Selective Oxidation Of 2,5-furandimethanol To 2,5-furandicarboxylic Acid With Supported Gold Catalysts

Biomass is an extremely abundant renewable carbon resource.As a bio-based diacid with a rigid ring,2,5-furandicarboxylic acid is similar to petroleum-based diacid terephthalic acid in structure.Its copolyester with ethylene glycol is comparable to PET in thermal and mechanical properties,but some properties such as gas barrier and biodegradability are better than PET.At present,a major factor hindering the development of furan-based polyesters is the high cost of 2,5-furandicarboxylic acid（FDCA）monomers.The scientific and industrial circles currently focus on the low-cost preparation of 2,5-furandicarboxylic acid from the 5-hydroxymethylfurfural.However,after decades of research,the price of 2,5-furandicarboxylic acid is still ten times or even dozens of times the price of terephthalic acid.Our group has developed a synthetic route for the preparation of 2,5-furanodimethanol from cheap biomass-derived chemical furfural in the early stage.On this basis,this paper developed an efficient catalytic system for the oxidation of 2,5-furanodimethanol to 2,5-furandicarboxylic acid by supported metal catalysts.The research results are as follows:We developed an Au/CeO₂-rod catalyst rich in oxygen vacancies to achieve efficient oxidation of 2,5-furandimethanol to 2,5-furandicarboxylic acid in 92%yield.The reaction conditions were 80℃ and 2MPaO₂ with 4 equivalent of Na₂CO₃ for 6 h.This process has mild conditions and high catalytic efficiency.It is a new green and atom economic method for the preparation of 2,5-furandicarboxylic acid with oxygen as the oxidant.Results show that the carrier has a significant effect on the oxidation of2,5-furandimethanol,and CeO₂ rich in oxygen vacancies has been proved to be the best carrier for loading gold nanoparticles to catalyze the oxidation of 2,5-furandimethanol.The catalytic activity of Au/CeO₂-rod prepared by the hydrothermal method was significantly higher than that of cuboid and octahedral ceria.The high activity of Au/CeO₂-rod can be attributed to the growth of the CeO₂-rod support along a specific crystal plane,exposing more highly active（100）crystal planes,making the metal-support interaction between Au nanoparticles and the support stronger,forming more oxidized Au species and oxygen vacancies,promoting the substrate adsorption and oxygen activation process,and finally greatly improving the catalytic activity.In addition,Au/CeO₂-rod has a large specific surface area,which is conducive to better dispersion of gold nanoparticles.The oxidation pathway of 2,5-furandimethanol on Au/CeO₂ catalyst is:BHMF→HMF→HMFCA→FFCA→FDCA,and the rate-determining step is HMFCA to FFCA.In the study of the oxidation process,the alkaline environment with appropriate strength greatly promoted the oxidation process,which can be attributed to the formation of gem-diol intermediates promoted by alkali.Too strong alkalinity may lead to the decomposition of substrates or intermediates,while the oxidation rate is lower when the alkalinity is weak.The oxygen pressure has little effect on the reaction rate,which may be because O₂ is used as an indirect oxygen source to supplement the consumption of water in the system,and water molecules are the direct oxygen source in the oxidation process.