Preparation Of Confined Nanostructured Metal Catalysts And Their Catalytic Oxidation Performance For Ethanol

With the development of science and technology and the progress of human society,the demand for energy and fossil raw materials continues to increase.To meet the needs of sustainable development,people gradually turn their attention to biomass materials and biomass energy.Bioethanol is one of the earliest biomass energy sources,which is widely used as an additive for automobile fuel.In addition,biomass ethanol can be further catalyzed to produce a variety of high value-added chemicals to obtain high economic value.The oxidation reaction of ethanol is one of the reaction ways to produce other chemicals.The oxidation reaction of ethanol is mainly divided into liquid phase oxidation of ethanol and gas-phase oxidation.The main product of liquid-phase oxidation is acetic acid,and the main product of gas-phase oxidation is acetaldehyde.Hydrotalcite is an excellent catalyst precursor due to its lamellar and interlamellar limited domain properties,which can be used to prepare confined structure catalysts.In this paper,the confined nano-metal catalysts were prepared by controlling the reduction temperature of CoAlRu-LDHs and CoCuAl-LDHs,and were used for liquid and gas phase oxidation of ethanol respectively.The morphology,composition and structure of the final sample were determined by characterization,and the possible reaction mechanism was speculated based on the characterization results.In this paper,confined Ru/RuO_x/CoAl-LDHs were we’re obtained by using CoAlRu-LDHs as the precursor and treated for 3 h in H₂ atmosphere at 150℃.Ru nanoparticles are confined to the laminates of hydrotalcite.It was found that H₂ reduction temperature affected the composition and valence state of the catalyst.The characterization results show that Ru³⁺in hydrotalcite laminates is reduced to Ru₀ after 100℃.When the reduction temperature was raised to 150℃.The Ru⁰ formed Ru nanoparticles,while the unreduced Ru formed RuO_x and obtained localized Ru/RuO_x/CoAl-LDHs.The samples treated at 150℃ had the best liquid phase catalytic performance for ethanol oxidation,with ethanol conversion of 90.27%and acetic acid selectivity of 97.16%.After temperature increased to 300℃,the structure of hydrotalcite disappears completely,RuO_x disappears completely,while CoO and Co⁰ begin to appear,forming Ru-Co/CoAlO_xstructure.In liquid-phase oxidation of ethanol,Ru/RuO_x/CoAl-LDHs obtained after 150℃ has the best catalytic performance.This may be due to the synergy between Ru⁰,RuO_x,and Co,Ru⁰ is the main active site,RuO_x is the oxygen supplying component,and Co²⁺in hydrotalcite substrate is responsible for activating oxygen and providing alkaline sites.In this paper,Co-Cu/CoCuAlO_x catalyst with a confined structure was prepared by CoCuAl-LDHs as catalyst precursor in H₂ at 650℃.The formation process is divided into the following stages:first,the formation of Cu nanoparticles,Cu²⁺in the hydrotalcite laminate was reduced to Cu nanoparticles in H₂ at 150℃.In the second stage,the secondary reduction of Cu and the generation of Co⁰,the crystal phase of Cu₂O appeared when the H₂ treatment temperature was raised to 250℃,and the crystal phase of Co⁰ appeared when the temperature was further raised to 350℃.In the third stage,Cu₂O crystal phase disappears and Co-Cu bimetallic nanoparticles are produced.When the temperature is raised to 550℃,Cu₂O disappears.After raised to 650℃,Co-Cu/CoCuAlO_x catalyst with a confined structure is formed.After temperature raised to 750℃,the metal nanoparticles increase sharply and the confined structure disappears.The results show that Co-Cu/CoCuAlO_x have the best catalytic performance,with ethanol conversion of 84.00%and acetic acid selectivity of 86.75%According to characterization results,it is speculated that Cu and part of Cu⁺are the components of activated oxygen,while Cois the site of ethanol adsorption.