The role played by an iodine-containing promoter in the formation of active polycrystalline silver catalyst surface

The programmed temperature desorption method was used to study the interaction of oxygen with the surface of a polycrystalline silver catalyst promoted with iodine. Ethyl iodide almost did not interact with the unoxidized surface of silver. The adsorption of C₂H₅I on the oxidized catalyst surface resulted in the formation of two adsorbed iodine forms, silver iodide and iodine deeply dissolved in subsurface silver crystal lattice layers. The character of oxygen adsorption from the iodine-containing surface of the catalyst was determined by the amount and form of adsorbed iodine. In the presence of a iodine-containing promoter, the concentration of oxide-like oxygen sharply decreased, and the amount of strongly bound atomically adsorbed oxygen responsible for the selective transformation of ethylene glycol into glyoxal increased.     

Identification of nitrogen-containing species obtained by nitric oxide adsorption on the surface of model gold catalysts

Nitric oxide adsorption at 300–500 K on gold particles supported on an alumina film has been investigated for the first time by in situ X-ray photoelectron spectroscopy. Two nitrogen-containing adsorption species can form on the surface of gold particles. By test experiments on NO adsorption on the stepped face (533) of a gold single crystal, these species have been identified as adsorbed nitrogen atoms (which are detected throughout the temperature range examined) and a surface complex with N₂O stoichiometry (which is stable in a narrow temperature range of 325–425 K).     

Synthesis of mesoporous bimetallic Pt-Sn catalytic coatings from polynuclear precursors for fine organic synthesis processes

A new method is developed to obtain nanosized catalytic Pt-Sn/TiO₂ coatings on the inner surface of a capillary microreactor during adsorption of polynuclear carbonyl Pt-Sn complexes on mesoporous TiO₂. Titanium oxide sol prepared in the presence of template (Pluronic F127 surfactant) is supported in dynamic mode. Pt-Sn bimetallic catalysts with an average particle size of 1.5–2 nm are synthesized by adsorption of the bimetallic [Pt₃(CO)₃(SnCl₃)₂(SnCl₂·H₂O)] _n ^2n? complex followed by thermal treatment. Physicochemical properties of samples (thickness, structure and morphology, chemical composition of the material, electronic state, specific surface area, pore volume and size distribution) are characterized by a set of methods (HR TEM, SEM, powder XRD, XRF, XPS, low-temperature nitrogen adsorption). Conditions to prepare the uniform non-peelable Pt-Sn/TiO₂ coating on the inner surface of a silica capillary with good adhesion are determined. To increase the TiO₂ thickness, multilayered TiO₂ films are synthesized by layerby layer deposition. The coating thickness is found to increase with an increase in the capillary diameter. The coating of a capillary with a diameter of 0.55 mm after 14-fold deposition is characterized by a thickness of 2 μm and an average pore size of 5.4 nm. The solvent effect on the adsorption of Pt-Sn carbonyl complexes into the TiO₂ support is studied. The amount of the adsorbed complex increases in the following order: ethanol < acetone ～ tetrahydrofuran. The physicochemical properties of the active component (surface concentration, dispersion, and composition) can be fine-tuned by varying the deposition method, precursor concentration in the initial solution, and temperature conditions of activation treatment. The catalyst activity in citral hydrogenation was 0.06–0.54 min^?1, with the selectivity with respect to unsaturated alcohols reaching 90% at citral conversion above 95%.     

Interactions of NO with iron deposited on alumina

The interaction of nitric oxide with single-crystal surfaces of alumina at temperatures of 298, 473, and 673 K, which had been covered by various amounts of iron, was studied using X-ray photoelectron spectroscopy. The iron was deposited onto Al₂O₃ in the Fe⁰ state. At low coverages, iron was partially oxidized due to its interaction with Al₂O₃. Scanning auger mapping analysis showed that the iron was randomly distributed on the Al₂O₃ surface. The amount of adsorbed NO increased with increasing iron coverage. However, at very high iron coverages, there was a decrease in adsorption. This indicated that the aluminum ions may have activated the NO adsorption on the iron atoms. For increasing temperature there was also an increase in adsorption for high iron coverages, but the adsorption decreased with increasing temperature for low iron coverages. Sticking probability calculations indicated that the adsorption was mobile and dissociative. Binding energy of the nitrogen peaks indicated that NO was adsorbed onto the Fe/Al₂O₃ surface as a nitride.     

