Perovskite Type Oxide Used For Active Catalytic Removal And Corresponding Reaction Mechanism Study Of Type Small Molecule Gases Pollutionon

Eliminating pollutant gas in the atmosphere environment is imminent.Catalytic purification technology is the easy handling method to convert pollutant gas efficiently into harmless material for by adding catalyst,which is realized by reducing the activation energy of the reaction.Perovskite-type oxides due to the excellent redox property,accommodating a wide range of reactive ion,and excellent thermal stability,etc,are widely used in pollutant gas catalytic removal research.This research is aiming to prepare highly efficient perovskite catalysts to eliminate specific small molecules gas pollutants.Combined with in-situ DRIFTs and density functional theory?DFT?calculations,the corresponding catalytic reaction mechanism was studied in detail.And the target product generation process and rate-determining step were described.The results of this research are as follows:A series of LaFeO₃,La₂Cu₂O₄,and Cu-doped perovskite-typed LaB_0.8Cu_0.2O₃?B = Fe,Co,and Mn?catalysts were studied for the selective catalytic combustion of acrylonitrile?C2H₃CN?.The physicochemical properties of these materials were characterized by XRD,N₂ sorption,H₂-TPR,and XPS,thereafter correlating to their diverse evolutions of N₂ yield.The best performance was achieved over the LaFe_0.8C_0.2O₃ sample owing to an easy transformation from Cu²⁺ to Cu₀ at low temperatures.Moreover,the mechanism on selective catalytic combustion of acrylonitrile over LaFeO₃ and LaFe_0.8Cu_0.2O₃ was investigated by in-situ DRIFTs and DFT calculations.It has been noted that malonic was acquired on the surface of LaFe_0.8Cu_0.2O₃ and the acrylic species steadily existed over LaFeO₃,indicating that the strongly oxidative copper ion promotes an oxidation of C-terminal to carboxylic acid species at low temperatures.In addition,the copper substitution into LaFeO₃ can greatly reduce energy barrier for the transformation from-NH-O to-N-OH,which is thought as the rate-determining step for N₂ formation.Iron-based perovskites,of LaFe_1-xB'_xO_3-??B' = Cu,Pd?formula,were proposed as effective materials for the ammonia selective catalytic oxidation to nitrogen?NH₃-SCO?.Effects on N₂ yield,of copper or palladium substitutions in B position,and of perovskite dispersion over Al₂O₃ support,were reported.Copper and palladium substitution in perovskite lattice significantly promotes the NH₃ conversion rate,owing to the outstanding redox capacity displayed by the substituted compositions at low temperature?T<300??.While N₂ yield decreases upon Cu-doping,it retains as high as 80-90%over Pd-containing catalysts.Copper substitution enhances low-temperature oxygen mobility,which is favorable to N-H bond fracture of adsorbed-ONH₃ species that results in high NO formation.Palladium substitution results in an opposite effect,and high selectivity towards N₂ is obtained.Additionally,N₂ yield is significantly improved at high temperature,when perovskite active phase is dispersed over Al₂O₃ support.Combining in-situ DRIFTS and density functional theory?DFT?calculations,NH₃-SCO to N₂ reaction pathway over Fe-based perovskites is proposed to follow an Eley-Rideal?E-R?mechanism,during which gaseous NH₃ reacts with adsorbed-ONH₂ species to form surface diazo species?-N=N-?.For LaFeO₃,the rate-determining step is the-ON₂H₂ to-ON₂H reaction?overcoming an energy barrier of 3.48 eV?,while for LaFe_0.95Pd_0.05O₃,the rate-determining step is O-N bond cleavage?energy barrier of 1.55 eV?that explains then higher N₂ yield measured for the Pd-containing perovskite catalyst.The selective catalytic reduction of NO by methanol?CH₃OH-SCR?was studied over LaFe_0.8Cu_0.2O₃ and Ag/Al₂O₃-The catalysts were characterized by X-ray diffraction?XRD?,X-ray photoelectron spectroscopy?XPS?,H₂-temperature programmed reduction?H₂-TPR?,as well as temperature programmed desorption of NOads + O_2ads(NO_ads+O_2ads-TPD).In CH₃OH-SCR catalytic test,for LaFe_0.8Cu_0.2O₃ material,the NO conversion increases from 5%at 200 ? to around 95%at 450 ?and can be maintained at>95%above 450 ?,with N₂ as the main product?YN₂?60%?.Activity is related to low temperature redox properties of Cu²⁺ from the structure and significantly improvement of Fe³⁺ reduction degree.In contrast,Ag/Al₂O₃ was virtually inactive in the studied temperature range.In situ diffuse reflectance infrared fourier transform spectroscopy?in-situ DRIFTS?was used to inform on the adsorbed species and surface intermediate in order to elucidate the reaction mechanism differences over the two catalysts.Compared with Ag/Al₂O₃,CH₃OH is more easily oxidized to methoxy species?-O-CH₃?over LaFe_0.8Cu_0.2O₃,which is proposed to active surface C-containing species.The surface adNOx species observed over Cu-RG are mainly reactive nitrites/nitrates species,which could further reacted with-O-CH₃ species to form formohydroxamic acid?CHO-N?H?OH?.While over Ag/Al₂O₃,nitrate species accumulated over alumina surface and dehydration of CH₃OH occurs.Therefore,no enolic intermediate of SCR can be observed.The reaction pathway over LaFe_0.8Cu_0.2O₃ was proposed based on density functional theory?DFT?calculations The C-N bond coupling accompanied with the first H transfer step is identified as the dominant reaction step in CH₃OH-SCR process.A series of Co based perovskite oxides were used in catalytic oxidation of toluene to produce CO₂ and H₂O.Firstly,the catalytic activity of toluene was improved by introducing different types of active ions through doping in A-site?Sr,Ca,Ce,K,Na?and B-site?Mn,Cu,Ni,Pd?.It was found that A-site doping by Sr²⁺ leads to reduction of Co⁴⁺ to Co³⁺ at low temperature?<300 ??.Sr doping could cause more oxygen.deficiency,in order to obtain the electronic balance:LaCo₃+O₃ ? La_1-xSr_x²⁺Co_1-x³⁺Co⁴⁺_xO₃.The formation of oxygen vacancies is conducive to the adsorption of reactant and oxygen species,so as to effectively improve toluene catalytic activity.Mn doping also improve the oxidation of toluene,which is interpreted as with high state of Mn⁴⁺ in the structure of Co-O-Mn uneven distribution of electron density.Subsequently,the influence of Mn doping was compared,and it was found that when the Mn doping amount was 0.1(LaCo_0.9Mn_0.1O₃),the oxidation-reduction performance of the superoxide ion was optimal.The influences of different state of Mn and Pd in materials were also studied.It was found that toluene oxidation performance is optimal over LaCoMn_0.1O₃ and LaCoPd_0.5O₃ materials,due to the well-dispersion of MnO₂ and PdO.LaCoO₃ was further treated with acid/base,and the difference of performance was compared.It was found that treated with low concentration of HNO₃ material obtained more defects.The other as part of La³⁺ dissolved after acid treatment and Co²⁺ enter into A-site.According to the charge compensation,the B-site Co³⁺ was replaced by Co⁴⁺,which greatly improved the reducibility of the low temperature section.Therefore,the toluene oxidation activity of the acid treated material HNO₃-LaCoO₃ was the best.In conclusion,the doping of A andB active ions,the high dispersion of active components and the etching effect of acid can effectively improve the catalytic oxidation performance of toluene.