Mixed Oxides of Hydrotalcites as Catalysts for Nopol Epoxidation
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Mixed oxides catalysts derived from Mg/Al hydrotalcite-type materials with molar ratios of 1, 2, 3 and 4 were synthesized, characterized and tested in nopol epoxidation. A combined oxidant of hydrogen peroxide and acetonitrile was used in the presence of acetone and water as solvents. Catalysts were characterized by X-ray diffraction (XRD), N2 adsorption, scanning electron microscopy (SEM), atomic absorption spectrophotometry (AAS), basicity by CO2-TPD, and infrared spectroscopy (FTIR). SEM analysis showed in all materials irregular non-homogeneous aggregates. Basicity of mixed oxides increased with Mg/Al ratio. The effect of temperature and basicity of the catalysts on the catalytic activity was analyzed. The best conversion and selectivity were obtained (60 °C, 2 h) over the most basic catalyst HT4C (mixed oxide Mg/Al = 4), with 99% conversion, epoxide selectivity of 38% and a selectivity of 36% to a campholenic aldehyde analogue compound, which duplicate the activity reported over a heterogeneous catalyst based on askanite–bentonite solid starting from nopol epoxide. In terms of TOF the most active catalyst, which also combines an acceptable conversion, was mixed oxide HT3C (mixed oxide Mg/Al = 3).
KeywordsHydrotalcite-type-materials Hydrogen peroxide Nopol epoxide Campholenic aldehyde analogue
The authors thank financial support from Universidad de Antioquia and Patrimonio Autónomo Fondo Nacional de Financiamiento para la Ciencia, la Tecnología y la Innovación, Francisco José de Caldas, Contrato RC-0572-2012 and the Project PRG2014-1091.
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