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Titolo:
In situ MAS NMR spectroscopy of surface compounds formed from methanol andfrom a toluene/methanol mixture on basic zeolite X
Autore:
Hunger, M; Schenk, U; Seiler, M; Weitkamp, J;
Indirizzi:
Univ Stuttgart, Inst Chem Technol, D-70550 Stuttgart, Germany Univ Stuttgart Stuttgart Germany D-70550 nol, D-70550 Stuttgart, Germany
Titolo Testata:
JOURNAL OF MOLECULAR CATALYSIS A-CHEMICAL
fascicolo: 1-2, volume: 156, anno: 2000,
pagine: 153 - 161
SICI:
1381-1169(20000520)156:1-2<153:ISMNSO>2.0.ZU;2-I
Fonte:
ISI
Lingua:
ENG
Soggetto:
SIDE-CHAIN ALKYLATION; CATION-EXCHANGED ZEOLITES; ALKALI-MODIFIED ZEOLITES; CONTINUOUS-FLOW CONDITIONS; TOLUENE; CATALYSTS; FAUJASITE; ADSORPTION; CONVERSION; FRAMEWORK;
Keywords:
side-chain alkylation of toluene; formate species; basic zeolites; in situ MAS NMR spectroscopy; flow conditions;
Tipo documento:
Article
Natura:
Periodico
Settore Disciplinare:
Physical, Chemical & Earth Sciences
Citazioni:
33
Recensione:
Indirizzi per estratti:
Indirizzo: Hunger, M Univ Stuttgart, Inst Chem Technol, Pfaffenwaldring 55, D-70550 Stuttgart, Germany Univ Stuttgart Pfaffenwaldring 55 Stuttgart Germany D-70550 any
Citazione:
M. Hunger et al., "In situ MAS NMR spectroscopy of surface compounds formed from methanol andfrom a toluene/methanol mixture on basic zeolite X", J MOL CAT A, 156(1-2), 2000, pp. 153-161

Abstract

The conversion of methanol and a toluene/methanol mixture on a basic form of zeolite X has been investigated by in situ MAS NMR spectroscopy, both under batch and flow conditions at temperatures between 573 K and 723 K. The zeolite CsNaX/24CsOH used as basic catalyst was prepared by cesium ion exchange and subsequent impregnation with cesium hydroxide followed by calcination. By C-13 MAS NMR spectroscopy, the formation of surface compounds that caused signals at 166 and 171 ppm was observed. The compound that gave riseto the signal at 166 ppm was formed by conversion of methanol on zeolite CsNaX/24CsOH at 573 K. Upon purging the catalyst with dry nitrogen at temperatures from 623 K to 723 K, the compound, at 166 ppm, was transformed into the compound at 171 ppm. This process could be reversed by addition of methanol at 573 K. Based on a comparison between the MAS and CP/MAS spectra of the compounds at 166 and 171 ppm, and on literature data, the compound at 166 ppm was assigned to formate species. These formate species are formed bydehydrogenation of methanol to formaldehyde and subsequent reaction with the zeolite framework. The main content of the compound at 171 ppm, occurring as MAS spinning sideband pattern with a chemical shift anisotropy of Delta sigma = -40 +/- 2 ppm and an asymmetry parameter of eta = 0.8 +/- 0.1, isdue to carbonate species. In situ C-13 MAS NMR studies of the conversion of toluene/methanol mixtures on zeolite CsNaX/24CsOH indicated that the above-mentioned formate species could play an active role as alkylating agent in the side-chain alkylation of toluene. (C) 2000 Elsevier Science B.V. All rights reserved.

ASDD Area Sistemi Dipartimentali e Documentali, Università di Bologna, Catalogo delle riviste ed altri periodici
Documento generato il 01/12/20 alle ore 10:59:55