Efficient Synthesis of C4 Compound with Low Carbon Emission from Acetaldehyde: Aldol Condensation Catalyzed by Regulable Acidic–Alkaline Al/Mg Sites of CuMgAlO

Aldol condensation is an optimal method for carbon growth free from the thermo-cleavage technique of fossil resources with high carbon emissions. To further develop a catalyst with high activity and selectivity, a CuMgAl layered double oxide, named X/CuMgAlO, is successfully obtained after calcinating the MgAl hydrotalcite precursor doped with Cu2+. The resulting sample is applied as a catalyst in the self-condensation of acetaldehyde to crotonaldehyde. On the basis of the investigation of the reaction conditions, sample 15/CuMgAlO has presented to be the optimal catalyst in the aldol condensation of acetaldehyde to form crotonaldehyde with the conversion and selectivity of 92.3% and 80.4%, respectively. NH3-TPD, CO2-TPD, IGC, and Py-IR were applied to investigate the synergistic effect of the acidic and alkaline sites. It has been verified that a suitable acidity could be regulated through the addition of Cu species, and more Lewis acidic sites from Al sites can be formed due to the Jahn–Teller effect, the enhanced electronegativity of Cu, and the shattered lamellar layer in the calcinated CuMgAlO. Besides, the relatively mild acid could guarantee high selectivity to the target crotonaldehyde. Considering that aldol condensation could create a new carbon bond without the use of fossil resources, carbon emissions are significantly reduced in the field of fine-chemical synthesis industry.