Economizing on Precious Metals in Three‐Way Catalysts: Thermally Stable and Highly Active Single‐Atom Rhodium on Ceria for NO Abatement under Dry and Industrially Relevant Conditions**

We show for the first time that atomically dispersed Rh cations on ceria, prepared by a high‐temperature atom‐trapping synthesis, are the active species for the (CO+NO) reaction. This provides a direct link with the organometallic homogeneous Rh^I complexes capable of catalyzing the dry (CO+NO) reaction. The thermally stable Rh cations in 0.1 wt % Rh₁/CeO₂ achieve full NO conversion with a turn‐over‐frequency (TOF) of around 330 h^?1 per Rh atom at 120 °C. Under dry conditions, the main product above 100 °C is N₂ with N₂O being the minor product. The presence of water promotes low‐temperature activity of 0.1 wt % Rh₁/CeO₂. In the wet stream, ammonia and nitrogen are the main products above 120 °C. The uniformity of Rh ions on the support, allows us to detect the intermediates of (CO+NO) reaction via IR measurements on Rh cations on zeolite and ceria. We also show that NH₃ formation correlates with the water gas shift (WGS) activity of the material and detect the formation of Rh hydride species spectroscopically.     

合成方法对Rh/CeO2-ZrO2-La2O3催化剂的结构、表面性能及DeNOx活性的影响

用沉积沉淀法合成两种不同系列的CeO2-ZrO2-La2O3混合氧化物(ZrO2和La2O3沉积CeO2粒子(标记为A-x)以及CeO2和La2O3沉积ZrO2粒子(标记为B-x)),并用作Rh催化剂的载体。XRD、拉曼、TPR、XPS和O2脉冲等表征结果显示出不同的沉积顺序将导致不同的结构和氧化还原性能,且B-x具有更高的氧迁移性、储氧能力和表面Ce浓度。当其负载Rh后,Rh/B-x催化剂具有更高的NO和CO转化率及N2选择性,且Ce的最佳含量为50at%。这可能归因于Rh负载于富铈表面形成更多有利于NO分解的表面Ce3+活性位。     

Electronic Metal-Support Interaction-Modified Structures and Catalytic Activity of CeOx Overlayers in CeOx/Ag Inverse Catalysts

Electronic metal-support interactions (EMSIs) of oxide-supported metal catalysts strongly modifies the electronic structures of the supported metal nanoparticles. The strong influence of EMSIs on the electronic structures of oxide overlayers on metal nanoparticles employing cerium oxides/Ag inverse catalysts is reported herein. Ce₂O₃ overlayers were observed to exclusively form on Ag nanocrystals at low cerium loadings and be resistant to oxidation treatments up to 250 °C, whereas CeO₂ overlayers gradually developed as the cerium loading increased. Ag cubes enclosed by {001} facets with a smaller work function exert a stronger EMSI effect on the CeO_x overlayers than Ag cubes enclosed by {111} facets. Only the CeO₂ overlayers with a fully developed bulk CeO₂ electronic structure significantly promote the catalytic activity of Ag nanocrystals in CO oxidation, whereas cerium oxide overlayers with other electronic structures do not. These results successfully extend the concept of EMSIs from oxide-supported metal catalysts to metal-supported oxide catalysts.     

Caracterisation De Catalyseurs ZrxCe1–xO2 et Etude De Leur Reactivite Dans L'Oxydation Des Suies Par ATD/ATG

Thermal analysis has been used to investigate the crystallization of Zr_xCe_1-xO₂ mixed oxides, prepared by co-precipitation of corresponding hydroxides. For x≤0.5, small crystals of CeO₂, were formed at low temperatures (373 K). For x>0.5an exothermic peak at 420°C (693 K) was observed after calcination under a flow of air ofhydroxide samples. This peak was associated with the formation of a Zr_xCe_1-xO₂ solid solution (XRD) in a tetragonal phase (Raman). The solids calcined at 700°C (973 K) present a reactivity towards the carbon black oxidation. The thermal analysis coupled with a gas chromatograph (GC) were used to follow this reactivity. Simultaneous study of the activity (thermal analysis) and the selectivity (GC) in CO or CO₂ of the different catalysts revealed an important parameter: acatalyst-soot particle contact. We also obtained a more precise comparison of Zr_xCe_1-xO₂ oxides in the catalytic soot combustion. This revised version was published online in August 2006 with corrections to the Cover Date.     

