Kinetics of low temperature CO oxidation over Pt/SnO2 catalyst

In a CO−O₂ stoichiometric mixture, the kinetic parameters, reaction order, rate constant and activation energy of CO oxidation over a Pt/SnO₂ catalyst have been measured using a fixed bed flow reactor near 0°C. The results show that it is a first-order reaction. The activation energy of CO oxidation over Pt/SnO₂ prepared with SnO₂ calcined at 300°C was approximately 21 kJ/mol. The activation energy of CO oxidation over Pt/SnO₂ changed slowly with SnO₂ calcination temperature above 400°C, and reached approximately 45 kJ/mol.     

Microwave-assisted hydrothermal synthesis of Pt/SnO2 gas sensor for CO detection

In this paper, the Pt/SnO₂ nanostructures were prepared via a facile one-step microwave assisted hydrothermal route. The structure of the introduced Pt/SnO₂ and its gas-sensing properties toward CO were investigated. The results from the TEM test reveal that Pt grows on the SnO₂ nanostructure, which was not found for bulk in this situ method, constructing Pt/SnO₂. The results indicated that the sensor using 3.0 wt% Pt/SnO₂ to 100 ppm carbon monoxide performed a superior sensing properties compared to 1.5 wt% and 4.5 wt% Pt/SnO₂ at 225 °C. The response time of 3.0 wt% sensor is 16 s to 100 ppm CO at 225 °C. Such enhanced gas sensing performances could be attributed to the chemical and electrical factors. In view of chemical factors, the presence of Pt facilitates the surface reaction, which will improve the gas sensing properties. With respect to the electrical factors, the Pt/SnO₂ plays roles in increasing the sensor’s response due to its characteristic configuration. In addition, the one-step in situ microwave assisted process provides a promising and versatile choice for the preparation of gas sensing materials.     

Direct oxidation of methane at low temperature using Pt/C,Pd/C,Pt/C-ATO and Pd/C-ATO electrocatalysts prepared by sodium borohydride reduction process

The main objective of this paper was to characterize the voltammetric profiles of the Pt/C,Pt/C-ATO,Pd/C and Pd/CATO electrocatalysts and study their catalytic activities for methane oxidation in an acidic electrolyte at 25 ℃ and in a direct methane proton exchange membrane fuel cell at 80 ℃. The electrocatalysts prepared also were characterized by X-ray diffraction( XRD) and transmission electron microscopy( TEM). The diffractograms of the Pt/C and Pt/C-ATO electrocatalysts show four peaks associated with Pt face-centered cubic( fcc) structure,and the diffractograms of Pd/C and Pd/C-ATO show four peaks associated with Pd face-centered cubic( fcc) structure. For Pt/C-ATO and Pd/C-ATO,characteristic peaks of cassiterite( SnO_2) phase are observed,which are associated with Sb-doped SnO_2( ATO) used as supports for electrocatalysts. Cyclic voltammograms( CV) of all electrocatalysts after adsorption of methane show that there is a current increase during the anodic scan. However,this effect is more pronounced for Pt/C-ATO and Pd/C-ATO. This process is related to the oxidation of the adsorbed species through the bifunctional mechanism,where ATO provides oxygenated species for the oxidation of CO or HCO intermediates adsorbed in Pt or Pd sites. From in situ ATR-FTIR( Attenuated Total Reflectance-Fourier Transform Infrared) experiments for all electrocatalysts prepared the formation of HCO or CO intermediates are observed,which indicates the production of carbon dioxide. Polarization curves at 80 ℃in a direct methane fuel cell( DMEFC) show that Pd/C and Pt/C electroacatalysts have superior performance to Pd/C-ATO and Pt/C-ATO in methane oxidation.     

Synthesis,characterization and electrocatalytic activity for ethanol oxidation of carbon supported Pt,Pt–Rh,Pt–SnO2 and Pt–Rh–SnO2 nanoclusters

Nanoclusters of Pt, Pt–Rh, Pt–SnO₂ and Pt–Rh–SnO₂ were successfully synthesized by polyol method and deposited on high-area carbon. HRTEM and XRD analysis revealed two phases in the ternary Pt–Rh–SnO₂/C catalyst: solid solution of Rh in Pt and SnO₂. The activity of Pt–Rh–SnO₂/C for ethanol oxidation was found to be much higher than Pt/C and Pt–Rh/C and also superior to Pt–SnO₂/C. Quasi steady-state measurements at various temperatures (30–60 °C), ethanol concentrations (0.01–1 M) and H₂SO₄ concentrations (0.02–0.5 M) showed that Pt–Rh–SnO₂/C is about 20 times more active than Pt/C in the potential range of interest for the fuel cell application.     

