Construction Of Nitrogen Doped Carbon Supported Transition Metal Catalyst And Selective Catalytic Oxidation Of 1,2-Propanediol To Lactic Acid

Selective conversion of biomass-derived polyols to value-added chemicals has important significance of chemistry,which can reduce the chemical production and utilization of traditional fossil fuels.1,2-propanediol（PDO）is an important vicinal-diol compound,which can be regenerated by hydrolysis of polyols.Through the method of catalytic oxidation,it can converted into lactic acid,pyruvate,hydroxyacetone and other important C3 products.At present,the catalysts have reported which can catalyze the conversion of PDO to lactic acid are mainly composed of precious metal elements such as Au,Pd,Pt.However,due to the high cost and small storage of precious metal,it is difficult to realize large-scale application.In recent years,metal and nitrogen co-doped carbon materials have attracted extensive attention.Studies have shown that when nitrogen doped carbon（N/C）materials combined with transition metals,which can regulate the electronic structure of N/C.It can generate metal nitrogen doped carbon（M-N/C）matrix,which has many exposed M-N_x sites and metal nanoparticles（M-NPs）,showing good catalytic activity in catalytic oxidation.In this paper,Cu-NPs was encapsulated by ultrathin 2D copper and nitrogen-doped carbon（Cu-N-C）nanosheets（Cu@Cu-N-C NSs）and Copper,cobalt bimetallic with nitrogen co-doped carbon nanosheets catalysts（Cu_xCo_y-N/C）were designed and constructed.Through the pyrolytic synthesis that silk fibroin protein loading Cu-Co ion complex,which can be used besids as a new type of non-noble metal replaceable catalyst,also in the selective catalytic oxidation of 1,2-propanediol to produce lactic acid.The main research results are as follows:1.Nitrogen-rich carbon nanosheets lodaing copper nanoparticles was prepared by high temperature pyrolysis,which used the readily carbonized precursors of copper（Ⅱ）-silk fibroin complex（Cu@Cu-N/C）.The results were characterized by XRD,TEM and XPS.For the oxidation of PDO to LA with excellent activity（76.9%）and selectivity（88.5%）under 1.0 MPa O₂ and 120℃for 8 h,superior to most of the reported Cu-NPs catalysts.By combining experiment discover that the Cu-N_x sites and encapsulated Cu-NPs in the Cu-N-C NSs synergistically contribute to the high activity and LA selectivity for the PDO oxidation.The LA selectivity can be further promoted to be 94.2%under the milder non-pressurized O₂ conditions(100 m L min^-1 O₂ and 90℃),accompanying with 39.8%PDO conversion,which is about 2.2 times higher than that of the active carbon supported gold nanoparticles（1%Au/C）catalyst.2.Two single metals Cu-N_x/C and Co-N_x/C and bimetallic Cu_xCo_y-N/C catalyst synthesized by high temperature pyrolysis using the chelating ability of silk fibroin protein to adsorb Cu（Ⅱ）and Co（Ⅱ）precursors.The size of Cu/Co nanoparticle controlled by changing the loading amount of Cu（Ⅱ）/Co（Ⅱ）and the pyrolysis time.The morphology and structure of the catalysts evaluated by XRD,TEM,XPS,AFM,etc.LA was prepared by selective catalytic oxidation of PDO for 10 h at 90℃and O₂flow rate of 200 m L min^-1.Results showed that bimetallic Cu_xCo_y-N/C exhibited better catalytic activity（51%PDO conversion and 91.6%lactate selectivity）than single metal Cu-N_x/C and Co-N_x/C.The introduction of active component Co can produce synergistic effect,coordination effect or global effect between the metal Cu and Co,resulting in excellent catalytic activity and stability in the test of catalytic PDO oxidation.