Nitrogen-Doped Carbon Supported Co-Cu Dual-Metal Synergistic Catalysis Toward The Selective Oxidation Of 5-Hydroxymethylfurfural

Fine chemicals and fuels mainly originate from traditional fossil resources in modern industry.Converting renewable biomass into high-value chemicals alleviates the energy crisis and promotes the global carbon chemical cycle.5-hydroxymethylfurfural（HMF）,an important platform compound in biomass conversion,can produce a series of valuable chemicals due to its various functional groups.As one of the important products from HMF oxidation,2,5-furanedicarboxylic acid（FDCA）is considered as an ideal alternative for the petroleum derivative-terephthalic acid（PTA）to produce degradable bio-plastics.Noble metals,such as Au,Pt,Pd,and Ru,are widely employed as catalysts for traditional thermal catalytic HMF oxidation,unfortunately,their unabundant and high cost make it difficult to afford large-scale commercial production of FDCA.In recent years,non-noble metal oxides have shown good HMF oxidation activity,with FDCA yields over 90%.However,they suffer from low catalytic efficiency and poor reactivity,and depend on high temperature and pressure reaction conditions.To solve the problems of the above non-noble metal catalysts,in this paper,nitrogen-doped carbon and metal Co are used as the support and active center,respectively.The electronic structure of the active center is optimized through component,size,and coordination regulation,and the catalyst’s adsorption characteristics and the mechanism of synergistic catalysis are further elucidated.The specific research content is as follows:The nitrogen-doped carbon supported Co nanoparticles（NPs）catalysts（Co-M-CN_x）doped with different metals（M=Mn,Fe,Ni,and Cu）were constructed using a metal-organic framework assembly-pyrolysis strategy.Experimental results showed that Cu dopant can significantly improve the reactivity of catalysts.Under low catalyst dosage(20 mmol _HMF g_cat^-1),Co-Cu_1.4-CN_x still exhibited a high FDCA yield（96%）for HMF oxidation,far superior to Co-CN_x（FDCA yield:24%）.Specifically,the FDCA productivity is as high as 1605μmmol _FDCA g_cat^-1 h^-1,surpassing most non-precious and precious metal catalysts.Density functional theory（DFT）calculation results showed that,compared with the pristine Co NPs,the transfer of electrons from the Cu atoms to the Co atoms led to the downshifted d-band center of Co-Cu dual-metal NPs,which optimizes the intermediates adsorption（^*HMFCA and^*FFCA）,thus reducing the energy barriers during the HMF to FDCA conversion process,and significantly improving the catalytic efficiency.To reduce the reaction pressure of HMF oxidation,an atomically dispersed Co-Cu dual-metal catalyst（a-Co/Cu-NC）was constructed on nitrogen-doped carbon support via a metal sites strategy.The structural characterizations indicate that both Co and Cu are dispersed in a single-atom form and coordinate with N atoms.Control experiments suggested that Co NPs are difficult to catalyze HMF oxidation,and atomically dispersed metal sites in the catalyst are the main active centers under ambient pressure.The FDCA yield of a-Co/Cu-NC catalyst reached 98%,with a productivity of 21.5mol _FDCAmol_metal^-1 h^-1.The catalytic activity is five times higher than commercial Pt/C and much higher than a-Co-NC and a-Cu-NC.Mechanism studies indicate that Co/Cu dual-metal single-atom sites show enhanced oxygen activation ability,which accelerates the transfer of electrons from the catalyst surface to O₂ molecules,thus promoting the regeneration of the active sites.Therefore,the HMF oxidation controlled by the adsorption-catalysis mechanism of the catalyst could achieve excellent catalytic activity at low oxygen levels while avoiding side reactions induced by high concentrations of oxygen.In this paper,by optimizing the electronic structure of active sites of catalyst,the FDCA yield and catalytic efficiency for HMF oxidation reaction were improved,and the conversion of HMF to FDCA under environmental pressure has been realized with high efficiency;In addition,a detailed exploration of the mechanism of enhanced activity and possible reaction mechanisms provides theoretical guidance and practical verification for the design of similar organic small molecule oxidation catalysts.