Structures and catalytic properties of PtRu electrocatalysts prepared via the reduced RuO2 nanorods array

Structures and properties of PtRu electrocatalyts, derived from the aligned RuO2 nanorods (RuO2NR), are investigated using scanning electron microscopy, transmission electron microscopy, X-ray diffraction, X-ray photoelectron spectroscopy, and cyclic voltammetry toward COads and methanol oxidation. The catalytic activity of methanol oxidation and the CO tolerance are promoted significantly by reducing RuO2 into Ru metal before decorating with Pt. Reduction of RuO2NR was carried out by either thermal decomposition at 650 degrees C in vacuum or H2-reduction at 130 degrees C in low-pressure hydrogen. Reduction assisted by hydrogen allows infiltrating decomposition at low temperature and produces an array of nanorods with rugged walls featuring small Ru nuclei and larger surface area. Pt-RuNR, whose surface Pt:Ru ratio=0.58:0.42 was prepared by decorating with 0.1 mg cm(-2) Pt on the H2-reduced array containing 0.39 mg cm(-2) Ru, demonstrates a favorable combination of CO tolerance and high methanol oxidation activity superior to other RuO2NR-derived catalysts. When compared with a commercial electrocatalyst of PtRu (1:1) alloy (<4 nm), the activity of Pt-RuNR in methanol oxidation is shown to be somewhat lower at potential<0.48 V and higher at potential>or=0.48 V.     

Temperature effects in carbon monoxide and methanol electrooxidation on platinum–ruthenium: influence of grain boundaries

The temperature dependence of methanol and CO monolayer oxidation is studied on carbon-supported PtRu (1:1 atomic ratio) electrodes with different metal percentages (5, 30, and 60 wt.%) in an aqueous H₂SO₄ electrolyte. High-resolution transmission microscopy confirms that at high (30 or 60 wt.%) metal percentage PtRu nanostructures with a high concentration of intercrystalline boundaries are formed. These nanostructures comprise multiple-twinned particles, particles with intersecting randomly oriented intergrain boundaries, or particles with parallel intergrain boundaries. Formation of such nanostructures leads to a decrease of the apparent activation energy of the methanol and CO monolayer oxidation, while the Tafel slope and the reaction order in methanol show minor dependence on the type of nanostructure. Materials with a high concentration of grain boundary regions may be of interest for practical applications in direct methanol or proton exchange fuel cells fed with reformate.     

Property and structure of various platinum catalysts for low-temperature carbon monoxide oxidations

The oxidation of carbon monoxide (CO) has received more attention in the last two to three decades owing to its importance in different fields. To control this CO pollution, catalytic converters have been investigated. Different types of catalysts have been used in a catalytic converter for CO emission control purposes. Platinum (Pt)-based noble metal catalysts show great potential for CO oxidation in catalytic converters with high thermal stability and tailoring flexibility. Pt metal catalysts modified with promoters such as alkali metals and reducible metal oxides have received great attention for their superior catalytic activities in CO oxidation. Temperature, close environment of the catalyst, and chemical composition in the surface layer of the catalyst have a huge effect on the active phase dispersion and O₂ adsorption capacity of the Pt metal catalysts. The main difference in activities of Pt metal catalyst for CO oxidation in O₂ or H₂ atmosphere has found. The addition of supports in Pt metal catalysts has improved their performances and reduced their cost. These improvement strongly depends on the surface structure, morphology, number of active sites, and various Pt-O interactions. Many research articles have already been published in CO oxidation over Pt metal catalysts, but no review article dedicated to CO oxidation is available in the literature.     

