Study On The Effect Of Different Oxide Carrier Characteristics On CO Oxidation Reaction On Supported Gold Catalyst Under CO₂ Laser Atmosphere

Supported nano-gold catalysts（Au/M_xO_y）have unlimited potential for environmental purification and green sustainable chemical reactions.Unlike palladium or platinum-based catalysts,gold-based catalysts are very active even under relatively mild conditions.For CO oxidation reaction,the main factors affecting the activity of gold-based catalysts are:（1）the size of gold nanoparticles;（2）Interaction between gold nanoparticles and supports;（3）The types of metal oxide supports.Among these factors,the average size of gold nanoparticles and the interaction between gold and thesupport have been fully studied,because they can be adjusted and controlled by selecting different preparation methods,calcination conditions,gold loading and other parameters,while metal oxide supports have great differences in their physical and chemical properties,even though many research works have been published on the simple model reaction of CO oxidation,however,there is still a lack of systematic and in-depth research.While,there have been no reports on the CO oxidation reaction over nano-gold catalysts supported by a series of oxide with different properties under high CO₂concentration and oxygen deficient atmosphere conditions in CO₂ lasers.In this paper,the size of gold nanoparticles was controlled by the gold sol-gel method,and the second metal oxide（Mn,Fe,Co,Ni,La,Zr,Ce,Mo,W,Cu,Mg）supports were added onγ-Al₂O₃ using the monolayer dispersion theory to reduce the influence of different morphology and surface area of the oxide support on the experimental results.The activity of the catalysts for carbon monoxide reaction in a CO₂-rich atmosphere was investigated and the relationships between the catalytic performance of catalysts and the supports themselves were investigated,and the following conclusions were obtained,respectively.（1）Gold nanoparticles with controllable size were prepared by gold sol-gel method and loaded onγ-Al₂O₃ and 11 types of alumina-based oxides supports.The average size of gold nanoparticles is about 10.5 nm on different oxide supports.The CO conversions over12 oxide supports and corresponding gold catalysts with respect to reaction temperature were tested in a carbon dioxide rich and oxygen poor atmosphere and a carbon dioxide free and oxygen rich atmosphere,respectively.We found that in an atmosphere rich in carbon dioxide and poor in oxygen,only CuO/γ-Al₂O₃、Mn₂O₃/γ-Al₂O₃、Fe₂O₃/γ-Al₂O₃、Co₃O₄/γ-Al₂O₃and Ni O/γ-Al₂O₃exhibits better CO conversion rate thanγ-Al₂O₃ other oxides show extremely low CO conversion rate and even no reaction at 400℃.However,after gold deposition,the oxidation activity of medium strong acid and medium strong basic metal oxide supported Au catalysts was significantly improved compared with the support.And the higher the standard heat of formation（-ΔH_f⁰）per O atom of the other oxide support,the higher the CO oxidation reaction rates of the gold loaded catalysts!The catalysts with higher reaction rate are Au/Mn₂O₃/γ-Al₂O₃>Au/CuO/γ-Al₂O₃>Au/Ce O₂/γ-Al₂O₃.The results of the reaction in the oxygen rich atmosphere without CO₂ showed that the high concentration of CO₂ greatly inhibited the CO oxidation activity on the gold catalyst,especially for the gold catalysts with basic supports.（2）Small-sized（<2 nm）gold nanoparticles were prepared by deposition and precipitation method,and then loaded on metal oxide support prepared above to improve the CO conversion of the catalyst in the atmosphere rich in carbon dioxide.The experimental results show that the average size of gold nanoparticles has a significant impact on the reaction activity.In a carbon dioxide rich atmosphere at 30℃,almost all gold loaded catalysts have significantly improved their reaction activity and are,which are higher than the corresponding catalysts prepared by the gold sol-gel method,but the degree of improvement varies.The first few catalysts with the best reaction rate are:Au/γ-Al₂O₃>Au/Co₃O₄/γ-Al₂O₃>Au/Zr O₂/γ-Al₂O₃.The average particle size of gold particles of these three catalysts is about 1 nm,which is smaller than other gold-loaded catalysts.The introduction of Au did not improve the CO conversion over strong acid and strong base oxides supported catalysts;The higher the standard heat of formation（-ΔH_f⁰）per O atom of the other oxidesupport,the higher the CO oxidation reaction rate of the gold loaded catalyst,which is the same as the conclusion drawn in the first chapter of the work!The activity results under the oxygen rich atmosphere indicate that high concentration of CO₂has a strong inhibitory effect on the reaction activity of the alkaline oxides supported gold catalysts.（3）On the basis of the work in Chapter 1,the strong interaction between gold and the support was strengthened by increasing the calcination temperature of the gold loaded catalyst prepared by the gold sol-gel method to 600℃,and the influence of the enhanced interaction between gold and support on the CO oxidation reaction performance was explored.It was found that in the CO₂ rich atmosphere at 200℃,Compared with the CO oxidation rate of Au/M_xO_y/γ-Al₂O₃-300 catalyst,the CO oxidation reaction rate of Au/M_xO_y/γ-Al₂O₃-600 catalyst increased from 1.2 to 27.3 times.To sum up,enhancing the strong interaction between gold and support by increasing the calcination temperature of the gold-loaded catalyst can improve the CO oxidation performance in the atmosphere rich in carbon dioxide.Strengthening the interaction between gold and support has a significant impact on Au/Co₃O₄/γ-Al₂O₃、Au/Fe₂O₃/γ-Al₂O₃、Au/CuO/γ-Al₂O₃ these three catalysts.