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.