Kelvin Probe Force Microscopy Study of a Pt/TiO2 Catalyst Model Placed in an Atmospheric Pressure of N2 Environment

A catalyst model comprising platinum nanoparticles deposited on a TiO₂(110) wafer was prepared in a vacuum, transferred in air, and characterized with a Kelvin probe force microscope placed in a N₂ environment. The topography and local work function of individual nanoparticles were observed with single‐nanometer resolution in the N₂ environment of one atmosphere pressure. Some nanoparticle presented positive shifts of work function relative to that of the TiO₂ surface, while the others showed negative shifts. This finding suggests heterogeneous properties of the nanoparticles exposed to air and then N₂. The ability of the advanced microscope was demonstrated in observing the work function of metal nanoparticles on a metal oxide support even in the presence of vapor environments.     

Atomic‐Scale Insight into Exsolution of CoFe Alloy Nanoparticles in La0.4Sr0.6Co0.2Fe0.7Mo0.1O3−δ with Efficient CO2 Electrolysis

In situ exsolution of metal nanoparticles in perovskite under reducing atmosphere is employed to generate a highly active metal–oxide interface for CO₂ electrolysis in a solid oxide electrolysis cell. Atomic‐scale insight is provided into the exsolution of CoFe alloy nanoparticles in La_0.4Sr_0.6Co_0.2Fe_0.7Mo_0.1O_3?δ (LSCFM) by in situ scanning transmission electron microscopy (STEM) with energy‐dispersive X‐ray spectroscopy and DFT calculations. The doped Mo atoms occupy B sites of LSCFM, which increases the segregation energy of Co and Fe ions at B sites and improves the structural stability of LSCFM under a reducing atmosphere. In situ STEM measurements visualized sequential exsolution of Co and Fe ions, formation of CoFe alloy nanoparticles, and reversible exsolution and dissolution of CoFe alloy nanoparticles in LSCFM. The metal–oxide interface improves CO₂ adsorption and activation, showing a higher CO₂ electrolysis performance than the LSCFM counterparts.     

Graphene‐Coated ZnO and SiO2 as Supports for CoO Nanoparticles with Enhanced Reducibility

The insertion of a graphene layer between cobalt and a substrate modifies the morphology and the oxidation/reduction properties of supported cobalt particles. Co forms a relatively flat structure on ZnO and SiO₂, whereas individual Co nanoparticles are formed after graphene coating of these substrates. The graphene layer moderates the formation of cobalt oxide in 5×10^?7 mbar O₂ and promotes the reduction of oxidized Co in H₂ at lower temperature. Angle‐resolved XPS measurements indicate that this is mainly a consequence of the restricted interaction of cobalt with the oxide supports. After the low‐pressure redox treatments, the graphene layer maintains a relatively high quality with a small number of defect sites.     

常温常湿条件下Au/Fe2O3催化剂上CO氧化反应的稳定性

用共沉淀法制备了Ａｕ／Ｆｅ２Ｏ３催化剂,考察了焙烧温度及金含量对Ａｕ／Ｆｅ２Ｏ３催化剂上ＣＯ氧化反应的影响,结果表明,焙烧温度及金含量对催化剂的稳定性均有较大影响,金含量为３％,３００℃焙烧制得的样品具有较好的稳定性和抗水性,在常温湿条件下可连续反应４３０ｈ保持ＣＯ完全转化;催化剂的稳定性与单质金及α－Ｆｅ２Ｏ３的粒径成反比,并与金及铁的化学状态有关,金粒子聚集、氧化态金含量的减少及催化剂表面碳酸根物种的累积可能是导致催化剂活性衰减的主要原因。     

High‐Performance Ru1/CeO2 Single‐Atom Catalyst for CO Oxidation: A Computational Exploration

By means of density functional theory computations, we examine the stability and CO oxidation activity of single Ru on CeO₂(111), TiO₂(110) and Al₂O₃(001) surfaces. The heterogeneous system Ru₁/CeO₂ has very high stability, as indicated by the strong binding energies and high diffusion barriers of a single Ru atom on the ceria support, while the Ru atom is rather mobile on TiO₂(110) and Al₂O₃(001) surfaces and tends to form clusters, excluding these systems from having a high efficiency per Ru atom. The Ru₁/CeO₂ exhibits good catalytic activity for CO oxidation via the Langmuir–Hinshelwood mechanism, thus is a promising single‐atom catalyst.     

