Highly Dispersed MOF-derived Catalysts For Selective Hydrogenation Of Biomass-derived Carbonyl Compounds

Concerns have focused on selective conversion of renewable biomass to target chemicals and fuels due to sustainable development.For selective hydrogenation,although some objective oxygenated products were obtained,corrosive acids or high pressure was often used in these systems.Selective synthesis for biomass-derived chemicals under mild conditions has still been a huge challenge to date.Based on ZIF,a series of Co/NC catalysts are prepared by controlled calcination process of ZIF-67 and evaluated for selective hydrogenation of biomass-derived carbonyl compounds.Under the same reaction conditions,catalytic performances on the catalysts decrease gradually with calcination time prolonging:Co/NC-10>Co/NC-30>Co/NC-60.In order to promote the catalytic activity for biomass-derived carbonyl compounds under milder reaction conditions,Ru-Co/NC is obtained by highly dispersed Co nanoparticle reducing Ru precursor.At 80?,Ru-Co/NC presents ethyl levulinate conversion 100%,and gamma-valerolactone(GVL)selectivity,99.0%,and it enhances hydrogenation performance of various biomass-derived carbonyl compounds.The catalysts were further characterized by elemental analysis,ICP,SEM,N2-adsorption and desorption,XRD,CO2-TPD,Raman analysis,TEM and other characterization methods to determine the physicochemical properties of catalysts.Through a variety of characterization methods,the results show that high catalytic performance onCo/NC-10 can be attributed to the suitable Co particle size(0.37 nm)and rich pyridine nitrogen to bring the medium-strength base potential.With the addition of Ru in Co/NC-10,the Ru-Co alloy structure on Ru-Co/NC was formed and electron transferring from Co to Ru renders Co electropositive and Ru electronegative,facilitating adsorption and hydrogenation of C-=O in carbonyl compounds on the interface of Ru?--Co?+.Additionally,hydrogenation performances of ethyl levulinate and furfural remain stable on Ru-Co/NC after three cycles.Additionally,the catalysts of Co3ZnC-Co/NC were prepared by impregnating method and controlled calcination process.Under the same condition,the catalytic performance of selective hydrogenation of ethyl levulinate was in the following order:Co3ZnC-Co/NC(600??)>Co3ZnC-Co/NC(650 ?)>Co3ZnC-Co/NC(700 ?)>Co3ZnC-Co/NC(750 ?).The catalysts were characterized and the XRD result showed that with the annealing temperature rise constantly,the Co nanoparticle size of Co3ZnC-Co/NC catalysts were increased from 1.8 to 7.8 nm from Scherrer's formula and the phase composition converted form Co3ZnC to Co phases.Compared with Co/NC catalysts,the excellent performance of Co3ZnC-Co/NC-600 may attribute to the suitable Co particle size and the medium-strength base,which promotes the lactonization of intermediate product and improves the selectivity of gamma-valerolactone.Finally,the catalyst of Co/C was synthesized without N element by directly reduced Co-MOF-71 with aqueous NaBH4.The result showed that the conversion of selective hydrogenation of ethyl levulinate was highly up to 96.8%at 80 °C.However,Co/C presents low selectivity(57.2%)due to lack of base.Morevoer,gamma-valerolactone can further be converted to 1,4-pentanediol and 2-methyltetrahydrofuran at 150°C compared with Co3ZnC-Co/NC catalysts,which present gamma-valerolactone selectivity,99.0%,under the same condition.These results further confirmed that the base is very crucial to the selective hydrogenation of ethyl levulinate,it not only can promote the conversion of the intermediate product,but inhibit the further reaction of gamma-valerolactone.