Time‐Resolved,In Situ DRIFTS/EDE/MS Studies on Alumina‐Supported Rhodium Catalysts: Effects of Ceriation and Zirconiation on Rhodium–CO Interactions

The effects of ceria and zirconia on the structure–function properties of supported rhodium catalysts (1.6 and 4 wt % Rh/γ‐Al₂O₃) during CO exposure are described. Ceria and zirconia are introduced through two preparation methods: 1) ceria is deposited on γ‐Al₂O₃ from [Ce(acac)₃] and rhodium metal is subsequently added, and 2) through the controlled surface modification (CSM) technique, which involves the decomposition of [M(acac)_x] (M=Ce, x=3; M=Zr, x=4) on Rh/γ‐Al₂O₃. The structure–function correlations of ceria and/or zirconia‐doped rhodium catalysts are investigated by diffuse reflectance infrared Fourier‐transform spectroscopy/energy‐dispersive extended X‐ray absorption spectroscopy/mass spectrometry (DRIFTS/EDE/MS) under time‐resolved, in situ conditions. CeO_x and ZrO₂ facilitate the protection of Rh particles against extensive oxidation in air and CO. Larger Rh core particles of ceriated and zirconiated Rh catalysts prepared by CSM are observed and compared with Rh/γ‐Al₂O₃ samples, whereas supported Rh particles are easily disrupted by CO forming mononuclear Rh geminal dicarbonyl species. DRIFTS results indicate that, through the interaction of CO with ceriated Rh particles, a significantly larger amount of linear CO species form; this suggests the predominance of a metallic Rh phase.     

Bildung und thermische stabilität von rhodium-oxiden

Thermoanalytical and X-ray studies were carried out on rhodium and on rhodium compounds. They proved that the orthorhombic β-Rh₂O₃ is the most stable oxide under normal pressure. The low temperature form (χ-Rh₂O₃) with corundum structure was formed only in the decomposition of rhodium compounds (hydroxide, nitrate, sulfate). It transforms slowly and irreversibly to the high temperature modification (β-Rh₂O₃) upon heating in the range 750-1000°C. The rutile-type oxide RhO₂ could be prepared also under normal pressure at about 450-600°C by decomposition of Rh-nitrate or Rh-hydroxide. It decomposes irreversibly and probably topotactically to χ-Rh₂O₃ at higher temperatures. The thermal decomposition of Rh₂O₃ depends on the oxygen pressure, it decreases from 1130°C at 760 torr to 900°C at 10 torr. This pressure dependence was determined by TG and DTG and was used for calculating the heat of dissociation of Rh₂O₃. For a medium temperature ΔH^o₁₂₈₇=92.7 kcal mol^?1 which is in the order of the heat of formation of Rh₂O₃. Both χ- and β-Rh₂O₃ are decomposed readily to Rh in reducing atmosphere at about 100-150°C. The linear thermal expansion of the Rh-sesquioxides is very similar, about 5.5 × 10^?6 in the average.Die wichtigsten Ergebnisse der hier beschriebenen thermoanalytischen Untersuchungen über die Bildung und die Stabilität der Rhodiumoxide sind folgende:Die Aufoxidation von metallischem Rhodium findet je nach Korngrösse im Bereich von etwa 300-1000°C statt. Beim Rhodiummohr bildet sich dabei zuerst die metastabile Korundform (χ-Rh₂O₃), sonst immer gleich die stabile, orthorhombische Hochtemperaturform (β-Rh₂O₃).Die Zersetzung von Rhodiumhydroxid, Rh-nitrat, und Rh-sulfat geht immer über das α-Rh₂O₃ zum β-Rh₂O₃, wobei diese polymorphe Umwandlung äusserst träge abläuft. Bei kurzzeitigem Erhitzen ist χ-Rh₂O₃ auch noch bei 1000°C stabil.     

