Catalytic Oxidation Of Glycerol Into Dihydroxyacetone By Composite Metal Oxide-supported Noble Metals

Biodiesel is a green and environmentally friendly renewable fuel,which has a broad market.A large number of by-product glycerol has been obtained in the production process of biodiesel,which leads to low price because of its oversupply.Therefore,how to improve the utilization value of glycerol is the focus of the present research.Selective oxidation of glycerol is an important conversion pathway for the synthesis of high value-added chemicals such as dihydroxyacetone（DHA）.At present,there are few heterogeneous catalysts used for the oxidation of glycerol to prepare DHA with high conversion and high selectivity,mainly including Au/Cu O,Au/ZnO,Au/Zn Ga-LDH,Pt-Bi/MWCNTs,Pt-Sb/MWCNTs,etc.In this thesis,in order to prepare the catalyst with high activity and selectivity of dihydroxyacetone for glycerol oxidation,it mainly focuses on the gold and platinum catalysts supported by composite oxides.The relationship between the selectivity of dihydroxyacetone,the main research content and conclusions are as follows:the relationship between the structure and composition of the catalyst and the catalytic activity and selectivity of dihydroxyacetone were studied.The main research contents and conclusions are as follows:（1）A series of composite copper-manganese oxides（Cu-Mn-O）supports with different copper-manganese molar ratios were synthesized by sodium carbonate deposition-precipitation method,and Au/Cu-Mn-O catalysts were prepared by urea deposition-precipitation method.The experimental results of glycerol oxidation in the absence of alkali showed that the introduction of Mn O_Xinto Cu O carrier could significantly improve the catalytic activity and selectivity of dihydroxyacetone,compared with the Au/Cu O catalyst.When the Au/Cu_0.95Mn_0.05O_Xcatalyst was tested in the transformation of glycerol to dihydroxyacetone under the temperature of 50℃for 10 hours,the glycerol conversion reached 93.4%and the selectivity of dihydroxyacetone was 62.9%.The high catalytic activity of the catalyst Au/Cu_0.95Mn_0.05O_Xmainly comes from the strong interaction between the support and the metal,proved by XPS characterization.H₂O₂decomposition experiments showed that the addition of Mn ions can accelerate the decomposition of H₂O₂during glycerol oxidation reaction,inhibit C-C bond cleavage to some extent,reduce the formation of by-products such as CO₂,and ensure the high selectivity for dihydroxyacetone.（2）A series of composite zinc-zirconium oxides（Zn-Zr-O）supports with different zinc-zirconium molar ratios were synthesized by sodium carbonate deposition-precipitation method,and Au/Zn-Zr-O catalysts were prepared by urea deposition-precipitation method.The experimental results of glycerol oxidation without alkali showed that the catalytic performance of Au/Zn-Zr-O catalyst was significantly higher than that of Au/ZnO and Au/ZrO₂catalysts.After optimizing the reaction conditions,the conversion of glycerol reached 94.5%,and the selectivity of dihydroxyacetone was61.4%over the Au/Zn_0.95Zr_0.05O_Xcatalyst under the condition of 65℃for 4hours.Compared with Au/ZnO catalyst,the conversion of glycerol increased by 20.3%and the selectivity of dihydroxyacetone increased by10%.TEM characterization showed that Au/Zn_0.95Zr_0.05O_Xhad suitable Au nanosizes,and XPS characterization proved that there was a strong interaction between Au and Zn_0.95Zr_0.05O_X.（3）Used H₂PtCl₆and BiCl₃as platinum and bismuth sources.ZrO₂as a carrier.Pt nanoparticles were loaded support by Na BH₄reduction method,and the theoretical loading of Pt and Bi was 5wt%for Pt-Bi/ZrO₂catalysts.It was found that the ZrO₂supported Pt-Bi catalyst has excellent catalytic performance for glycerol to DHA.Compared with Pt-Bi/OCNTs catalyst,Pt-Bi/ZrO₂catalyst showed better catalytic activity.After reaction at atmospheric pressure and 60℃for 10 hours,the conversion of glycerol oxidation reached 74.4%,and the selectivity of dihydroxyacetone was49.2%.Compared with Pt-Bi/OCNTs catalyst,the conversion of glycerol increased by 33.9%,and the selectivity of dihydroxyacetone increased by about 8%.The TEM characterization showed that Pt-Bi/ZrO₂had a lot of strip structure.The XPS characterization showed that the electronic structure of metal Pt in Pt-Bi/ZrO₂changed obviously,proved a strong interaction between the Pt and the promoter Bi.These may contribute to its excellent catalytic performance.In a word,the conversion of glycerol oxidation and the selectivity of dihydroxyacetone can be obviously improved over the precious metals catalysts using complex oxides as carriers.This is of great significance for improving the activity of glycerol oxidation and controlling the distribution of products.