Effect of thermal treatment on phase composition and ethanol oxidation activity of a carbon supported Pt50Sn50 alloy catalyst

A carbon supported Pt–Sn electrocatalyst in the Pt/Sn atomic ratio 50:50 was prepared by the reduction of Pt and Sn precursors with formic acid and thermally treated at 200 °C (i.e., in the presence of solid tin) and 500 °C (in the presence of molten tin) in flowing hydrogen. In the absence of thermal treatment, X-ray diffraction (XRD) analysis showed a solid solution of Sn in the face centered cubic (fcc) Pt and SnO₂. After thermal treatment, the formation of a main phase of hexagonal PtSn (niggliite) and a secondary phase of cubic Pt₃Sn was observed in the Pt50Sn50 catalyst. The relative amount of the PtSn phase increased with increasing thermal treatment temperature. The presence of molten tin gave rise to the formation of some big particles during annealing at 500 °C. The activity for the ethanol oxidation reaction (EOR) of the as-prepared catalyst was higher than that of both thermally treated catalysts and Pt75Sn25/C and Pt50Ru50/C by E-TEK. The higher activity for the EOR of the as-prepared Pt–Sn catalysts was ascribed to the presence of a large amount of SnO₂. Dedicated to Teresa Iwasita’s 65th birthday.     

Platinum-Tin/Tin Oxide/CNT Catalysts for High-Performance Electrocatalytic Ethanol Oxidation

Ethanol is a promising liquid clean energy source in the energy conversion field. However, the self-poisoning caused by the strongly adsorbed reaction intermediates (typically, CO) is a critical problem in ethanol oxidation reaction. To address this issue, we proposed a joint use of two strategies, alloying of Pt with other metals and building Pt/metal-oxide interfaces, to achieve high-performance electrocatalytic ethanol oxidation. For this, a well-designed synthetic route combining wet impregnation with a two-step thermal treatment process was established to construct PtSn/SnO_x interfaces on carbon nanotubes. Using this route, the alloying of Pt−Sn and formation of PtSn−SnO_x interfaces can simultaneously be achieved, and the coverage of SnO_x thin films on PtSn alloy nanoparticles can be facilely tuned by the strong interaction between Pt and SnO_x. The results revealed that the partial coverage of SnO_x species not only retained the active sites, but also enhanced the CO anti-poisoning ability of the catalyst. Consequently, the H−PtSn/SnO_x/CNT-2 catalyst with an optimized PtSn−SnO_x interface showed significantly improved performances toward the ethanol oxidation reaction (825 mA mg_Pt⁻¹). This study provides deep insights into the structure-performance relationship of PtSn/metal oxide composite catalysts, which would be helpful for the future design and fabrication of high-performance Pt-based ethanol oxidation reaction catalysts.     

Pt/TiO2催化剂上CO氧化反应动力学研究

利用沉积沉淀法制备了Pt/TiO₂催化剂, 将其在不同温度下焙烧, 以得到不同颗粒尺寸的Pt. 并将这些样品用于CO催化氧化反应以及反应动力学研究. 结果表明: 焙烧温度对催化剂有明显影响, Pt 颗粒尺寸随着焙烧温度的升高而增加; 与此同时, CO催化活性随焙烧温度的升高呈先增加后降低的趋势, 其中, 400℃焙烧的样品表现出最高的催化活性. 反应动力学结果表明, 催化剂上CO氧化反应表观速率方程为r=5.4×10^-7p_CO^0.17p_O2^0.36,说明在该催化剂上CO氧化遵循Langmuir-Hinshelwood机理. 同时, 对催化剂进行了CO化学吸附红外光谱和O₂化学吸附表征. 结果表明, 随着焙烧温度的升高, 催化剂上CO和O₂吸附量均呈现先升高后降低的趋势, 这与反应结果和反应动力学方程一致, 说明反应受到催化剂表面上CO和O₂吸附浓度的影响. 而在400℃焙烧的催化剂上, CO和O₂吸附量均最高, 因此其反应活性也最好. 这可能是焙烧过程影响了Pt 和TiO₂之间的相互作用引起的.     