ZrO_2晶相对MoO_x/ZrO_2催化剂结构及其甲醇选择氧化性能的影响

以纯的单斜氧化锆(m-ZrO2)和四方氧化锆(t-ZrO2)为载体,采用浸渍法分别合成了具有不同MoOx表面密度的MoOx/m-ZrO2和MoOx/t-ZrO2催化剂,并结合粉末X射线衍射,Raman光谱和H2程序升温还原等技术表征了不同ZrO2晶相对MoOx分散状态、结构以及甲醇氧化反应性能的影响.在低于锆表面MoOx的单层分散阈值(～5nm-2)时,m-ZrO2比t-ZrO2能够更有效地分散MoOx,形成高分散的孤立或二维结构的MoOx物种,避免了晶相MoO3的出现.当Mo表面密度超过单层分散阈值后,经过600℃焙烧,MoOx与ZrO2载体发生固相反应生成晶相ZrMo2O8,m-ZrO2比t-ZrO2更有利于ZrMo2O8的生成.提高Mo表面密度,催化剂表面的酸性随之增强,说明晶相ZrMo2O8比分散的MoOx物种具有更强的酸性.t-ZrO2与MoOx作用形成的强酸中心更有利于催化甲醇脱水生成二甲醚,但m-ZrO2使得MoOx具有更高的氧化还原能力和催化甲醇选择氧化反应的活性.ZrO2晶相对MoOx/ZrO2催化剂影响的研究结果将有助于研究VOx等其它金属氧化物催化剂以及发展酸性和氧化还原性双功能催化剂体系.     

一氧化碳低温催化氧化

一氧化碳 (CO) 催化氧化反应因在实际生活中应用广泛而受到人们普遍关注,如激光器中微量CO的消除、封闭体系中CO的消除、汽车尾气净化以及质子交换膜燃料电池中少量CO的消除等。本文总结了近年来CO低温催化氧化研究进展,包括催化剂及其制备方法、CO氧化反应机理以及不同环境气氛对催化剂CO低温氧化性能的影响。催化剂的制备方法主要包括传统浸渍法、共沉淀法、沉积-沉淀法、溶胶-凝胶法、离子交换法、化学气相沉积法、溶剂化金属原子浸渍法等。催化剂可分为贵金属催化剂、非贵金属催化剂、以分子筛为载体的催化剂和合金催化剂等。CO氧化反应机理方面的相关报道较多,人们针对不同催化剂体系提出了各种假设。不同环境气氛对催化剂CO低温氧化性能的影响主要分为H₂O、CO₂、H₂和其它气氛等4部分进行描述。最后对该领域的发展前景进行了展望。     

High throughput screening of low temperature CO oxidation catalysts using IR thermography

The catalytic oxidation of carbon monoxide to carbon dioxide is an important process used in several areas such as respiratory protection, industrial air purification, automotive emissions control, CO clean-up of flue gases and fuel cells. Research in this area has mainly focused on the improvement of catalytic activity at low temperatures. Numerous catalyst systems have been proposed, including those based on Pt, Pd, Rh, Ru, Au, Ag, and Cu, supported on refractory or reducible carriers or dispersed in perovskites. Well known commercial catalyst formulations for room temperature CO oxidation are based on CuMn2O4 (hopcalite) and CuCoAgMnOx mixed oxides. We have applied high-throughput and combinatorial methodologies to the discovery of more efficient catalysts for low temperature CO oxidation. The screening approach was based on a hierarchy of qualitative and semi-quantitative primary screens for the discovery of hits, and quantitative secondary screens for hit confirmation, lead optimization and scale-up. Parallel IR thermography was the primary screen, allowing one wafer-formatted library of 256 catalysts to be screened in approximately 1 hour. Multi-channel fixed bed reactors equipped with imaging reflection FTIR spectroscopy or GC were used for secondary screening. Novel RuCoCe compositions were discovered and optimized for CO oxidation and the effect of doping was investigated for supported and bulk mixed oxide catalysts. Another family of active hits that compare favorably with the Pt/Al2O3 benchmark is based on RuSn, where Sn can be used as a dopant (e.g. RuSn/SiO2) and/or as a high surface area carrier (e.g., SnO2 or Sn containing mixed metal oxides). Also, RuCu binary compositions were found to be active after a reduction pretreatment with hydrogen.     