Fabrication of Hierarchical Fe3O4@SiO2@P(4VP‐DVB)@Au Nanostructures and Their Enhanced Catalytic Properties

Hierarchical Fe₃O₄@SiO₂@P(4VP‐DVB)@Au nanostructures were prepared in which the slightly cross‐linked, thin poly(4‐vinylpyridine‐co‐divinylbenzene) (P(4VP‐DVB)) shells were constructed onto Fe₃O₄@SiO₂ nanospheres, followed by in situ embedding of gold nanocrystals homogeneously into the P4VP chains. These slightly cross‐linked chains, easily swollen by the reactants, make the gold nanocrystals accessible to the reactants, and the thin shell (about 15 nm) reduces the diffusion distance of the reactants to the active gold nanocrystals (about 5 nm), thereby enhancing their catalytic activity and utility. At the same time, confinement of gold nanocrystals within the P4VP shells prevents their migration and coagulation during catalytic transformations. Hence the nanocomposites exhibit high activity (up to 4369.5 h^?1 of turnover frequency (TOF)) and controllable magnetic recyclability without any significant loss of gold species after ten runs of catalysis in the reduction of 4‐nitrophenol.     

Nitrogen‐Enriched Fe3O4@Carbon Nanospheres Derived from Fe3O4@3‐Aminophenol/Formaldehyde Resin Nanospheres Based on a Facile Hydrothermal Strategy: Towards a Robust Catalyst Scaffold for Platinum Nanocrystals

Robust nitrogen‐enriched Fe₃O₄@carbon nanospheres have been fabricated as a catalyst scaffold for Pt nanoparticles. In this work, core–shell Fe₃O₄@3‐aminophenol/formaldehyde (APF) nanocomposites were first synthesized by a simple hydrothermal method, and subsequently carbonized to Fe₃O₄@N‐Carbon nanospheres for in situ growth of Pt nanocrystals. Abundant amine groups were distributed uniformly onto Fe₃O₄@N‐Carbon nanospheres, which not only improved the dispersity and stability of the Pt nanocrystals, but also endowed the Pt‐based catalysts with good compatibility in organic solvents. The dense three‐dimensional cross‐linked carbon shell protects the Fe₃O₄ cores against damage from harsh chemical environments, even in aqueous HCl (up to 1.0 m ) or NaOH (up to 1.0 m ) solutions under ultrasonication for 24 hours, which indicates that it can be used as a robust catalyst scaffold. In the reduction of nitrobenzene compounds, the Fe₃O₄@N‐Carbon@Pt nanocatalysts show outstanding catalytic activity, stability, and recoverability.     

Metal–Organic Framework (MOF) Template Based Efficient Pt/ZrO2@C Catalysts for Selective Catalytic Reduction of H2 Below 90 °C

Selective catalytic reduction (SCR) of NO_x with H₂ as a reductant is the most promising denitration technology at low temperature. Achieving the conversion of NO_x into N₂ at ambient temperature not only prolongs the service life of the catalyst, but also provides more freedom for the arrangement of denitration units throughout the flue gas treatment equipment. However, the development of highly efficient, stable, and environmentally benign supported platinum‐based catalysts for H₂‐SCR at ambient temperature is still a major challenge. Herein, a 0.5 wt % Pt/ZrO₂@C catalyst, which was composed of carbon‐coated octahedral ZrO₂ with highly dispersed Pt particles, was prepared by using a new stabilization strategy based on UiO‐66‐NH₂ (a zirconium metal–organic framework) as a template. The catalytic performance of this Pt/ZrO₂@C in H₂‐SCR was tested and confirmed to achieve near 100 % NO_x conversion at 90 °C. Also, 70 % N₂ selectivity of the catalyst was achieved. The morphology, structure, and porous properties of the as‐synthesized nanocomposites were characterized by using data obtained from field‐emission SEM, TEM, XRD, Raman spectroscopy, thermogravimetric analysis, X‐ray photoelectron spectroscopy, and N₂ adsorption–desorption isotherms. The results show that residual carbon formed by pyrolysis treatment is coated on octahedral ZrO₂, and effectively prevents the agglomeration of platinum particles on the surface.     

