Nanotubules-supported Ru nanoparticles for preferential CO oxidation in H2-rich stream

CO present in H₂ provided as fuel for polymer electrolyte membrane fuel cells (PEMFC) can degrade the electrochemical performance and needs efficient removal, which can be accomplished by CO preferential oxidation (PROX). PROX catalytic activities in a H₂-rich stream were tested and compared using ruthenium (Ru) nanoparticles supported on two different nanotubularly structured materials, carbon nanotubes (CNTs) and halloysite nanotubes (HNTs). In both of the support materials the morphology remains unchanged after Ru deposition and reduction, demonstrating that their tubular structure is thermally-stable. The catalytic results show that the Ru/HNTs perform better than Ru/CNTs at temperatures below about 110 °C, owing to the easier reducibility of Ru particles over the former than the latter. However, Ru/HNTs can only reach a maximum CO conversion of 55%, with an O₂ selectivity of around 27% applying an O₂/CO mole ratio = 1 at 123 °C, which is insufficient for PROX applications. CNTs, on the other hand, provide larger surface area and have functional groups with stronger interaction with Ru nanoparticles, presenting a better Ru dispersion, which accounts for the superior catalytic activity at higher reaction temperature. Ru/CNTs catalyst exhibits a CO conversion over 90% and O₂ selectivity of around 50% applying the same O₂/CO mole ratio at temperatures above 120 °C.     

Pt/TiO2 composite nanoparticles synthesized by electron beam irradiation for preferential CO oxidation

This paper describes a novel synthesis method of stabilizer-free Pt/TiO₂ composite nanoparticles using electron beam irradiation. The chemical compositions were analyzed by inductively coupled plasma-atomic emission spectroscopy. The microstructures of the samples were observed by using transmission electron microscope. Pt nanoparticles with the sizes of 2–4 nm were deposited on TiO₂ without any use of stabilizers. The concentrations of Pt ions and 2-propanol notably affected the size and shape of Pt nanoparticles. Their reactions of preferential CO oxidation were measured in temperature region from 60 to 140 °C. The Pt/TiO₂ catalyst with spherical Pt nanoparticles exhibited a 67% of CO conversion rate and 100% of selectivity at a low temperature of 60 °C.     

Production of intermetallic catalysts of deep CO and hydrocarbon oxidation

The possibility of producing (Ni, Co, Mn) Al _x intermetallides using the technique of self-propagating high-temperature synthesis and their subsequent processing with the purpose of using them as catalysis in the process of complete oxidation of CO and hydrocarbons is considered. Phase composition, microstructure, and morphology of alloys and catalysts based on them are studied. Dependences of activity and stability on composition are determined. These catalysts are shown to possess high activity and their development is considered to be a promising direction in the catalysis of deep oxidation processes.     

Effect of water addition on catalytic activity of nanosized gold catalysts for CO oxidation

The effect of water in the reactant gas on the catalytic activity for CO oxidation over Au/Co3O4 catalysts has been investigated. Water in the reactant gas had a negative effect on the catalytic activity for CO oxidation in Au/Co3O4 catalyst. Furthermore, it was observed that the average particle size of gold on Au/Co3O4 catalysts increased after stability testing both in dry and wet conditions.     

Characterization and catalytic performance of Co/SBA-15 supported gold catalysts for CO oxidation

Cobalt-containing SBA-15 supported gold catalysts for low-temperature CO oxidation were prepared and characterized by N₂ adsorption/desorption, X-ray diffraction, transmission electron microscopy, inductively coupled plasma-atom emission spectroscopy and X-ray photoelectron spectroscopy techniques. The effects of cobalt and gold content on the catalyst activity were investigated in detail. Among them, 2% Au/40% Co/SBA-15 shows the highest activity, its complete conversion temperature for CO is at 273 K. It was believed that both the dispersion of Co₃O₄ and the high surface areas caused by SBA-15 contribute to the good activities of cobalt-containing SBA-15 supported gold catalysts. Furthermore, the strong metal-support interaction between gold and cobalt oxides is greatly related to the catalytic performance.     