A pyrazine bis‐adduct of a binuclear rhodium(II) carboxylate containing 3,4,5‐triethoxybenzoate as the ­equatorial ligand

The title compound, tetrakis(μ‐3,4,5‐triethoxy­benzoato‐κ²O:O′)­bis­[(pyrazine‐κN)­rhodium(II)](Rh—Rh), [Rh₂(C₁₃H₁₇O₅)₄(C₄H₄N₂)₂], crystallizes on an inversion centre in the triclinic space group . The equatorial carboxyl­ate ligands bridge the two Rh^II atoms, giving a binuclear lantern‐like structure. The pyrazine mol­ecules occupy the two axial coordination sites. The phenyl rings are tilted by ca 10° with respect to the attached carboxyl­ate groups. The pyrazine planes have a torsion angle of ca 19° around the Rh—N bond with respect to the plane of the nearer carboxyl­ate group and are not coplanar with the Rh—Rh bond.     

Confined Ultrathin Pd‐Ce Nanowires with Outstanding Moisture and SO2 Tolerance in Methane Combustion

An efficient strategy (enhanced metal oxide interaction and core–shell confinement to inhibit the sintering of noble metal) is presented confined ultrathin Pd‐CeO_x nanowire (2.4 nm) catalysts for methane combustion, which enable CH₄ total oxidation at a low temperature of 350 °C, much lower than that of a commercial Pd/Al₂O₃ catalyst (425 °C). Importantly, unexpected stability was observed even under harsh conditions (800 °C, water vapor, and SO₂), owing to the confinement and shielding effect of the porous silica shell together with the promotion of CeO₂. Pd‐CeO_x solid solution nanowires (Pd‐Ce NW) as cores and porous silica as shells (Pd‐CeNW@SiO₂) were rationally prepared by a facile and direct self‐assembly strategy for the first time. This strategy is expected to inspire more active and stable catalysts for use under severe conditions (vehicle emissions control, reforming, and water–gas shift reaction).     

Synthesis,Structural Characterization and Physical Properties of a New Member of Ternary Lithium Layered Compounds – Li2RhO3

Li₂RhO₃ was synthesized by solid state reaction and its crystal structure was refined from X‐ray powder data by the Rietveld‐method. The compound was obtained as a black powder and crystallizes in the monoclinic space group C2/m, with unit cell parameters a = 5.1198(1), b = 8.8497(1), c = 5.1030(1) Å, β = 109.61(2) °, V = 217.80(1), and Z = 4. The structure determination shows that the oxygen atoms in Li₂RhO₃ form an approximate cubic close packing, where all octahedral voids are occupied by Rh⁴⁺ and Li⁺ cations. The structure is closely related to the α‐NaFeO₂ and Li₂MnO₃ layered structure types (layered variants of the NaCl‐type), but in Li₂RhO₃ the lithium and rhodium atoms are partially disordered. Li₂RhO₃ behaves as a semiconductor with rather small activation energy of 7.68 kJ · mol^–1 and is thermally stable up to 1273 K in argon atmosphere. According to measurements of the magnetic susceptibility in the temperature range from 2 to 330 K, Li₂RhO₃ is paramagnetic, obeys the Curie–Weiss law at temperatures above 150 K, and has an effective magnetic moment of 1.97 μ_B at 300 K.     

Ligand-Protected Ultrasmall Pd Nanoclusters Supported on Metal Oxide Surfaces for CO Oxidation: Does the Ligand Activate or Passivate the Pd Nanocatalyst?

