Preferential oxidation of carbon monoxide in hydrogen-rich gas over platinum-cobalt-alumina aerogel catalysts

The performance of the platinum-cobalt catalysts in a carbon monoxide preferential oxidation (PROX) reactor was investigated for polymer electrolyte fuel cell systems. First, the PROX reaction was analyzed based on two major reactions involved in it, i.e., oxidation of carbon monoxide and the H₂-O₂ reaction. Both reactions were affected by the other reaction depending on the reaction temperature regions, but the extent of the influence is not so large. The platinum-cobalt catalysts were found to exhibit high performance in PROX of carbon monoxide in rich hydrogen as a result of catalytic synergy effect between platinum and cobalt. In order to improve such synergy effect, the catalysts were prepared by sol-gel method and subsequent supercritical drying. The platinum-cobalt catalysts prepared by the single step sol-gel procedure exhibited higher activity for PROX than the catalysts prepared by the conventional impregnation. Supercritical drying preserved the active species of platinum-cobalt phase, therefore, the platinum-cobalt composite aerogel catalyst exhibited excellent ability for the carbon monoxide removal.     

高选择性低汽气比一氧化碳低温变换催化剂的研究

实验室试验表明,添加助剂的低汽气比一氧化碳低温变换催化剂,在保证活性和稳定性的基础上,明显地提高了选择性,其甲醇生成量可降为原来的1/4左右。     

Copolymerization of ethylene and carbon monoxide using [(dppp)Pd(H2O)(TsO)](TsO) as a catalyst precursor: rate equation

The influence of CO and C₂H₄ pressures on their copolymerization catalyzed by the precursor [(dppp)Pd(H₂O)(TsO)](TsO) in MeOH has been studied up to 8 Mpa of total pressure at 363 K. Several rate equations, based on two different models, are presented. The so called “one site model” involves a tetracoordinate Pd^II cation in which only one coordination site is available to the monomers. The “two sites model” involves a pentacoordinate Pd^II cation in which the monomers coordinate the metal simultaneously at two different sites. In both cases, the other three sites are occupied by the growing polymer chain and the chelating diphosphine. The rate equation that fits the experimental data better is used to optimize the ratio of the monomers pressures to obtain a maximum reaction rate for a given total pressure.     

Plasma-assisted preparation of Fe-Cu bimetal catalyst for higher alcohols synthesis from carbon monoxide hydrogenation

Plasma-assisted Fe-Cu/SiO₂ catalysts were prepared by impregnation technique and characterized by X-ray diffraction (XRD), nitrogen adsorption and desorption isotherms, X-ray photoelectron spectroscopy (XPS) and temperature-programmed reduction (H₂-TPR) techniques. Catalytic performances for carbon monoxide hydrogenation to higher alcohols were carried out in a fixed-bed reactor at the conditions of T = 300 °C, P = 5 MPa, H₂/CO = 2, GHSV = 6000 ml/g_cat h. Plasma-promoted Fe-Cu bimetal catalyst (FeCuSi-PC) possessed much better catalytic performances than those of conventional sample in the selective hydrogenation of carbon monoxide. XRD and XPS analysis suggested that the plasma assistance in the catalyst preparation remarkably diminished the particle size, improved the catalyst dispersion, and issued an exposure of more copper and iron species on the catalyst surface. The mechanism of plasma on catalyst crystallize size was also discussed.     

Cu-K/Al2O3 based catalysts for conversion of carbon dioxide to methane and carbon monoxide

Abstract

A series of Cu-K/Al₂O₃ catalysts were synthesized by wet impregnation technique. The reduced catalysts were further used for conversion of carbon dioxide to methane and carbon monoxide. Moreover, the fresh and used catalysts were characterized to investigate the changes in the surface morphology, metal dispersion, surface area, crystalline phases, and functional groups of studied catalysts. The SEM analysis of fresh and spent catalysts showed no remarkable difference in surface morphology with irregular shaped agglomerated particles. Furthermore, TEM micrographs presented the well distribution of metal catalyst over alumina support. The decrease in surface area from 115 to 77?m²/g for Cu_1.62-K_0.5/Al₂O₃ after reaction was related to sintering and oxidation of catalyst during reaction. XRD revealed the disappearance of some minor peaks which can be associated with the sintering of spent catalyst. FTIR also presented some new peak for spent catalyst which can be linked with metal oxides. Moreover, various reaction conditions of temperature (230, 400, and 600?°C), pressure (1 and 7?bar), and feed molar ratio of H₂/CO₂ (2:1 and 4:1) were investigated using different Cu loading (0, 1, 1.25, 1.62, and 4 weight percent). A maximum CO₂ conversion of 63% with 39% CH₄ selectivity was achieved by using Cu_1.62-K_0.5/Al₂O₃ at 600?°C, molar ratio of H₂/CO₂ 4 under 7?bar. The presence of K on the surface of synthesized catalyst increased the CO₂ conversion from 48% (Cu₁/Al₂O₃) to 55% (Cu₁-K_0.5/Al₂O₃) at above mentioned reaction conditions which suggested the promoter effect of K during conversion of carbon dioxide.     

