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.
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