Pd Nanoparticles Supported on Triangle-Shaped La2O2CO3 Nanosheets: A New Highly Efficient and Durable Catalyst for Selective Hydrogenation of Cinnamaldehyde to Hydrocinnamaldehyde

A catalyst in which Pd nanoparticles are supported on triangle-shaped La₂O₂CO₃ nanosheets exposing predominantly the (001) planes (Pd/La₂O₂CO₃-TNS; where TNS denotes triangular nanosheets) was prepared by a facile solvothermal method. The Pd/La₂O₂CO₃-TNS catalysts exhibited excellent catalytic activity and recycling stability for hydrogenation of cinnamaldehyde to hydrocinnamaldehyde with turnover frequency of up to 41 238 h⁻¹. This enhanced activity of Pd/La₂O₂CO₃-TNS results from strong metal–support interactions. Structure analysis and characterization demonstrated that surface-oxygen-enriched La₂O₂CO₃-TNS supports exposing (001) planes are beneficial to charge transfer between the Pd nanoparticles and triangle-shaped La₂O₂CO₃ nanosheets and increase the electron density of Pd. Moreover, the modulated electronic states of the Pd/La₂O₂CO₃-TNS catalysts can enhance the adsorption and activation of hydrogen to enhance the hydrogenation activity.     

Strong Metal–Support Interactions between Pt Single Atoms and TiO2

Strong metal–support interaction (SMSI) has gained great attention in the field of heterogeneous catalysis. However, whether single‐atom catalysts can exhibit SMSI remains unknown. Here, we demonstrate that SMSI can occur on TiO₂‐supported Pt single atoms but at a much higher reduction temperature than that for Pt nanoparticles (NPs). Pt single atoms involved in SMSI are not covered by the TiO₂ support nor do they sink into its subsurface. The suppression of CO adsorption on Pt single atoms stems from coordination saturation (18‐electron rule) rather than the physical coverage of Pt atoms by the support. Based on the new finding it is revealed that single atoms are the true active sites in the hydrogenation of 3‐nitrostyrene, while Pt NPs barely contribute to the activity since the NP sites are selectively encapsulated. The findings in this work provide a new approach to study the active sites by tuning SMSI.     

Au/Fe2O3催化剂的制备及其对富氢气体中一氧化碳选择性氧化的催化性能

 采用共沉淀法制备了1.5%Au/Fe2O3催化剂,考察了加料方式对Au/Fe2O3催化剂化学组成及其催化富氢气体中CO选择性氧化性能的影响. 结果表明,正加法制备的Au/Fe2O3催化剂的性能明显好于反加法制备的催化剂,80 ℃时前者对富氢气体中CO选择性氧化反应的转化率为94%,CO2选择性为65%,连续反应10 h,催化剂活性没有变化. XRD,XPS和TEM等的测试结果表明,正加法制备的Au/Fe2O3催化剂中金粒子的平均粒径为2～4 nm,金粒子高度分散在载体上,并与载体之间发生了较强的相互作用,从而表现出较高的催化性能.     

Cr2O3-Co3O4／SiO2对十八醇氧化生成十八酸反应的催化性能

 制备了一系列不同Cr／Co比例的Cr2O3－Co3O4／SiO2催化剂，并用XRD，FT－IR和BET等手段对催化剂进行了表征；考察了催化剂对十八醇氧化生成十八酸反应的催化性能，及反应条件（反应温度和反应时间）对催化性能的影响，确定了最佳反应条件．结果表明，金属硝酸盐在773K焙烧后转变成相应的氧化物并负载于二氧化硅上．Cr2O3－Co3O4／SiO2催化剂对十八醇氧化反应有很高的催化活性，十八酸选择性最高可达99．93％，收率可达52．44％．Cr2O3－Co3O4／SiO2催化剂的活性明显高于单一的Cr2O3／SiO2或Co3O4／SiO2催化剂     

Stabilization of Palladium Nanoparticles on Nanodiamond–Graphene Core–Shell Supports for CO Oxidation

Nanodiamond–graphene core–shell materials have several unique properties compared with purely sp²‐bonded nanocarbons and perform remarkably well as metal‐free catalysts. In this work, we report that palladium nanoparticles supported on nanodiamond–graphene core–shell materials (Pd/ND@G) exhibit superior catalytic activity in CO oxidation compared to Pd NPs supported on an sp²‐bonded onion‐like carbon (Pd/OLC) material. Characterization revealed that the Pd NPs in Pd/ND@G have a special morphology with reduced crystallinity and are more stable towards sintering at high temperature than the Pd NPs in Pd/OLC. The electronic structure of Pd is changed in Pd/ND@G, resulting in weak CO chemisorption on the Pd NPs. Our work indicates that strong metal–support interactions can be achieved on a non‐reducible support, as exemplified for nanocarbon, by carefully tuning the surface structure of the support, thus providing a good example for designing a high‐performance nanostructured catalyst.     

