(569c) Clarifying the Effects of Varied Pore Diameter for Promotion of Amine-Silanol Interactions in the Nitroaldol Reaction

Heterogeneous primary amine catalysts functionalized on SBA-15 are advantageous for the nitroaldol reaction because of interactions between the basic active sites of the amines and acidic silanol groups on the surface of the silica support. It is established that the combined effects of these sites promote activity, and it is thus desirable to design materials with heightened acid-base cooperativity.

Previous work has noted heightened nitroaldol reaction activity with a moderate pore diameter of 4.5 nm. However, recent results showing the impact of micropores on catalytic activity have the potential to alter the perceived optimum pore size. It is now understood that activity may be strongly affected by microporosity and that this variable must be controlled in future work. Novel synthesis methods have enabled the construction of SBA-15-type supports with both negligible micropore volume and varied pore diameter, which provide a basis for more useful analysis.

Our results indicate a new optimal pore diameter of 9 nm for materials with limited micropore volume. However, activity varies across each support for reasons that are not fully understood. Further analysis will be necessary to diagnose the cause of these differences, which is currently unknown but may reveal important material properties once understood. Overall, this work aims to elucidate the effects of pore size and microporosity on the nitroaldol reaction through improved methods of both synthesis and analysis, more broadly impacting other reactions aided by acid-base cooperativity and the field of catalytic material design.