Catalytic Upgrading of Biomass-Derived Methyl Ketones to Liquid Transportation Fuel Precursors by an Organocatalytic Approach

A highly efficient water‐tolerant, solid‐base catalyst for the self‐condensation of biomass‐derived methyl ketones to jet‐diesel fuel precursors was developed by grafting site‐isolated secondary amines on silica‐alumina supports. It is shown that apart from the nature and density of amine groups and the spatial separation of the acidic and basic sites, the acidity of the support material plays a critical role in defining the catalytic activity. It is also found that a combination of weakly acidic silanol/aluminol with secondary amine groups can mimic proline catalysts and are more effective in catalyzing the selective dimerization reaction than the combination of amines with organic acids. In situ FTIR measurements demonstrate that acidic groups activate methyl ketones through their carbonyl groups leading to a favorable CC bond formation step involving an enamine intermediate. DFT analysis of the reaction pathway confirms that CC bond formation is the rate‐limiting step. Dimerize it: A highly efficient, water‐tolerant, solid‐base organocatalyst for selective dimerization of biomass‐derived methyl ketones was developed by tethering amines on a Brønsted acidic silica–alumina support. C4–C15 methyl ketones can be catalytically upgraded to the dimer products with high selectivity. DFT analysis and experimental data suggest that CC bond formation is the rate‐determining step.