Electrochemical Conversion Of Biomass-derived Glycerol

Being a large-quantity byproduct from the industrial production of biodiesel,glycerol?GLY?shows a great potential to be converted into many high valued-added chemicals and intermediates.Sustainable energy-driven electrochemical oxidation is a green way to achieve GLY conversion.The development of high-performance electrocatalysts is the key to the electrochemical oxidation of GLY.At present,the catalysts for GLY electrochemical oxidation is mainly based on precious metals including platinum?Pt?,palladium?Pd?and gold?Au?,all of which are expensive and suffer from some drawbakcs such as poor activity and/or selectivity,catalyst poisoning and so forth.To address this issue,a series of nanostructured catalysts were prepared and further examined for GLY electrooxidation.The activity and product distribution of GLY oxidation over the electrocatalysts were investigated.The adsorption,migration,bonding behavior of GLY/intermediates on the catalyst surface were also studied.The effect of catalyst structures on GLY oxidation was analyzed.This project could provide valuable guidance for the large-scale application of GLY electrooxidation.The main content of this thesis is listed as follows:?1?A series of graphene nanosheet?GNS?supported Pt,PtNi,PtRu,PtRh,PtRuNi and PtRhNi catalysts were synthesized by one-pot polyol-assisted reduction method.The properties of GLY oxidation were investigated.Transmission electron microscopy?TEM?and X-ray diffraction?XRD?results show that the average particle size of the catalyst was about 2 nm,and that the resulting catalysts have an alloyed structure.Electrochemical tests show that the PtRhNi/GNS and PtRh/GNS catalysts possess remarkable peak current densities of 5.58 and4.47 mA cm^-2,which are 22 and 18 times higher than that of the Pt/GNS catalyst,respectively.High-performance liquid chromatograph?HPLC?results show that the PtRuNi/GNS exhibits better selectivity toward C3 products than PtRhNi/GNS.It was found that the introduction of Ru facilitated the formation of C3 products while the addition of Rh was beneficial for the cleavage of the C-C bonds.?2?Core-shelled Pt@Pd nanoparticles?Pt@Pd NPs?were synthesized via a seed-mediated growth method,in which Pd nanocubes?Pd NCs?were employed as seeds.The peak current densities of Pd NCs and Pt@Pd NPs for GLY oxidation are 2.12 and 3.22 mA cm^-2,respectively,which are higher than those of the Pd/C(0.91 mA cm^-2)and Pt/C(0.66 mA cm^-2).HPLC results show that the Pd NCs possess the largest glyceraldehyde selectivity of 61.2%,while the Pt@Pd NP is the only catalyst which can produce glycolic acid from GLY elecrooxidaiton.This could be atributed to the facile cleavage of C-C bonds arisen from the synergistic effects of Pt and Pd.?3?Core-shelled PdAu@Ag,Pt_xAu_y@Ag,and Pt@Ag skeletons were synthesized via a seed-mediated growth method,in which Ag NPs were used as sacrificial seeds.A large number of granular protuberances and lattice strains are noted from the Pt_xAu_y@Ag core-shelled NPs.The Pt@Ag NPs are characteristic of a three dimension skeleton-like structure,consisting of numerous interconnected networks.The Ag seeds in the Pt_xAu_y@Ag and Pt@Ag are almost completely etched.In contrast,the Ag seeds in the PdAu@Ag core-shell remains intact.The surface of the PdAu@Ag NPs is covered by uneven Pd layers and some small Pd NPs.A strong lattice strain is noted from the NPs.Electrochemical results indicate that these catalysts show superior activity for GLY oxidation.The peak current densities of the PdAu@Ag,Pt₄Au₆@Ag and Pt@Ag are 3.39,3.1 and 7.57 mA cm^-2,respectively,which are significantly higher than those of the Pt(0.66 mA cm^-2),Pd(0.91 mA cm^-2)and Au(0.1 mA cm^-2).The product distribution also depends on the composition and structures of the catalysts.Among the catalysts,the Pt@Ag NPs yield the largest dihydroxyacetone selectivity of 82.6%.The Pt₄Au₆@Ag possesses a dihydroxyacetone selectivity of 77.1%at 1.1V while the Pt₆Au₄@Ag exhibits the largest glyceraldehyde selectivity of 35.0%at 1.1V.With increasing Au content,the selectivities of C3 products decrease.The PdAu@Ag tends to produce more dihydroxyacetone?77.1%?at high potentials while Au@Ag tends to generate more C1/C2products.The excellent activity and product selectivity of the PdAu@Ag,Pt_xAu_y@Ag and Pt@Ag skeleton for GLY oxidation can be attributed to the unique structures of the catalysts and the synergy between the components.The optimized experimental results show that the product distribution of GLY oxidation is not only related to the structure of the catalyst but also affected by the reaction conditions.The formation of glyceraldehyde is facilitated at low GLY concentrations.The largest value of 92.6%is obtained when GLY concentration is 0.05 M.The generation of dihydroxyacetone is suppressed when KOH concentration is higher than 0.5 M.There is no straightforward time-dependence of dihydroxyacetone selectivity on reaction time.It is demonstrated that GLY electrochemical oxidation and electrochemical hydrogen evolution can be succesfully coupled from a 1.5 V solar panel powered electrolysis cell,consisting of a Pt@Ag anode and a Pt cathode.