Active Oxygen in Oxide Catalytic Systems for Environmental Catalysis

Summary. The effect of the synthesis conditions of individual and modified with Mn Ni- and Co-oxide systems on the content and the mobility of their active oxygen has been studied by means of chemical and IR spectral analyses. The results obtained show that the main part of the active oxygen in Ni-oxide system is located on the catalyst’s surface (O_s ^* is approximately 73% of the total active oxygen), while Co-oxide system is characterized by much lower surface active oxygen content. Ni- and Co-oxide systems modified with Mn have comparatively higher active oxygen content as compared to the individual ones. Data of the IR spectral analysis reveal that Mn, as a modifying component, affects the mobility of the active oxygen, the latter contributing to the activity of oxide systems in oxidation processes. The high content of loosely bonded active oxygen formed during the synthesis determines a high catalytic activity of the studied samples in reactions of complete oxidation in the low temperature region.     

Catalytic degradation of methylene blue in aqueous solutions over Ni- and Co- oxide systems

The oxidative catalytic degradation of the cationic dye methylene blue (MB) with NaOCl in aqueous solutions was studied using individual and iron modified Ni- and Co-oxide systems as catalysts. The adsorption extent and the contribution of the uncatalyzed oxidation on the overall degree of MB were determined. The results indicate that methylene blue—a representative of a class of dyestuffs resistant to biodegradation—could be successfully decolorized and degraded using nickel and cobalt oxide catalysts at room temperature. The highest catalytic activity manifests in the Co-oxide system which is consistent with the adsorption data. The oxidative degradation reaction proceeds via first-order kinetics. Temperature has a relatively small effect on the methylene blue degradation kinetics. The results obtained reveal that the catalysts investigated are suitable for oxidative destruction of methytlene blue dye in wastewaters.      

The Solid-State-Grinding Synthesis of Maganese-Modified Cobalt Oxides and Application in the Low-Temperature CO Preferential Oxidation in H<Subscript>2</Subscript>-Rich Gases

A series of MnOx modified cobalt oxides with different atomic molar ratios of Mn/(Mn?+?Co) were prepared by a soft reactive grinding route and investigated for CO preferential oxidation in H₂. It was found that as-prepared Mn-doped cobalt oxides exhibited superior activity compared to the single constituted oxides, other Mn–Co–O mixed oxides synthesized by solution-based route, and other grinding-derived mixed metal oxides M–Co–O (M?=?Zn, Ni, Cu, Fe). The grinding-derived MnCo10 catalyst with Mn/(Mn?+?Co) molar ration of 10% showed the best CO oxidation activity and higher selectivity at low temperature. The surface richness of Co³⁺ was not found as increasing the Mn molar ratio in the present work. However, the incoporation of MnOx with proper amount into Co₃O₄ could produce high surface area, high structure defects, and rich surface active oxygen species, while the ability to supply the active oxygen species was suggested to play the crucial role in promoting the catalytic performance of Mn–Co–O mixed oxides.     

Nanocrystalline ceria–praseodymia and ceria–zirconia solid solutions for soot oxidation

The relative effects of Zr⁴⁺ and Pr^3+/4+ dopants on the structure, redox properties, and catalytic performance of nanosized ceria was studied. The investigated ceria?Czirconia and ceria?Cpraseodymia (CP) solid solutions were prepared by a modified coprecipitation method, characterized by a variety of techniques, and evaluated for soot oxidation. The characterization results indicate that CP has more surface and bulk oxygen vacancies, redox sites, and lattice oxygen mobility, and better thermal stability. Besides having low specific surface area, CP is more active in soot oxidation. This better activity has been attributed to the presence of more surface and bulk oxygen vacancies, which promote the adsorption of gas-phase oxygen and the formation and mobility of large numbers of active oxygen species.     

Performance of birnessite-type manganese oxide in the thermal-catalytic degradation of polyamide 6

Birnessite-type manganese oxide (BMO) was prepared by oxidation of Mn(NO₃)₂ with H₂O₂ in KOH solution. The nature and the extent of degradation of polyamide 6 (PA6) in the presence of samples were analysed by thermogravimetric analysis under static air atmosphere at several heating rates between 5 and 30 °C min^?1. The surface and structure of BMO were characterized using infrared (IR) spectroscopy, X-ray diffraction, and thermal analysis techniques. The acid sites of BMO were investigated by IR using pyridine as a molecular probe. The activation energy for degradation estimated by Kissinger method for PA6 and BMO/PA6 system containing 10 mass% of BMO was found to be 212 and 144 kJ mol^?1 under air, respectively. The catalytic activity observed in BMP catalyst was associated to a high lattice oxygen mobility.     