On the oxidation behaviour of monolithic TiB2 and Al2O3-TiB2 and Si3N4-TiB2 composites

In view of the susceptibility of TiB₂ to oxidation, the thermal stability of monolithic TiB₂ and of Al₂O₃-30 vol% TiB₂ and Si₃N₄-20 vol% TiB₂ composites was investigated. The temperature at which TiB₂ ceramic starts to oxidize is about 400°C, oxidation kinetics being controlled by diffusion up toT≈900°C and in the first stage of the oxidation at 1000°C and 1100°C (up to 800 min and 500 min respectively), and by a linear law at higher temperatures and for longer periods. Weight gains in the Al₂O₃-TiB₂ composite can be detected only at temperatures above ≈700°C and the rate governing step of the oxidation reaction is characterized by a one-dimensional diffusion mechanism atT=700°C andT=800°C and by two-dimensional diffusion at higher temperatures. Concerning the Si₃N₄-TiB₂ composite, three different oxidation behaviours related to the temperature were observed, i.e. up to ≈1000°C the reaction detected regards only the second phase; at ≈1000<T<≈1200°C, the diffusion of O₂ or N₂ through an oxide layer is proposed as the rate-governing step; atT〉=1200°C, a linear kinetic indicates the formation of a non protective scale.     

The adsorption of carbon monoxide on a platinum electrode

The adsorption of CO from 0.5 M H₂SO₄ solution on platinum has been studied using CO labelled with C-14. The adsorption of CO on Pt occurs in the potential range of hydrogen adsorption as well as in the double layer region. In the whole potential range the rate of adsorption follows first order kinetics. From the surface concentrations and charges for oxidation of adsorbed species it follows that the product of chemisorption consists at least of two kinds of species. One of them is the COOH radical probably formed by the reaction of CO with water.     

Unravelling the Promotional Effect of La2O3 in Pt/La-TiO2 Catalysts for CO2 Hydrogenation

This work reports the preparation of a La₂O₃-modified Pt/TiO₂ (Pt/La-TiO₂) hybrid through an excess-solution impregnation method and its application for CO₂ hydrogenation catalysis. The Pt/La-TiO₂ catalyst is characterized by XRD, H₂ temperature-programmed reduction (TPR), TEM, X-ray photoelectron spectroscopy (XPS), Raman, EPR, and N₂ sorption measurements. The Pt/La-TiO₂ composite starts to catalyze the CO₂ conversion reaction at 220 °C, which is 30 °C lower than the Pt/TiO₂ catalyst. The generation of CH₄ and CO of Pt/La-TiO₂ is 1.6 and 1.4 times greater than that of Pt/TiO₂. The CO₂ temperature-programmed desorption (TPD) analysis confirms the strengthened CO₂ adsorption on Pt/La-TiO₂. Moreover, the in situ FTIR experiments demonstrate that the enhanced CO₂ adsorption of Pt/La-TiO₂ facilitates the formation of the active Pt–CO intermediate and subsequently boosts the evolution of CH₄ and CO. The cycling tests reveal that Pt/La-TiO₂ shows reinforced stability for the CO₂ hydrogenation reaction because the La species can prevent Pt nanoparticles (NPs) from sintering. This work may provide some guidance on the development new rare-metal-modified hybrid catalysts for CO₂ fixation.     

