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.     

Ruthenium‐Immobilized Periodic Mesoporous Organosilica: Synthesis,Characterization, and Catalytic Application for Selective Oxidation of Alkanes

Periodic mesoporous organosilica (PMO) is a unique material that has a crystal‐like wall structure with coordination sites for metal complexes. A Ru complex, [RuCl₂(CO)₃]₂, is successfully immobilized onto 2,2’‐bipyridine (BPy) units of PMO to form a single‐site catalyst, which has been confirmed by various physicochemical analyses. Using NaClO as an oxidant, the Ru‐immobilized PMO oxidizes the tertiary C?H bonds of adamantane to the corresponding alcohols at 57 times faster than the secondary C?H bonds, thereby exhibiting remarkably high regioselectivity. Moreover, the catalyst converts cis‐decalin to cis‐9‐decalol in a 63 % yield with complete retention of the substrate stereochemistry. The Ru catalyst can be separated by simple filtration and reused without loss of the original activity and selectivity for the oxidation reactions.     

Au/FeOx-羟基磷灰石催化CO氧化反应中羟基磷灰石和FeOx的作用

近期我们报道了Au/FeO_x-羟基磷灰石(HAP, Ca₁₀(PO₄)₆(OH)₂)催化剂应用于CO氧化反应的研究结果,该催化剂不仅具有很高的低温CO氧化活性和反应稳定性, 同时也具有很好的高温抗烧结性能, 即使600℃焙烧后依然能够维持很好的CO氧化反应活性. 为了进一步研究Au/FeO_x-HAP催化CO氧化反应中HAP和FeO_x的作用, 本文对该催化剂进行了更加深入的表征. X射线光电子能谱结果表明, HAP能与Au和FeO_x形成强相互作用, 进而在高温条件下稳定Au和FeO_x纳米粒子. 根据原位漫反射红外结果, FeO_x则主要通过改变反应路径和中间产物的方式起到促进催化剂CO氧化活性的作用. 结合透射电镜, 穆斯堡尔谱和原位漫反射红外结果可知, Au/FeO_x-HAP催化剂良好的反应稳定性源于其优异的抗碳酸盐累积能力.     

Characteristics of Au/MgxAlO hydrotalcite catalysts in CO selective oxidation

Gold catalysts, supported on a solid base of Mg_xAlO hydrotalcite, were prepared by a modified deposition precipitation method for CO selective oxidation. The preparation parameters and pretreatment of the catalysts were investigated. The pH and the HAuCl₄ concentration in the initial solution, and the Mg/Al molar ratio of Mg_xAlO affected the pH in the final solution and determined the actual gold loading of the catalyst. The calcination temperatures of the Mg_xAlO support and the Au/Mg_xAlO catalyst dominated the Au³⁺/Au⁰ ratio on the catalyst. The pretreatment of the catalyst as well as the gold loading and the Au³⁺/Au⁰ ratio, critically determined the activity of the catalyst for CO selective oxidation. Based on XPS and in situ DR-FTIR analyses, a mechanism for CO selective oxidation on 2%Au/Mg₂AlO was proposed. The hydroxyl group on Mg₂AlO also participated in the reaction.     

Mesoporous Cu-Ce-Ox Solid Solutions from Spray Pyrolysis for Superior Low-Temperature CO Oxidation

Development of Pt group metal-free catalysts for low-temperature CO oxidation remains critical. In this work, active and stable mesoporous Cu-Ce-O_x solid solutions are prepared by using spray pyrolysis. The specific surface areas and pore volumes reach as high as 170 m² g⁻¹ and 0.24 cm³ g⁻¹, respectively. The results of CO oxidation study suggest that (1) the catalyst obtained by spray pyrolysis possesses much higher activity than those made by co-precipitation, sol-gel, and hydrothermal methods; (2) the optimal Cu_0.2-Ce_0.8-O_x solid solution presents a reactivity over 28 times that of both single-component CuO and CeO₂ at 70 °C. Based on the study of pure-phase Cu-Ce-O_x solid solutions by selective leaching of segregated CuO_x species, the active center for CO oxidation is confirmed as the bimetallic Cu-Ce-O site, whereas the individual CuO_x particles not only act as spectators but also block the active Cu-Ce-O sites. A low apparent activation energy of approximately 48 kJ mol⁻¹ is detected for CO oxidation at the Cu-Ce-O site, making Cu-Ce-O_x solid solutions able to present high activity at low temperature. Furthermore, the Cu-Ce-O_x catalysts exhibit excellent stability and thermal tolerance toward CO oxidation.     