Carbon Monoxide Oxidation by Polyoxometalate‐Supported Gold Nanoparticulate Catalysts: Activity,Stability, and Temperature‐ Dependent Activation Properties

Nanoparticulate gold supported on a Keggin‐type polyoxometalate (POM), Cs₄[α‐SiW₁₂O₄₀]⋅n H₂O, was prepared by the sol immobilization method. The size of the gold nanoparticles (NPs) was approximately 2 nm, which was almost the same as the size of the gold colloid precursor. Deposition of gold NPs smaller than 2 nm onto POM (Au/POM) was essential for a high catalytic activity for CO oxidation. The temperature for 50 % CO conversion was −67 °C. The catalyst showed extremely high stability for at least one month at 0 °C with full conversion. The catalytic activity and the reaction mechanism drastically changed at temperatures higher than 40 °C, showing a unique behavior called a U‐shaped curve. It was revealed by IR measurement that Au^δ+ was a CO adsorption site and that adsorbed water promoted CO oxidation for the Au/POM catalyst. This is the first report on CO oxidation utilizing Au/POMs catalysts, and there is a potential for expansion to various gas‐phase reactions.     

Carbon Monoxide Oxidation by Polyoxometalate‐Supported Gold Nanoparticulate Catalysts: Activity,Stability, and Temperature‐ Dependent Activation Properties

Nanoparticulate gold supported on a Keggin‐type polyoxometalate (POM), Cs₄[α‐SiW₁₂O₄₀]?n H₂O, was prepared by the sol immobilization method. The size of the gold nanoparticles (NPs) was approximately 2 nm, which was almost the same as the size of the gold colloid precursor. Deposition of gold NPs smaller than 2 nm onto POM (Au/POM) was essential for a high catalytic activity for CO oxidation. The temperature for 50 % CO conversion was ?67 °C. The catalyst showed extremely high stability for at least one month at 0 °C with full conversion. The catalytic activity and the reaction mechanism drastically changed at temperatures higher than 40 °C, showing a unique behavior called a U‐shaped curve. It was revealed by IR measurement that Au^δ+ was a CO adsorption site and that adsorbed water promoted CO oxidation for the Au/POM catalyst. This is the first report on CO oxidation utilizing Au/POMs catalysts, and there is a potential for expansion to various gas‐phase reactions.     

The Interaction of Oxygen with Silver Powders. A Comparison Between Esca Results and Volumetric Measurement

Interactions of oxygen with silver powders have been studied with a combination of angle-resolved ESCA and volumetric adsorption. Three states of adsorbed oxygen, i.e., atomically adsorbed oxygen, dissolved oxygen, and surface oxide, are characterized by 0(1s)-ESCA peaks at binding energies of 530.2, 532.0, and 529.3 eV respectivcly. The ESCA studies also suggest that atomically adsorbed oxygen dissolves into the subsurface of silver powders at temperatures above 100 °C, and then transforms into oxide (Ag₂O) at 175 °C. Adsorbed oxygen on the silver powders was partially desorbed at temperatures higher than 180 °C. The transformation and desorption information obtained from ESCA satisfactorily explains the variation of the adsorption isotherm with temperature obtained from the volumetric adsorption of oxygen on Ag/SiO₂ catalysts.     

AFM study of the adsorption of pyrrole and formation of the polypyrrole film on gold surface

Pyrrole (Py) adsorption and following electropolymerisation processes onto partially atomically flat Au (111) surfaces from aqueous solution of 0.1 M Py plus 0.1 M LiClO₄ have been investigated by non-contact atomic force microscopy. The adsorbed layers were examined, firstly in-situ, in solution of Py plus electrolyte and in pure electrolyte, and secondly ex-situ, in dried condition in air atmosphere. AFM images show clearly that in all cases the surface of the Au (111) electrode is covered with polymolecular adsorbed layer of Py. Electropolymerisation of the adsorbed Py layer causes some typical changes in the nanostructure of the layer: relatively larger nuclei disappear and honeycomb-like structures and ensembles of the middle size nuclei appear.     

