Construction of Highly Active Metal-Containing Nanoparticles and FeCo-N4 Composite Sites for the Acidic Oxygen Reduction Reaction

Metal-containing nanoparticles (M-NPs) in metal/nitrogen-doped carbon (M-N-C) catalysts have been considered hostile to the acidic oxygen reduction reaction (ORR). The relation between M-NPs and the active sites of metal coordinated with nitrogen (MN_x) is hard to establish in acid medium owing to the poor stability of M-NPs. Herein, we develop a strategy to successfully construct a new FeCo-N-C catalyst containing highly active M-NPs and MN₄ composite sites (M/FeCo-SAs-N-C). Enhanced catalytic activity and stability of M/FeCo-SAs-N-C is shown experimentally. Calculations reveal that there is a strong interaction between M-NPs and FeN₄ sites, which can favor ORR by activating the O−O bond, thus facilitating a direct 4 e⁻ process. Those findings firstly shed light on the highly active M-NPs and FeN₄ composite sites for catalyzing acid oxygen reduction reaction, and the relevant reaction mechanism is suggested.     

Effect of Larger Pore Size on the Sorption Properties of Isoreticular Metal–Organic Frameworks with High Number of Open Metal Sites

Four isostructural CPO-54-M metal-organic frameworks based on the larger organic linker 1,5-dihydroxynaphthalene-2,6-dicarboxylic acid and divalent cations (M=Mn, Mg, Ni, Co) are shown to be isoreticular to the CPO-27 (MOF-74) materials. Desolvated CPO-54-Mn contains a very high concentration of open metal sites, which has a pronounced effect on the gas adsorption of N₂, H₂, CO₂ and CO. Initial isosteric heats of adsorption are significantly higher than for MOFs without open metal sites and are slightly higher than for CPO-27. The plateau of high heat of adsorption decreases earlier in CPO-54-Mn as a function of loading per mole than in CPO-27-Mn. Cluster and periodic density functional theory based calculations of the adsorbate structures and energetics show that the larger adsorption energy at low loadings, when only open metal sites are occupied, is mainly due to larger contribution of dispersive interactions for the materials with the larger, more electron rich bridging ligand.     

Interplay of Electronic and Steric Effects to Yield Low‐Temperature CO Oxidation at Metal Single Sites in Defect‐Engineered HKUST‐1

In contrast to catalytically active metal single atoms deposited on oxide nanoparticles, the crystalline nature of metal‐organic frameworks (MOFs) allows for a thorough characterization of reaction mechanisms. Using defect‐free HKUST‐1 MOF thin films, we demonstrate that Cu⁺/Cu²⁺ dimer defects, created in a controlled fashion by reducing the pristine Cu²⁺/Cu²⁺ pairs of the intact framework, account for the high catalytic activity in low‐temperature CO oxidation. Combining advanced IR spectroscopy and density functional theory we propose a new reaction mechanism where the key intermediate is an uncharged O₂ species, weakly bound to Cu⁺/Cu²⁺. Our results reveal a complex interplay between electronic and steric effects at defect sites in MOFs and provide important guidelines for tailoring and exploiting the catalytic activity of single metal atom sites.     

杭锦2#土的光谱特征及非均相Fenton反应机理

杭锦2#土是内蒙古鄂尔多斯杭锦旗地区发现的层状含铁天然矿物,利用Ｘ射线衍射、吡啶吸附红外光谱及Ｘ射线光电子能谱技术对样品的性质进行了表征。X射线光电子能谱表明杭锦2#土骨架结构中Si和Al原子结合能与标准硅氧四面体和铝氧八面体中Si和Al结合能相比明显增加,表面存在Lewis酸位和Brönsted酸位,且杭锦2#土中铁物种以Fe(Ⅲ)和Fe(Ⅱ)形式存在于骨架结构中;非均相Fenton反应中杭锦2#土的Fe(Ⅱ)可与H₂O₂反应生成自由基(·OH)与Fe(Ⅲ),但反应速率慢且难以循环。酸活化后杭锦2#土中Si和Al的结合能进一步增加,铁物种部分转变为非结构铁并以Fe3+与Fe2+转移到样品表面;X射线光电子能谱、吡啶红外和氨气程序升温表征表明酸活化杭锦2#土表面Lewis酸位和Brönsted酸位增多;非均相Fenton反应中,酸活化杭锦2#土表面Fe3+与Fe2+可与H₂O₂循环反应,不断生成·OH并对甲基橙进行降解,且活化杭锦2#土表面Brönsted酸能够提供质子将H₂O₂包围,抑制其分解生成HO-₂并提供更多的·OH,Lewis酸能增加杭锦2#土表面吸附氧（O_ad）含量,而Fe2+可被O_ad氧化为Fe3+,促进Fe2+/Fe3+之间的循环,同时在氧化过程中电子转移到O_ad形成O·-₂,O·-₂能够与Brönsted酸提供的质子反应形成·OH,·OH与O·-₂均为氧化性自由基,能够提升活化杭锦2#土非均相Fenton反应活性。此外,X射线衍射表明酸活化使杭锦2#土中CO2-₃转化为对Fenton反应负面影响更小的SO2-₄进而提升其非均相Fenton反应活性。     

