Abstract
Mixed metal oxides are promising heterogeneous catalysts for biofuel production from lipids via alcoholysis, however, the impact of solid acidity and/or basicity on reactivity is comparatively poorly understood. Two systematically related families of MgO–ZrO2 mixed oxide catalysts were therefore prepared by different synthetic routes to elucidate the impact of surface acid-base properties on catalytic performance in the transesterification of tributyrin with methanol. The resulting materials were characterized by TGA-MS, ICP-OES, N2 porosimetry, XRD, TEM, XPS, DRIFTS, and CO2-temperature-programmed desorption (TPD). MgO–ZrO2 catalysts prepared by both non-aqueous impregnation and citric acid-mediated sol–gel routes exhibit excellent activity and stability. The citrate routes favor highly dispersed MgO and concomitant Lewis acid-base pair formation at the interface with zirconia. However, for both the citrate and impregnation routes, tributyrin transesterification occurs over a common, strongly basic MgO active site.
Highlights
Mixed metal oxides are of significant academic and industrial interest due to their tunable acid-base and redox properties
Thermal gravimetric differential thermal waswas explored by thermal analysis prior to calcination
The 14.3MZ–CT catalyst achieved 50% tributyrin conversion and ~40% selectivity to methyl butyrate, mirroring the performance of the lower loading 8.7MZ–CT sample, and we suggest that irrespective of initial MgO loading, citrate prepared catalysts converge to a common steady state
Summary
Mixed metal oxides are of significant academic and industrial interest due to their tunable acid-base and redox properties. Efforts to improve the base strength of ZrO2 have focused on its modification by alkaline earth metals such as calcium [6,7,8] and magnesium [5,9,10,11,12,13,14]. One application where alkaline earth metal oxides have shown much recent promise is the production of fatty acid methyl esters [17] (colloquially termed biodiesel) by the transesterification. Real bio-oils typically contain a wide, and ill-defined distributions free fatty acid content. Mg–Zr mixed oxides tributyrin transesterification with methanol under mild properties of of. Mg–Zr mixed oxides for for tributyrin transesterification with methanol under mild conditions. Mg–Zr mixed oxides, containing similar contents, were prepared conditions. Two families of Mg–Zr mixed oxides, containing similar MgO contents, were prepared via via non-aqueous impregnation or citrate-mediated processing.
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