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Design of Heterogeneous Catalysts via Multiple Active Site Positioning in Organic−Inorganic Hybrid Materials

Dufaud, Véronique and Davis, Mark E. (2003) Design of Heterogeneous Catalysts via Multiple Active Site Positioning in Organic−Inorganic Hybrid Materials. Journal of the American Chemical Society, 125 (31). pp. 9403-9413. ISSN 0002-7863. https://resolver.caltech.edu/CaltechAUTHORS:20170419-115603178

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Abstract

Catalytic materials bearing multiple sulfonic acid functional groups and positioned at varying distances from one another on the surface of mesoporous solids are prepared to explore the effects that the spatial arrangement of active sites have on catalytic activity and selectivity. A series of organosiloxane precursors containing either disulfide or sulfonate ester functionalities (synthons of the eventual sulfonic acid groups) are synthesized. From these molecular precursors, a variety of organic−inorganic hybrid, mesostructured SBA-15 silica materials are prepared using a postsynthetic grafting procedure that leads to disulfide and sulfonate ester modified silicas:  [Si]CH_2CH_2CH_2SS-pyridyl, 2·SBA, [Si]CH_2CH_2CH_2SSCH_2CH_2CH_2[Si], 3·SBA, [Si]CH_2CH_2(C_6H_4)(SO_2)OCH_2CH_3, 4·SBA, and [Si]CH_2CH_2(C_6H_4)(SO_2)OC_6H_4O(SO_2)(C_6H_4)CH_2CH_2[Si], 6·SBA ([Si] = (⋮SiO)_x(RO)_(3-x)Si, where x = 1, 2). By subsequent chemical derivatization of the grafted species, thiol and sulfonic acid modified silicas are obtained. The materials are characterized by a variety of spectroscopic (^(13)C and ^(29)Si CP MAS NMR, X-ray diffraction) and quantitative (TGA/DTA, elemental analysis, acid capacity titration) techniques. In all cases, the organic fragment of the precursor molecule is grafted onto the solid without measurable decomposition, and the precursors are, in general, attached to the surface of the mesoporous oxide by multiple siloxane bridges. The disulfide species 2·SBA and 3·SBA are reduced to the corresponding thiols 7·SBA and 8·SBA, respectively, and 4·SBA and 6·SBA are transformed to the aryl sulfonic acids 11·SBA and 12·SBA, respectively. 7·SBA and 8·SBA differ only in terms of the level of control of the spatial arrangement of the thiol groups. Both 7·SBA and 8·SBA are further modified by oxidation with hydrogen peroxide to produce the alkyl sulfonic acid modified materials 9·SBA and 10·SBA, respectively. The performances of the sulfonic acid containing SBA-15 silica materials (with the exception of 12·SBA) are tested as catalysts for the condensation reaction of phenol and acetone to bisphenol A. The alkyl sulfonic acid modified material 10·SBA derived from the cleavage and oxidation of the dipropyl disulfide modified material 3·SBA is more active than not only its monosite analogue 9·SBA, but also the presumably stronger acid aryl sulfonic acid material 11·SBA. It appears that a cooperative effect between two proximal functional groups may be operating in this reaction.


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http://dx.doi.org/10.1021/ja034594sDOIArticle
http://pubs.acs.org/doi/abs/10.1021/ja034594sPublisherArticle
http://pubs.acs.org/doi/suppl/10.1021/ja034594sPublisherSupporting Information
Additional Information:© 2003 American Chemical Society. Received 10 February 2003. Published online 11 July 2003. Published in print 1 August 2003. V.D. acknowledges the Centre National de la Recherche Scientifique for a sabbatical leave in the laboratory of Professor Davis at Caltech and the NATO Division Affairs for a fellowship. We thank Dr. Chris Dillon and Helen Chuang for assistance with the catalytic experiments and Drs. Gerald P. Niccolai and Andrea P. Wight for fruitful discussions.
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Funding AgencyGrant Number
North Atlantic Treaty Organization (NATO)UNSPECIFIED
Centre National de la Recherche Scientifique (CNRS)UNSPECIFIED
Issue or Number:31
Record Number:CaltechAUTHORS:20170419-115603178
Persistent URL:https://resolver.caltech.edu/CaltechAUTHORS:20170419-115603178
Official Citation:Design of Heterogeneous Catalysts via Multiple Active Site Positioning in Organic−Inorganic Hybrid Materials Véronique Dufaud*,† and and Mark E. Davis* Journal of the American Chemical Society 2003 125 (31), 9403-9413 DOI: 10.1021/ja034594s
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:76687
Collection:CaltechAUTHORS
Deposited By: Ruth Sustaita
Deposited On:19 Apr 2017 21:42
Last Modified:03 Oct 2019 17:04

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