Investigating cooperative interactions for the nitroaldol reaction and condensation: Clarifying the impact of microporosity and pore size on catalytic activity of mesoporous aminosilica materials

Mesoporous aminosilica materials are active and selective heterogeneous catalysts for the nitroaldol reaction and have many physical and structural characteristics that can be tuned to desired effects. Previous work investigated the impact of tuning pore diameter on catalytic activity in the nitroaldol reaction and observed the highest activity with an MCM-41 support containing pores with an average diameter of 4.5 nm. Our understanding now suggests that these results may have been influenced by differences in microporosity between materials, undermining a comparison between non-microporous MCM-41 and SBA-15 that is known to have micropores. In this work, we introduce a line of SBA-15 supports with negligible microporosity and varied pore diameter. Compared to typical syntheses of SBA-15, these materials show increased catalytic activity as a result of decreased microporosity. Interestingly, a material with a pore diameter of 7.1 nm yields the highest activity among SBA-15-type materials with reduced micropore volume. This is similar to the catalytic activity recorded with an MCM-41 material, suggesting that perceived effects of pore diameter are less important than effects of microporosity. Since SBA-15 is more hydrothermally stable than MCM-41, the ability to use it as a suitable alternative for the nitroaldol reaction when microporosity is reduced is encouraging for future development.