Water‐Splitting Electrocatalysis in Acid Conditions Using Ruthenate‐Iridate Pyrochlores

The pyrochlore solid solution (Na_0.33Ce_0.67)₂(Ir_1?xRu_x)₂O₇ (0≤x≤1), containing B‐site Ru^IV and Ir^IV is prepared by hydrothermal synthesis and used as a catalyst layer for electrochemical oxygen evolution from water at pH<7. The materials have atomically mixed Ru and Ir and their nanocrystalline form allows effective fabrication of electrode coatings with improved charge densities over a typical (Ru,Ir)O₂ catalyst. An in situ study of the catalyst layers using XANES spectroscopy at the Ir L_III and Ru K edges shows that both Ru and Ir participate in redox chemistry at oxygen evolution conditions and that Ru is more active than Ir, being oxidized by almost one oxidation state at maximum applied potential, with no evidence for ruthenate or iridate in +6 or higher oxidation states.     

In situ IR reflectance absorption spectroscopy studies of the effect of Nafion on CO adsorption and electrooxidation at Pt nanoparticles

We have synthesized colloidal Pt nanoparticles with a mean particle size of 2.6±0.4 nm by reducing PtCl₂ dissolved in N,N-dimethylacetamide with t-BuMe₂SiH. The latter compound acted both as a reducing agent and a stabilizer of the Pt nanoparticles. Pt nanoparticles were deposited onto the Au substrate and IR reflectance absorption spectroscopy (IRRAS) was applied to investigate CO adsorption and oxidation at the surface of the catalyst. The reactivity of the catalyst covered with Nafion was compared with the reactivity of the catalyst without Nafion. In addition, the reactivity of the colloidal Pt was compared with the reactivity of bulk polycrystalline Pt. We found that CO oxidation proceeds at lower over-potentials at nanoparticles than at polycrystalline Pt. The IRRAS data indicate that the difference in the reactivity may be explained by a different mechanism of the oxidation reaction; Langmuir–Hinshelwood at Pt nanoparticles and island formation and growth at polycrystalline Pt. We have also observed that a film of Nafion slows down the CO oxidation reaction. The IRRAS spectra for CO adsorbed at Pt nanoparticles covered by Nafion were significantly different from the spectra recorded for the nanoparticles in the absence of Nafion. The spectroscopic features suggest that in the presence of Nafion the nanoparticles experience regions of lower and higher proton concentration.This paper is dedicated to Prof. G. Horanyi on the occasion of his 70th birthday and in recognition of his contribution to electrochemistry.     

Bipyridine‐Assisted Assembly of Au Nanoparticles on Cu Nanowires To Enhance the Electrochemical Reduction of CO2

We report a new strategy to prepare a composite catalyst for highly efficient electrochemical CO₂ reduction reaction (CO₂RR). The composite catalyst is made by anchoring Au nanoparticles on Cu nanowires via 4,4′‐bipyridine (bipy). The Au‐bipy‐Cu composite catalyzes the CO₂RR in 0.1 m KHCO₃ with a total Faradaic efficiency (FE) reaching 90.6 % at ?0.9 V to provide C‐products, among which CH₃CHO (25 % FE) dominates the liquid product (HCOO^?, CH₃CHO, and CH₃COO^?) distribution (75 %). The enhanced CO₂RR catalysis demonstrated by Au‐bipy‐Cu originates from its synergistic Au (CO₂ to CO) and Cu (CO to C‐products) catalysis which is further promoted by bipy. The Au‐bipy‐Cu composite represents a new catalyst system for effective CO₂RR conversion to C‐products.     

Using the Interaction between Copper and Manganese to Stabilize Copper Single-atom for CO Oxidation.

The interaction between Cu and Mn has been used to immobilize the Cu single-atom on MnO₂ surface by redox-driven hydrolysis. Comprehensive structure and property characterizations demonstrate that the existence of an Cu−Mn interaction on the catalyst surface can effectively restrain the aggregation of Cu single atoms and improve carbon monoxide (CO) oxidation activity. The interaction of forming the Cu−O−Mn entity is beneficial for CO catalytic activity as the migration of reactive oxygen species and the coordination effect of active centers accelerate the reaction. In particular, 3%-Cu₁/MnO₂ shows an oxygen storage capacity (OSC) value (342.75 μmol/g) more than ten times that of pure MnO₂ (27.79 μmol/g) and has high CO catalytic activity (T_90%=80 °C), it can maintain CO conversion of 95 % after 15 cycles. This work offers a reliable method for synthesizing Cu single-atom catalysts and deepens understanding of the interaction effect between single transition metal atoms and supports that can improve the catalytic activity of CO oxidation.     

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.     

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.     

