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Titolo:
Structure sensitivity of supported ruthenium catalysts for ammonia synthesis
Autore:
Jacobsen, CJH; Dahl, S; Hansen, PL; Tornqvist, E; Jensen, L; Topsoe, H; Prip, DV; Moenshaug, PB; Chorkendorff, I;
Indirizzi:
Haldor Topsoe Res Labs, DK-2800 Lyngby, Denmark Haldor Topsoe Res Labs Lyngby Denmark DK-2800 s, DK-2800 Lyngby, Denmark Tech Univ Denmark, Inst Appl Chem, DK-2800 Lyngby, Denmark Tech Univ Denmark Lyngby Denmark DK-2800 l Chem, DK-2800 Lyngby, Denmark Tech Univ Denmark, Interdisciplinary Res Ctr Catalysis, ICAT, DK-2800 Lyngby, Denmark Tech Univ Denmark Lyngby Denmark DK-2800 , ICAT, DK-2800 Lyngby, Denmark
Titolo Testata:
JOURNAL OF MOLECULAR CATALYSIS A-CHEMICAL
fascicolo: 1-2, volume: 163, anno: 2000,
pagine: 19 - 26
SICI:
1381-1169(200012)163:1-2<19:SSOSRC>2.0.ZU;2-C
Fonte:
ISI
Lingua:
ENG
Soggetto:
IRON SURFACES; PROMOTER; NITROGEN; RU(0001); CARBON; N-2; DISSOCIATION; ACTIVATION; KINETICS; FE(111);
Keywords:
ruthenium; ammonia synthesis; structure sensitivity; B-5 sites;
Tipo documento:
Article
Natura:
Periodico
Settore Disciplinare:
Physical, Chemical & Earth Sciences
Citazioni:
39
Recensione:
Indirizzi per estratti:
Indirizzo: Jacobsen, CJH Haldor Topsoe Res Labs, Nymollevej 55, DK-2800 Lyngby, Denmark Haldor Topsoe Res Labs Nymollevej 55 Lyngby Denmark DK-2800
Citazione:
C.J.H. Jacobsen et al., "Structure sensitivity of supported ruthenium catalysts for ammonia synthesis", J MOL CAT A, 163(1-2), 2000, pp. 19-26

Abstract

The catalytic ammonia synthesis activities of four supported ruthenium catalysts are reported. It is seen that Ru/MgAl2O4 is more active than two similar Ru/C catalysts, which are significantly more active than Ru/Si3N4. Theactivity differences cannot be satisfactorily explained solely by the differences in dispersion. Recent results from single crystal studies and DFT calculations have shown that ammonia synthesis over ruthenium catalysts is avery structure sensitive reaction, more so than on iron catalysts. It is suggested that special Bs-type sites are primarily responsible for the catalytic activity of the present supported Ru catalysts. It is shown how the number of such Bs-type sites depends on the Ru crystal size for a given crystal morphology. We have found that the activity of the Ru/MgAl2O4 catalyst increases significantly during the initial part of a test run. This activityincrease is paralleled by the disappearance of crystals smaller than ca. 1.0nm due to sintering and a resulting formation of larger crystals. We conclude that there exists a lower limit to the desired crystal size of Ru in supported ammonia synthesis catalysts. This is in agreement with a low number of Bs-type sites expected for such crystal sizes. Furthermore, we suggestthat the support plays a decisive role in controlling the morphology of the Ru crystals and the resulting change in abundance of Bs-type sites is themain cause for the significant activity variations observed for Ru catalysts with different supports. Finally, the support may also influence the electronic and catalytic properties of neighboring Bs-type sites. (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 24/11/20 alle ore 23:57:53