Polyoxometalates were grafted covalently on SBA-15 by a two-step procedure. The dehydroxylated mesoporous silica was first modified by reaction with methyltrichlorosilane in presence of triethylamine. The resulting solid was fully characterized and contained a mixture of mono- and digrafted species . These surface Si–Cl bonds can react with lacunary polyoxometalates as in solution, yielding to a ≡Si–O–POM linkage. However, solid state MAS NMR shows that only the digrafted species react with the polyoxometalate. This new grafting method opens the way to the synthesis of a new class of catalysts which could operate in solution without leaching. 1. Introduction Polyoxometalates (POMs) form a class of inorganic compounds made of early-transition metals in their highest oxidation states [1]. POM-based materials are of increasing interest in many application fields ranging from medicine [2] to catalysis [3] and electronics [4] owing to their unique, versatile, and tuneable properties. POMs have received a particularly extensive attention in catalysis because of their acid-base and redox properties coming from their chemical composition. However, having recourse to a matrice is absolutely necessary to prepare POMs-based materials in order to enhance the availability of active sites. For this purpose, two main strategies are described in the literature [5, 6]: (i) a direct synthesis or one-pot synthesis involving the incorporation of POM units in a matrice which is carried out in situ using the sol-gel technique; (ii) a postsynthetic procedure, involving a multistep strategy in contrast with the previous one, which is usually performed by impregnation technique. The second approach is widely used due to its easy implementation but suffers from several drawbacks including the difficulty to achieve high POMs loadings without significant decrease in surface area and ordering, the loss of initial high dispersity of supported POM units via leaching or the loss of homogeneity due to minor changes in the structure. All these drawbacks lead to reduce both activity and stability of immobilized POMs. In a previous article, the concepts and strategy of surface organometallic chemistry (SOMC) were used to circumvent these problems associated with a conventional impregnation technique [7]. Thus the interactions between POM units and the silica support were carefully controlled using anhydrous POMs and partially dehydroxylated silica to afford a POMs-based material with well-defined surface species including one species covalently linked to the silica support. Otherwise, the
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