Selectively Catalytic Oxidation Of 1,2-Propanediol Over Pd/Ag,Cu/Au,and Cu Nanoparticles

The increasingly pressing energy crisis has greatly contributed to the development of biomass energy.Glycerol,a by-product in biodiesel production,can be used as the feedstock for the synthesis of many chemicals,such as 1,2-propanediol,acrolein,triacetylglycerol,and glyceric acid,via various processes.Among the chemicals,1,2-propanediol can be easily synthesized through the hydrogenolysis of glycerol with the yield of more than 90%.Furthermore,with the scaling-up coproduction of dimethyl carbonate and 1,2-propanediol by the transesterification method,1,2-propanediol utilization is not well developed,especially in China,due to its using only as a paint solvent.The green environmental process of utilizing renewable and low-cost biomass 1,2-propanediol into high value-added chemicals has a high theoretical research and application value.In our present paper,catalytic oxidation of 1,2-propanediol over nanoparticles was investigated,including catalytic oxidation of 1,2-propanediol to lactic acid under atmospheric pressure over Pd-Ag bimetallic nanoparticles,catalytic oxidation of 1,2-propanediol to lactic acid over bimetallic Cu@Au core/shell nanoparticles,and catalytic oxidation of 1,2-propanediol to carboxylic acids over copper nanoparticles.The effects of the structure and particle size of the metal nanocatalysts on the catalytic performance were investigated.The effect of reaction temperatures,1,2-propanediol concentrations,O₂ flow rate/pressure,Na OH concentrations,and catalyst loading on the oxidation reaction of 1,2-propanediol were investigated in detail.The mechanism of catalytic reaction was discussed and the kinetics of catalytic reaction was simulated.1.Catalytic oxidation of sustainable 1,2-propanediol with O₂ under atmospheric pressure to high-valued lactic acid was investigated over Pd-Ag bimetallic nanoparticle catalysts.The Pd-Ag bimetallic nanoparticles were prepared by the wetness chemical reduction method with Tween as the organic modifier.The Pd-Ag bimetallic nanoparticles were composed of the Pd nanoparticles with the average particle sizes of 3.8-7.3 nm and the Ag nanoparticles with the average particle sizes of 15.2-30.2 nm.XRD,HRTEM and XPS analysis certified that there existed an alloy trend between Pd and Ag nanoparticles.The Pd-Ag bimetallic nanoparticles with a low Pd content effectively catalyzed the selective oxidation of 1,2-propanediol to lactic acid.When the catalytic oxidation of 1,2-propanediol with O₂ under atmospheric pressure was carried out over Pd0.15Ag0.85 catalyst at 85 ? for 6 h in a Na OH aqueous solution,the lactic acid selectivity was 92.8% at the 1,2-propanediol conversion of 82.7%.The kinetics for the catalytic oxidation of 1,2-propanediol over the Pd-Ag nanoparticles were affected by the Pd and Ag contents.2.Bimetallic Cu@Au core/shell nanoparticles were prepared by the wet chemical reduction method using Tween as the organic modifier.The Cu@Au nanoparticles exhibited higher catalytic activity for the oxidation of 1,2-propanediol under mild reaction conditions than the sole Au nanoparticles.Cu@Au nanoparticles with small-sized Cu nanoparticles?60 nm?had higher catalytic activity than that with large-sized Cu nanoparticles?107 nm?.The Cu@Au nanoparticles with the mole ratios of Au to Cu of 0.015:0.985 and 0.035:0.965 exhibited high catalytic activities for the catalytic oxidation of 1,2-propanediol to lactic acid.Carrying out the reaction over bimetallic Cu0.985Au0.015 catalyst at 100 ? for 4 h in a Na OH aqueous solution,the 1,2-propanediol conversion was 89.3% with the lactic acid selectivity of 76.1%.A power function type reaction kinetic model well fitted the experimental data over the Cu0.985Au0.015 nanocatalyst,and the reaction activation energy was 34.1 k J mol-1.3.Copper nanoparticles with different particle sizes were prepared by a wet chemical reduction method in the presence of organic modifiers,such as citric acid?CA?,hexadecyl trimethyl ammonium bromide,Tween-80?Tween?,and polyethylene glycol 6000.The product selectivities in the catalytic oxidation of 1,2-propanediol were significantly affected by the particle size of the metallic Cu0 nanoparticle.The small-sized Cu CA nanoparticles with the average particle size of 15.2 nm favored the formation of acetic and formic acids while the Cu Tween nanoparticles with the average particle size of 26.9 nm favored the formation of lactic acid.The copper nanoparticle catalysts exhibited good recycling performance.