A series of tetrabutylammonium (TBA) salts of the transition metal mono-substituted silicotungstates [SiW 11 M(H 2 O)O 39 ] nÀ , M = Co II , Fe III , Mn III , (SiW 11 M) were explored as homogeneous catalysts for the oxidation of geraniol and styrene with H 2 O 2 . The most active homogeneous catalysts (SiW 11 Co and SiW 11 Fe) were immobilized onto an amine-functionalized SBA-15 (aptesSBA-15) and the resulting composites were characterized using several techniques (FT-IR, FT-Raman, UV-Vis/DRS, elemental analysis, powder XRD, SEM and N 2 adsorption-desorption isotherms). The catalytic performance of the new composites SiW 11 Co@aptesSBA-15 and SiW 11 Fe@aptesSBA-15 was investigated under similar experimental conditions to those used for homogeneous counterparts. 2,3-Epoxygeraniol and benzaldehyde were the main products obtained from geraniol and styrene oxidation, respectively, for all the catalysts. SiW 11 Co and SiW 11 Co@aptesSBA-15 showed to be the most active catalysts for the oxidation of geraniol and styrene.The recyclability of the composite SiW 11 Co@aptesSBA-15 was investigated for three reaction cycles. The stability of the composites was confirmed using several techniques after catalytic cycles.

A comparative study of the electrochemical behaviour of several transition metal substituted polyoxotungstates in acetonitrile solution with tetra-n-butylammonium perchlorate as a supporting electrolyte is presented. Tetra-nbutylammonium salts of Keggin-type polyoxoanions, α- m− , the co-existence of spe-

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