Doping Pd/SiO(2) with Na(+): changing the reductive etherification of C[double bond, length as m-dash]O to furan ring hydrogenation of furfural in ethanol

The production of biofuels and chemicals by hydrogenation of furfural has attracted much attention recently. Herein the effect of Na(+) doping on the catalytic performance of Pd/SiO(2) in hydrogenation and reductive-etherification of furfural in ethanol was systematically studied. Two Pd/SiO(2) catalysts with and without the modification by Na(+) were prepared by impregnation and calcination. Their catalytic properties were compared for the hydrogenation of furfural and furfural diethyl acetal under mild conditions. The silanol groups on Pd/SiO(2) catalysed the acetalization of furfural and alcohol and the resulted acetal underwent hydrogenolysis on Pd nanoparticles (NPs) with an average particle size of 8 nm, leading to a moderate yield (∼58%) of furfuryl ethyl ether. Doping Na(+) on Pd/SiO(2) led to the diminishing of silanol groups as well as strong interaction between Na(+) and Pd NPs. No acetalization occurred on Na(+) modified Pd/SiO(2) due to the exchange of H(+) of Si–OH with Na(+), thus the reductive etherification of C[double bond, length as m-dash]O group in furfural was completely inhibited. Meanwhile the hydrogenation of furan-ring over Na(+) coordinated Pd NPs could proceed with very high selectivity (>90%) forming tetrahydrofurfural in high yield. Kinetics study on the hydrogenation of furfural diethyl acetal over Pd/SiO(2) and Na(+) doped Pd/SiO(2) suggested that the Na(+) greatly impeded the hydrogenolysis of C–O–C bond of acetal, while the hydrogenation of the furan ring took place selectively.