Platinum/Carbon nanotube nanocomposite synthesized in supercritical fluid as electrocatalysts for low-temperature fuel cells

Carbon nanotube (CNT)-supported Pt nanoparticle catalysts have been synthesized in supercritical carbon dioxide (scCO(2)) using platinum(II) acetylacetonate as metal precursor. The structure of the catalysts has been characterized with transmission electron micrograph (TEM) and X-ray photoelectron spectroscopy (XPS). TEM images show that the platinum particles' size is in the range of 5-10 nm. XPS analysis indicates the presence of zero-valence platinum. The Pt-CNT exhibited high catalytic activity both for methanol oxidation and oxygen reduction reaction. The higher catalytic activity has been attributed to the large surface area of carbon nanotubes and the decrease in the overpotential for methanol oxidation and oxygen reduction reaction. Cyclic voltammetric measurements at different scan rates showed that the oxygen reduction reaction at the Pt-CNT electrode is a diffusion-controlled process. Analysis of the electrode kinetics using Tafel plot suggests that Pt-CNT from scCO(2) provides a strong electrocatalytic activity for oxygen reduction reaction. For the methanol oxidation reaction, a high ratio of forward anodic peak current to reverse anodic peak current was observed at room temperature, which implies good oxidation of methanol to carbon dioxide on the Pt-CNT electrode. This work demonstrates that Pt-CNT nanocomposites synthesized in supercritical carbon dioxide are effective electrocatalysts for low-temperature fuel cells.     

Structural and electrocatalytic features of Pt/C catalysts fabricated in supercritical carbon dioxide

Pt/carbon black samples fabricated from dimethyl (1,5-cyclooctadiene) platinum(II) in supercritical CO₂ are characterized in relation to possible applications in methanol fuel cell. The problem of precise material characterization is addressed in frames of X-ray diffractometry, transmission electron microscopy, and electrochemical techniques of the true surface area determination. The catalysts with Pt loading of 20–40 wt.% consist of nm-size particles, with the lattice defectiveness dependent on the fabrication mode. To check the effect of support, various types of carbon blacks (Vulcan XC72R and acetylene black AC-1) are used. In contrast to commercial HiSpec catalysts, no pronounced increase of particle size with Pt loading is found. Specific steady-state activity towards methanol oxidation appears to be essentially higher than for commercial catalysts, mostly because the self-poisoning effects are less pronounced. As for poisoning of Pt with organic species (resulting from the ligand of precursor), its effects are demonstrated to be minor after CO or methanol adsorption accompanied by desorption of contaminating by-product.     

Boosting fuel cell performance with a semiconductor photocatalyst: TiO2/Pt-Ru hybrid catalyst for methanol oxidation

A hybrid carbon fiber electrode (CFE) consisting of TiO2 semiconductor photocatalyst and Pt-Ru catalyst has been developed to boost the performance of direct methanol fuel cells (DMFC). These two catalyst nanoparticles are deposited on opposite sides of the carbon fiber paper such that methanol oxidation is carried out catalytically on Pt-Ru and photocatalytically on TiO2 under UV-light irradiation. Since both catalysts carry out methanol oxidation independently, we observe an additive effect in the current generation. The carbon support fibers provide a large network to collect the electrons from both of these catalytic processes and thus assist in efficient current generation. In addition, TiO2 improves the performance of the Pt-Ru catalyst in dark, indicating possible surface area improvement or diminished poisoning effects. The concept of incorporating a photocatalyst provides new ways to minimize precious metal content and enhance the performance of DMFCs. At low catalyst loadings (0.15 mg/cm2) at 295 K, a 25% enhancement in the peak power density is observed upon illumination with light.     

In-situ X-ray absorption spectroscopy study of Pt and Ru chemistry during methanol electrooxidation