Herein, we report on the synthesis of ultrasmall Pd nanoclusters (∼2 nm) protected by L-cysteine [HOCOCH(NH₂)CH₂SH] ligands (Pd_n(L-Cys)_m) and supported on the surfaces of CeO₂, TiO₂, Fe₃O₄, and ZnO nanoparticles for CO catalytic oxidation. The Pd_n(L-Cys)_m nanoclusters supported on the reducible metal oxides CeO₂, TiO₂ and Fe₃O₄ exhibit a remarkable catalytic activity towards CO oxidation, significantly higher than the reported Pd nanoparticle catalysts. The high catalytic activity of the ligand-protected clusters Pd_n(L-Cys)_m is observed on the three reducible oxides where 100 % CO conversion occurs at 93–110 °C. The high activity is attributed to the ligand-protected Pd nanoclusters where the L-cysteine ligands aid in achieving monodispersity of the Pd clusters by limiting the cluster size to the active sub-2-nm region and decreasing the tendency of the clusters for agglomeration. In the case of the ceria support, a complete removal of the L-cysteine ligands results in connected agglomerated Pd clusters which are less reactive than the ligand-protected clusters. However, for the TiO₂ and Fe₃O₄ supports, complete removal of the ligands from the Pd_n(L-Cys)_m clusters leads to a slight decrease in activity where the T_100% CO conversion occurs at 99 °C and 107 °C, respectively. The high porosity of the TiO₂ and Fe₃O₄ supports appears to aid in efficient encapsulation of the bare Pd_n nanoclusters within the mesoporous pores of the support.     

Low temperature carbon monoxide catalytic oxidation at the Pd/Ce–Zr–Al–Ox catalyst

The homogeneous chemical composition ceria–zirconia–alumina (Ce–Zr–Al–O_x) nano-alloy were successfully synthesized by surfactant-assisted parallel flow co-precipitation method and applied as supports for low temperature CO oxidation. The experiment conditions were studied in detailed. At 0.92 wt% Pd loading, 30,000 ppm CO could be completely oxidized to CO₂ at 30 °C at a WHSV of 4,380 ml g^?1 h^?1 over the Pd/Ce–Zr–Al–O_x (n_Ce:n_Zr = 3:1) catalyst. Pd/Ce–Zr–Al–O_x catalysts were systematical studied by mean of BET, XRD and TEM analysis. XRD characterization showed that zirconium element entered into cubic structure of ceria and leaded to structure distortion. Addition of aluminum increased specific surface area of ceria–zirconia solid solution substantially. The average pore diameter of Ce–Zr–Al–O_x support palladium catalysts were the key impact factor for CO oxidation. When the Pd/Ce–Zr–Al–O_x catalysts had highly dispersed palladium nanoparticles, large average pore diameter, suitable surface area and pore volume, the activity of CO oxidation was the best.     

Effect of surface hydration on the photocatalytic activity of oxide catalysts in the CO oxidation

The effect of the state of hydrated surface of the bulk oxide photocatalysts, TiO₂, CeO₂, and ZnO on the rate of UV-induced oxidation of CO with atmospheric oxygen was studied. The activity of dehydroxylated catalyst samples evacuated at temperatures of >350 °C toward CO photooxidation decreases in the series CeO₂ > ZnO ≈ TiO₂, while that of partially hydrated samples after pretreatment at 20 °C changes in the order TiO₂ > ZnO ≥ CeO₂ ≈ 0. According to the results, the difference in the photocatalytic activity toward CO oxidation on the dehydrated ZnO, TiO₂, and CeO₂ catalysts is attributable to different concentrations of oxygen vacancies, which are formed more readily after high-temperature treatment on ZnO and CeO₂ and thus promote higher rate of CO photooxidation. Using a new technique for recording transmittance IR spectra, it was found that photoirradiation in the presence of adsorbed water and O₂ gives peroxides and hydroperoxides, with their concentrations decreasing in the series TiO₂ >> ZnO >> CeO₂. Most likely, these species are active intermediates of CO photooxidation with oxygen in the presence of adsorbed water. The hydrophobization effect was detected upon TiO₂ modification with zinc, resulting in removal of surface acid sites capable of adsorbing water. The TiO₂ modification with zinc increases the activity of CO photooxidation with respect to the oxidation catalyzed by samples pretreated at low temperatures (20—60 °C).     

