JACS: low consumption and high efficiency photocatalytic synthesis of important biomass compounds FDCA

In recent years, more and more attention has been paid to the production of renewable resource chemicals 5-hydroxymethylfurfural (HMF) produced by C6 carbohydrate dehydration is listed as one of the 12 sustainable biomass value-added chemicals by the U.S Department of energy All kinds of high value chemicals obtained from HMF or its derivatives are produced by various catalytic methods Among these chemicals, 2,5-furan dicarboxylic acid (FDCA) is considered as an important monomer substitute for petroleum derivative terephthalic acid However, in addition to FDCA, the oxidation of HMF can produce several lower value products including 2,5-dimethylfuran (DFF), 5-hydroxymethyl-2-furanic acid (HFCA) Therefore, it is a challenge to use molecular O2 to oxidize HMF to obtain high yield FDCA At present, the selective oxidation of HMF to FDCA is carried out on noble metal catalysts at high temperature (80-150 ℃) The disadvantages of these thermal catalytic oxidation methods include high cost of noble metal catalysts, high energy consumption (because of high reaction temperature), high oxygen pressure and super alkaline requirements, which hinder the development of industrial applications Therefore, it is of great value to develop a route of selective oxidation of HMF to FDCA under mild conditions In recent years, photocatalysts driven by light and using O2 as oxidant have attracted more and more attention in the field of oxidation and transformation of organic compounds Because photocatalytic processes are usually carried out under mild conditions, energy consumption can be greatly reduced However, the photocatalytic oxidation of alcohols with oxygen molecules has some problems such as low efficiency and poor selectivity When a strong oxidizing substance is produced in the photocatalysis system, the non selective process is dominant, and the peroxidization often occurs, resulting in the poor selectivity of the product In order to realize the effective transformation from HMF to FDCA, the team led by Zhang Zehui, associate professor from South Central University for Nationalities and Professor Deng Kejian, designed a catalytic system that can generate oxidants from molecular O2 at room temperature and atmospheric pressure, and has the appropriate oxidation ability to oxidize HMF to FDCA without over oxidation CopZ chemical structure (source: Journal of the American Chemical Society) is a natural enzyme with high redox activity, which can promote many types of reactions in organisms, and has high activity and reaction selectivity The direct use of enzymes in chemical reactions is limited by their instability under industrial conditions Nevertheless, the efficiency of enzyme catalysis has inspired the strategy of developing selective oxidation catalyst by simulating enzyme active center Metalloporphyrin and Metallophthalocyanine are two of the most studied biomimetic catalysts with high redox activity The single cobalt thiopyrazine (CopZ) showed only moderate photocatalytic activity (40% conversion of HMF) for HMF oxidation selection It is noted that CopZ molecules are hydrophobic and tend to aggregate in aqueous solution, reducing the contact between CopZ catalyst and reactants, thus reducing the performance of the catalyst In order to reduce aggregation, carriers can be found to disperse them As a metal free semiconductor, graphite carbonitride (g-c3n4) has the advantages of low toxicity, low cost, high electron transfer ability and high thermal stability In this study, g-c3n4 is used as the carrier to fix CopZ In the experiment part of Journal of the American Chemical Society, CopZ / g-c3n4 photocatalyst was prepared by chemical method and characterized Then, the prepared photocatalyst was used to test its selective conversion performance In the part of experimental results and discussion, the strong interaction between CopZ and g-c3n4 in the catalyst, the photocatalytic performance of CopZ / g-c3n4, the influence of pH of reaction system on the photocatalytic performance of CopZ / g-c3n4, the stability of heterogeneous catalyst, the preliminary mechanism of identifying oxide and the photocatalytic oxidation process of CopZ / g-c3n4 were studied Possible mechanism of catalytic oxidation (source: Journal of the American Chemical Society) this study shows that CopZ / g-c3n4 is a highly efficient photocatalyst, which selectively oxidizes HMF to FDCA using oxygen molecules in the air as benign oxidants under simulated sunlight At room temperature and atmospheric pressure, the system is neutral and alkaline, which can achieve excellent product yield in aqueous solution Another selective oxidation product DFF can also be produced in good yield under the condition of slight acidity The experimental results show that there is a strong interaction between CopZ and g-c3n4 in CopZ / g-c3n4 catalyst, which is the key factor of excellent performance The interaction can promote the ability of 1 O 2 formation of CoPz and inhibit the ability of g-C 3 N 4 to produce hydroxyl radicals It is predicted that 1O2 can selectively oxidize HMF to FDCA In addition, there is no problem in the recovery of CopZ / g-c3n4 catalyst This study reveals a new way to develop efficient photocatalysts from biomimetic catalysts, and may also stimulate the research on the production of value-added chemicals using light energy Paper link: http://pubs.acs.org/doi/10.1021/jacs.7b08861 brief introduction of corresponding author: http://www.scuec.edu.cn/s/51/t/366/5b/4d/info23373.htm http://www.scuec.edu.cn/s/51/t/1404/5b/42/info23362.htm