Methanol electrooxidation in a 0.5 M sulfuric acid electrolyte containing 1.0 M CH3OH was studied on 30% Pt/carbon and 30% PtRu/carbon (Pt/Ru = 1:1) catalysts using X-ray absorption spectroscopy (XAS). Absorption by Pt and Ru was measured at constant photon energy in the near edge region during linear potential sweeps of 10-50 mV/s between 0.01 and 1.36 V vs rhe. The absorption results were used to follow Pt and Ru oxidation and reduction under transient conditions as well as to monitor Ru dissolution. Both catalysts exhibited higher activity for methanol oxidation at high potential following multiple potential cycles. Correlation of XAS data with the potential sweeps indicates that Pt catalysts lose activity at high potentials due to Pt oxidation. The addition of Ru to Pt accelerates the rate of methanol oxidation at all potentials. Ru is more readily oxidized than Pt, but unlike Pt, its oxidation does not result in a decrease in catalytic activity. PtRu/carbon catalysts underwent significant changes during potential cycling due to Ru loss. Similar current density vs potential results were obtained using the same PtRu/carbon catalyst at the same loading in a membrane electrode assembly half cell with only a Nafion (DuPont) solid electrolyte. The results are interpreted in terms of a bifunctional catalyst mechanism in which Pt surface sites serve to chemisorb and dissociate methanol to protons and carbon monoxide, while Ru surface sites activate water and accelerate the oxidation of the chemisorbed CO intermediate. PtRu/carbon catalysts maintain their activity at very high potentials, which is attributed to the ability of the added Ru to keep Pt present in a reduced state, a necessary requirement for methanol chemisorption and dissociation.     

Supercritical,Freezing and Thermal Drying Process of Resorcinol‐Formaldehyde Polymer based Nano‐carbons and their Highly Loaded PtRu Anode Electrocatalyst for DMFC

The capillary condensation is affected by micropore and nanopore of catalyst layer on fuel cell. Due to limitation of sluggish mass transport and electrocatalytic activity, to retain the pore skeleton of carbon and metal nanoparticles are very significant for enhanced utilizations of pore structure in electrochemical reaction. Besides, thickness of electrocatalyst layer is very crucial due to one of the factor affected by cell performance of direct methanol fuel cell. Highly loaded four Pt?Ru anode catalysts supported on resorcinol‐formaldehyde (RF) polymer based on meso‐porous carbons (80 wt.% Pt?Ru/carbon cryogel, 80 wt.% Pt?Ru/carbon xerogel and 80 wt.% Pt?Ru/carbon aerogel) and conventional carbon (80 wt.% Pt?Ru/Vulcan XC‐72) were prepared by colloidal method for direct methanol fuel cell. These catalysts were characterized by X‐Ray diffraction (XRD), High resolution transmission electron microscopy (HR‐TEM) and X‐ray photoemission (XPS). The results of CO stripping voltammetry, cyclic voltammetry (CV) and single cell test performed on DMFC show that Pt?Ru/carbon cryogel and Pt?Ru/carbon aerogel exhibits better performances in comparison to Pt?Ru/carbon xerogel and Pt?Ru/Vulcan XC‐72. It is thus considered that particle size, oxidation state of metal and electrochemical active surface area of these catalysts are important role in electrocatalytic activity in DMFC.     

制备方法对PtMo/C催化剂上CO电催化氧化性能的影响

用化学还原法、胶体法和Adams法制备了PtMo/C电催化剂, 对其物理化学性质及其在CO电氧化反应中的催化性能进行了对比研究. TEM和XRD测试结果表明, 胶体法制备的催化剂颗粒在载体炭上均匀分布, 颗粒粒径约5 nm；由化学还原法制备的颗粒尺寸较大, 而Adams法制备的颗粒尺寸达数十纳米, 并有严重的团聚现象. CO消除伏安法测试结果表明, 三种制备方法中胶体法制备的PtMo/C催化剂具有最高的电化学表面积和电催化活性. 与常用的Pt/C催化剂相比, PtMo/C催化剂中Pt上弱吸附态CO的电氧化均得到了促进, 而强吸附态CO则不受影响. 这些结果表明PtMo颗粒的尺寸分布和在载体上的分散状况是影响PtMo/C催化剂电催化性能的主要因素. 胶体法制备的PtMo/C与常用的PtRu/C相比, 电化学表面积虽然较低, 但在低电势下CO的起始氧化电势只有0.15 V, 而且在0.15～0.5０ V之间发生电氧化的CO达到其总量的1/3.     