Ultralow-weight loading Ni catalyst supported on two-dimensional vermiculite for carbon monoxide methanation

Nickel-based catalysts represent the most commonly used systems for CO methanation. We have successfully prepared a Ni catalyst system supported on two-dimensional plasma-treated vermiculite (2D-PVMT) with a very low Ni loading (0.5 wt%). The catalyst precursor was subjected to heat treatment via either conventional heat treatment (CHT) or the plasma irradiation method (PIM). The as-obtained CHT-Ni/PVMT and PIM-Ni/PVMT catalysts were characterized with scanning electron microscopy (SEM), energy dispersive X-ray (EDX), X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), inductively coupled plasma-atomic emission spectroscopy (ICP-AES) and high-angle annular dark field scanning transmission electron microscopy (HAADF-STEM). Additionally, CHT-NiO/PVMT and PIM-NiO/PVMT catalysts were characterized with hydrogen temperature programmed reduction (H₂-TPR). Compared with CHT-Ni/PVMT, PIM-Ni/PVMT exhibited superior catalytic performance. The plasma treated catalyst PIM-Ni/PVMT achieved a CO conversion of 93.5% and a turnover frequency (TOF) of 0.8537 s^-1, at a temperature of 450℃, a gas hourly space velocity of 6000 ml·g^-1·h^-1, a synthesis gas flow rate of 65 ml·min^-1, and a pressure of 1.5 MPa. Plasma irradiation may provide a successful strategy for the preparation of catalysts with very low metal loadings which exhibit excellent properties.     

一氧化碳干燥技术及应用

本文阐述了光气生产中一氧化碳冷冻脱水-分子筛吸附的干燥技术,使得干燥后一氧化碳水份含量≤100ppm,提高了光气及光气化产品的质量和设备使用寿命,保证了光气安全生产。     

Oxidation protection of carbon materials by acid phosphate impregnation

Acid phosphate impregnation, with ozone pre-treatment, improves the oxidation resistance of carbon materials (polycrystalline graphite and pitch-based carbon fiber), as shown by weight measurement in air up to 1500 °C. The impregnation involves using phosphoric acid and dissolved aluminum hydroxide in the molar ratio 12:1 and results in a rough, white and hard aluminum metaphosphate coating of weight about 20% of that of the carbon before the treatment. Without ozone pre-treatment, the impregnation is not effective. Without aluminum hydroxide, the impregnation even degrades the oxidation resistance of the carbon.     

Reduction of nitrogen oxides by carbon monoxide over an iron oxide catalyst under dynamic conditions

The reduction of NO and N₂O by CO over a silica-supported iron oxide catalyst was investigated by the transient response method, with different initial oxidation states of the catalyst, i.e. completely reduced (Fe₃O₄), or oxidised (Fe₂O₃). The influence of CO pre-adsorption was also studied. From the material balance on the gas phase species, it was shown that the composition of the catalyst changes during relaxation to steady-state. The degree of reduction of the catalyst at steady-state could thus be estimated. During the transient period, CO was shown to inhibit N₂O as well as NO reductions by adsorption on reduced sites. The activity of the reduced catalyst was found to be substantially higher as compared to the oxidised catalyst for both reactions. On this basis, it was attempted to keep the catalyst in a reduced state by periodically reducing it with CO. As a result, a significant increase in the performance of the reactor with respect to steady-state operation could be achieved for N₂O reduction by CO. Finally, the dynamic behaviour of the N₂O–CO and NO–CO reactions made it possible to evidence reaction steps, the occurrence of which could not be shown during our previous investigations on the separate interactions of the reactants with the catalyst.     

