Glycerol Etherification with Light Alcohols Promoted by Supported H₃PW₁₂O₄₀

Abstract

Glycerol etherification with tert-butyl alcohol or ethanol was investigated using H₃PW₁₂O₄₀ supported on various supports (SiO₂, active carbon, ZrOH _X and NbOH _X ) and the sulfonated resins Amberlyst 35, as reference catalyst. Supported catalysts with optimised H₃PW₁₂O₄₀ dispersion were prepared via an incipient wetness impregnation of the vacuum-treated support with an aqueous H₃PW₁₂O solution under reduced pressure. The support coverage with the Keggin anions represents 0.4 monolayer. Microcalorimetry of NH₃ adsorption reveals significant influence of the nature of the support on the acid strength of the supported catalysts which can be correlated with the strength of the H₃PW₁₂O₄₀ interaction with the support, studied by DTA and XRD. It was shown that the glycerol etherification with ethanol is a more acidic-demanding reaction than glycerol etherification with tert-butyl alcohol. Indeed, while all the supported catalysts catalyse the glycerol etherification with tert-butyl alcohol at 120 °C such as Amberlyst 35, only H₃PW₁₂O₄₀ supported on carbon or silica promotes the glycerol etherification with ethanol at 200 °C according to their higher strength. Finally, H₃PW₁₂O₄₀ supported on carbon shows a water tolerance comparable to that of the sulfonated resins.