Investigation of pore-size effects on base catalysis using amino-functionalized monodispersed mesoporous silica spheres as a model catalyst

The effects of pore size on base catalysis have been studied using amino-functionalized monodispersed mesoporous silica spheres (NH2-MMSS). By changing the surfactant that is used for the template and also the synthetic conditions, NH2-MMSS with similar particle diameters (560–600 nm) and different pore sizes (0–2.66 nm) were successfully prepared. Because the NH2-MMSS that were obtained had the same shapes, particle diameters and mesopore alignments, any differences in catalytic activity could be substantially attributed to differences in their pore sizes. We employed the nitroaldol condensation between benzaldehyde derivatives and nitromethane as a base catalysis reaction. It was found for the first time that the reaction mostly proceeds inside the mesopores (the effectiveness factor: 0.63) and that the optimum pore size for the NH2-MMSS was affected by changing the type and number of the substituent groups on the reactants. In addition, NH2-MMSS was found to be an excellent catalyst due to the radial alignment of the mesopores compared to the other types of mesoporous silica.