通过CeOx修饰提高金纳米颗粒在CO氧化反应中的催化活性和耐久性

CO催化氧化是一个重要的经典反应,与许多应用息息相关,包括痕量CO气体检测、汽车尾气净化和安全防护等,吸引了人们广泛的研究兴趣.负载型Au纳米颗粒在CO氧化等许多反应中有着与众不同的催化活性,具有广泛的应用前景,但依然存在着稳定性差、易团聚失活的问题.人们通过应用多孔载体隔离Au纳米颗粒,在Au纳米颗粒表面覆盖金属氧化物、二氧化硅或碳,以及对Au纳米粒子进行封装等方法解决这些问题.尤其是利用金属氧化物与Au纳米粒子间的强相互作用对其进行覆盖或封装,有效地提高了Au催化材料的稳定性.但以上策略操作流程复杂,不利于应用.本文发展了一种简单有效的方法,通过EDTA的络合作用引入CeOx对Au纳米粒子进行修饰,得到的CeOx@Au/SiO2催化剂活性和耐久性明显提升.采用X射线衍射(XRD)和高分辨透射电子显微镜(HRTEM)证明了CeOx成功地修饰在Au纳米颗粒上.且通过EDTA引入CeOx所制备的CeOx@Au/SiO2催化剂结构明显不同于直接加入纳米CeO2所得到的CeOx-Au/SiO2的结构.EDTA的络合作用能有效地连结Ce与Au物种,经焙烧消除EDTA后,加强了CeOx与Au间相互作用,最终在Au纳米粒子表面形成丰富的CeOx颗粒与原子级厚度的CeOx层.进一步应用X射线光电子能谱(XPS)和氢气程序升温还原(H2-TPR)等手段研究了CeOx修饰对Au纳米粒子的影响.XPS结果表明,CeOx@Au/SiO2催化剂带正电的Au+和Au3+的浓度明显高于一般的Au/SiO2和直接加入CeO2制备得到的CeOx-Au/SiO2催化剂.H2-TPR同样表明,CeOx修饰调变了Au纳米粒子的氧化还原性.这些均对其在CO催化氧化反应中的催化活性具有重要影响将CeOx@Au/SiO2催化剂用于CO催化氧化反应中,160°C时,CO转化率达98.8％,至180°C后实现了CO的完全转化.而一般的Au/SiO2催化剂在160°C时CO转化率仅为4.0％,CO的完全转化则需340°C.直接加入纳米CeO2所得到的CeOx-Au/SiO2催化剂,其催化活性略有提升,CO完全转化所需的温度为300°C.这充分证明了通过CeOx修饰Au纳米粒子,能有效提升其催化活性.原位漫反射红外光谱(DRIFT)结果表明,CeOx修饰促进了CO在Au表面的吸附,并能形成[Au(CO)2]δ+物种;同时还观察到大量的单齿CO32? 物种信号,反映了CeOx@Au/SiO2催化剂表面存在丰富的活性氧物种.通入O2后,观察到了大量CO32?物种信号和气相CO2,印证了催化剂表面发生的CO催化氧化过程,也表明其具有非常高的催化活性.考察了CeOx@Au/SiO2催化剂的耐久性,发现经50 h CO氧化反应,催化剂依然能有效保持活性.相比之下,Au/SiO2催化剂经10 h反应后,开始明显失活.由此可见,CeOx@Au/SiO2催化剂具有相当高的耐久性.在600°C将催化剂焙烧3 h,发现Au/SiO2催化剂中Au纳米粒子存在明显团聚现象,而CeOx@Au/SiO2催化剂的Au纳米粒子依然均匀分布在载体表面,且粒径未发生明显变化.     

