Conversion of ethanol to butadiene over mesoporous In2O3-promoted MgO-SiO2 catalysts

Mesoporous MgO-SiO2 mixed oxide catalysts were prepared for the conversion of ethanol to 1,3-butadiene. Mesoporosity was obtained by using SBA-15 material as support for magnesia or by applying one-pot synthesis method wherein magnesia precursor, such as, magnesium methoxide or ethoxide, was admixed to the synthesis gel of the SBA-15 material. The SBA-15 support was wet-impregnated by Mg(NO3)(2) solution or wet-kneaded with Mg(OH)(2) precipitate. The synthesized samples were mesoporous, however, the alkoxide in the synthesis gel hindered the formation of regular SBA-15 structure. In wet-kneaded and one-pot-synthesized samples the presence of Mg-O-Si bonds was confirmed by X-ray diffractometry. The acid-base properties of the preparations were characterized by the room-temperature adsorption capacity for CO2 and NH3. Formation of Mg-O-Si bonds were shown to be responsible for the increased acidity/basicity of the samples. The best catalysts were the wet-kneaded sample and the sample synthesized using methoxide as magnesium source. Over these catalysts the butadiene yield reached 15 % at 400-425 degrees C. To enhance the ethanol-to-butadiene activity the mixed oxides were promoted by In2O3. Additive In2O3 significantly improved dehydrogenation activity generating more acetaldehyde, and suppressed dehydration activity giving less ethylene and diethyl ether. Butadiene yields above 40% were achieved.