The
metal-catalyzed selective hydrogenation of biomass-derived
molecules is in great demand but is challenging due to the complex
reaction pathways. Herein, we report a persuasive example for achieving
selective hydrogenation of furfural over Pd catalysts by controllable
sorption of molecules in zeolite micropores. The key to this success
is fixation of Pd nanoparticles inside of silicalite-1 zeolite with
controllable wettability (Pd@S-1-OH) by functionalizing silanol groups
into the zeolite framework. In the hydrogenation of furfural as a
model reaction, the Pd@S-1-OH catalyst with appropriate hydrophilicity
exhibits extraordinary selectivity for the formation of furan, giving
furan selectivity as high as >99.9% with a complete conversion
of
furfural, outperforming the conventional Pd nanoparticles supported
on zeolite crystals (Pd/S-1) and S-1 zeolite fixed Pd catalysts without
an artificially functionalized silanol group (Pd@S-1). The extraordinary
performance of Pd@S-1-OH is reasonably attributed to the controllable
diffusion of molecules within the hydrophilic zeolite micropores,
which favors the adsorption of furfural and a series of byproducts
but promotes the desorption of furan. Very importantly, Pd@S-1-OH
is stable and gives the furan productivity of ∼583.3 g gPd–1 day–1 in a continuous
test.