A study of the surface region of the Mo-V-Te-O catalysts for propane oxidation to acrylic acid

The bulk mixed Mo-V-Te oxides possess high activity and selectivity in propane oxidation to acrylic acid and represent well-defined model catalysts for studies of the surface molecular structure-activity/selectivity relationships in this selective oxidation reaction. The elemental compositions, metal oxidation states, and catalytic functions of V, Mo, and Te in the surface region of the model Mo-V-Te-O system were examined employing low energy ion scattering (LEIS) and X-ray photoelectron spectroscopy (XPS). This study indicated that the surfaces of these catalysts are terminated with a monolayer, which possesses a different elemental composition from that of the bulk. The rates of propane consumption and formation of propylene and acrylic acid depended on the topmost surface V concentration, whereas no dependence of these reaction rates on either the surface Mo or Te concentrations was observed. These findings suggested that the bulk Mo-V-Te-O structure may function as a support for the unique active and selective surface monolayer in propane oxidation to acrylic acid. The results of this study have important practical consequences for the development of improved selective oxidation catalysts by introducing surface metal oxide components to form new surface active V-O-M sites for propane oxidation to acrylic acid.     

高分散PtRu/C催化剂的制备及对甲醇及吸附态CO的电催化氧化

采用化学还原浸渍法在两种不同条件下制备炭载PtRu催化剂,通过XRD和TEM技术对催化剂的晶体结构及微观形貌进行了分析,运用循环伏安法、线性扫描法来检测不同条件下制备的催化剂对甲醇及吸附态CO(COad)电催化氧化活性的影响.结果表明,不同条件下制备的催化剂Pt和Ru形成合金的程度不同,Pt-Ru合金原子的颗粒在载体炭上的粒径大小和分布不同,导致催化剂对甲醇及COad的电氧化催化活性不同.其中以甲醛为还原剂在乙二醇体系中制备的催化剂PtRu/C-2能形成较好的合金状态,粒径小,分布均匀,对甲醇及COad的氧化具有较高的电催化活性.     

凝胶网格共沉淀法制备Cu/ZnO/Al2O3合成甲醇催化剂

随着工业污染和温室效应等环境问题及能源危机和资源危机的日益严重,以二氧化碳为原料催化合成甲醇等化学品已成为C;化工研究中最重要的前沿课题之一[‘－’j．CO。加氢合成甲醇的研究虽已有     

Hydrogen Spillover Enhanced Hydroxyl Formation and Catalytic Activity Toward CO Oxidation at the Metal/Oxide Interface

H₂‐promoted catalytic activity of oxide‐supported metal catalysts in low‐temperature CO oxidation is of great interest but its origin remains unknown. Employing an FeO(111)/Pt(111) inverse model catalyst, we herewith report direct experimental evidence for the spillover of H(a) adatoms on the Pt surface formed by H₂ dissociation to the Pt?FeO interface to form hydroxyl groups that facilely oxidize CO(a) on the neighboring Pt surface to produce CO₂. Hydroxyl groups and coadsorbed water play a crucial role in the occurrence of hydrogen spillover. These results unambiguously identify the occurrence of hydrogen spillover from the metal surface to the noble metal/metal oxide interface and the resultant enhanced catalytic activity of the metal/oxide interface in low‐temperature CO oxidation, which provides a molecular‐level understanding of both H₂‐promoted catalytic activity of metal/oxide ensembles in low‐temperature CO oxidation and hydrogen spillover.     

