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Characterization of Pd/MgO Catalysts: Role of Organometallic Precursor-Surface Interactions (Articolo in rivista)

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Characterization of Pd/MgO Catalysts: Role of Organometallic Precursor-Surface Interactions (Articolo in rivista) (literal)

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Dal Santo V. 1, Sordelli L.1, Dossi C. 2,Recchia S. 2, Fonda E. 3, Vlaic G. 3, Psaro R. 1 (2001)
Characterization of Pd/MgO Catalysts: Role of Organometallic Precursor-Surface Interactions
in Journal of catalysis (Print)
(literal)

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Dal Santo V. 1, Sordelli L.1, Dossi C. 2,Recchia S. 2, Fonda E. 3, Vlaic G. 3, Psaro R. 1 (literal)

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L'articolo pone l'attenzione sull'importanza dell'approccio di chimica organometallica di superficie nella preparazione di nanoparticelle metalliche supportate. In questa pubblicazione viene inoltre mostrata l'importanza della caratterizzazione EXAFS per l'indagine strutturale di nanoparticelle supportate e la necessità di un approccio multitecnica (HRTEM, DRIFT-FTIR, TPR). La rivista, edita dal gruppo Elsevier, e' uno dei periodici piu' prestigiosi nel campo della catalisi (Impact Factor = 3.12 ; \"Top ten high-impact chemistry journal\" nel decennio 1992-2002 secondo ISI Essential Science Indicators). (literal)

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The aim of this work was the structural characterization of the surface chemistry of Pd(acac)2 on different magnesia surfaces. On MgO500 a strong chemisorption occurred, leading to dispersion at molecular level of the metallic complex. EXAFS confirms the model of surfacecomplex interaction via ligand only. In contrast, weak surfacecomplex interaction leads to the formation of islands of multilayers as observed for MgOAIR and SiO2 surfaces. The precursorsupport interaction strongly influences the final properties of the metal phase: a well-dispersed, strongly bound precursor, as occurs on MgO500, leads to a metal phase with similar properties; poorly interacting precursor molecules lead to large particles, as occurs on SiO2 and MgOAIR. We have demonstrated that the controlled reaction of organometallic compounds with surfaces of inorganic oxides is a necessary prerequisite to distribute the active phase in a highly dispersed form, and how this surface process is dependent on the nature of the adsorption state of the molecular precursor. It was also confirmed that small palladium particles in close contact with the basic sites of the support are the catalytic active species in the n-heptane dehydrocyclization. (literal)

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1. CNR-ISTM 2. Dipartimento di Scienze CC, FF, MM, Universita` degli Studi dell'Insubria, Como 3.Dipartimento di Scienze Chimiche, Università di Trieste and Elettra S.p.A, Trieste (literal)

Titolo

Characterization of Pd/MgO Catalysts: Role of Organometallic Precursor-Surface Interactions (literal)

Abstract

Pd(acac)2 was supported on a highly dehydroxylated and decarbonated magnesium oxide surface (MgO500), on an untreated MgO surface (MgOAIR), and on a silica. EXAFS and DRIFT data indicate that the organopalladium complex is adsorbed intact on all the surfaces, but its dispersion is dependent on the nature of the surface. On MgO500, dispersion at the molecular level occurs, in contrast to the formation of islands of multilayers on MgOAIR and silica. The final properties of the metal phase, formed by H2 treatment at 500°C, are dependent on precursor-surface interactions. HRTEM analysis shows a narrow distribution of the metal particles centered at 0.6 nm on MgO500, and a wide diameter distribution around 6.1 and 9.9 nm on MgOAIR and SiO2 respectively. In the n-heptane dehydrocyclization at 500°C, the highest selectivity is shown by Pd/MgO500 catalysts and it is consistent with a predominant fraction of very small particles in close contact with surface basic sites. (literal)

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