NH2-SiO2-C3H7 with abundant surface groups exposure as the efficient catalyst for the Aldol condensation reaction

Abstract

The species and amount of the surface groups are closely related with the catalytic performance for a heterogeneous catalyst. High content of alkylamino (50 mol%) and n-propyl (15 mol%) were simultaneously introduced onto the surface of SiO2 nanospheres with a one step reverse-phase microemulsion method. Accompanying the formation of plenty of surface nano-bulges, a high ratio (86.5 %) of the silicon species were exposed on the surface of this novel material. Abundant of surface groups including Si-NH2 (5.5 mmol g−1), Si-C3H7 (1.7 mmol g−1), and Si-OH (6.1 mmol g−1) coexisted on the surface enabled this novel material to be a very efficient catalyst for the Aldol condensation reaction between benzaldehyde and n-heptanal. Higher content of alkylamino supplied more catalytic sites. Proper ratio of silanol-to-alkylamino (a little higher than 1) facilitated the adsorption of the substrate molecules and strengthened the cooperation between alkylamino and silanol. Surface hydrophobic modification with n-propyl further facilitated the adsorption of the substrate molecules at the presence of the byproduct of water. Conversion of 99 % was successfully obtained at a lower temperature (90 °C) and in a very short time of 25 min with the present material being used as the catalyst. In some other Aldol condensation reactions, the present catalyst NH2-SiO2-C3H7 also showed excellent catalytic performance.