Selective Oxidation Of 5-Hydroxymethylfurfural With Novel Catalysts

Biomass is a clean and renewable source and can act as an important part of future sustainable energy.Currently,the process of biomass transformation mainly start with fermentation or chemical transformation to produce a series of platform chemicals,such as succinic acid,5-hydroxymethylfurfural?5-HMF?and so on.Then,value-added commercial chemicals or fuels can be obtained from platform chemicals via oxidation,hydrogenation or other reactions.Among them,2,5-furan dicarboxylic acid?FDCA?and 2,5-diformylfuran?DFF?,the products of 5-HMF oxidation,widely used in industrial applications,have arisen great attention in the field of biomass transformation.However,there are several problems need to resolve in the current 5-HMF oxidation process,such as introduction of strong base,high cost of noble catalysts and low utilization of non-noble catalysts.To address these problems,zinc hydroxycarbonate?ZOC?supported Au-Pd alloyed catalysts?Au-Pd/ZOC?,Mn-Co-O mixed oxide catalysts and M_nOx supported on modified titania?P25??M_nO_x/P25-600-5h?were synthesized.The phase composition,micro-structure and redox properties were characterized to investigate the relationship between structure and catalytic activity.The main results are listed as follows:The support ZOC was prepared via hydrothermal method and used for the synthesis of Au-Pd/ZOC catalysts by deposition-precipitation method.Over 99%yield of FDCA could be obtained under weak base conditions for 5-HMF oxidation.According to characterization results,Au-Pd alloys were formed and well dispersed on the support ZOC.Meanwhile,the syngnetic effect of Au and Pd could promote the catalytic activity.To investigate the effect of support on catalytic performance,various Au-Pd alloyed catalysts were synthesized using different supports.Surprisingly,the catalytic activities were in accordance with the pH value order of the corresponding support suspensions.In addition,the addition of weak base not only enhanced the yield of FDCA but also stabilized the support ZOC by preventing ZOC from the reaction with formed carboxylic acid intermediates/products,thus allowing Au-Pd/ZOC to be recycled for at least six times without significant loss of activity.In order to decrease the cost of catalysts,Mn-Co-O mixed oxides were synthesized via liquidphase mixing and further solid calcination,which could showed higher activity than M_nO₂ and Co₃O₄.The highest activity was obtained with Mn/Co molar ratio of 1 and calcination temperature at 400 ?,which could result in 42.6%conversion of 5-HMF and 98.0%selectivity to DFF in 2 h.These results indicated that the Mn-Co binary oxides could increase the Mn⁴⁺/Mn³⁺ atomic ratio and the exposed lattice oxygen content,thus accelerating HMF oxidation into DFF.Furthermore,the Mn-Co binary oxides could be used for five consecutive runs without significant loss of activity.To increase utilization of active phase M_nOx,the M_nO_x/P25-a-b catalysts were prepared via impregnation method using modified titania?P25?,where a and b are calcined temperature and time,respectively.The M_nO_x/P25-600-5h showed the best catalytic performance,resulting 33.2%conversion of 5-HMF and 97.0%selectivity to DFF in 2 h.According to characterization results,the high catalytic performance of M_nO_x/P25-600-5h could be due to the enhanced the oxygen mobility,which could result from the optimized surface anatase/rutile ratio of corresponding support P25.In addition,the decrease of acidity sites after calcination could restrict the side reactions of 5-HMF and increase the selectivity to DFF.