Bifunctional hybrid organosiliceous catalysts for aldol condensation – hydrogenation tandem reactions of furfural in continuous-flow reactor

A series of organic-inorganic hybrid bifunctional organosiliceous catalysts with accessible pendant amine groups as single basic sites (such as propylamine, diethylamine, pyrrolidine) and Pd nanoparticles was prepared from suitable synthesis processes. Pd/MCM-41 silica decorated with propylamine groups was highly active and selective for the single-reactor tandem aldol condensation/crotonization reaction between furfural with methyl isobutyl ketone, followed by hydrogenation, to access renewable biosolvent and biofuel precursors in the branched alkane range at mild temperature (80–100 ºC). The catalyst was characterized in detail using XRD, C and N elemental analysis, ICP-OES, TGA/DTA, HR-TEM, N₂ adsorption/desorption at 77 K, solid-state ¹³C and ²⁹Si MAS NMR and FT-IR spectroscopy CO₂ as acid probe. The catalyst was robust when operated in a dual fixed-bed reactor achieving steady 20 % furfural conversion for 12 h on stream with preferential formation of 1-(furan-2-yl)− 5-methylhexan-3-one.