AgMn/HZSM-5催化剂上室温O3氧化脱除空气中的苯：Mn含量和水含量的影响

考察了Mn含量和水含量对AgMn/HZSM-5（AgMn/HZ）催化剂上室温O₃氧化（OZCO）脱除空气中苯的影响. 研究发现,Mn含量为2.4 wt%的AgMn/HZ催化剂（AgMn/HZ（2.4））具有大的比表面积和高的MnO_x分散度,OZCO活性和稳定性最高. 反应后的程序升温脱附结果表明,2.4 wt%的Mn含量能有效抑制苯和甲酸在催化剂上的残留. 当Mn含量≤ 2.4 wt%时,催化剂分解O₃的活性在苯氧化过程中占主导;当Mn含量 > 2.4 wt%时,苯的活化起主要作用. 基于AgMn/HZ（2.4）催化剂优越的反应活性和稳定性,进一步研究了湿气流中该催化剂上苯的氧化. 与干气流相比,水汽的加入能显著提高催化剂的反应活性和稳定性,且以0.1-0.2 vol%水含量时最优.     

Effect of the nature of support and Cu precursor on the activity of copper-containing catalysts in CO oxidation

We have studied the catalytic activity of supported copper-containing catalysts based on ZSM-5, Al₂O₃, and SiO₂ in oxidation of CO. We have established that the difference between the activities of systems with 1.8% copper content obtained from different precursors is determined by the different reducibilities of their active sites, the number of such sites, and the distribution of the metal ions. The fact that the activity is highest for 1.8% Cu-ZSM-5 obtained from copper acetate is due to the relatively higher number of associated Cu²⁺ cations in square planar coordination in a non-lattice oxygen environment, which have high reducibility, and the higher overall oxygen content O_ads + O_OH in the surface layer of the catalyst.     

synthesis and properties of β-brominated metal complexes of meso-triphenylcorrole

Spectral properties and chemical stability of Mn(III), Mn(IV), Fe(III), Fe(IV), and Cu(III) complexes of β-octabromotriphenylcorrole [(β-Br)₈(ms-Ph)₃Cor], synthesized from β-unsubstituted compounds by their reaction with molecular bromine, were studied. Cyclic voltammetry, electron microscopy, and X-ray spectral microanalysis were used to obtain electrochemical characteristics of metal corroles M(β-Br)₈(ms-Ph)₃Cor and gain insight into the surface texture of active catalysts on the basis of metal corroles. The electron-acceptor β-bromine substitution in the MCor macrocycle shifts the equilibrium in electron-donor solvents to lower oxidation states of the metals and also stabilizes manganese and destabilizes copper complexes in the protondonor medium HOAc-H₂SO₄. The electrocatalytic activity of the complexes in the reduction of molecular oxygen depends on the nature of the ligand and increases in the order Mn ≤ Cu ? Fe in the case of β-octabrominated macrocycles. The character of distribution of active centers on the surface of the catalysts was established for the first time.     

Dual-template synthesis of defect-rich mesoporous Co3O4 for low temperature CO oxidation

CO oxidation is a benchmark in heterogeneous catalysis for evaluation of redox catalysts due to its practical relevance in many applications and the fundamental problems associated with its very high activity at low temperatures. Among which, Co₃O₄ is one of the most active non-precious metal catalysts. Exposed crystal planes and cobalt sites are considered to be important for its high catalytic activity. Herein, we demonstrate an enhanced CO oxidation activity by a defect-rich mesoporous Co₃O₄ that prepared by a designed dual-template method. Two different kinds of silicas are used as hard-templates at the same time, resulting in a defect-rich mesoporous Co₃O₄ with a surface area as high as 169 m²/g. This catalyst exhibited a very high catalytic activity for low temperature CO oxidation with a light-off temperature at −73 ^oC under the space velocity of 80,000 mL h^-1 g_cat^-1. Further studies reveal that the high surface area promotes the lattice oxygen mobility, surface rich of Co²⁺ species and active oxygen species are crucial for the high catalytic activity. Moreover, the dual-template approach paves a way towards the design and construction of high-surface-area mesoporous metal oxides for various applications.     