Cu含量对Pd-Cu/铝土矿CO氧化催化剂结构和性能的影响

利用资源丰富的天然铝土矿经NaOH溶液水热处理后焙烧,获得比表面积达174 m²·g^-1铝土矿载体,制备了双金属Pd-Cu为活性组分的催化剂,金属Pd负载量为0.5%（质量百分数）,以CO氧化反应为探针反应,详细考察了Cu含量的变化对催化剂物化性能的影响。研究发现,Cu的引入有利于提高金属Pd的分散度,同时随着Cu含量的变化,金属Pd与Cu之间以及金属与铝土矿载体之间的相互作用随之改变。催化剂的CO氧化反应性能评价结果表明,Pd和Cu负载量分别为0.5%和4%的样品（PdCu₄/MB）催化反应性能最佳。结合表征结果认为,PdCu₄/MB的高活性归因于良好的Pd和Cu分散度,金属Pd、Cu以及金属与载体之间较强的相互作用。此外,CO-TPD表征结果说明较强的CO吸附能力和从载体中获取氧的能力也有利于提高PdCu₄/MB样品的CO氧化反应性能。     

Cu含量对Pd-Cu/铝土矿CO氧化催化剂结构和性能的影响

利用资源丰富的天然铝土矿经NaOH溶液水热处理后焙烧,获得比表面积达174 m²·g^-1铝土矿载体,制备了双金属Pd-Cu为活性组分的催化剂,金属Pd负载量为0.5%（质量百分数）,以CO氧化反应为探针反应,详细考察了Cu含量的变化对催化剂物化性能的影响。研究发现,Cu的引入有利于提高金属Pd的分散度,同时随着Cu含量的变化,金属Pd与Cu之间以及金属与铝土矿载体之间的相互作用随之改变。催化剂的CO氧化反应性能评价结果表明,Pd和Cu负载量分别为0.5%和4%的样品（PdCu₄/MB）催化反应性能最佳。结合表征结果认为,PdCu₄/MB的高活性归因于良好的Pd和Cu分散度,金属Pd、Cu以及金属与载体之间较强的相互作用。此外,CO-TPD表征结果说明较强的CO吸附能力和从载体中获取氧的能力也有利于提高PdCu₄/MB样品的CO氧化反应性能。     

Selectively Chemocatalytic Conversion of Fructose to 1,2‐Propylene Glycol over Ru‐WOx/Hydroxyapatite Catalyst†

The conversion of fructose to 1,2‐propylene glycol (PG) is an important process from cellulosic biomass to high‐value added chemicals. Herein, Ru‐WO_x/hydroxyapatite (HAP) catalyst was employed for this reaction and reached up to 91.3% yield of PG at 180 °C, 1 MPa initial hydrogen for 8 h in water. On this catalyst, Ru and WO_x were highly dispersed on HAP support and they interacted with each other to form a special catalytic center. The lack of isolated Ru or RuW alloy site led to a moderate activity for hydrogenolysis and hindered the further conversion of PG to propanol. The weak basic HAP support efficiently prevented the humin formation. This precisely controlled catalyst has potential in green PG production.     

Supported Pd–Cu Bimetallic Nanoparticles That Have High Activity for the Electrochemical Oxidation of Methanol

Monodisperse bimetallic Pd–Cu nanoparticles with controllable size and composition were synthesized by a one‐step multiphase ethylene glycol (EG) method. Adjusting the stoichiometric ratio of the Pd and Cu precursors afforded nanoparticles with different compositions, such as Pd₈₅–Cu₁₅, Pd₅₆–Cu₄₄, and Pd₃₉–Cu₆₁. The nanoparticles were separated from the solution mixture by extraction with non‐polar solvents, such as n‐hexane. Monodisperse bimetallic Pd–Cu nanoparticles with narrow size‐distribution were obtained without the need for a size‐selection process. Capping ligands that were bound to the surface of the particles were removed through heat treatment when the as‐prepared nanoparticles were loaded onto a Vulcan XC‐72 carbon support. Supported bimetallic Pd–Cu nanoparticles showed enhanced electrocatalytic activity towards methanol oxidation compared with supported Pd nanoparticles that were fabricated according to the same EG method. For a bimetallic Pd–Cu catalyst that contained 15 % Cu, the activity was even comparable to the state‐of‐the‐art commercially available Pt/C catalysts. A STEM‐HAADF study indicated that the formation of random solid‐solution alloy structures in the bimetallic Pd₈₅–Cu₁₅/C catalysts played a key role in improving the electrochemical activity.     