一氧化碳吸附干燥器的技术改进

针对原吸附干燥器存在内部盘管焊接接头容易泄漏、设备使用寿命短、材质浪费较大等问题,对其进行了改进。将其中的气体分布改为筛孔板结构,在盘管和总管之间增加异径接头,在夹套与内筒之间增加加强圈,改进后的吸附干燥器结构合理,投资省,效率高,运行平稳。     

CO低温氧化霍加拉特催化剂的研究

综述了CO低温氧化霍加拉特（Hopcalite）催化剂的活性影响因素、催化机理、催化剂失活原因以及最新研究进展,并展望了以后的发展方向。     

Hydrogenation of carbon monoxide under mechanical activation conditions

The work focuses on the hydrogenation of carbon monoxide over solid catalysts undergoing mechanical activation by ball milling. The rate of carbon monoxide conversion at individual ball impacts was estimated by measuring the impact frequency, the mass of powders involved in individual impacts and their duration. The rate of the mechanochemical hydrogenation process was compared with the one of the corresponding thermal process. An enhancement of the catalyst activity under mechanical activation conditions is observed.     

Effect of sintering on the catalytic activity of a Pt based catalyst for CO oxidation: Experiments and modeling

The goal of this paper was to make the link between sintering of a 1.6% Pt/Al₂O₃ catalyst and its activity for CO oxidation reaction. Thermal aging of this catalyst for different durations ranging from 15 min to 16 h, at 600 and 700 °C, under 7% O₂, led to a shift of the platinum particle size distributions towards larger diameters, due to sintering. These distributions were studied by transmission electron microscopy. The number and the surface average diameters of platinum particles increase from 1.3 to 8.9 nm and 2.1 to 12.8 nm, respectively, after 16 h aging at 600 °C. The catalytic activity for CO oxidation under different CO and O₂ inlet concentrations decreases after aging the catalyst. The light-off temperature increased by 48 °C when the catalyst was aged for 16 h at 600 °C. The CO oxidation reaction is structure sensitive with a catalytic activity increasing with the platinum particle size. To account for this size effect, two intrinsic kinetic constants, related either to platinum atoms on planar faces or atoms on edges and corners were defined. A platinum site located on a planar face was found to be 2.5 more active than a platinum site on edges or corners, whatever the temperature. The global kinetic law {r (mol m⁻² s⁻¹) = 103 × exp(−64,500/RT)[O₂]^0.74[CO]^−0.5)} related to a reaction occurring on a platinum atom located on planar faces allows a simulation of the CO conversion curves during a temperature ramp. Modeling of the catalytic CO conversion during a temperature ramp, using the different aged catalysts, allows prediction of the CO conversion curves over a wide range of experimental conditions.     

Nitrogen-doped carbon nanotubes synthesized with carbon nanotubes as catalyst

Nitrogen-doped carbon (CN_x) nanotubes were synthesized with carbon nanotubes (CNTs) as catalyst by detonation-assisted chemical vapor deposition. CN_x nanotubes exhibited compartmentalized bamboo-like structure. Electron energy loss spectroscopy and elemental mapping studies indicated that the synthesized tubes contained high concentration of nitrogen (ca. 17.3 at.%), inhomogeneously distributed with an enrichment of nitrogen within the compartments. X-ray photoelectron spectroscopy analysis revealed the presence of pyridine-like N and graphitic N incorporated into the graphitic network. The catalytic activity of CNTs for CN_x nanotube growth was ascribed to the nanocurvature and opening edges of CNT tips, which adsorbed C_n/CN species and assembled them into CN_x nanotubes.     

Development of carbon nanotube and carbon xerogel supported catalysts for the electro-oxidation of methanol in fuel cells

Multiwalled carbon nanotubes and high surface area mesoporous carbon xerogel were prepared and used as supports for monometallic Pt and bimetallic Pt-Ru catalysts. In order to assess the influence of the oxygen surface groups of the support, the mesoporous carbon xerogel was also oxidized with diluted oxygen before impregnation. Various reduction protocols were tested, the best results corresponding to reduction with sodium borohydride. High dispersion catalysts were obtained, which showed quite good performance in the electro-oxidation of methanol. In particular, a remarkable increase in the activity was observed when the Pt-Ru catalysts were supported on the oxidised xerogel. This effect was explained in terms of the metal oxidation state, as shown by XPS. It has been shown that the oxidised support helps to maintain the metals in the metallic state, as required for the electro-oxidation of methanol. This effect was negligible in the case of the Pt catalysts.     