Catalyst Design for Methacrolein Oxidation to Methacrylic Acid

Heteropoly compounds (HPCs) with the general formula CsMHPVMo₁₁O₄₀are prepared and tested as catalysts. The influence of elements entering the formula on the catalyst properties is studied: Cs defines the acidity and specific area, V controls the selectivity, and the transition metal M defines the mobility of oxygen in the bulk and the catalyst activity. The mechanism of methacrolein oxidation over HPCs is investigated. Using the response method and mass spectrometry of the reaction mixture, it is shown that only the catalyst oxygen atoms take part in the formation of methacrylic acid and that the transport of active oxygen to adsorbed methacrolein plays a key role in the oxidation process. A correlation between the HPC activity and the redox ability of the metal cation M ⁿ⁺ M ^{n+ i} (i= 1 or 2) is found. New catalysts for methacrolein oxidation to methacrylic acid are developed on the basis of this correlation. These are the salts of PVMo-poly acid with Cs, Cu, and the transition metal M as cations. These catalysts are more active (a conversion of up to 91%) and selective (up to 98%) compared to conventional catalysts for methacrolein oxidation to methacrylic acid.     

甲烷氧化偶联含锂多元复合氧化物催化剂的失活机理

对甲烷氧化偶联反应活性较高的多元复合氧化物催化剂（Ｌｉ－Ｔｉ－Ｌａ，Ｌｉ－Ｍｎ－Ｌａ，Ｌｉ－Ｎｉ－Ｌａ）的稳定性和失活机理进行了初步探讨，利用ＸＲＤ，ＩＲ，ＸＰＳ和Ｏ２－ＴＰＤ等方面对催化剂进行了表征，结果表明，催化剂在高温及反应气氛的作用下，表面锂的流失，使体相晶格中的锂向表面扩散，导致含锂活性相结构的分解（或部分分解），从而减少了体相相氧空位和生氧种的数量，降低了晶格氧的活动性，致使催化剂活必     

Oxidation of I- and S2- Anions by Oxygen in Aqueous Suspensions of Silica Gel

Oxidation of I^- and S^{2 -} anions on the silica gel surface by atmospheric oxygen was studied at room temperature. The possibility and rate of oxidation processes are determined by the content of silica gel and oxygen in the systems. Tentative interpretation of the results is based on the assumption that a highly reactive singlet ¹O₂ species is formed in the oxygen ensemble on the silica surface.     

钾改性Mn/Ce0.65Zr0.35O2催化剂催化氧化甲苯

Volatile organic compounds (VOCs) are both harmful to human health and the environment; however, catalytic combustion offers a promising method for VOC purification because of its high efficiency without secondary pollution. Although manganese-based catalysts have been well studied for VOC catalytic oxidation, their catalytic activity at low temperature must be improved. Alkali metals as promoters have the potential to modulate the electronic and structural properties of the catalysts, improving their catalytic activity. Herein, a Ce_0.65Zr_0.35O₂ support was prepared by co-precipitation and MnO_x/Ce_0.65Zr_0.35O₂ catalysts were obtained through the incipient-wetness impregnation method. The catalytic properties of K-modified MnO_x/Ce_0.65Zr_0.35O₂ for toluene oxidation with different molar ratios of K/Mn were investigated. In addition, the catalysts were characterized by XRD, UV/visible Raman, Hydrogen temperature program reduction (H₂-TPR), Oxygen temperature programmed desorption (O₂-TPD), X-ray photoelectron spectroscopy (XPS) and in situ diffuse reflectance FTIR spectroscopy (DRIFTS) experiments. The results showed that alkali metal doping with K significantly improved the catalytic activity. In particular, when the molar ratio of K/Mn was 0.2, the monolith catalyst Mn/Ce_0.65Zr_0.35O₂-K-0.2 exhibited the best performance with the lowest complete conversion temperature T₉₀ of 242 ℃ at a GHSV of 12000 h⁻¹. The XRD results suggested that MnO_x was uniformly distributed on the surface of the catalyst and that Mn⁴⁺ partially reduced to Mn³⁺ on the addition of K. The Raman spectrum demonstrated that with increasing K content, both the β- and α-MnO₂ phases coexisted on the Mn/Ce_0.65Zr_0.35O₂-K-0.2 catalyst, increasing the number of surface defect sites. The H₂-TPR experiment results confirmed that Mn/Ce_0.65Zr_0.35O₂-K-0.2 exhibited the lowest reduction temperature and good reducibility. From the O₂-TPD experiments, it was clear that Mn/Ce_0.65Zr_0.35O₂-K-0.2 contained the most surface adsorbed oxygen species and excellent lattice oxygen mobility, which benefitted the toluene oxidation activity. In addition, the XPS results suggested that the content of surface adsorbed oxygen species of the Mn/Ce_0.65Zr_0.35O₂-K-0.2 catalyst was the highest among all the tested samples. In addition, toluene-TPSR in N₂ as measured by in situ DRIFTs analysis demonstrated that available lattice oxygen was present in the Mn/Ce_0.65Zr_0.35O₂-K-0.2 catalyst. Therefore, the Mn/Ce_0.65Zr_0.35O₂-K-0.2 catalyst exhibited the best redox properties and oxygen mobility of the prepared samples and showed excellent activity toward toluene oxidation. Therefore, it was concluded that the addition of an appropriate amount of K improved the redox performance of the catalyst and increased the number of surface defect sites and mobility of the lattice oxygen of the catalyst as well as the concentration of the surface active oxygen species, thereby significantly improving catalytic ability.     

