Study On Cu/SAPO-34 Zeolites And Cobalt-based Metal Oxide Catalysts For Abatement Of Pollutions Emitted From Lean-Burn Exhaust

Lean-burn engines have been widely adopted because of the excellent power and high fuel economy.However,the exhaust contains lots of NO_x,CO and other pollutants,which seriously impairs the environment as well as human health,and makes the relevant emission regulations increasingly strict.The traditional three-way catalyts can not be applied under the condition of high air-fuel ratio,while the SCR（selective catalytic reduction）technology and catalytic oxidation are the most effective methods to remove NO_xand CO in lean-burn exhaust,respectively.In this thesis,by the design of high-efficiency Cu-based molecular sieve and Co-based oxide catalyst,the efficient elimination of NO_xand CO has been achieved.This topic has important social significance and potential application prospects.Firstly,a series of Cu-modified SAPO-34 catalysts with various copper loadings was synthesized via a pH-controlling ion-exchange method.At lower loadings Cu species exists predominantly as isolated cations inside the ellipsoidal cavity of SAPO-34 zeolites,while Cu O gradually generates on the external surface at higher loadings.The results reveal that isolated Cu²⁺cations are active sites for C₃H₆-SCR.The presence of Cu O species enhances C₃H₆activation,which thus,improves the C₃H₆-SCR performance at temperatures below 400°C.At higher temperatures,however,the formation of Cu O accelerates the non-selective oxidation of C₃H₆and causes the activity decline.These findings suggest that the active temperature window of HC-SCR over Cu/SAPO-34 catalysts can be tailored by tuning the proportion of copper species to fit the need in real applications,which provides new insights into understanding and designing high-efficient Cu-based zeolite catalysts.Next,the La-Sr-Co-O perovskite was prepared by citrate acid complex method,and nitric acid was then employed to dissolved Srcations to obtain A site-deficient perovskite.The changes of phase structure,coordination environment and electronic properties of the A site-deficient perovskite were carefully investigated by XRD,XAFS,ICP and XPS.The catalytic activity was also evaluated through the CO and NO oxidation reaction.The results show that the catalyst is reconstructed by acid treatment through selective dissolving SrCO₃and SrO.The deficiency of Sr（A-site）leads to the generation of more oxygen vancancies,which facilitates the activation of the lattice oxygen species.Therefore,the A site-deficient perovskite performed higher CO and NO oxidation ability at low temperatures.Moreover,a series of mesoporous SiO₂-encapsulated nano-Co₃O₄catalysts with different crystallite sizes was synthesized by adjusting the hydrothermal reaction period,which possessed unique pitaya-like structure with high CO oxidation activity and thermal stability.Among them,the CS-2h catalyst exhibits the superior catalytic oxidation performance,due to the smaller crystallite size and higher redox capability.In comparison with the supported Co₃O₄/SiO₂and pure Co₃O₄,the encapsulated Co₃O₄@SiO₂exhibits increased oxygen storage capacity,enhanced CO₂desorption behavior and higher lattice oxygen reactivity,which thus shows the higher CO oxidation activity.Additionally,the encapsulation structure of the as-prepared catalyst can effectively restrain the aggregation of Co₃O₄during high temperature operations and improves the utilization efficiency of cobalt resources.The Co₃O₄@SiO₂is also less prone to deactivation induced by the accumulation of surface carbonate at low temperature,and presents better regeneration performance and water resistance.The kinetic results demonstrate that the L-H mechanism is followed over the pure Co₃O₄nanoparticles catalyst,while the CO oxidation over the silica-supported Co₃O₄catalysts obey to both L-H and MVK mechanism.