Selective CO oxidation on a Ru/Al<Subscript>2</Subscript>O<Subscript>3</Subscript> catalyst in the surface ignition regime: 1. Fine purification of hydrogen-containing gases

Selective CO oxidation in a mixture simulating the methanol steam reforming product with an air admixture was studied over Ru/Al₂O₃ catalysts in a quasi-adiabatic reactor. On-line monitoring of the gas temperature in the catalyst bed and of the residual CO concentration at different reaction conditions made it possible to observe the ignition and quenching of the catalyst surface, including transitional regimes. A sharp decrease in the residual CO concentration takes place when the reaction passes to the ignition regime. The evolution of the temperature distribution in the catalyst bed in the ignition regime and the specific features of the steady-state and transitional regimes are considered, including the effect of the sample history. In selective CO oxidation and in H₂ oxidation in the absence of CO, the catalyst is deactivated slowly because of ruthenium oxidation. In both reactions, the deactivated catalyst can be reactivated by short-term treatment with hydrogen. A 0.1% Ru/Al₂O₃ catalyst is suggested. In the surface ignition regime, this catalyst can reduce the residual CO concentration from 0.8 vol % to 10–15 ppm at O₂/CO = 1 even in the presence of H₂O and CO₂ (up to ～20 vol %) at a volumetric flow rate of ～100 1 (g Cat)^?1 h^?1, which is one magnitude higher than the flow rates reported for this process in the literature.     

Synthesis of Ni–Ru Alloy Nanoparticles and Their High Catalytic Activity in Dehydrogenation of Ammonia Borane

We report the synthesis and characterization of new Ni_xRu_1?x (x=0.56–0.74) alloy nanoparticles (NPs) and their catalytic activity for hydrogen release in the ammonia borane hydrolysis process. The alloy NPs were obtained by wet‐chemistry method using a rapid lithium triethylborohydride reduction of Ni²⁺ and Ru³⁺ precursors in oleylamine. The nature of each alloy sample was fully characterized by TEM, XRD, energy dispersive X‐ray spectroscopy (EDX), and X‐ray photoelectron spectroscopy (XPS). We found that the as‐prepared Ni–Ru alloy NPs exhibited exceptional catalytic activity for the ammonia borane hydrolysis reaction for hydrogen release. All Ni–Ru alloy NPs, and in particular the Ni_0.74Ru_0.26 sample, outperform the activity of similar size monometallic Ni and Ru NPs, and even of Ni@Ru core‐shell NPs. The hydrolysis activation energy for the Ni_0.74Ru_0.26 alloy catalyst was measured to be approximately 37 kJ mol^?1. This value is considerably lower than the values measured for monometallic Ni (≈70 kJ mol^?1) and Ru NPs (≈49 kJ mol^?1), and for Ni@Ru (≈44 kJ mol^?1), and is also lower than the values of most noble‐metal‐containing bimetallic NPs reported in the literature. Thus, a remarkable improvement of catalytic activity of Ru in the dehydrogenation of ammonia borane was obtained by alloying Ru with a Ni, which is a relatively cheap metal.     

Platinum submonolayer-monolayer electrocatalysis: An electrochemical and X-ray absorption spectroscopy study

A new Pt monolayer electrocatalyst concept is described and the results of electrochemical and X-ray absorption spectroscopy (XAS) studies are presented. Two new methods that facilitate the application of this concept in obtaining ultra-low-Pt-content electrocatalysts have been developed. One is the electroless (spontaneous) deposition of a Pt submonolayer on Ru nanoparticles, and the other is a deposition of a Pt monolayer on Pd nanoparticles by redox displacement of a Cu adlayer. The Pt submonolayer on Ru (PtRu₂₀) electrocatalyst demonstrated higher CO tolerance than commercial catalysts under conditions of rotating disk experiments. The long-term stability test showed no loss in performance over 870 h using a fuel cell operating under real conditions, even though the Pt loading was approximately 10% of that of the standard Pt loading. In situ XAS indicated an increase in d-band vacancy of deposited Pt, which may facilitate partly the reduced susceptibility to CO poisoning for this catalyst. The kinetics of O₂ reduction on a Pt monolayer on Pd nanoparticles showed a small enhancement in comparison with that from a Pt nanoparticle electrocatalyst. The increase in catalytic activity is partly attributed to decreased formation of PtOH, as shown by XAS experiments.     

Enhanced electrochemical activity for ethanol oxidation on the carbon-supported Pt3Te nanocatalysts by addition of Ru

Ternary Pt–Te–Ru catalysts with different atomic ratios were synthesized by reducing the precursor with formic acid. The physical and electrochemical characterization of the Pt₃TeRu_0.25/C catalyst was performed by transmission electron microscopy (TEM), X-ray diffraction, energy-dispersive X-ray spectroscopy equipped with TEM (TEM-EDX), X-ray photoelectron spectrometer, ethanol oxidation, and CO stripping. In TEM images, the Pt₃TeRu_0.25/C nanoparticles with an average particle size of around 2.9 nm were well dispersed on the carbon support. The Pt₃TeRu_0.25/C catalyst was superior to the Pt₃Te/C catalyst in respect of catalytic activity, durability, and CO tolerance. The positive effect of the Ru presence in the Pt₃TeRu_0.25/C catalyst was ascribed to the interactions of Ru or Ru oxides.