Upgrading Furfural to Bioderived Products: Selectivity of Aminosilica Catalysts in Aldol Chemistry

Aldol chemistry is a key carbon–carbon-bond-forming reaction that can be used to upgrade small molecules from biomass sources to essential products. The design of high-performance catalytic materials can improve the feasibility of these biomass upgrading reactions. Specifically, aminosilica catalysts have been highly studied for aldol chemistry, yet this research has mostly involved symmetric ketones, such as acetone. For biomass upgrading, it is also desirable to study these catalysts in reactions with nonsymmetric reactants. In this work, a basis is established for the use of aminosilica catalysts in furfural aldol chemistry by studying the effects of the amine type and ketone reactant structure on catalyst activity and selectivity. It is observed that the ketone length impacts the relative activity of each amine type. Using ketones with long alkyl chains, such as 2-undecanone, the 1° aminosilica catalyst has higher activity than the 2° aminosilica catalyst. The selectivity of the catalysts is evaluated, and it is found that 2° NMP-SBA-15 is more selective for linear and condensation products than 1° NMP-SBA-15. Accordingly, the data are consistent with steric interactions between the methyl group and nonsymmetric ketones affecting activity and selectivity, causing changes in the relative performance of 1° and 2° amines. It is shown that 1° NMP-SBA-15 has higher activity and selectivity for branched products compared to 2° NMP-SBA-15. Overall, the results highlight the importance of catalyst design in creating active and selective catalysts for important upgrading reactions such as aldol chemistry.