Highly Oxidized Platinum Nanoparticles Prepared through Radio‐Frequency Sputtering: Thermal Stability and Reaction Probability towards CO

Platinum‐oxide nanoparticles were prepared through the radio‐frequency (RF) discharge sputtering of a Pt electrode in an oxygen atmosphere. The structure, particles size, electronic properties, and surface composition of the RF‐sputtered particles were studied by using transmission electron microscopy and X‐ray photoelectron spectroscopy. The application of the RF discharge method resulted in the formation of highly oxidized Pt⁴⁺ species that were stable under ultrahigh vacuum conditions up to 100 °C, indicating the capability of Pt⁴⁺–O species to play an important role in the oxidation catalysis under real conditions. The thermal stability and reaction probability of Pt⁴⁺ oxide species were analyzed and compared with those of Pt²⁺ species. The reaction probability of PtO₂ nanoparticles at 90 °C was found to be about ten times higher than that of PtO‐like structures.     

Co3O4−CeO2 Nanocomposites for Low-Temperature CO Oxidation

In an effort to combine the favorable catalytic properties of Co₃O₄ and CeO₂, nanocomposites with different phase distribution and Co₃O₄ loading were prepared and employed for CO oxidation. Synthesizing Co₃O₄-modified CeO₂ via three different sol-gel based routes, each with 10.4 wt % Co₃O₄ loading, yielded three different nanocomposite morphologies: CeO₂-supported Co₃O₄ layers, intermixed oxides, and homogeneously dispersed Co. The reactivity of the resulting surface oxygen species towards CO were examined by temperature programmed reduction (CO-TPR) and flow reactor kinetic tests. The first morphology exhibited the best performance due to its active Co₃O₄ surface layer, reducing the light-off temperature of CeO₂ by about 200 °C. In contrast, intermixed oxides and Co-doped CeO₂ suffered from lower dispersion and organic residues, respectively. The performance of Co₃O₄-CeO₂ nanocomposites was optimized by varying the Co₃O₄ loading, characterized by X-ray diffraction (XRD) and N₂ sorption (BET). The 16–65 wt % Co₃O₄−CeO₂ catalysts approached the conversion of 1 wt % Pt/CeO₂, rendering them interesting candidates for low-temperature CO oxidation.     

Structure and Thermal Properties of [Rh(NH3)5Cl](WO4)x(MoO4)1s-x (x = 0, 0.5, 1)

The isostructurality of [Rh(NH₃)₅Cl](WO₄) _x (MoO₄)_1s-x (x = 0, 0.5, 1) complex salts is shown, and their thermal properties are compared. In a hydrogen atmosphere, transformations begin at T ∼ 200°C. According to the powder XRD data, the phase composition of the end products is markedly different. For the Rh—Mo system, the dependence (V/Z) of the atomic volume on the composition is presented. The thermal decomposition product [Rh(NH₃)₅Cl](MoO₄) (T _fin = 800°C) is shown to be the disordered Mo_0.5Rh_0.5 solid solution (a = 2.757(2) ?, c = 4.428(4) ?, P6₃/mmc space group).     

CO oxidation with oxygen of the catalyst and gas-phase oxygen over (0.5−15)%СоО/СеО<Subscript>2</Subscript>