Pt-SnO2 / C催化剂对乙醇和吸附态CO的电催化氧化

由于乙醇最有可能成为直接甲醇燃料电池（DMFC）的替代燃料，因此近年来。对乙醇的电化学氧化及直接乙醇燃料电池的研究已引起人们的很大兴趣。甲醇毒性较大并且易透过Nafion膜进入阴极造成阴极的混合电位而影响DMFC的阴极性能．这是制约DMFC走向实用化的主要问题之一。因此人们在致力于研究直接甲醇燃料电池的同时．也寻求其它的小分子醇作为甲醇的替代燃料。乙醇是除甲醇以外最简单的醇．它来源广泛．无毒，是可再生和环保型能源．并且也有较高的能量密度和反应活性。但是乙醇在电极上的完全氧化因涉及到C-C键的断裂要比甲醇困难．阳极反应动力学过程也比较缓慢。到目前为止铂基催化剂仍然是乙醇氧化最好的催化剂．虽然也有使用非铂催化剂研究乙醇的电氧化，但催化活性远不如铂基催化剂高。     

The effect of platinum on the SnO<Subscript>2</Subscript> sorption properties

Chemisorption of SO₂ and O₂ at Pt-modified SnO₂ is studied by using the vacuum static method, with simultaneous recording of electrical conductivity, over the 22 to 300°C temperature range. The SnO₂ surface modification results in the increasing of SO₂ adsorption and weakening of the gas-surface bonding. The chemisorption enhances the samples’ electrical conductivity. The surface pretreatment with oxygen leads to the decreasing of the successive SO₂ chemisorption.     

Defect pyrochlores as catalyst supports

The possibility of designing an active support for dispersed Pt for an automobile exhaust converter was demonstrated. Complete reduction of NO to N₂ is accomplished above 250°C by the defect-pyrochlore support Pb₂Pb_xRu_2?xO_6+δ, and oxidation of hydrocarbons or CO to CO₂ is achieved by the dispersed Pt.     

Oxide supported platinum electrocatalysts for hydrogen and alcohol fuel cells

Efficient oxide supported electrocatalysts for hydrogen and alcohol fuel cells are developed. They are characterized by a low content of platinum, exhibit high activity in the oxidation of low-molecular alcohols and tolerance to the CO poisoning. It is shown that the application of catalysts developed (Pt/SnO₂-SbO _x ) enables one to raise the power of fuel cells operating on ethanol approximately by two times as compared with similar fuel cells with commercial PtRu/C catalysts.     

Mild Synthesis of Pt/SnO2/Graphene Nanocomposites with Remarkably Enhanced Ethanol Electro‐oxidation Activity and Durability

We have designed a new Pt/SnO₂/graphene nanomaterial by using L ‐arginine as a linker; this material shows the unique Pt‐around‐SnO₂ structure. The Sn²⁺ cations reduce graphene oxide (GO), leading to the in situ formation of SnO₂/graphene hybrids. L ‐Arginine is used as a linker and protector to induce the in situ growth of Pt nanoparticles (NPs) connected with SnO₂ NPs and impede the agglomeration of Pt NPs. The obtained Pt/SnO₂/graphene composites exhibit superior electrocatalytic activity and stability for the ethanol oxidation reaction as compared with the commercial Pt/C catalyst owing to the close‐connected structure between the Pt NPs and SnO₂ NPs. This work should have a great impact on the rational design of future metal–metal oxide nanostructures with high catalytic activity and stability for fuel cell systems.     

Electrocatalysis on binary alloys: II. Oxidation of molecular hydrogen on supported Pt+Ru alloys

The electrocatalytic properties of Pt+Ru alloys supported on graphitized carbon have been studied using oxide-free metal alloys that have been well characterized for phase identification, specific metal surface area, and surface composition. The CO tolerance of the Pt+Ru alloys for the oxidation of CO contaminated hydrogen in hot concentrated H₃PO₄ increases monotonically with Ru content of the surface and is a direct result of a decreasing coverage of the alloy by adsorbed CO. Furthermore, the strength of bonding of adsorbed CO with the metal surface decreases dramatically with increasing Ru content in the surface. The absolute activity of Pt+Ru alloys for the oxidation of CO contaminated hydrogen is a complex function of temperature and electrode potential. At 160°C, pure Pt is the most active catalyst at all potentials, but at temperatures lower than 120°C the reaction-limiting current for pure Ru exceeds that of pure Pt. At any temperature from 110–160°C or any electrode potential from 0–0.3V (HE), the variation of electrocatalytic activity with alloy composition indicates only dilution of the activity of the more active component.     

