富氧条件下Co/ZSM-5催化剂对C_3H_8选择还原NO_x的性能

采用多种物理化学手段研究了在模拟的轻型柴油车尾气中不同Co担载量及Cu掺杂的Co/ZSM-5催化剂的Co组分分散状态、可还原性、NO吸附脱附性质对C3H8选择性催化还原NOx性能的影响。结果表明,浸渍法制备的Co/ZSM-5催化剂上既有外表面上的Co3+和Co2+物种,也有孔内的Co2+离子。富氧条件下Co/ZSM-5催化剂上C3H8选择性催化还原NOx的活性主要与ZSM-5载体孔外表面分散的CoOx物种中的钴离子可还原能力和NO吸附脱附性能密切相关。Co/ZSM-5催化剂上适宜的Co担载量约为4.0wt%,低担载量时随Co担载量增加,表面CoOx物种中钴离子可还原能力增强,C3H8选择性催化还原NOx的低温转化活性增加;高担载量时,随Co担载量增加,单位Co离子的NO吸附量的减少以及催化剂表面活性中心数的减少,导致了Co/ZSM-5催化剂NOx的转化率和催化剂比速率(k)的下降。孔外表面Co3O4晶体的存在使催化剂表面产生较强的NO吸附,并在高温时有利于C3H8的氧化燃烧,使C3H8选择性催化还原NOx的活性降低。     

富氧条件下Co/ZSM-5催化剂对C3H8选择还原NOx的性能

采用多种物理化学手段研究了在模拟的轻型柴油车尾气中不同Co担载量及Cu掺杂的Co/ZSM-5催化剂的Co组分分散状态、可还原性、NO吸附脱附性质对C₃H₈选择性催化还原NO_x性能的影响。结果表明,浸渍法制备的Co/ZSM-5催化剂上既有外表面上的Co³⁺和Co²⁺物种,也有孔内的Co²⁺离子。富氧条件下Co/ZSM-5催化剂上C₃H₈选择性催化还原NO_x的活性主要与ZSM-5载体孔外表面分散的CoO_x物种中的钴离子可还原能力和NO吸附脱附性能密切相关。Co/ZSM-5催化剂上适宜的Co担载量约为4.0wt%,低担载量时随Co担载量增加,表面CoO_x物种中钴离子可还原能力增强,C₃H₈选择性催化还原NO_x的低温转化活性增加;高担载量时,随Co担载量增加,单位Co离子的NO吸附量的减少以及催化剂表面活性中心数的减少,导致了Co/ZSM-5催化剂NO_x的转化率和催化剂比速率（k）的下降。孔外表面Co₃O₄晶体的存在使催化剂表面产生较强的NO吸附,并在高温时有利于C₃H₈的氧化燃烧,使C₃H₈选择性催化还原NO_x的活性降低。     

制备方法对Co-MOR催化剂CH4选择还原NO性能的影响

采用离子交换法、浸渍法制备一系列的Co-MOR 催化剂, 并将其用于CH₄选择性催化还原 NO_x(CH₄-SCR)反应. 运用X 射线衍射(XRD)、X 射线荧光光谱(XRF)、扫描电子显微镜(SEM)、紫外-拉曼(UVRaman)光谱、X射线光电子能谱(XPS)、NO程序升温脱附(NO-TPD)等手段对催化剂进行了表征. 结果表明, 浸渍法制备的催化剂, Co以Co₃O₄形式存在; 而离子交换法制备的催化剂, Co以离子形式进入丝光沸石(MOR)骨架之中, 在催化剂上形成更多的Co²⁺和[Co-O-Co]²⁺, 形成更均匀NO吸附中心和CH₄-SCR反应活性中心. 催化剂活性评价表明离子交换法制备的催化剂具有更宽的活性温度区间, Co(0.30)-MOR 催化剂在327-450℃温度范围内NO转化率大于50%.     