用于CO低温氧化负载型纳米金催化剂研究进展

一氧化碳(CO)催化氧化反应因在工业、环保、军事、人类生活等方面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。近年来关于纳米金催化剂用于CO低温氧化反应的研究已成为备受关注的热点。阐述了金颗粒尺寸、载体种类、制备方法、制备条件等对催化剂活性的影响,总结了催化机理的研究现状和导致催化剂失活的因素,最后对其未来的发展进行了展望。     

Ru-Pt core-shell nanoparticles for preferential oxidation of carbon monoxide in hydrogen

Most of the world's hydrogen supply is currently obtained by reforming hydrocarbons. 'Reformate' hydrogen contains significant quantities of CO that poison current hydrogen fuel-cell devices. Catalysts are needed to remove CO from hydrogen through selective oxidation. Here, we report first-principles-guided synthesis of a nanoparticle catalyst comprising a Ru core covered with an approximately 1-2-monolayer-thick shell of Pt atoms. The distinct catalytic properties of these well-characterized core-shell nanoparticles were demonstrated for preferential CO oxidation in hydrogen feeds and subsequent hydrogen light-off. For H2 streams containing 1,000 p.p.m. CO, H2 light-off is complete by 30 (composite function)C, which is significantly better than for traditional PtRu nano-alloys (85 (composite function)C), monometallic mixtures of nanoparticles (93 (composite function)C) and pure Pt particles (170 ( composite function)C). Density functional theory studies suggest that the enhanced catalytic activity for the core-shell nanoparticle originates from a combination of an increased availability of CO-free Pt surface sites on the Ru@Pt nanoparticles and a hydrogen-mediated low-temperature CO oxidation process that is clearly distinct from the traditional bifunctional CO oxidation mechanism.     

Enhanced activity and stability of Cu-Mn and Cu-Ag catalysts supported on nanostructured mesoporous CeO2 for CO oxidation

Cu, Mn and Ag nanoparticles are loaded on nanostructured mesoporous CeO2 as catalysts for CO oxidation. The Cu/CeO2 catalyst exhibits an obvious deactivation after the stability test at 95 degrees C for 60 h. This is caused by carbon deposition as confirmed by FTIR spectroscopy, Raman spectroscopy and thermogravimetry-differential scanning calorimetry-mass spectroscopy (TG-DSC-MS) analysis. It is found that the Cu-Mn or Cu-Ag binary metal catalysts supported on the nanostructured CeO2 exhibit much improved activity and stability in CO oxidation. In ease case, carbon deposition is absent in the similar stability test, due to enhanced oxygen adsorption property.     

Effects of microwave power and polyvinyl pyrrolidone on microwave polyol process of carbon-supported Cu catalysts for CO oxidation

The purpose of this study was to prepare an activated carbon (AC)-supported copper catalyst by a simple method - the microwave polyol process - and to evaluate the effects of microwave power and protecting agent on the resulting catalyst activity. The catalysts were characterized by Brunauer-Emmett-Teller (BET) surface area, X-ray diffraction (XRD), and field-emission scanning electron microscopy (FESEM). Experimental results indicated that a microwave power of 700 W was highly effective, and that copper particles (60 (±18) nm) dispersed well on the AC support, even in the absence of the protecting agent poly-vinyl pyrrolidone (PVP). The AC-supported Cu⁰ catalyst generated high catalytic activity for CO oxidation (90% CO conversion at 175 °C).     

Mo2C as a carrier of Cu-Co-Fe oxide catalysts in oxidation reaction of CO

Physicochemical characteristics of Cu-Co-Fe oxide catalysts applied to molybdenum carbide and their catalytic activity in the CO oxidation reaction have been studied. It has been shown that for a more efficient use of Mo₂C as a carrier of catalysts, it should be processed with a mixture of HF + HNO₃ acids with the aim to increase the defectiveness of the structure.     

