONVERSION; OXYGEN; DEHYDROGENATION; CARBIDES;
Tipo documento:
Article
Natura:
Periodico
Settore Disciplinare:
Physical, Chemical & Earth Sciences
Citazioni:
38
Recensione:
Indirizzi per estratti:
Indirizzo: Iglesia, E Lawrence Berkeley Lab, Div Mat Sci, Berkeley, CA 94720 USA Lawrence Berkeley Lab Berkeley CA USA 94720 eley, CA 94720 USA
Citazione:
W.P. Ding et al., "Synthesis, structural characterization, and catalytic properties of tungsten-exchanged H-ZSM5", J PHYS CH B, 105(18), 2001, pp. 3928-3936

Abstract

W-exchanged H-ZSM5 was prepared by sublimation of WCl6 at 673 K followed by hydrolysis of exchanged WClx species at 523 K. D-2 exchange with residualOH groups showed that each W initially replaced about two zeolitic protonsfor W/A1 ratios of 0.29 and 0.44, consistent with the formation of (WO2)(2) containing W6+ species bridging two cation exchange sites. As temperatures reached similar to 973 K during D-2-OH exchange, these species reduced to (WO2)(+) with the concurrent formation of one OD group. CH4 conversion turnover rates (per W) and C-2-C-12 selectivities are very similar to those observed on a Mo/H-ZSM5 sample with similar cation exchange level. As in thecase of Mo/H-ZSM5, WOx/H-ZSM5 precursors are initially inactive in CH4 reactions, but they activate during induction with the concurrent evolution ofCO, H2O, and an excess amount of H-2 The reduction and carburization processes occurring during CH4 reactions and the structure of the exchanged WOx precursors was probed using in situ X-ray absorption spectroscopy (XAS), XAS studies confirmed the isolated initial nature of the exchanged WOx precursors after hydrolysis and dehydration and the formation of WCx clusters similar to0.6 nm in diameter during CH4 reactions at 973 K, The structural andcatalytic resemblance between W- and Mo-exchanged H-ZSM5 is not unexpected, in view of chemical similarities between oxides or carbides of Mo and W. The synthesis of exchanged WOx precursors and their subsequent carburization during CH4 reactions, however, are more difficult than the corresponding processes for the MoOx counterparts. This may account for previous reports of lower CH4 reaction rates and aromatics selectivities on W/H-ZSM5 compared with those observed on Mo/H-ZSM5 and with those reported hen for rigorously exchanged W/H-ZSM5.

ASDD Area Sistemi Dipartimentali e Documentali, Università di Bologna, Catalogo delle riviste ed altri periodici
Documento generato il 13/07/20 alle ore 03:47:35