Catalytic Conversion Of Polyhyderoxyl Alcohols To Monocarboxylic Acids Catalyzed By Supported Ni,Cu,and Pt Nanometal Catalysts

As a 10%by-product of the biodiesel total output,glycerol is in excess due to the mass production and application of biodiesel.At the same time,a large number of by-products of dimethyl carbonate produced by transesterification and 2-propanediol also appeared market surplus problem.However,the low-value polyols can be converted into high-value monocarboxylic acids by catalytic conversion of glycerol and propylene glycol to monocarboxylic acids,such as formic acid,lactic acid,acetic acid and so on.Therefore,this conversion technology has theoretical and practical application valueIn this paper,three types of supported nano-metal catalysts were developed for the conversion of polyhydroxy alcohol to monocarboxylic acid,including selective synthesis of lactic acid over Ni/HAP(hydroxyapatite)catalyst,1,2-propanediol oxidation to monocarboxylic acid over Pt/Graphene catalyst and 1,2-propanediol oxidation to monocarboxylic acid over Cu/HAP catalyst.The experiment results indicated the structure-activity relationship between the structure of supported nano-metal catalyst and the catalytic activity of catalytic conversion of polyol to monocarboxylic acid.The reaction mechanism of catalytic synthesis of monocarboxylic acid from glycerol and propylene glycol was discussed.The results are summarized as followsNano-hydroxyapatite supported metal Ni0 nanoparticles(Nix/HAP)were prepared by wet chemical reduction method.The catalytic activity of Nix/HAP catalyst for the conversion of glycerol to lactic acid is higher than that of pure metal Ni0 nanoparticles in NaOH aqueous solution,which can effectively catalyze the conversion of high concentration glycerol(1.5-3 mol L-1)to lactic acid.The Nix/HAP catalysts exhibited higher catalytic activity for glycerol conversion to lactic acid than the sole metallic NiO nanoparticles.When the reaction was carried out over the Ni0.2/HAP catalyst with the initial glycerol and NaOH concentrations of 2.0 and 2.2 mol L-1 at 200 ? for 2 h,the selectivity of lactic acid reached 94.7%at the glycerol conversion of 92.1%Pt0 nanoparticles were prepared by wet chemical reduction method and deposited on the surface of graphene.By controlling the platinum content,Ptx/Graphene nanocatalysts with Pt0 particles dispersed uniformly were prepared.The Pt0.03/Graphene catalyst shows good activity of catalyzing the oxidation of 1,2-propanediol to produce lactic acid,acetic acid and formic acid at 120-160 ?After reacting at 160 ? for 4 h,Pt0.03/Graphene catalyst catalyzed the oxidation of 1,2-propanediol.When the conversion rate was 97.1%,the total selectivity of monobasic acid was 96.5%.Besides,too high temperature and too long time will lead to further oxidation of carboxylic acidHydroxyapatite nanorod-supported metallic Cu0 nanoparticle catalysts(Cux/HAP)were prepared by the wetness chemical reduction method.The metallic Cu0 nanoparticles were well dispersed on the surfaces of the HAP nanorods.The alkaline HAP nanorods inhibited the crystal growth of the metallic Cu0 nanoparticles.The HAP nanorods also retarded the oxidation of the metallic Cu0 nanoparticles.The Cux/HAP catalyst exhibited a higher catalytic activity for the oxidation of 1,2-propanediol with gaseous oxygen to lactic,acetic,and formic acids with the total selectivity of 70.3%even at a lower reaction temperature of 140 ?.The total selectivity of lactic,acetic,and formic acids reached 93.1%at a mild reaction temperature of 180 ?.However,the sole monometallic Cu0 nanoparticles or HAP nanorods had no catalytic activity for the oxidation of 1,2-propanediol.The metallic Cu0 nanoparticles and alkaline HAP nanorods in the Cux/HAP catalyst synergistically catalyzed the oxidation of 1,2-propanediol to carboxylic acid.