| Experimental and modelization approach in the study of acid-site energy distribution by base desorption. Part I: modified silica surfaces. | |
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MedLine Citation:
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PMID: 16851124 Owner: NLM Status: PubMed-not-MEDLINE |
Abstract/OtherAbstract:
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The acid properties of pure and modified silica surfaces were studied by 2-phenylethylamine (PEA) desorption in a thermogravimetric (TGA) apparatus, carrying out the experiments at different heating rates (5 < beta/(degrees C.min(-1)) < 30). The samples, containing about 13 wt % alumina, titania, and zirconia, were prepared by the sol-gel route from molecular precursors. The textural, structural, and surface properties of the materials were studied by complementary techniques (ICP, XRD, N(2) physisorption, SEM-EDS, and XPS). The chemical modification of the silica surface by enrichment with Al, Ti, or Zr, in amounts of about 90, 50, and 60% of that introduced in the preparation as determined by XPS, justified the increase of acidity of the modified silica surfaces compared with that of pure silica. The total number of strong acid sites was found to be in the order of SZ > SA > ST >> S. Two different kinetic approaches were applied to the thermogravimetric data to kinetically interpret the PEA desorption from the different types of acid sites. The classical differential Kissinger model was found to be inadequate in representing the very complex situation of the acid surfaces. A more complex model is proposed by simultaneously taking into account PEA desorption from the different acid sites by a set of parallel and independent desorption reactions following Arrhenius's kinetic law. The fraction of each type of acid site on each surface and the relevant activation parameters were optimized through a computational procedure. Very good fitting of the experimental-calculated desorption profiles corroborated the validity of the model. For each surface, the acid-site energy distribution is presented and discussed in relationship to the surface composition of the oxides. |
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Authors:
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Paolo Carniti; Antonella Gervasini; Simona Bennici |
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Publication Detail:
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Type: Journal Article |
Journal Detail:
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Title: The journal of physical chemistry. B Volume: 109 ISSN: 1520-6106 ISO Abbreviation: J Phys Chem B Publication Date: 2005 Feb |
Date Detail:
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Created Date: 2006-07-20 Completed Date: 2007-06-29 Revised Date: - |
Medline Journal Info:
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Nlm Unique ID: 101157530 Medline TA: J Phys Chem B Country: United States |
Other Details:
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Languages: eng Pagination: 1528-36 Citation Subset: - |
Affiliation:
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Dipartimento di Chimica Fisica ed Elettrochimica, Università degli Studi di Milano, via Camillo Golgi n. 19, I-20133 Milan, Italy. paolo.carniti@unimi.it |
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