Solid-state Chemical Synthesis Of CeO₂ Nanomaterials And Their Catalytic Properties Toward Co Oxidation

Carbon monoxide?CO?,as a toxic gas,can seriously affect people's health and cause great harm to the environment.In addition,fuel cell based on proton exchange membrane technology,CO easily adsorbed on the surface of anode catalyst,seriously destroyed the performance of battery.How to eliminate and convert CO is an urgent problem,CO catalytic oxidation technology is considered an effective and simple strategy.Noble metal catalysts with excellent CO catalytic performance are investigated extensively.However,some unavoidable factors,such as high cost,limited resources severely limit its wide application in the field of catalysis.Therefore,the exploration and development of low-cost and highly active non-precious metal catalyst is the key to the widespread implementation of CO catalytic oxidation.As a transition metal oxide,CeO₂ has abundant reserves and high oxygen storage capacity,showing its application advantages in the field of CO catalytic oxidation.However,CeO₂ is not very active at low temperature campared to noble metal catalysts.How to modify CeO₂ to increase the number of defects and improve CO catalytic performance is a critical issue.In order to solve the low activity under low temperature,we prepared CeO₂nanomaterials by solid state method,and adjusted the active crystal plane and the number of oxygen vacancies of CeO₂ by morphology control and heteroatom doping,which improved the catalytic performance of the obtained catalysts,and the stability and water resistance are enhanced.We have carried out the following parts:?1?CeO₂ nanomaterials with different morphologies were synthesized by solid-state method,including CeO₂ nanorods with a diameter of about 20 nm,CeO₂ flakes with a thickness of about 30 nm,and CeO₂ nanoparticles with a particle size of 5-10nm.The composition and structural characteristics of the obtained materials were determined by various characterization methods,and their catalytic oxidation properties to CO were investigated.The results show that pure CeO₂ nanoparticles,nanosheets and nanorods can be prepared by reacting different cerium salts with potassium hydroxide?KOH?,oxalate and trimesic acid?H₃BTC?.The CeO₂ obtained by different cerium salts with oxalic acid is a sheet-like morphology,which indicates that the type of cerium salt have influenced the thickness of the product.The effects of acidity for reactants of solid state reaction on the morphology of the product were studied.The results show that the acidity of the reaction system is the main factor affecting the morphology of the final CeO₂ sample,which mainly affects the thickness of CeO₂ sample.The acidity of the reaction system is gradually weakened,and the thickness of the sheet of the obtained product is gradually thinned.The results of CO catalytic oxidation performance of different morphological samples exhibited different CO catalytic oxidation performance,and CeO₂ nanoparticles could completely convert CO at 280°C;CeO₂ nanorods can achieve complete conversion of CO at 350°C;CeO₂ nanosheets can achieve complete conversion of CO at 380°C.CeO₂ nanoparticles have the best CO oxidation catalytic activity.?2?The transition metal doped CeO₂ nanoparticles?CuO_x-CeO₂?were synthesized by solid-state chemical reaction.The composition and morphology of the metal doped CeO₂ nanoparticles were analyzed by various characterization methods.The catalytic performance of Cu O_x-CeO₂ for CO oxidation was investigated.The effects of doping amount and calcination temperature on the structure and properties of the catalyst were investigated.The results show that the CuO_x-CeO₂ catalysts with a particle size of about 5-10 nm was synthesized by room-temperature solid-state chemical method.The reason for the improvement of catalytic performance is mainly due to the generation of oxygen vacancies and the formation of highly dispersed copper oxide.In order to improve the catalytic performance,we further optimized the heat treatment conditions?increasing the heating rate and reducing the preservation period?,successfully controlled the surface oxygen vacancies on the catalyst surface and the distribution of Cu on the surface to promote the catalytic performance.The CuO_x-CeO₂ composite achieves complete catalytic oxidation of CO at 110°C.?3?The copper and zirconium species were doped into cerium oxide nanoparticles by in situ solid-state method,and the CuO_x-ZrO₂-CeO₂ nanocatalysts were obtained.The CO catalytic oxidation performance of the products obtained by different Cu/Zr molar ratios were investigated,and the influence of the introduction of Zr on the structure and properties of the catalyst was studied in detail.The results show that the introduction of Zr can significantly increases the concentration of oxygen vacancy,Cu⁺and Ce³⁺of the catalyst,which promote the improvement of catalytic activity and thermal stability of CuO_x-CeO₂ nanomaterials.