Selectivity Control in Photocatalytic Transfer Hydrogenation of Bio-based Aldehydes

Graphical Hydrodeoxygenation and reductive etherification of biomass-derived aldehydes were realized on the same Pd/TiO 2 photocatalyst via photocatalytic transfer hydrogenation using aliphatic alcohols as hydrogen donor, and the selectivity was easily switched by the substrate concentration. The development of selectivity control strategies based on external operational conditions without modification of catalyst is an attractive but challenging issue in photocatalysis. Herein we reported the substrate concentration-switched selectivity in photocatalytic transfer hydrogenation of biomass-derived aromatic aldehydes. With the same catalyst, hydrodeoxygenation was realized at low aldehyde concentration and reductive etherification was realized at high aldehyde concentration. Mechanistic studies revealed that the substrate concentration affected the electron density on catalyst, thus controlled the initial reduction of formyl group and types of intermediates. Competitive adsorption of these intermediates on the catalyst affected hydrogenolysis of C−O bonds in the later stage. This method is easy to handle, and achieved selective hydrogenation of diverse bio-based aldehydes to corresponding deoxygenated products and unsymmetric ether products as potential fuel additives under mild conditions. This work sheds light on the effect of substrate concentration on the selectivity in photocatalysis.