Journal of Colloid and Interface Science 302 (2006) 214–229 www.elsevier.com/locate/jcis Preparation, structure and thermal stability of onium- and amino-functionalized silicas for the use as catalysts supports T. Kovalchuk a , H. Sfihi b,c,e , L. Kostenko a , V. Zaitsev a , J. Fraissard b,d,∗ a Chemistry Department, National Taras Chevchenko University, 64 Vladimirskaya str., Kiev 01033, Ukraine b Laboratoire de Physique Quantique, ESPCI, 10 Rue Vauquelin, 75231 Paris cedex 05, France c Département de Physique, UFR SMBH, Université Paris 13, 74 rue Marcel Cachin, 93012 Bobigny Cedex, France d Université Pierre et Marie Curie, 4 place Jussieu, 75005 Paris, France e UMR CNRS 7142, France Received 26 March 2006; accepted 4 June 2006 Available online 8 June 2006 Abstract We explored and compared several synthetic methods of grafting silica with strong (alkyltriphenylphosphonium, tetralkylammonium, propyl- pyridinium and dialkylimidazolium) and weak (γ -aminopropyl, γ -(N -imidazolyl)propyl) anion-exchanging groups starting with commercially available chloroalkyl- and γ -aminopropylsilanes. Structure of the intermediate and final materials was investigated by elemental analysis, titration, 13 C, 29 Si, 31 P MAS NMR, DRIFT, and TPD MS. The derivatives of alkyltriphenylphosphonium, propylpyridinium and dialkylimidazolium cation can be prepared with satisfactory quaternisation yields (ca. 30–100%) via the nucleophilic substitution of γ -chloropropyl groups either in the silane or in chloropropylsilica, resulting in bonded phases with moderate densities: 0.2–1.0 group nm −2 (onium salts) and 0.2–1.5 group nm −2 (amines). Parallel one-pot end-capping/hydrophobization can be done if a mixture of target silane with end-capping reagent or γ -chloropropylsilane is used. The grafted layer is highly stable at the level of Si–C bonds and decomposes at ca. 400 ◦ C, while the onium functions begin to decompose at ca. 250 ◦ C, lowering the thermal stability of materials. Thus, anion-exchanging silicas can be envisaged for the use as catalyst supports at moderate temperatures.  2006 Elsevier Inc. All rights reserved. Keywords: Functionalization; Grafting; Silica; End-capping; Ion-exchanger; 13 C NMR; 29 Si NMR; 31 P NMR; DRIFT 1. Introduction The modification of silica by organosilanes, affording ther- mally and hydrolytically stable Si–C bonds, is a widely used method for the preparation of recyclable solids for catalysis and chromatographic separations [1–3]. So far the immobi- lization of various organic bases, acids, ion exchanging and chelating groups has been achieved [2,4–9]. The course of our research in the field of supported catalysts required the prepa- ration of silica-based anion exchangers for which the desired silanes were not commercially available. Despite the numer- ous literatures devoted to this subject, achieving satisfactory loadings of anion-exchanging group is difficult. Herein we * Corresponding author. E-mail address: jfr@ccr.jussieu.fr (J. Fraissard). report the synthetic routes used for functionalization of sil- icas with strong and weak anion-exchanging groups achiev- ing densities of 0.2–1.0 group nm −2 (onium groups) and 0.2– 1.5 group nm −2 (γ -aminopropyl and γ -(N -imidazolyl)propyl groups). We study their structure and thermal properties in view of their application as supports for immobilization of het- eropolyoxometalate anions and the subsequent use in acid and oxidation catalysis [10]. Silanization with organosilanes, having Si–OEt [11] and Si–Cl [12] anchors is the most valuable synthetic route of func- tionalization. Their reaction with silanol groups constitutes the main modification pathway. The degree of surface hydration in- fluences the number of reactive silanol groups, and, hence, the loading of functional groups, as well as their structure (cova- lent grafting, Scheme 1A, and cross-linking, Scheme 1B). It is, therefore, crucial to control the activation of silica, depending 0021-9797/$ – see front matter  2006 Elsevier Inc. All rights reserved. doi:10.1016/j.jcis.2006.06.003