Simple Preparation and Application of TEMPO‐Coated Fe3O4 Superparamagnetic Nanoparticles for Selective Oxidation of Alcohols

The organic oxidant TEMPO (2,2,4,4‐tetramethylpiperdine‐1‐oxyl) was immobilized on iron oxide (Fe₃O₄) superparamagnetic nanoparticles by employing strong metal‐oxide chelating phosphonates and azide/alkyne “click” chemistry. This simple preparation yields recyclable TEMPO‐coated nanoparticles with good TEMPO loadings. They have excellent magnetic response and efficiently catalyze the oxidation of a wide range of primary and secondary alcohols to aldehydes, ketones, and lactones under either aerobic acidic Mn^II/Cu^II oxidizing Minisci conditions, or basic NaOCl Anelli conditions. The nanoparticles could be recycled more than 20 times under the Minisci conditions and up to eight times under the Anelli conditions with good to excellent substrate conversions and product selectivities. Immobilization of the catalyst through a phosphonate linkage allows the particles to withstand acidic oxidizing environments with minimal catalyst leaching. Clicking TEMPO to the phosphonate prior to phosphonate immobilization, rather than after, ensures the clicked catalyst is the only species on the particle surface. This facilitates quantification of the catalyst loading. The stability of the phosphonate linker and simplicity of this catalyst immobilization method make this an attractive approach for tethering catalysts to oxide supports, creating magnetically separable catalysts that can be used under neutral or acidic conditions.     

Fe K‐Edge X‐ray Absorption Fine Structure Determination of γ‐Al2O3‐Supported Iron‐Oxide Species

The structure of FeO_x species supported on γ‐Al₂O₃ was investigated by using Fe K‐edge X‐ray absorption fine structure (XAFS) and X‐ray diffraction (XRD) measurements. The samples were prepared through the impregnation of iron nitrate on Al₂O₃ and co‐gelation of aluminum and iron sulfates. The dependence of the XRD patterns on Fe loading revealed the formation of α‐Fe₂O₃ particles at an Fe loading of above 10 wt %, whereas the formation of iron‐oxide crystals was not observed at Fe loadings of less than 9.0 wt %. The Fe K‐edge XAFS was characterized by a clear pre‐edge peak, which indicated that the Fe?O coordination structure deviates from central symmetry and that the degree of Fe?O?Fe bond formation is significantly lower than that in bulk samples at low Fe loading (<9.0 wt %). Fe K‐edge extended XAFS oscillations of the samples with low Fe loadings were explained by assuming an isolated iron‐oxide monomer on the γ‐Al₂O₃ surface.     

微波诱导Fe2O3/Al2O3催化剂催化氧化处理水中苯酚

 以γ-Al2O3为载体,采用浸渍-焙烧法制备了Fe2O3/Al2O3催化剂,并将其应用于微波诱导催化氧化处理模拟含酚废水. X射线衍射和X射线荧光光谱测试结果表明,活性组分氧化铁在催化剂中以α-Fe2O3的形式存在,其含量为3.71%. 与载体氧化铝相比,Fe2O3/Al2O3催化剂的比表面积和平均孔径及平均孔容略有降低. 对于100 mg/L的模拟含酚废水,最佳的处理工艺条件为: 微波辐照功率400 W,辐照时间5 min,催化剂加入量60 g/L,H2O2浓度600 mg/L,体系pH＞4. 在此工艺条件下,水中苯酚的去除率达97.98%. 催化剂连续使用20次后苯酚去除率仍达96.34%. 表观反应动力学研究表明,在氧化铁催化剂存在的条件下,微波诱导H2O2产生氧化性极强的羟基自由基,整个反应过程可分为微波诱导阶段和催化氧化阶段,两个阶段的氧化过程均符合一级反应动力学规律.     

Synthesis of Imidazo[1,2‐a]pyridines Using Fe3O4@SiO2 as an Efficient Nanomagnetic Catalyst via a One‐Pot Multicomponent Reaction

A one‐pot multicomponent synthesis of imidazo[1,2‐a]pyridine derivatives by using pyridin‐2‐amines, aldehydes, and terminal alkynes in the presence of a catalytic amount of silica‐supported iron oxide (Fe₃O₄@SiO₂) nanoparticles in refluxing EtOH in good‐to‐excellent yields is reported.