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Titolo:
COMPUTER-SIMULATION OF ZEOLITE STRUCTURE AND REACTIVITY USING EMBEDDED-CLUSTER METHODS
Autore:
SHERWOOD P; DEVRIES AH; COLLINS SJ; GREATBANKS SP; BURTON NA; VINCENT MA; HILLIER IH;
Indirizzi:
CCLRC DARESBURY LAB WARRINGTON WA4 4AD CHESHIRE ENGLAND UNIV MANCHESTER,DEPT CHEM MANCHESTER M13 9PL LANCS ENGLAND
Titolo Testata:
Faraday discussions
fascicolo: 106, , anno: 1997,
pagine: 79 - 92
SICI:
1359-6640(1997):106<79:COZSAR>2.0.ZU;2-V
Fonte:
ISI
Lingua:
ENG
Soggetto:
AB-INITIO CALCULATIONS; BRONSTED ACIDIC SITES; HYDROXYL-GROUPS; WATER-ADSORPTION; CHEMICAL-SHIFT; FORCE-FIELDS; BROAD-LINE; CATALYSTS; COMPLEXES; SILICA;
Tipo documento:
Article
Natura:
Periodico
Citazioni:
48
Recensione:
Indirizzi per estratti:
Citazione:
P. Sherwood et al., "COMPUTER-SIMULATION OF ZEOLITE STRUCTURE AND REACTIVITY USING EMBEDDED-CLUSTER METHODS", Faraday discussions, (106), 1997, pp. 79-92

Abstract

The use of bare cluster models to understand the nature of zeolite-substrate interactions may be improved to take account of the environment of the Bronsted acid site. We consider two models for introducing the electrostatic effects of the zeolite lattice. The first involves generating a specialised correction potential by fitting a non-periodic array of ca. 60 point charges to the difference between the bare cluster and periodic potentials. The second starts by fitting a periodic array of atomic charges to the potential of the infinite lattice and thenbuilds up a classical cluster of ca. 2000 atoms into which the QM cluster is embedded. Such embedded cluster calculations, employing a T3 cluster, with electron correlation at the density functional theory level, are described, to model the interaction of water at a Bronsted acid site. Structures of the water-zeolite complex, and associated vibrational frequencies and H-1 NMR shifts are calculated and compared with calculations of bare clusters of varying size and with experimental data. We then describe a mixed quantum mechanical-molecular mechanical (QM-MM) model derived by combining charges from the second model with astandard aluminosilicate force held. We report preliminary results onthe effect of embedding on the energetics of a prototypical hydrocarbon cracking reaction; the methyl-shift reaction of a propenium ion coordinated to the acid site.

ASDD Area Sistemi Dipartimentali e Documentali, Università di Bologna, Catalogo delle riviste ed altri periodici
Documento generato il 27/11/20 alle ore 16:12:57