Catalytic Active Site for NO Decomposition Elucidated by Surface Science and Real Catalyst

Comprehensive studies combining surface science and real catalyst were performed to get further insight into catalytic active site and reaction mechanism for NO decomposition over supported palladium and cobalt oxide-based catalysts. On palladium single-crystal model catalysts, adsorption, dissociation and desorption behavior of NO was found to be closely related to the surface structures, the stepped surface palladium being active for dissociation of NO. In accordance with this result, the activity of powder Pd/Al₂O₃ catalysts for NO decomposition was directly related to the number of step sites exposed on the surface, suggesting that the step sites act as the catalytic active site for NO decomposition on Pd/Al₂O₃. NO decomposition over cobalt oxide was found to be significantly promoted by addition of alkali metals. Surface science study and catalyst characterization led to the same conclusion that the interface between the alkali metal and Co₃O₄ serves as the catalytic active site. From the results of in situ Fourier transform infrared (FT-IR) spectroscopy and isotopic transient kinetic analysis, a reaction mechanism was proposed in which the reaction is initiated by NO adsorption onto alkali metals to form NO₂⁻ species and then NO₂⁻ species react with the adsorbed NO species to form N₂ over the interface between the alkali metal and Co₃O₄.     

Effect of metal substitution for cobalt on the oxygen adsorption properties of YBaCo<Subscript>4</Subscript>O<Subscript>7</Subscript>

YBaCo₄O₇ compound is capable to intake and release a large amount of oxygen in the temperature range of 200–400°C. In the present study, the effect of Zn, Ga and Fe substitution for Co on the oxygen adsorption/desorption properties of YBaCo₄O₇ were investigated by thermogravimetry (TG) method. Due to fixed oxidation state of Zn2+ ions, the substitution of Zn²⁺ for Co²⁺ suppresses the oxygen adsorption of YBaCo_4−xZn_xO₇. The substitution of Ga³⁺ for Co³⁺ also decreases the oxygen absorption capacity of YBaCo_4−xGa_xO₇. This can be explained by the strong affinity of Ga³⁺ ions towards the GaO₄ tetrahedron. Compared with Zn- and Ga-substituted samples, the drop of oxygen adsorption capacity is smallest for Fe-substituted samples because of the similar changeability of oxidation states of Co and Fe ions.     

Reaction Kinetics and Mechanism of Selective NO Reduction on a CoZSM-5 Catalyst as Studied by SSITKA

The dynamics of ¹³C transfer from methane to carbon dioxide was studied under the steady-state reaction conditions of selective NO reduction with methane on a CoZSM-5 catalyst at various reactant (NO, CH₄, and O₂) concentrations and temperatures. It was found that the reaction occurs by a two-pathway mechanism with the participation of Co²⁺ sites (or CoO _x clusters) and paired Co²⁺–OH sites localized at the boundary between the clusters and the zeolite; in this case, the rate of the reaction at boundary sites was higher by more than one order of magnitude. Based on the numerical simulation of isotopic response curves, the concentrations of intermediate compounds and the rate constants of particular steps were evaluated; differences in the kinetics via the above reaction pathways were found and analyzed.     

Effect of transition metal additives on composite cobalt catalyst for NO x reduction with CH4

The CoH-BZZ and CoH-BMZ catalysts have good catalytic activity in the selective catalytic reduction of NO (NO-SCR) by methane, but have less selectivity at the reaction temperatures above 600°C. It was found that the addition of different transition metals to CoH-BZZ took different effect on SCR of NO by methane. Besides, Zn additives improved effectively the selectivity of methane towards NOx reduction. The nature of the active sites is characterized by diffuse reflectance H₂-TPR and XPS. These techniques show that in both CoZn-BZZ and CoZn-BMZ catalysts the cobalt is present as mononuclear Co²⁺ species, and the bind energy also decreased compared with CoH-composites (-BZZ and -BMZ). Reactivity of both CoZn-BZZ and CoZn-BMZ is much higher than that found on Co based catalysts in temperature range between 500 and 650°C.     

Effect of epitaxial growth on the formation of the cobalt catalysts of the Fischer-Tropsch synthesis

Mixed oxides Co_xAl_yO₄ with different Al/Co ratios applied as supports for the catalysts of the Fischer-Tropsch synthesis were prepared using the solid-state chemical reaction. The Co_xAl_yO₄ supports were prepared by modifying gibbsite with various cobalt salts (acetate, nitrate, and basic carbonate). The use of basic cobalt carbonate gives the Co(20%)/Co_xAl_yO₄ catalyst, which provides an increased yield of hydrocarbons C₅₊ and a decreased methane content compared to the impregnation catalyst Co(30%)/Al₂O₃. The introduction of small amounts of rhenium additives makes it possible to enhance the yield of hydrocarbons C₅₊ (179 g m⁻³) and also to increase the selectivity with respect to the C₅–C₁₈ fraction. The introduction of basic cobalt carbonate into the support, most likely, creates favorable conditions for the epitaxial growth of the precursor of the active phase. Dedicated to Academician G. A. Abakumov on the occasion of his 70th birthday. Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 9, pp. 1856–1860, September, 2007.     

