A novel alkali- and nitrate-free impregnation route and subsequent calcination and hydrothermal treatment have been used for Mg�Al hydrotalcite (HT) coatings on alumina.1 The resulting Mg�HT/Al2O3 catalysts significantly outperform conventional2 and macroporous3 bulk hydrotalcites prepared via co-precipitation in the transesterification of C4�C18triglycerides for fatty acid methyl ester (FAME) production, with rate enhancements increasing with alkyl chain length. This work overcomes the mass transport limitations in biodiesel synthesis from viscous oils in bulk microporous hydrotalcites.XRD of the hydrotalcite-coated materials reveals a common set of reflections at 11.6�, 23.4�, 35�, 39.6�, 47.1�, and 61.1� characteristic of Mg�Al hydrotalcites, in good agreement with those observed for a conventional co-precipitated analogue (ConvHT). Surface areas of Mg�HT/Al2O3 are comparable to the alumina support for low Mg loadings, decreasing >9 wt% Mg but still remaining twice those of the Conv-HT. These HTs coatings possess significantly lower base site densities than the co-precipitated Conv-HT, but exhibit Turnover Frequencies (TOFs) for the transesterification of short and long chain TAGs far exceeding those achievable over conventional hydrotalcites, offering new possibilities for heterogeneously catalysed biodiesel production. This rate enhancement is attributed to improved accessibility of bulky triglycerides to active surface base sites over the higher area alumina support compared to conventional hydrotalcites (wherein many active sites are confined within the micropores). We have developed a simple, low cost route to depositing crystalline hydrotalcite coatings over high area alumina from benign precursors that affords highly active, reusable solid base catalysts for FAME production under mild conditions3.References [1] J.J. Creasey, A. Chieregato, J.C. Manayil, C.M.A. Parlett, K. Wilson, A.F. Lee, Catal. Sci. Technol. 2014  , 4, 861-870[2] F. Cavani, F. Trifiro, A. Vaccari, Catal. Today 1991  , 11, 73�291.[3] J.J. Woodford, J.P. Dacquin, K. Wilson, A.F. Lee, Energy Environ. Sci. 2012  , 5, 145�6150.

Alkali- and nitrate-free synthesis of highly active Mg-Al hydrotalcite-coated alumina for FAME production

248th National Meeting (2014)

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