NO adsorption on the stoichiometric and reduced SnO2(110) surface

The adsorption of NO molecules on the perfect and defective (110) surfaces of SnO₂ was studied with first-principles methods at the density-functional theory level. It was found that NO mainly interacts via the nitrogen atom with the bridging oxygens of the stoichiometric surface while the coordinatively unsaturated surface Sn atoms are less reactive. On the oxygen-deficient surface, NO is preferentially adsorbed at the vacancy positions, with the nitrogen atom close to the former surface oxygen site. Regardless of the adsorption site, the unpaired electron is located mainly on the NO molecule and only partly on surface Sn atoms. The results for the SnO₂ surface are compared to literature results on the isostructural TiO₂ rutile (110) surface. Dedicated to Professor Karl Jug on the occasion of his 65th birthday     

A Theoretical Study of the Interaction of Hydrogen and Oxygen with Palladium or Gold Adsorbed on Pyridine‐Like Nitrogen‐Doped Graphene

The interaction of H₂ and O₂ molecules in the presence of nitrogen‐doped graphene decorated with either a palladium or gold atom was investigated by using density functional theory. It was found that two hydrogen molecules were adsorbed on the palladium atom. The interaction of these adsorbed hydrogen molecules with two oxygen molecules generates two hydrogen peroxide molecules first through a Eley–Rideal mechanism and then through a Langmuir–Hinshelwood mechanism. The barrier energies for this reaction were small; therefore, we expect that this process may occur spontaneously at room temperature. In the case of gold, a single hydrogen molecule is adsorbed and dissociated on the metal atom. The interaction of the dissociated hydrogen molecule on the surface with one oxygen molecule generates a water molecule. The competitive adsorption between oxygen and hydrogen molecules slightly favors oxygen adsorption.     

大肠杆菌为模板制备Au@TiO_2催化剂及其CO氧化反应活性

许多微生物对金属离子有较强的吸附还原能力.本文利用大肠杆菌(DH5α)对金属离子较强的吸附与还原能力制备了Au@DH5α,再利用大肠杆菌的水分来水解钛酸四丁酯,得到Au@DH5α-Ti(OH)4样品,焙烧去除大肠杆菌后得到氧化钛包裹的纳米金粒子催化剂Au@TiO2.以N2吸附,X射线衍射(XRD),紫外-可见漫反射光谱(UV-VisDRS),热重-差热分析(TG-DTA),透射电镜(TEM)对所得材料进行表征.结果表明:该催化剂具有与大肠杆菌类似的杆状结构,以大肠杆菌为生物模板生成的氧化钛孔道结构在一定程度上抑制了金粒子的聚集长大.随菌体用量的增加,金粒子减小,等离子共振吸收发生紫移,催化剂有较大的比表面积,但催化剂中积炭量也会增加.将该催化剂用于CO氧化反应,发现当菌体用量为100或150mL时,制得的金催化剂可在80℃下将CO完全氧化为CO2.     

First‐principles calculation of OH−/OH adsorption on gold nanoparticles

The OH^? and OH adsorption structures on Au₅₅ and Au₁₃ nanoparticles surfaces are analyzed using density functional theory. The most stable OH^? adsorption site of Au₅₅ and Au₁₃ nanoparticles is found to be the vertex top site followed by the (111)‐(100) edge bridge site. On the contrary, the stability order of OH adsorption is opposite to that of OH^?. The adsorption of OH^? is calculated to be weaker than that of OH, which shows different charge transfer and interactions with gold surface. Coadsorption on nanoparticles is studied to find that multiple OH^? species prefer the most stable sites of single OH^? adsorption. The hydrogen bonding between adsorbed OH^? on gold surface is a key factor in stabilizing the adsorbates on the Au surface. © 2015 Wiley Periodicals, Inc.     

Adsorption sites of an iron-aluminum catalyst for ammonia oxidation as studied by the IR spectroscopy of the adsorbed NO probe molecule

The state of surface adsorption sites in the IK-42-1 oxide catalyst for ammonia oxidation depending on catalyst preparation conditions (the nature of raw materials and the temperature of calcination) was studied in this work with the use of the diffuse reflectance IR spectroscopy of the adsorbed NO probe molecule. Hematite, which was prepared by a sulfate or chloride technology, was used as the starting raw material; Al₂O₃ binding agents were prepared by the reprecipitation or hydration of thermally activated gibbsite; and acetic or nitric acid was used as an electrolyte. The samples were calcined at 900–1000°C. It was found that mono- and dinitrosyl complexes with reduced coordinatively unsaturated Fe²⁺ cations and nitrite-nitrate complexes were formed upon the adsorption of NO on the catalyst surface (regardless of the catalyst preparation conditions). The samples differed in the amount and degree of coordinative unsaturation of adsorption sites depending on the preparation conditions. It was concluded that the most coordinatively unsaturated Fe²⁺ adsorption sites observed were formed on the surface of a solid solution of iron cations in aluminum oxide, which was formed in the course of catalyst preparation. It was found that an increase in the catalyst calcination temperature resulted in a decrease in the number of coordinatively unsaturated adsorption sites, which correlated with the observed decrease in the yield of NO. This correlation had the shape of a saturation curve, which can reflect the occurrence of a reaction in the diffusion mode at high degrees of conversion for the majority of catalysts.     