Enhanced Electrochemical Nitrate-to-Ammonia Performance of Cobalt Oxide by Protic Ionic Liquid Modification

Electrochemical conversion of nitrate to ammonia is an appealing way for small-scale and decentralized ammonia synthesis and waste nitrate treatment. Currently, strategies to enhance the reaction performance through elaborate catalyst design have been well developed, but it is still of challenge to realize the promotion of reactivity and selectivity at the same time. Instead, a facile method of catalyst modification with ionic liquid to modulate the electrode surface microenvironment that mimic the role of the natural MoFe protein environment is found effective for the simultaneous improvement of NH₃ yield rate and Faradaic efficiency (FE) at a low NaNO₃ concentration of 500 ppm. Protic ionic liquid (PIL) N-butylimidazolium bis(trifluoromethylsulfonyl)imide ([Bim]NTf₂) modified Co₃O_4−x is fabricated and affords the NH₃ yield rate and FE of 30.23±4.97 mg h⁻¹ mg_cat.⁻¹ and 84.74±3.43 % at −1.71 and −1.41 V vs. Ag/AgCl, respectively, outperforming the pristine Co₃O_4−x. Mechanistic and theoretical studies reveal that the PIL modification facilitates the adsorption and activation of NO₃⁻ as well as the NO₃⁻-to-NH₃ conversion and inhibits hydrogen evolution reaction competition via enhancing the Lewis acidity of the Co center, shuttling protons, and constructing a hydrogen bonded and hydrophobic electrode surface microenvironment.     

Uncovering Dynamic Edge-Sites in Atomic Co−N−C Electrocatalyst for Selective Hydrogen Peroxide Production

Understanding the nature of single-atom catalytic sites and identifying their spectroscopic fingerprints are essential prerequisites for the rational design of target catalysts. Here, we apply correlated in situ X-ray absorption and infrared spectroscopy to probe the edge-site-specific chemistry of Co−N−C electrocatalyst during the oxygen reduction reaction (ORR) operation. The unique edge-hosted architecture affords single-atom Co site remarkable structural flexibility with adapted dynamic oxo adsorption and valence state shuttling between Co^(2−δ)+ and Co²⁺, in contrast to the rigid in-plane embedded Co₁−N_x counterpart. Theoretical calculations demonstrate that the synergistic interplay of in situ reconstructed Co₁−N₂-oxo with peripheral oxygen groups gives a rise to the near-optimal adsorption of *OOH intermediate and substantially increases the activation barrier for its dissociation, accounting for a robust acidic ORR activity and 2e⁻ selectivity for H₂O₂ production.     

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.     

Modulating Metal-Nitrogen Coupling in Anti-Perovskite Nitride via Cation Doping for Efficient Reduction of Nitrate to Ammonia

The complexes of metal center and nitrogen ligands are the most representative systems for catalyzing hydrogenation reactions in small molecule conversion. Developing heterogeneous catalysts with similar active metal-nitrogen functional centers, nevertheless, still remains challenging. In this work, we demonstrate that the metal-nitrogen coupling in anti-perovskite Co₄N can be effective modulated by Cu doping to form Co₃CuN, leading to strongly promoted hydrogenation process during electrochemical reduction of nitrate (NO₃⁻RR) to ammonia. The combination of advanced spectroscopic techniques and density functional theory calculations reveal that Cu dopants strengthen the Co−N bond and upshifted the metal d-band towards the Fermi level, promoting the adsorption of NO₃⁻ and *H and facilitating the transition from *NO₂/*NO to *NO₂H/*NOH. Consequently, the Co₃CuN delivers noticeably better NO₃⁻RR activity than the pristine Co₄N, with optimal Faradaic efficiency of 97 % and ammonia yield of 455.3 mmol h⁻¹ cm⁻² at −0.3 V vs. RHE. This work provides an effective strategy for developing high-performance heterogeneous catalyst for electrochemical synthesis.     