Modified Ceria-Zirconia Fluorite-Like Catalysts for the Combustion of Methane

For dispersed ceria-zirconia-based solid solutions prepared via the polymerized complex method and annealed at 700℃, effects of bulk doping by Ca, Mn, Co, Bi or Nb cations and surface modification by Mn and Pt on their structural features, surface/bulk oxygen reactivity and catalytic activity in methane combustion are considered. With up to 20 mol% doping, a structural type of homogeneous solid solutions of anion-deficient fluorite with disordered anion vacancies is formed. Doping by transition metal cations or Pt increases the mobility and reactivity of the surface/bulk oxygen. A broad variation in specific rates of methane combustion for the studied systems was observed, suggesting structural sensitivity of this reaction. In general, there is no universal relationship between the oxygen mobility, the reactivity and the catalytic activity in methane combustion, which is explained by the factor of specific methane activation on surface active sites. For the Pt-promoted samples, Pt efficiency in methane activation depends on the Pt-support interaction, and the most favorable ones being mixed Pt/MnOx and Pt/NbOx clusters on the surface of the supports that exhibit high lattice oxygen mobilities.     

Comparative study of Co/TiO<Subscript>2</Subscript>, Co–Mn/TiO<Subscript>2</Subscript> and Co–Mn/Ti–Ce catalysts for oxidation of elemental mercury in flue gas

The Co–Mn/Ti–Ce catalyst prepared by sol–gel and impregnation method was evaluated for catalytic oxidation of Hg⁰ in the simulated flue gas compared with Co/TiO₂ and Co–Mn/TiO₂. The results showed that Co–Mn/Ti–Ce catalyst exhibited higher catalytic activity (around 93% Hg⁰ removal efficiency in the temperature of 150 °C with 6% O₂, 400 ppm NO, 200 ppm SO₂ and 3% H₂O) than Co/TiO₂ and Co–Mn/TiO₂. Based on the characterization results of N₂ adsorption–desorption, XRD, UV–Vis, XPS, H₂-TPR and Hg-TPD, it could be concluded that the lower band gap, better reducibility and mercury adsorption capability and the presence of Co³⁺/Co²⁺, Mn⁴⁺/Mn³⁺ and Ce⁴⁺/Ce³⁺ redox couples as well as surface oxygen species contributed to the excellent Hg⁰ oxidation removal performance. In addition, well dispersion of active components and a synergetic effect among Co, Mn and Ce species might improve the activity further. A Mars–Maessen mechanism is thought to be involved in the Hg⁰ oxidation. The lattice oxygen derived from MnO _x or CoO _x would react with adsorbed Hg⁰ to form HgO and the consumption of lattice oxygen could be replenished by O₂. For Co–Mn/Ti–Ce, MnO _x?1 could be alternatively reoxidized by the lattice oxygen derived from adjacent CoO _x and CeO _x which is beneficial to the Hg⁰ oxidation.     

STUDIES OF MULTICOMPONENT COMPLEX OXIDE CATALYST FOR OXIDATIVE COUPLING OF METHANE Ⅷ.DEACTIVATION OF Li-DOPED Li-Me-La (Me=Ti,Mn,Ni)MULTICOMPONENT OXIDE CATALYST

The deactivation of highly active multicomponent oxide Li-La-Me(Me=Ti,Mn,Ni)catalyst at high reaction temperature has been studiedThe surface and bulk structure of the catlysts were characlerized by meansof XRD.IR.XPS.BET.O_2-TPD.etc The results show that the deactivationof the catalyst at high reaction temperature is mainly due to the loss ofsurface lithium As a result the ditfusion of lithium from bulk to surfaceleads to the decomposition of the active phase containing lithium whichlowers the number of oxygen yaeanctes and decreases the mobility of latticeoxygen.     