High-throughput technology for novel SO2 oxidation catalysts

We review the state of the art and explain the need for better SO₂ oxidation catalysts for the production of sulfuric acid. A high-throughput technology has been developed for the study of potential catalysts in the oxidation of SO₂ to SO₃. High-throughput methods are reviewed and the problems encountered with their adaptation to the corrosive conditions of SO₂ oxidation are described. We show that while emissivity-corrected infrared thermography (ecIRT) can be used for primary screening, it is prone to errors because of the large variations in the emissivity of the catalyst surface. UV-visible (UV-Vis) spectrometry was selected instead as a reliable analysis method of monitoring the SO₂ conversion. Installing plain sugar absorbents at reactor outlets proved valuable for the detection and quantitative removal of SO₃ from the product gas before the UV-Vis analysis. We also overview some elements used for prescreening and those remaining after the screening of the first catalyst generations.     

High-throughput technology for novel SO2 oxidation catalysts

Abstract

We review the state of the art and explain the need for better SO₂ oxidation catalysts for the production of sulfuric acid. A high-throughput technology has been developed for the study of potential catalysts in the oxidation of SO₂ to SO₃. High-throughput methods are reviewed and the problems encountered with their adaptation to the corrosive conditions of SO₂ oxidation are described. We show that while emissivity-corrected infrared thermography (ecIRT) can be used for primary screening, it is prone to errors because of the large variations in the emissivity of the catalyst surface. UV-visible (UV-Vis) spectrometry was selected instead as a reliable analysis method of monitoring the SO₂ conversion. Installing plain sugar absorbents at reactor outlets proved valuable for the detection and quantitative removal of SO₃ from the product gas before the UV-Vis analysis. We also overview some elements used for prescreening and those remaining after the screening of the first catalyst generations.     

CuO/CeO2 catalysts prepared with different cerium supports for CO oxidation at low temperature

The activity of a catalyst depends on the nature of its support, its active site, and its preparation method. This study aimed to employ various types of CeO₂ supports such as commercial CeO₂ and self-prepared CeO₂ for the preparation of copper catalysts. The CuO/CeO₂ catalysts were prepared using the polyol process and impregnation method. The catalysts were characterized using Brunauer–Emmett–Teller analysis, scanning electron microscopy, and X-ray analysis, and their catalytic activity for CO removal was evaluated in a microcatalytic reactor. The experimental results showed that the catalytic activity of the CuO/CeO₂ catalysts with different calcination temperatures decreased in the following order: 500 °C > 300 °C > 700 °C. Compared to the impregnation method, the polyol process generated well-dispersed metal particles over the support and showed higher CO removal efficiency with low activation energy. Compared to CuO/CeO₂ catalysts with commercial CeO₂, those with CeO₂ that was self-prepared by pyrolysis had a large pore volume and good crystal structure of CeO₂ and showed good performance. The catalytic activity for CO removal was in the following order: CuO/CeO₂-P (pyrolysis) > CuO/CeO₂-C (commercial) > CuO/CeO₂-D (deposition precipitation). CuO/CeO₂-P catalysts showed good activity even at low temperature. The CuO/CeO₂-P(300)-P-120 min catalyst was found to possess the good CO removal rate when the oxygen content was 6%, CO concentration was 500 ppm, catalyst weighed 1.0 g, pollutant gas velocity was 500 mL min⁻¹, SV was 3.7 × 10⁴ h⁻¹, and reaction temperature was 150 °C.     

Preparation and characterization of nanosized gold catalysts supported on Co3O4 and their activities for CO oxidation

Gold catalysts supported on Co3O4 were prepared by co-precipitation (CP), deposition-precipitation (DP), and impregnation (IMP) methods. The Au/Co3O4 catalysts were characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS), and temperature programmed reduction (TPR) to understand the different activities for CO oxidation with different preparation methods. Gold particles below 5 nm supported on Co3O4 by DP method were found to be more exposed to the surface than those by CP and IMP methods, and this catalyst was highly active and stable in CO oxidation. Finally, catalytic activity of Au/Co3O4 catalyst for CO oxidation was strongly dependent on the gold particle size.     