负载型催化剂的表面相互作用及其在大气分子污染物NO和CO消除中的应用基础研究

负载型催化剂具有重要的应用背景,研究表面分散组分与载体之间的相互作用.对于了解催化过程的本质,进而设计开发高效实用的催化剂均有重要的指导意义.本课题组近年来在该领域中进行了一些探索研究,涉及的催化剂以负载型金属氧化物(如CuO/γ-Al_2O_3,CuO/Ce_xZr_(1-x)O_2和CuO/Ti_xSn_(1-x)O_2等)为主,涉及的反应包括CO完全氧化和NO+CO反应.通过改变活性组分的负载量、添加改性剂和改变样品制备条件等制得一系列样品,用多种固体催化剂表征手段考察各组分在催化剂中的作用以及在上述催化反应中的活性变化规律.研究表明:(1)金属氧化物和卤化物等离子化合物在氧化物载体表面的分散容量和分散后的一些性质均可从"嵌入模型"的考虑得到解释;(2)处于不同载体表面的活性物种或同一载体表面不同结构的活性物种,由于其存在状态的差异使得其氧化还原性质和催化性质不同;(3)在相关催化剂体系中进行的CO完全氧化和NO+CO反应的结果显示,通过探索催化剂的"组成-结构-性质"间的关系,有可能为实际催化剂的设计提供理论参考.     

Hyperporous‐Carbon‐Supported Nonprecious Metal Electrocatalysts for the Oxygen Reduction Reaction

Highly porous carbonaceous nonprecious metal catalysts for the oxygen reduction reaction are prepared by carbonization of low‐cost metalloporphyrin‐based hyper‐crosslinked polymers (MPH‐X). With high surface area (2768 m² g⁻¹), hierarchical porous structure, and high metal loading (9.97 wt %), the obtained hyperporous carbon MPH‐Fe/C catalyst exhibits high oxygen reduction reaction (ORR) activity with a half‐wave potential (0.816 V) that is comparable to the 0.819 V of commercial Pt/C. Stability tests reveal that MPH‐Fe/C also exhibits outstanding long‐term durability and methanol tolerance. Our findings may offer an alternative approach to produce nonprecious metal ORR catalysts on a large scale owing to the low‐cost MPH‐X precursors with diverse metal types.     

Catalytic oxidation activity of Pt3O4 surfaces and thin films

The catalytic oxidation activity of platinum particles in automobile catalysts is thought to originate from the presence of highly reactive superficial oxide phases which form under oxygen-rich reaction conditions. Here we study the thermodynamic stability of platinum oxide surfaces and thin films and their reactivities toward oxidation of carbon compounds by means of first-principles atomistic thermodynamics calculations and molecular dynamics simulations based on density functional theory. On the Pt(111) surface the most stable superficial oxide phase is found to be a thin layer of alpha-PtO2, which appears not to be reactive toward either methane dissociation or carbon monoxide oxidation. A PtO-like structure is most stable on the Pt(100) surface at oxygen coverages of one monolayer, while the formation of a coherent and stress-free Pt3O4 film is favored at higher coverages. Bulk Pt3O4 is found to be thermodynamically stable in a region around 900 K at atmospheric pressure. The computed net driving force for the dissociation of methane on the Pt3O4(100) surface is much larger than that on all other metallic and oxide surfaces investigated. Moreover, the enthalpy barrier for the adsorption of CO molecules on oxygen atoms of this surface is as low as 0.34 eV, and desorption of CO2 is observed to occur without any appreciable energy barrier in molecular dynamics simulations. These results, combined, indicate a high catalytic oxidation activity of Pt3O4 phases that can be relevant in the contexts of Pt-based automobile catalysts and gas sensors.     

Investigation of the surface heterogeneity of solids from reversed-flow inverse gas chromatography

In the present work, the novel methodology of the inverse gas chromatographic technique of reversed-flow gas chromatography (RF-GC) was applied to the well-studied catalytic oxidation of carbon monoxide over silica supported Pt, Rh and Pt-Rh alloy catalysts. Adsorption energies, local isotherms, local monolayer capacities, surface diffusion coefficients, lateral interaction energies and energy distribution functions are simultaneously determined in a single experiment. The variation of the determined physicochemical parameters against the nature of the studied catalysts (Pt content) is consistent with the observed catalytic activity. The energy distribution functions, estimated by means of RF-GC, give useful information about the "topography" and the nature of the active sites on the catalyst surface, similar to those of experimental techniques, such as Thermal Desorption Spectroscopy studies of the adsorption of CO on group VIII noble metal surfaces. The experimentally found results explain the superior activity of Pt0.25 + Rh0.75 alloy, in comparison to that of the pure Pt and Rh catalysts.