Hydrogen dissociation on oxide covered MgH2 by catalytically active vacancies

MgH₂ is an important ingredient in modern reactive hydride composites to be used as hydrogen storage materials. The surface composition and chemical state of ball-milled MgH₂ is studied during hydrogen desorption by means of X-ray photoelectron spectroscopy. Simultaneously, the desorption rate of hydrogen is monitored, which is compared to dissociative properties of the surface investigated by hydrogen-deuterium exchange experiments. It is found that MgH₂ is also oxide covered during desorption demonstrating that MgO is able to recombine atomic hydrogen. The corresponding catalytic sites are associated with low coordinated surface vacancies on the oxide. The maximum surface concentration of these vacancies is very small, which is countered by a very high turnover frequency due to a small activation energy for dissociation of hydrogen of 0.1 eV on the single vacancy. The study provides insight into the catalytic role played by the oxide additives in MgH₂, which are superior catalysts for hydrogen sorption even when compared to 3d-metals.     

官能团及修饰位点对金属有机骨架化合物（MOFs）CO2/CH4分离性能的影响：蒙特卡洛模拟研究

In order to explore the in uence of modification sites of functional groups on landfill gas (CO₂/CH₄) separation performance of metal-organic frameworks (MOFs), six types of organic linkers and three types of functional groups (i.e. -F, -NH₂, -CH₃) were used to construct 36 MOFs of pcu topology based on copper paddlewheel. Grand canonical Monte Carlo simulations were performed in this work to evaluate the separation performance of MOFs at low (vacuum swing adsorption) and high (pressure swing adsorption) pressures, respectively. Simulation results demonstrated that CO₂ working capacity of the unfunctionalized MOFs generally exhibits pore-size dependence at 1 bar, which increases with the decrease in pore sizes. It was also found that -NH₂ functionalized MOFs exhibit the highest CO₂ uptake due to the enhanced Coulombic interactions between the polar -NH₂ groups and the quadrupole moment of CO₂ molecules, which is followed by -CH₃ and -F functionalized ones. Moreover, positioning the functional groups -NH₂ and -CH₃ at sites far from the metal node (site b) exhibits more significant enhancement on CO₂/CH₄ separation performance compared to that adjacent to the metal node (site a).     

The Role of Lewis Acid Sites in γ-Al2O3 Oligomerization

Olefin oligomerization by γ-Al₂O₃ has recently been reported, and it was suggested that Lewis acid sites are catalytic. The goal of this study is to determine the number of active sites per gram of alumina to confirm that Lewis acid sites are indeed catalytic. Addition of an inorganic Sr oxide base resulted in a linear decrease in the propylene oligomerization conversion at loadings up to 0.3 wt %; while, there is a >95 % loss in conversion above 1 wt % Sr. Additionally, there was a linear decrease in the intensity of the Lewis acid peaks of absorbed pyridine in the IR spectra with an increase in Sr loading, which correlates with the loss in propylene conversion, suggesting that Lewis acid sites are catalytic. Characterization of the Sr structure by XAS and STEM indicates that single Sr²⁺ ions are bound to the γ-Al₂O₃ surface and poison one catalytic site per Sr ion. The maximum loading needed to poison all catalytic sites, assuming uniform surface coverage, was ∼0.4 wt % Sr, giving an acid site density of ∼0.2 sites per nm² of γ-Al₂O₃, or approximately 3 % of the alumina surface.     

钾对CuSO4/TiO2脱硝催化剂的失活效应(英文)

为了减少碳排放，在世界各地兴建了越来越多的生物质电厂。钾元素是生物质电厂烟气中的一种典型元素并且可以引起脱硝催化剂的失活。具有优异抗SO₂性能的CuSO₄/TiO₂催化剂被认为是一种有前景的非钒基脱硝催化剂。但是，钾对CuSO₄/TiO₂催化剂的影响仍不清楚。本文研究了钾对CuSO₄/TiO₂催化剂的影响并且与商业V₂O₅-WO₃/TiO₂ (VWTi)催化剂作了比较，采用多种表征方法对催化剂样品进行了表征。钾可以引起CuSO₄/TiO₂和VWTi催化剂的失活，但是CuSO₄/TiO₂催化剂对钾的抵抗能力明显高于商业VWTi催化剂。钾会与CuSO₄/TiO₂催化剂中的CuSO₄发生反应生成CuO和...