Geometric effect promoted hydrotalcites catalysts towards aldol condensation reaction

In solid basic catalysis field, how to achieve optimized activity and desired stability through elaborate control over basic site properties remains a challenge. In this work, taking advantage of the structure memory effect of layered double hydroxides (LDHs), rehydrated Ca 4 Al 1- x Ga x -LDHs and Ca 4 Al 1- x In x -LDHs catalysts were prepared and applied in aldol condensation reaction that isobutyraldehyde (IBD) reacts with formaldehyde (FA) to obtain hydroxypivalaldehyde (HPA). Notably, the resulting re-Ca 4 Al 0.90 Ga 0.10 -LDHs exhibits an extraordinarily-high catalytic activity (HPA yield: 72%), which is to our best knowledge the highest level in this reaction. The weak Brönsted basic site, 7-coordinated Ca-OH group, which serves as an active site, catalyzes the condensation process and promotes the product desorption. Studies on structure-property correlations demonstrate that Ga as a structural promoter induces a moderate expansion of the laminate lattice, which results in a significant increase in the concentration of weak basic sites in re-Ca 4 Al 0.90 Ga 0.10 -LDHs, accounting for its high catalytic activity. This work illuminates that geometric structure of basic active sites can be tuned via introducing catalyst additive, which leads to a largely improved performance of hydrotalcite solid basic catalysts towards aldol condensation reaction. Ga as a structural promoter induces a moderate expansion of the laminate lattice, which results in a significant increase in the concentration of active sites in CaAlGa hydrotalcites, accounting for its high catalytic activity.