Influence of promoters on the performance of Au/MnOx and Pt/SnOx/SiO2 low-temperature CO oxidation catalysts

The influence of promoters on Pt/SnO_x/SiO₂ and Au/MnO_x low-temperature CO oxidation catalysts has been investigated under stoichiometric reaction conditions with no CO₂ added to the feed gas. The performance of Pt/SnO_x/SiO₂ catalysts is improved significantly by the addition of 1 wt.% Fe but reduced by the addition of 5 wt.%Fe, 1 wt.% Sb, 5 wt.% Sb, 1 wt.% As, 5 wt.%As and 1.8 wt.% P. The performance of Au/MnO_x is improved significantly by the addition of 1 at.% Ce but reduced by the addition of 1 at.% Co. For the catalysts and conditions examined, the Au/MnO_x catalysts are superior to the Pt/SnO_x/SiO₂ catalysts with respect to both activity and decay characteristics.     

Catalytic oxidation of CO on platinum

Using concepts recently developed in thermal decompositions of solids and reduction of bulk oxides by gases and (re)analysis of experimental literature data, a novel mechanism for the catalytic oxidation of CO by PtO₂ is proposed. Instead of the conventional Mars–van Krevelen scheme, the reactions proposed are: PtO₂(s) + 2CO ? Pt(g) + 2CO₂ and Pt(g) + O₂ ? PtO₂(g) → PtO₂(s). The first reaction determines the kinetics of CO oxidation and the second determines the kinetics of restoration of the PtO₂ layer. Thermochemical consideration of the kinetic features of this model, based on Langmuir’s quasi-equilibrium equations for evaporation of simple substances, allowed calculation of the reaction enthalpy and the absolute rate of CO oxidation. These results are in good agreement with experimental data. The proposed mechanism explains the origin of the surface-retexturing effect, the limited loss of Pt metal from the catalyst, the mechanism of PtO₂ regeneration by oxygen, the strong effect of CO₂ in reducing the CO oxidation rate and the three-fold variation of the Arrhenius E parameter with temperature.     

Mechanism of CO oxidation in excess H2 over CuO/CeO2 catalysts: ESR and TPD studies

The oxidation of CO with oxygen over (0.25–6.4)% CuO/CeO₂ catalysts in excess H₂ is studied. CO conversion increases and the temperature range of the reaction decreases by 100 K as the CuO content is raised. The maximal CO conversion, 98.5%, is achieved on 6.4% CuO/CeO₂ at 150°C. At T > 150°C, the CO conversion decreases as a result of the deactivation of part of the active sites because of the dissociative adsorption of hydrogen. CO is efficiently adsorbed on the oxidized catalyst to form CO-Cu⁺ carbonyls on Cu₂O clusters and is oxidized by the oxygen of these clusters, whereas it is neither adsorbed nor oxidized on Cu⁰ of the reduced catalysts. The activity of the catalysts is recovered after the dissociative adsorption of O₂ on Cu⁰ at T ～ 150°C. The activation energies of CO, CO₂, and H₂O desorption are estimated, and the activation energy of CO adsorption yielding CO-Cu⁺ carbonyls is calculated in the framework of the Langmuir-Hinshelwood model.     

In situ FT-IR studies of NO decomposition on Pt/TiO2 catalyst under UV irradiation

Photodecomposition of NO on the well-dispersed Pt/TiO₂ catalyst under UV irradiation was studied by in situ DRIFT (Diffuse-Reflectance Infrared Fourier-Transform) spectroscopy. 2 wt% Pt/TiO₂ catalyst was prepared by photochemical deposition method. The photocatalytic activity of Pt/TiO₂ is highly dependent on its pretreatment. Although the catalyst exhibited a highly adsorption capability to NO after hydrogen reduction or thermal evacuation at 500°C, no evidence upon NO decomposition was observed under UV irradiation. While reducing the catalyst at 300°C in the hydrogen flow, it not only exhibited an intense NO adsorption but also conducted a direct decomposition of NO to N₂ and O₂ under UV irradiation. The hydrogen reduction at 200°C led to a weaker NO adsorption. During UV irradiation, the IR peaks of NO fully disappeared and N₂O was formed. It is concluded that the photochemical prepared Pt/TiO₂ catalyst after activating at mild reduction conditions is highly active for NO photodecomposition. The effective oxidation states of the active components, the surface structure and the reaction mechanisms will be discussed.