NOx-Sorbing Metal Oxides, MnOx–CeO2. Oxidative NO Adsorption and NOx–H2 Reaction

(n)MnO_x–(1?n)CeO₂ binary oxides have been studied for the sorptive NO removal and subsequent reduction of NO_x sorbed to N₂ at low temperatures (≤150 °C). The solid solution with a fluorite-type structure was found to be effective for oxidative NO adsorption, which yielded nitrate (NO^? ₃) and/or nitrite (NO^? ₂) species on the surface depending on temperature, O₂ concentration in the gas feed, and composition of the binary oxide (n). A surface reaction model was derived on the basis of XPS, TPD, and DRIFTS analyses. Redox of Mn accompanied by simultaneous oxygen equilibration between the surface and the gas phase promoted the oxidative NO adsorption. The reactivity of the adsorbed NO_x toward H₂ was examined for MnO_x–CeO₂ impregnated with Pd, which is known as a nonselective catalyst toward NO–H₂ reaction in the presence of excess oxygen. The Pd/MnO_x–CeO₂ catalyst after saturated by the NO uptake could be regenerated by micropulse injections of H₂ at 150 °C. Evidence was presented to show that the role of Pd is to generate reactive hydrogen atoms, which spillover onto the MnO_x–CeO₂ surface and reduce nitrite/nitrate adsorbing thereon. Because of the lower reducibility of nitrate and the competitive H₂–O₂ combustion, H₂–NO reaction was suppressed to a certain extent in the presence of O₂. Nevertheless, Pd/MnO_x–CeO₂ attained 65% NO-conversion in a steady stream of 0.08% NO, 2% H₂, and 6% O₂ in He at as low as 150 °C, compared to ca. 30% conversion for Pd/γ–Al₂O₃ at the same temperature. The combination of NO_x-sorbing materials and H₂-activation catalysts is expected to pave the way to development of novel NO_x-sorbing catalysts for selective deNO_x at very low temperatures.     

Triangle Cl−Ag1−Cl Sites for Superior Photocatalytic Molecular Oxygen Activation and NO Oxidation of BiOCl

BiOCl photocatalysis shows great promise for molecular oxygen activation and NO oxidation, but its selective transformation of NO to immobilized nitrate without toxic NO₂ emission is still a great challenge, because of uncontrollable reaction intermediates and pathways. In this study, we demonstrate that the introduction of triangle Cl−Ag₁−Cl sites on a Cl-terminated, (001) facet-exposed BiOCl can selectively promote one-electron activation of reactant molecular oxygen to intermediate superoxide radicals (⋅O₂⁻), and also shift the adsorption configuration of product NO₃⁻ from the weak monodentate binding mode to a strong bidentate mode to avoid unfavorable photolysis. By simultaneously tuning intermediates and products, the Cl−Ag₁−Cl-landen BiOCl achieved >90 % NO conversion to favorable NO₃⁻ of high selectivity (>97 %) in 10 min under visible light, with the undesired NO₂ concentration below 20 ppb. Both the activity and the selectivity of Cl−Ag₁−Cl sites surpass those of BiOCl surface sites (38 % NO conversion, 67 % NO₃⁻ selectivity) or control O−Ag₁−O sites on a benchmark photocatalyst P25 (67 % NO conversion and 87 % NO₃⁻ selectivity). This study develops new single-atom sites for the performance enhancement of semiconductor photocatalysts, and also provides a facile pathway to manipulate the reactive oxygen species production for efficient pollutant removal.     

Co0−Coδ+ Interface Double-Site-Mediated C−C Coupling for the Photothermal Conversion of CO2 into Light Olefins

Solar-driven CO₂ hydrogenation into multi-carbon products is a highly desirable, but challenging reaction. The bottleneck of this reaction lies in the C−C coupling of C₁ intermediates. Herein, we construct the C−C coupling centre for C₁ intermediates via the in situ formation of Co⁰−Co^δ+ interface double sites on MgAl₂O₄ (Co−CoO_x/MAO). Our experimental and theoretical prediction results confirmed the effective adsorption and activation of CO₂ by the Co⁰ site to produce C₁ intermediates, while the introduction of the electron-deficient state of Co^δ+ can effectively reduce the energy barrier of the key CHCH* intermediates. Consequently, Co−CoO_x/MAO exhibited a high C_2–4 hydrocarbons production rate of 1303 μmol g⁻¹ h⁻¹; the total organic carbon selectivity of C_2–4 hydrocarbons is 62.5 % under light irradiation with a high ratio (≈11) of olefin to paraffin. This study provides a new approach toward the design of photocatalysts used for CO₂ conversion into C₂₊ products.     

