| Due to the increasing demand for energy and the continuous consumption of fossil raw materials,the research of alternative energy and renewable energy has been widely concerned.Bioethanol is a renewable alternative to fossil fuel and has been used as fuel and fuel additive for many years.At the same time,bioethanol is also regarded as a platform chemical.It has great economic benefits to produce high value-added chemical products by catalytic oxidation of ethanol aqueous solution.In recent years,ruthenium metal catalysts have attracted much attention due to their high selectivity for acetic acid in the liquid phase oxidation of ethanol and relatively low material cost.However,their catalytic performance still needs to be improved,and the reaction mechanism also needs to be further studied.In this paper,based on the controlled preparation and performance improvement of ruthenium-based catalyst materials for liquid phase oxidation of ethanol,MgFeRu-LDHs and CoAlRu-LDHs were used as precursors to prepare two kinds of confined structure ruthenium-based catalyst materials:Ru/Mg1-xFexO and Ru/RuOx/CoAl-LDHs by hydrogen reduction method.The morphology,composition and structure of the samples were analyzed through a variety of characterization techniques,the catalyst reduction preparation process was speculated,and the mechanism of the ethanol oxidation reaction process was discussed.Establish a relationship between the structure and activity of the samples.The main research contents and results are as follows:(1)In this paper,MgFeRu-LDHs was used as the precursor and the confined structure of Ru-based nano-catalyst Ru/Mg1-xFexO was prepared by hydrogen reduction method at 300℃.Ru nanoparticles are confined in the weak phase of Mg-Fe composite oxide The structure and morphology of catalyst samples were obviously affected by the temperature of hydrogen reduction treatment.The results showed that Ru3+was gradually reduced to Ru0 in LDHs laminates at about 100℃.As the reduction temperature increases,the particle size of Ru particles gradually increases.After reduction at 200 ℃,the LDHs transforms into the sjoegrenite phase,forming a structure where Ru particles are supported on sjoegrenite.When the reduction temperature is 300℃,the main layer of LDHs collapses to form Mg1-xFexO,and the confined structure metal ruthenium nano-catalyst Ru/Mg1-xFexO is obtained.Continue to rise the temperature to 400℃,part of the metal iron is reduced and Ru0 continues to grow to form Ru/Mg1.xFexO-Fe.The results of the liquid phase oxidation of ethanol showed that the Ru/Mg1-xFexO catalyst prepared at a reduction temperature of 300℃showed the best catalytic performance.This may be due to the synergistic effect of the three components of Ru,Mg and Fe.It is speculated that Ru is the main catalytic active site,Mg and Fe are used as catalytic promoters,where Mg provides basic sites to activate the O-H bond and the Fe3+/Fe2+redox pair is used to activate oxygen.(2)In this paper,Ru/RuOx/CoAl-LDHs nanocatalysts with confined structure were prepared by hydrogen reduction method at 150℃ using CoAlRu-LDHs as precursors.Ru/RuOx composite structure nanoparticles were confined between LDHs layers.The temperature of hydrogen reduction obviously affects the structure and morphology of the catalyst sample.Various characterization techniques were used to explore the physicochemical properties of samples prepared by reduction at different temperatures and used them in the catalytic oxidation of ethanol.It was found that the samples prepared by reduction at 150℃had the best catalytic performance.This may be attributed to the synergistic effect of Ru/RuOx composite structure nanoparticles;in addition,the hydroxyl of the LDHs laminate acts as a basic site to activate the O-H bond,while Co2+is used to activate oxygen. |
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