The CO adsorption species on Co₃O₄ and (0.5-15%)CoO/CeO₂ catalysts have been investigated by temperature-programmed desorption and IR spectroscopy. At 20°C, the largest amount of CO is adsorbed on the 5%CoO/CeO₂ sample to form, on Co_m²⁺O_n²⁺ clusters, hydrogen-containing, bidentate, and monodentate carbonate complexes, whose decomposition is accompanied by CO₂ desorption at 300 and 450°C (1.1 × 10²⁰ g^–1). The formation of the carbonates is accompanied by the formation of Co⁺ cations and Co⁰, on which carbonyls form. The latter decompose at 20, 90, and 170°C to release CO (2.7 × 10¹⁹ g^–1). Part of the carbonyls oxidizes to CO₂ upon oxygen adsorption, and the CO₂ undergoes desorption at 20°C. Adsorbed oxygen decreases the decomposition temperature of the H-containing and bidentate carbonates from 300 to 100-170°C and maintains the sample in the oxidized state, which is active in subsequent CO adsorption and oxidation. CO oxidation by oxygen of the catalyst diminishes the activity of the sample in these processes and increases the decomposition temperature of the carbonate complexes. Taking into account the properties of the adsorption complexes, we concluded that the H-containing and bidentate carbonates are involved in CO oxidation by oxygen of the catalyst at ~170°C under isothermal conditions. The rate limiting step is the decomposition of the carbonates, a process whose activation energy is 65-74 kJ/mol.     

The decomposition of the oxalate precursor and the stability and reduction of the YBa2Cu4O8 superconductor studied by TG coupled with FTIR and by XRD

The 124 superconductor YBa₂Cu₄O₈ was prepared from the oxalate precursor Y₂(C₂O₄)₃. ·4BaC₂O₄·8CuC₂O₄·xH₂O at one atmosphere oxygen pressure. In O₂ the precursor decomposes in one step at 300°C and more gradually (300°–600°C) in Ar. The stability of the superconductor is strongly dependent on the gas atmosphere: in O₂ and in air there is no significant weight change as long as the temperature does not exceed 800°C, whereas in a 1% O₂-99%N₂ mixture decomposition starts at about 670°C with the formation of CuO and YBa₂Cu₃O_x withx<7. The reduction of YBa₂Cu₄O₈ in a 5% H₂-95% Ar mixture takes place in at least four major steps with formation of products such as Y₂O₃, BaO, Cu₂O, Cu, BaY₂O₄ and Ba₄Y₂O₇.     

Outstanding Methane Oxidation Performance of Palladium‐Embedded Ceria Catalysts Prepared by a One‐Step Dry Ball‐Milling Method

By carefully mixing Pd metal nanoparticles with CeO₂ polycrystalline powder under dry conditions, an unpredicted arrangement of the Pd‐O‐Ce interface is obtained in which an amorphous shell containing palladium species dissolved in ceria is covering a core of CeO₂ particles. The robust contact that is generated at the nanoscale, along with mechanical forces generated during mixing, promotes the redox exchange between Pd and CeO₂ and creates highly reactive and stable sites constituted by PdO_x embedded into CeO₂ surface layers. This specific arrangement outperforms conventional Pd/CeO₂ reference catalysts in methane oxidation by lowering light‐off temperature by more than 50°C and boosting the reaction rate. The origin of the outstanding activity is traced to the structural properties of the interface, modified at the nanoscale by mechanochemical interaction.     

An XPS study of the oxidation of noble metal particles evaporated onto the surface of an oxide support in their reaction with NO<Subscript><Emphasis Type="Italic">x</Emphasis></Subscript>

The interaction of the model catalysts Rh/Al₂O₃, Pd/Al₂O₃, Pt/Al₂O₃, and Pt/SiO₂ with NO _x (mixture of 10 Torr of NO and 10 Torr of O₂) was studied by X-ray photoelectron spectroscopy (XPS). Samples of the model catalysts were prepared under vacuum conditions as oxide films ≥100 Å in thickness on tantalum foil with evaporated platinum-group metal particles. According to transmission electron microscopic data, the platinum-group metal particle size was several nanometers. It was found by XPS that the oxidation of Rh and Pd nanoparticles in their interaction with NO _x occurs already at room temperature. The particles of platinum were more stable: their oxidation under the action of NO _x was observed at elevated temperatures of ～300°C. At room temperature, the interaction of platinum nanoparticles with NO _x hypothetically leads to the dissolution (insertion) of oxygen atoms in the bulk of the particles with the retention of their metallic nature. It was found that dissolved oxygen is much more readily reducible by hydrogen than the lattice oxygen of the platinum oxide particles.