Development of base metal oxide catalyst for automotive emission control

Activity of alumina was tested for CO and hydrocarbon oxidation using the flow reactor system. The mechanism of the CO oxidation was elucidated by isotopic tracer technique using a closed circulation system. CO oxidation was found to proceed via the formation of a carbonate type of intermediate species. Water enhances the CO oxidation and CO₂ retards alumina activity. Carbon deposition was also investigated during CO oxidation on alumina. Carbon formed was found to act as an in-situ active site that promoted CO oxidation. Results obtained showed alumina to be promising for CO oxidation. Pb showed opposite effects on CO and hydrocarbon reactions. Hydrocarbon reactivity test conducted showed that methanol is the most reactive on alumina giving 100% conversion at 500 °C. However, carbon deposited affected the formation of several products at this temperature. Further study on methanol oxidation using alkaline treated alumina showed better performance for auto emission control. CeO₂, known to have an oxygen storage capacity, was tested as an additive to alumina for methanol oxidation and propylene oxidation. Results proved that CeO₂-AL₂O₃ gave much higher activity for CO oxidation, methanol oxidation, and propylene oxidation than alumina.     

Nitric oxide and carbon monoxide permeation through glassy polymeric membranes for carbon dioxide separation

Minor components present in polymeric membrane gas separation can have a significant influence on the separation performance. Carbon monoxide and nitric oxide exist in post-combustion gas streams and can therefore influence CO₂ transport through membranes designed for that application. Here, the permeability of nitric oxide (NO) through three glassy polymeric membranes (polysulfone, Matrimid 5218 and 6FDA-TMPDA) was determined and found to be less than the CO₂ but greater than the N₂ permeability in each membrane. This study also investigated the influence of 1000 ppm CO on the mixed gas permeability of CO₂ and N₂ for two glassy polymeric membranes; polysulfone and 6FDA-TMPDA. For both membranes, CO competitive sorption resulted in a reduction in the measured permeability of CO₂ and N₂ even though present at only low concentration.     

Cerium phosphate-supported Au catalysts for CO oxidation

LaPO₄ and hydroxyapatite (Ca₁₀(PO₄)₆(OH)₂) are typical metal phosphates recently found to be useful for making supported metal or metal oxide catalysts, but CePO₄ (also belonging to the metal phosphate family) has been rarely used to make supported catalysts. It would be interesting to develop CePO₄-supported catalysts and explore their catalytic applications. Herein, hexagonal CePO₄ nanorods (denoted as CePO₄-H), hexagonal CePO₄ nanowires (CePO₄-HNW), monoclinic CePO₄ nanoparticles (CePO₄-M), and monoclinic CePO₄ nanowires (CePO₄-MNW) prepared by different methods were used to support gold via deposition-precipitation with urea (DPU). The gold contents of these catalysts were all around 1 wt%. The catalytic activities of these Au/CePO₄ catalysts in CO oxidation were found to follow the sequence of Au/CePO₄-MNW > Au/CePO₄-HNW > Au/CePO₄-M > Au/CePO₄-H. These catalysts were characterized by inductively coupled plasma-optical emission spectroscopy (ICP-OES), N₂ adsorption–desorption, X-ray diffraction (XRD), transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS), oxygen temperature-programmed desorption (O₂-TPD), and CO₂ temperature-programmed desorption (CO₂-TPD) to find possible correlations between the physicochemical properties and catalytic activities of these catalysts.     

CO高温变换催化剂浸渍条件研究

采用γ-Al₂O₃作载体,Ni^2＋、Cu^2＋和Mn^2＋水溶液为浸渍液,进行制备无铬CO高温变换催化剂浸渍条件的研究。由实验数据回归出Ni^2＋、Cu^2＋和Mn^2＋活性组分在载体上的浸渍动力学方程,得到Ni^2＋、Cu^2＋和Mn^2＋组分在载体上浸渍的速率常数为：k_Ni2＋= 0.000 2,k_Cu2＋=0.000 2,k_Mn2＋=0.001 6。Freundlich等温吸附表达式为：lnC_Ni2＋=－0.000 2 t＋4.447 4,lnC_Cu2＋=－0.000 2 t＋4.590 9和lnC_Mn2＋=－0.001 6 t＋3.589 5。考察了催化剂中活性组分含量与共浸渍组分浓度的关系,并得出从浸前液浓度来预测和控制催化剂成品中Ni^2＋、Cu^2＋和Mn^2＋活性组分含量的经验式。