Understanding the Role of Gallium as a Promoter of Magnesium Silicate Catalysts for the Conversion of Ethanol into Butadiene

In this study we explore the use of Ga as a new component in MgO-SiO2 catalysts for the Lebedev reaction (the one-pot conversion of ethanol to butadiene). Several characterisation techniques (XRD, temperature-programmed desorption of NH3, BET measurements, IR spectroscopy) and in situ spectroscopic studies (DRIFTS-MS) were performed with the aim to correlate the properties of the modified materials with the catalytic results. We concluded that the wet impregnation of Ga3+ on the MgO-SiO2 catalyst creates new Ga−O(H)−Si sites. These sites interact strongly with alcohol and not only facilitate its dehydrogenation to acetaldehyde and its transformation into the intermediate crotyl alcohol but also enhance the dehydration of the latter because of an improved acidity. However, an appropriate amount of gallium oxide is needed to avoid excessive acidity, which is conducive to an increased selectivity to ethylene.