Conversion of Ethanol and Acetaldehyde to Butadiene over MgO–SiO2 Catalysts: Effect of Reaction Parameters and Interaction between MgO and SiO2 on Catalytic Performance

For the effect of structural features on the catalytic performance of the conversion of ethanol and acetaldehyde to butadiene to be investigated, a series of MgO–SiO2 catalysts with different structural properties were synthesized by tuning the calcination temperature, investigated, and characterized. The best butadiene selectivity of 80.7% appears for the MgO–SiO2 catalyst calcined at 500 °C using a mixture of acetaldehyde/ethanol/water (22.5:67.5:10 wt %) as feed. Addition of the appropriate amount of water (10 wt %) improved butadiene selectivity by inhibiting the formation of 1-butanol and C6 compounds. Results from XRD, FT-IR, and 29Si MAS NMR indicate the generation of a significant amount of amorphous magnesium silicates along with few crystalline magnesium silicates for the catalyst calcined at 500 °C. XPS results indicate that it contains the lowest binding energies of both Si–O and Mg–O from Si–O–Mg bonds. For the catalysts calcined at low temperature (350 and 400 °C), more 1-butanol and C6 compounds formed, which are considered to be related to residual Mg(NO3)2. Additionally, more ethylene, diethyl ether, and butylene isomers were produced over the MgO–SiO2 catalyst calcined at 700 °C with the formation of forsterite Mg2SiO4. Further results from Fourier transform infrared spectroscopy after pyridine adsorption and CO2 temperature-programmed desorption show that the high catalytic performance is related to the presence of Lewis acidic sites and an intermediate number of basic sites.