Effect of One-Pot Rehydration Process on Surface Basicity and Catalytic Activity of MgyAl1-aREEaOx Catalyst for Aldol Condensation of Citral and Acetone
2016
Wang, Zheng | Lu, Guanzhong | Guo, Yun | Guo, Yanglong | Gong, Xue-Qing
The liquid phase synthesis of pseudoionones (PS) by the cross-aldol condensation of citral and acetone was investigated over MgAl mixed oxides containing rare earth elements (REE = Y, La, Eu), which were obtained from corresponding REE-modified hydrotalcite materials after calcination. The results showed that the unmodified and La(Eu)-modified MgAl mixed oxide catalysts showed relatively low activity, and Y-modified MgAl mixed oxides presented an unexpected high catalytic activity. PS selectivity of ∼85% and citral conversion of 100% were achieved at 60 °C for 3 h. On the basis of the characterizations of the structural, textural, and basic properties, it was found that Mg₃Al₁₋ₐYₐOₓ catalysts exhibited relatively well-developed small flake morphology with high surface area and pore volume, resulting in exposure of more basic sites on the catalyst surface. The formation of PS over Mg₃Al₁₋ₐYₐOₓ may be accompanied by gradual modification of the catalyst surface to form re-Mg₃Al₁₋ₐYₐOₓ through a rehydration process with produced water, which reconverts the O²– basic sites to OH– basic groups. Unlike La and Eu elements, the presence of Y could promote this “one-pot” or in situ rehydration process of MgAl mixed oxides during the aldol reaction. This Y-modified MgAl mixed oxides after a one-pot rehydration process with active Brønsted basic sites is responsible for the high activity in the cross-aldol condensation of citral and acetone.
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