The effects of the conditions of formation of Ag-Co zeolite supported systems on their activity in the oxidation of carbon monoxide

The activity of Ag-Co zeolite catalysts in the oxidation of CO was studied. The peculiarities of the formation of Ag-Co-NaX systems with different active metal ratios were studied. The temperatures of hydrogen absorption maxima in the H₂ temperature-programmed reduction spectra of Ag-Co-NaX systems with different Ag/Co ratios correlated with the catalytic activity in the oxidation of CO. Different valence states of silver (Ag⁺, Ag⁰) and cobalt (Co³⁺, Co²⁺) were observed by X-ray photoelectron spectroscopy. It was found that the mutual influence of these states in the surface layer of Ag-Co zeolite catalysts affected their activity.     

3d Metal complexes with 2-hydroxy-3-methoxybenzaliminopropyl and 4-hydroxy-3-methoxybenzaliminopropyl immobilized on aerosil as catalysts of ozone decomposition

The composition and structure of M(II) (Mn, Co, Cu) complexes with Schiff bases (L1 = 2-hydroxy-3-methoxybenzaliminopropyl, L2 = 4-hydroxy-3-methoxybenzaliminopropyl) immobilized on Aerosil and their catalytic activity in ozone decomposition were studied. The formation of pseudotetrahedral bisligand complexes M(L1)₂ and pseudooctahedral complexes M(L2)₂ on the modified surface of Aerosil was confirmed by IR and ESR spectroscopy and by diffuse reflectance spectroscopy (DSR). The catalytic activity of isostructural complexes in ozone decomposition varies in the order Mn > Co > Cu, and M(L₂)₂ complexes are more active than M(L1)₂.     

Using the Interaction between Copper and Manganese to Stabilize Copper Single-atom for CO Oxidation.

The interaction between Cu and Mn has been used to immobilize the Cu single-atom on MnO₂ surface by redox-driven hydrolysis. Comprehensive structure and property characterizations demonstrate that the existence of an Cu−Mn interaction on the catalyst surface can effectively restrain the aggregation of Cu single atoms and improve carbon monoxide (CO) oxidation activity. The interaction of forming the Cu−O−Mn entity is beneficial for CO catalytic activity as the migration of reactive oxygen species and the coordination effect of active centers accelerate the reaction. In particular, 3%-Cu₁/MnO₂ shows an oxygen storage capacity (OSC) value (342.75 μmol/g) more than ten times that of pure MnO₂ (27.79 μmol/g) and has high CO catalytic activity (T_90%=80 °C), it can maintain CO conversion of 95 % after 15 cycles. This work offers a reliable method for synthesizing Cu single-atom catalysts and deepens understanding of the interaction effect between single transition metal atoms and supports that can improve the catalytic activity of CO oxidation.     

Low-temperature catalytic oxidation of toluene over Mn–Co–O/Ce<Subscript>0.65</Subscript>Zr<Subscript>0.35</Subscript>O<Subscript>2</Subscript> mixed oxide catalysts

Ce_0.65Zr_0.35O₂ was prepared by co-precipitation method and a series of Mn_1-yCo_y/Ce_0.65Zr_0.35O₂ catalysts with different Mn/Co molar ratio were synthesized via the co-impregnation method. These catalysts were applied for gaseous toluene oxidation, which showed that the catalytic activity was significantly improved by the addition of Mn and Co. In particular, Mn–Co(1:1)/Ce_0.65Zr_0.35O₂ with Mn/Co molar ratio of 1:1 displayed the best result with the lowest complete conversion temperature of 242 °C under a GHSV of 12,000 h^?1. The as-prepared catalysts were characterized by X-ray diffraction, H₂ temperature-programmed reduction, N₂ adsorption–desorption, X-ray photoelectron spectroscopy and O₂ temperature-programmed desorption. These characteristics revealed that the coexistence of Mn and Co could enhance the redox property and generate more surface adsorbed oxygen, thereby improving the performance of the catalysts for toluene low-temperature oxidation. The Mn–Co(1:1)/Ce_0.65Zr_0.35O₂ exhibited the best catalytic activity and high stability. The excellent catalytic activity of the Mn–Co(1:1)/Ce_0.65Zr_0.35O₂ could be ascribed to a greater amount of surface adsorbed oxygen species and Mn⁴⁺ on the catalyst surface.