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Oxidation of styrene over molybdenum-containing hydrotalcite catalysts

Mg0.6Al0.4(OH)2(MoO4)0.2.mH2O was prepared via coprecipitation method and characterized by XRD, BET, EDS techniques. The solid has a hydrotalcite-like structure and molybdate anions stayed in the interlayer regions between two brucite sheets. The synthesized material has been used as heterogeneous catalyst for the liquid oxidation of styrene with air. The oxidation reaction was carried out at atmospheric pressure in the temperature range of 60-110 oC. The presence of molybdate anions plays role of active site for the conversion of styrene into benzaldehyde and styrene epoxide with the selectivity of 97-99 %. | Vietnam Journal of Chemistry, International Edition, 54(4): 454-458, 2016 DOI: 10.15625/0866-7144.2016-00346 Oxidation of styrene over molybdenum-containing hydrotalcite catalysts Nguyen Tien Thao*, Dang Van Long Faculty of Chemistry, Vietnam National University, Hanoi Received 19 February 2016; Accepted for publication 12 August 2016 Abstract Mg0.6Al0.4(OH)2(MoO4)0.2.mH2O was prepared via coprecipitation method and characterized by XRD, BET, EDS techniques. The solid has a hydrotalcite-like structure and molybdate anions stayed in the interlayer regions between two brucite sheets. The synthesized material has been used as heterogeneous catalyst for the liquid oxidation of styrene with air. The oxidation reaction was carried out at atmospheric pressure in the temperature range of 60-110 oC. The presence of molybdate anions plays role of active site for the conversion of styrene into benzaldehyde and styrene epoxide with the selectivity of 97-99 %. Keywords. Benzaldehyde, epoxide, molybdate, LDH, intercalation. 1. INTRODUCTION The hydrotalcite-like compounds are generally described by the empirical formula (M1−x 2+ 3+ M x(OH)2)x+(Xz−)x/z·mH2O, where M2+ and M3+ are the metal cations, Xz− represents the anions (CO32−,SO42-, MoO42- ), and m is the number of interlayer water molecules [1]. Thus, they are well known as anionic clays with the structure similar to that of brucite-like Mg(OH)2 where an isomorphous substitution of Mg2+ by a trivalent element M3+ occurs. In details, each magnesium cation in the brucite is octahedrally surrounded by hydroxyls, resulting octahedron shared edges to form infinite sheets with no net charge. When Mg2+ ions are replaced by a trivalent ion, a positive charge is generated in the brucite sheet. The positive charge is compensated by anions (Xz-) in the interlayer while water molecules fulfill in the interlayer free spacings [1–4]. Anionic clays based on hydrotalcite likecompounds have been attractive because of the diversity of .