The oxidation of carbon monoxide on iron oxide

The oxidation of CO on α-Fe₂O₃ was studied in a flow reactor. The conversion was complete at 650–660 K. The catalytic activity of iron oxide was higher than that of the ferrite-containing xMgOyFe₂O₃ catalyst. The adsorption of CO on iron oxide and the kinetics of interaction of carbon monoxide with oxygen atomically adsorbed on the surface of α-Fe₂O₃ were studied. The kinetic parameters of the oxidation of CO are evidence of the participation of adsorbed oxygen atoms, whose binding energy on the surface of α-Fe₂O₃ is lower than that on the surface of the magnesium ferrite-containing catalyst.     

Ru single atoms induce surface-mediated discharge in Na-O2 batteries

Sodium（Na）O₂ batteries have high energy density and low cost. However, high polarization, complex discharge products, and low Coulombic efficiency（CE） lead to poor cyclability. Here, we proposed an atomically dispersed Ru catalyst on nitrogen-doped graphene for Na-O₂ batteries. The catalysts enable the discharge to proceed via a surface-mediated route, which leads to uniform deposition of Na_2-xO₂ and low polarization during recharge. The first-principl...     

Heating effects on morphological and textural characteristics of individual and composite nanooxides

Morphological, structural and adsorption characteristics of nanooxides (fumed individual silica, alumina and titania, and composite silica/alumina, silica/titania and alumina/silica/titania) were compared after different treatments (wetting/drying, ball-milling, suspending/drying, heating) at different temperatures (373–1173 K) using low-temperature nitrogen adsorption data. The structural characteristics such as specific surface area (S _BET), pore volume (V _p), pore (PSD) and particle (PaSD) size distributions (calculated using self-consisting regularization procedure with respect to both PSD and PaSD), fractality, adsorption energy distributions depend differently on heating temperature because desorption of water molecularly and dissociatively adsorbed at a surface and in bulk of primary nanoparticles occurs over a wide temperature range at different rates. These processes affect both structural and energetic characteristics of nanooxides.     

Water‐Soluble Gold Nanoparticles: From Catalytic Selective Nitroarene Reduction in Water to Refractive Index Sensing

Water‐soluble gold nanoparticles (Au NPs) stabilized by a nitrogen‐rich poly(ethylene glycol) (PEG)‐tagged substrate have been prepared by reduction of HAuCl₄ with NaBH₄ in water at room temperature. The morphology and size of the nanoparticles can be controlled by simply varying the gold/stabilizer ratio. The nanoparticles have been fully characterized by TEM, high‐resolution (HR) TEM, electron diffraction (ED), energy‐dispersive X‐ray spectroscopy (EDS), UV/Vis, powder XRD, and elemental analysis. The material is efficient as a recyclable catalyst for the selective reduction of nitroarenes with NaBH₄ to yield the corresponding anilines in water at room temperature. Furthermore, the potential ability of the Au NPs as a refractive index sensor owing to their localized surface plasmon resonance (LSPR) effect has also been assessed.     

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.     

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.     

Reaction scheme of ammonia synthesis in the ECR plasmas

The reaction scheme of ammonia synthesis in the ECR plasma apparatus teas investigated from both identifications of the species in the plasmas and the adsorbed species on the surface of a steel substrate placed in the plasmas. The adsorbed species were considerably different when different kinds of plasmas are used. NH, species were adsorbed on the steel substrate surface in the nitrogen-hydrogen plasma, and N₂ molecules were adsorbed in the nitrogen plasma. By the application of a negative bias potential on the substrate, the adsorption of N atom or Fe-N bond formation was identified on the steel substrate surface. When the stainless steel wall of the chamber was covered with aluminum foil, the yield of NH,, radicals, which were on both the substrate and in the plasma, decreased. By exposure of the substrate, on which N₂ molecules or N atoms adsorbed, to the hydrogen plasma, N₂ and N disappeared from the steel substrate surface, forming ammonia. Moreover, the adsorption of NH,, radicals disappeared when the stainless steel wall surface was covered with aluminum foil. Thus, the surface of the stainless steel wall acts as a catalyst in ammonia formation. The formation of ammonia in the nitrogen-hydrogen ECR plasma, in which the steel substrate served as the catalyst, is not only through the dissociative adsorption of excited nitrogen molecules but also through the dissociative adsorption of nitrogen molecular ions.