Synthesis and characterization of CuO/Ce 1-x Ti x O2 catalysts used for low-temperature CO oxidation

A series of CuO/Ce(1-x)Ti(x)O(2) catalysts used for low-temperature CO oxidation were prepared by impregnation with the support derived from surfactant-assisted co-precipitation. The techniques of N(2) adsorption/desorption, X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS) and temperature-programmed reduction by H(2) (H(2)-TPR) were employed for catalyst characterization. It is found that the support CeO(2) prepared by the surfactant-assisted method possesses much larger specific surface area than the one obtained from conventional precipitation. Doping Ti in the support with Ti/Ce atomic ratio of 1:9 or 3:7 can further increase the surface area of CeO(2) and decrease its crystallite size. As a result, the active Cu species possess higher dispersion on the support Ce(1-x)Ti(x)O(2) than on pure CeO(2). The strong interaction between the dispersed Cu species and the support Ce(1-x)Ti(x)O(2) makes the catalysts possess much higher oxidation activity and thermal stability. However, when the ratio of Ti/Ce reaches 5:5, opposite effect is found, due to the highest surface concentration of Ti and the lack of surface highly dispersed copper species.     

Plasma-enhanced catalytic CuO nanowires for CO oxidation

We report the first experimental study of catalytic CO oxidation over copper oxide (CuO) nanowires (NWs) grown directly on copper meshes. The catalytic activity of CuO NWs is significantly improved by a brief argon or hydrogen radio frequency plasma treatment. The plasma enhancement effect comes from the generation of grain boundaries and the reduction of Cu(II) to the more active oxidation state Cu(I) according to our TEM, XPS, and kinetic study.     

Effects of mixed and ionic conduction in ZrO2 and ThO2 as CO oxidation catalysts

A comparison is made of the heterogeneous catalytic activities of ZrO₂, Zr_0.91Ca_0.09O_1.91 and Th_0.85La_0.15O_1.925 for the oxidation of CO by O₂. A correlation is evident with the magnitudes of the simultaneous bulk ionic and electronic conductivities. This is in accord with a postulated model for reaction at separate reactant absorption sites in which oxygen ions and electronic charge are transported in and on the surface of the oxide catalyst.     

Novel, benign, solid catalysts for the oxidation of hydrocarbons

The catalytic properties of two classes of solid catalysts for the oxidation of hydrocarbons in the liquid phase are discussed: (i) microporous solids, encapsulating transition metal complexes in their cavities and (ii) titanosilicate molecular sieves. Copper acetate dimers encapsulated in molecular sieves Y, MCM-22 and VPI-5 use dioxygen to regioselectively ortho-hydroxylate L-tyrosine to L-dopa, phenol to catechol and cresols to the corresponding o-dihydroxy and o-quinone compounds. Monomeric copper phthalocyanine and salen complexes entrapped in zeolite-Y oxidize methane to methanol, toluene to cresols, naphthalene to naphthols, xylene to xylenols and phenol to diphenols. Trimeric mu3-oxo-bridged Co/Mn cluster complexes, encapsulated inside Y-zeolite, oxidize para-xylene, almost quantitatively, to terephthalic acid. In almost all cases, the intrinsic catalytic activity (turnover frequency) of the metal complex is enhanced very significantly, upon encapsulation in the porous solids. Spectroscopic and electrochemical studies suggest that the geometric distortions of the complex on encapsulation change the electron density at the metal ion site and its redox behaviour, thereby influencing its catalytic activity and selectivity in oxidation reactions.Titanosilicate molecular sieves can oxidize hydrocarbons using dioxygen when loaded with transition metals like Pd, Au or Ag. The structure of surface Ti ions and the type of oxo-Ti species generated on contact with oxidants depend on several factors including the method of zeolite synthesis, zeolite structure, solvent, temperature and oxidant. Although, similar oxo-Ti species are present on all the titanosilicates, their relative concentrations vary among different structures and determine the product selectivity.