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Titolo:
Quantification of active sites for the determination of methanol oxidationturn-over frequencies using methanol chemisorption and in situ infrared techniques. 1. Supported metal oxide catalysts
Autore:
Burcham, LJ; Briand, LE; Wachs, IE;
Indirizzi:
Lehigh Univ, Zettlemoyer Ctr Surface Studies, Bethlehem, PA 18015 USA Lehigh Univ Bethlehem PA USA 18015 rface Studies, Bethlehem, PA 18015 USA Lehigh Univ, Dept Chem Engn, Bethlehem, PA 18015 USA Lehigh Univ Bethlehem PA USA 18015 ept Chem Engn, Bethlehem, PA 18015 USA Natl Univ La Plata, Ctr Invest & Desarrollo Proc Catalit, RA-1900 La Plata, Argentina Natl Univ La Plata La Plata Argentina RA-1900 A-1900 La Plata, Argentina
Titolo Testata:
LANGMUIR
fascicolo: 20, volume: 17, anno: 2001,
pagine: 6164 - 6174
SICI:
0743-7463(20011002)17:20<6164:QOASFT>2.0.ZU;2-V
Fonte:
ISI
Lingua:
ENG
Soggetto:
TEMPERATURE-PROGRAMMED DESORPTION; FOURIER SELF-DECONVOLUTION; VANADIUM-OXIDE; MOLECULAR-STRUCTURES; MOLYBDENUM TRIOXIDE; ALIPHATIC-ALCOHOLS; SURFACE-CHEMISTRY; FT-IR; ADSORPTION; TIO2;
Tipo documento:
Article
Natura:
Periodico
Settore Disciplinare:
Physical, Chemical & Earth Sciences
Citazioni:
74
Recensione:
Indirizzi per estratti:
Indirizzo: Wachs, IE Lehigh Univ, Zettlemoyer Ctr Surface Studies, Bethlehem, PA 18015 USA Lehigh Univ Bethlehem PA USA 18015 ies, Bethlehem, PA 18015 USA
Citazione:
L.J. Burcham et al., "Quantification of active sites for the determination of methanol oxidationturn-over frequencies using methanol chemisorption and in situ infrared techniques. 1. Supported metal oxide catalysts", LANGMUIR, 17(20), 2001, pp. 6164-6174

Abstract

Methanol oxidation over metal oxide catalysts is industrially important for the production of formaldehyde, but knowledge about the intrinsic catalysis taking place is often obscured by a lack of knowledge as to the number of active sites present on the catalyst surface. In the present study, the number of surface sites active in methanol oxidation has been determined over a wide range of supported metal oxide catalysts using quantitative methanol chemisorption and in-situ infrared titration techniques performed at an experimentally optimized temperature of 110 degreesC. It was found that a steric limitation of about 0.3 methoxylated surface species (e.g., strongly Lewis-bound CH3OHads, and dissociatively adsorbed -OCH3,ads, which are the reactive surface intermediates in methanol oxidation) exists per active deposited metal oxide metal atom across all supported metal oxides. Hence, theuse of methanol chemisorption for counting active surface sites is more realistic than other site-counting methods for the kinetic modeling of methanol oxidation, where during steady-state reaction the departure of the actual coverage of methoxylated surface intermediates from the maximum saturation surface coverage is of critical importance. Methanol oxidation turn-over frequencies (TOF = methanol molecules converted per second per active surface site) calculated using these new methanol chemisorption surface site densities increased by a factor of similar to3 the TOFs estimated in previous studies using the total number of deposited metal oxide metal atoms. Nevertheless, the support effect observed previously (TOFs for MoO3 and V2O5 supported on oxides of Zr similar to Ce > Ti > Al much greater than Si) remainsvirtually unchanged as a general trend in the present study and correlateswith the support cation electronegativity via bridging M-O -Support bonds. The methanol chemisorption technique may now be used with confidence to search for similar ligand effects in bulk metal oxides, where counting activesites has traditionally been very difficult (subject of part 2, Burcham, L. J.; Briand, L. E.; Wachs, 1. E. Langmuir 2001, 17, 6175, of the present two-paper series).

ASDD Area Sistemi Dipartimentali e Documentali, Università di Bologna, Catalogo delle riviste ed altri periodici
Documento generato il 05/04/20 alle ore 06:50:30