CoN1O2 Single-Atom Catalyst for Efficient Peroxymonosulfate Activation and Selective Cobalt(IV)=O Generation

High-valent metal-oxo (HVMO) species are powerful non-radical reactive species that enhance advanced oxidation processes (AOPs) due to their long half-lives and high selectivity towards recalcitrant water pollutants with electron-donating groups. However, high-valent cobalt-oxo (Co^IV=O) generation is challenging in peroxymonosulfate (PMS)-based AOPs because the high 3d-orbital occupancy of cobalt would disfavor its binding with a terminal oxygen ligand. Herein, we propose a strategy to construct isolated Co sites with unique N₁O₂ coordination on the Mn₃O₄ surface. The asymmetric N₁O₂ configuration is able to accept electrons from the Co 3d-orbital, resulting in significant electronic delocalization at Co sites for promoted PMS adsorption, dissociation and subsequent generation of Co^IV=O species. CoN₁O₂/Mn₃O₄ exhibits high intrinsic activity in PMS activation and sulfamethoxazole (SMX) degradation, highly outperforming its counterpart with a CoO₃ configuration, carbon-based single-atom catalysts with CoN₄ configuration, and commercial cobalt oxides. Co^IV=O species effectively oxidize the target contaminants via oxygen atom transfer to produce low-toxicity intermediates. These findings could advance the mechanistic understanding of PMS activation at the molecular level and guide the rational design of efficient environmental catalysts.     

Superior Storage Performance for NO in Modified Natural Mordenite

Natural mordenite (NMOR), modified by acid treatment and ion‐exchange, was employed for NO adsorption in the present study. The NO storage capacity of modified NMOR was greatly improved compared with its original correspondents, mainly due to the preservation of crystalline structure and the improvement of surface area of NMOR. Among all the modified NMOR, Ni‐NMOR exhibited the highest adsorption capacity for NO (1.20 mmol·g^?1) in the presence of 10% O₂ at 308 K. The influence of the main ingredients in flue gas on the storage capacity of NMOR for NO had also been investigated. In general, H₂O, CO₂ and SO₂ all displayed negative impact on NO adsorption due to their competitive adsorption on the surface of NMOR with NO, while the presence of O₂ greatly improved the adsorption of NO because of the formation of NO₂ and N₂O₃. Moreover, Ni‐NMOR exhibited high efficiency for NO_x removal through the NO_x adsorption‐plasma discharge process.     

以钴羰基簇合物为前驱体制备的钴基催化剂上F-T反应性能简

以含羧酸配体的钴羰基簇合物Co₂（CO）₆HCCCOOH,Co₃（CO）₉CCH₂COOH,Co₄（CO）₁₀HCCCOOH 为前驱体,γ-Al₂O₃为载体,通过浸渍法制备了一系列催化剂;同时以Co（NO₃）₂作为前驱体制备了参比催化剂. 对制备的催化剂进行了费托反应性能评价,并用透射电子显微镜、氨程序升温脱附和傅里叶变换红外光谱等手段对催化剂进行了表征. 结果发现,不同前驱体制备的催化剂对载体上Co的分布具有明显影响,进而影响催化剂活性. 反应结果表明,不同前驱体制备的催化剂上CO转化率及C₅₊选择性顺序为Co₃（CO）₉CCH₂COOH > Co₂（CO）₆HCCCOOH > Co₄（CO）₁₀HCCCOOH > Co（NO₃）₂.     

高硅 Na-ZSM-5 分子筛表面 NO 的常温吸附-氧化机理

 采用程序升温表面反应 (TPSR) 和原位漫反射红外光谱 (DRIFTS) 等手段研究了常温下 NO 和 O₂ 在高硅 Na-ZSM-5 分子筛上吸附-氧化反应机理. 结果表明, Na-ZSM-5 分子筛上 NO 的催化氧化过程中伴随着显著的 NO₂ 物理吸附, 表现为 NO 氧化和 NO₂ 吸附间的动态平衡. Na-ZSM-5 分子筛表面 NO_x 吸附物种的 TPSR 和原位 DRIFTS 表征表明, 化学吸附的 NO 和气相中的 O₂  在 Na-ZSM-5 表面反应生成吸附态的 NO₃, 并继续与 NO 作用生成弱吸附的 NO₂  和 N₂ O₄, 它们吸附饱和后释放出来; 其中, 强吸附的 NO₃ 在 NO 氧化过程中起到了反应中间体的作用, 同时也促进了 NO 的吸附.