Study On The Oxidation Reaction Of 5-hydroxymethylfurfural Over Au/TiO₂ Catalyst Syste

Biomass energy is an emerging renewable energy source,and 5-hydroxymethylfurfural（HMF）,as an important bio based platform compound,serves as a bridge between biomass resources and chemicals.Therefore,exploring the catalytic conversion of HMF into other platform compounds and gaining a deeper understanding of their mechanisms is of great significance for the further development and practical application of new renewable energy.At present,photocatalysis and thermal catalysis cannot be completely distinguished in terms of reaction activity in the literature,and the reaction mechanism is also unclear.At the same time,HMF has active chemical properties and is prone to side reactions during the reaction process,making it difficult to achieve the conversion of HMF to FDCA under mild conditions.In response to the above issues,this paper explores the correlation and differences between photocatalysis and thermal catalysis using an Au/Ti O₂ catalyst system,while attempting to achieve the conversion of HMF to FDCA under mild conditions.The specific research content and results of this paper are as follows:（1）The HMF catalytic oxidation process under visible and dark conditions at different temperatures（10,20,30℃）was investigated by synthesizing Au/anatase and Au/rutile catalysts.It was found that the HMFCA yield of Au/rutile and Au/anatase visible light driven catalytic HMF oxidation at low temperatures was 3.36 and 2 times higher than that of dark state,respectively,indicating that visible light can promote HMF oxidation to HMFCA under low temperature conditions.Further kinetic analysis of the reaction revealed that the apparent activation energies of Au/rutile for catalytic oxidation of HMF under visible light and dark states were 52.24 k J/mol and 92.57 k J/mol,respectively.The apparent activation energies of Au/anatase for catalytic oxidation of HMF under visible light and dark states were 48.42 k J/mol and 53.58 k J/mol,respectively.This indicates that visible light can reduce the reaction energy barrier and promote the oxidation reaction of HMF.Finally,through free radical quenching experiments and EPR testing,it was found that the main active species of visible light catalyzed HMF oxidation reaction by Au/rutile and Au/anatase were·O₂^-,¹O₂,and h⁺.Under dark state conditions,the main active species were ¹O₂ and trace amounts of·O₂^-.（2）A series of Au/Ti O₂ catalysts with different calcination temperatures and loading amounts were synthesized in an attempt to achieve HMF oxidation to FDCA under mild reaction conditions.It was found that as the calcination temperature increased,the size of Au nanoparticles increased and the oxidation performance of HMF decreased.Furthermore,it was found that with the increase of Au loading at 400℃,the HMF reaction activity showed a trend of first increasing and then remaining unchanged.When the load is 2.5wt%,the HMF conversion rate reaches 100%.Finally,Au/rutile（400℃,2.5wt%）catalyst was selected for optimization of reaction conditions.Under reaction conditions of 40 mg Au/rutile（2.5wt%,400℃）catalyst,80 mg Na OH,reaction temperature of 75℃,and reaction time of 10 h,100%HMF conversion rate and 57.38%FDCA yield were obtained.