On the Impact of the Preparation Method on the Surface Basicity of Mg–Zr Mixed Oxide Catalysts for Tributyrin Transesterification

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.

Keywords

• solid base
• MgO
• transesterification
• mixed oxide
• biodiesel