Showing papers on "Partial oxidation published in 2007"
TL;DR: The size and temperature range in which vacancy coalescence during oxidation of amine-stabilized iron nanoparticles takes place is analyzed and Maghemite is the crystallographic structure obtained from the complete oxidation of Iron nanoparticles under the authors' synthetic conditions.
Abstract: In the present work, we analyze the geometry and composition of the nanostructures obtained from the oxidation of iron nanoparticles. The initial oxidation of iron takes place by outward diffusion of cations through the growing oxide shell. This net material flow is balanced by an opposite flow of vacancies, which coalesce at the metal/oxide interface. Thus, the partial oxidation of colloidal iron nanoparticles leads to the formation of core−void−shell nanostructures. Furthermore, the complete oxidation of iron nanoparticles in the 3−8 nm size range leads to the formation of hollow iron oxide nanoparticles. We analyze the size and temperature range in which vacancy coalescence during oxidation of amine-stabilized iron nanoparticles takes place. Maghemite is the crystallographic structure obtained from the complete oxidation of iron nanoparticles under our synthetic conditions.
308 citations
TL;DR: In this paper, the authors compared the performance of a metal-coated α-Al2O3 foam with a capillary sampling technique with mass spectrometric species measurement.
291 citations
TL;DR: In this paper, the benefits and limitations of single-chamber solid oxide fuel cells (SC-SOFCs) are discussed based on the cell design, performance, and energy efficiency.
235 citations
TL;DR: In this article, the catalysts were obtained by thermal decomposition of the precursors and subsequent reduction in H2 stream, and the results showed that redox properties depended on the composition of the samples and on the nature of the phases present in the precursts.
Abstract: Cu/ZnO/Al2O3 catalysts (5–45 Cu at.%) derived from layered double hydroxide (LDH) precursors were studied for oxidative steam reforming of methanol (OSRM). The precursors were prepared by homogeneous precipitation with urea. The catalysts were obtained by thermal decomposition of the precursors and subsequent reduction in H2 stream. XRD, SEM, N2 adsorption, TPR and NH3 TPD techniques were employed for characterization. Catalytic activity tests were carried out in a fixed bed flow reactor at T = 200–400 8C, H2O/CH3OH/O2 molar ratios = 1.1/1/0.12 (CH3OH concentration = 17.8%), GHSV = 6 � 10 4 h � 1 . Tests of simple steam reforming (SRM), partial oxidation (POM) and CH3OH decomposition (DEC) were also carried out. TPR measurements showed that redox properties depended on the composition of the samples and on the nature of the phases present in the precursors. The area of metallic Cu, measured by N2O passivation method, was correlated to Cu content. The size of Cu particles was smaller than 10 nm for Cu content up to 18 at.%. NH3 TPD measurements showed acid sites with a wide strength distribution, the strongest ones being mainly related to Al2O3 or Zn aluminate. Catalytic activity was influenced by the chemical composition: kinetic constants for OSRM varied unevenly with Cu surface area, while those for SRM increased with Cu surface area. A reaction mechanism agreeing with OSRM, SRM and DEC data was hypothesized. The mechanism involved an oxidation-reduction cycle of Cu and also the participation of the oxide matrix. # 2007 Elsevier B.V. All rights reserved.
186 citations
TL;DR: In this paper, a series of Ni x Co y (where x, y are the respective metal loadings of 0, 1, 2 or 3 wt.%; x + y = 3 ) bimetallic catalysts supported on CaAl 2 O 4 / Al 2 O 3 have been studied for hydrogen/synthesis gas production via the catalytic partial oxidation (CPO) of methane.
151 citations
01 Jan 2007
TL;DR: In this article, the role and effectiveness of a plasma reactor for partial oxidation of methane is investigated using a rotating gliding arc which is a three dimensional version of a typical gliding arcs.
Abstract: Characteristics of a plasma reactor for partial oxidation of methane, especially focused on the role and effectiveness of plasma chemistry, is investigated. Partial oxidation of methane is investigated using a rotating gliding arc which is a three dimensional version of a typical gliding arc. The rotating gliding arc has both the characteristics of equilibrium and non-equilibrium plasma. Non-equilibrium characteristics of the rotating gliding arc can be increased by rotating an elongated arc string attached at both the tip of inner electrode and the edge of outer electrode. In this way, plasma chemistry can be enhanced and hydrogen selectivity can reach almost 100% that is much higher than thermal equilibrium condition. Also, the energy required to produce a unit mass of hydrogen (energy cost) is drastically reduced by increased effect of plasma chemistry. As a result, the present study enables the strategic approach of the plasma reforming process by means of through appropriate reactor design to maximize plasma effect and resulting in maximized reaction efficiency.
147 citations
TL;DR: In this paper, the Ni metal covered with silica (coat-Ni) showed excellent catalytic performance for the partial oxidation of methane into synthesis gas, whereas Ni metal catalyst supported on silica was rapidly deactivated for the reaction.
132 citations
TL;DR: In this article, the behavior of three different catalyst typologies, two based on Ni-Al2O3 and one constituted by Pt supported on CeO2, is studied for partial oxidation of propane (as representative of liquefied petroleum gas).
119 citations
TL;DR: Partial oxidation of methane (POM) to synthesis gas was studied over Ru catalysts (1% w/w) supported on silica, alumina and ceria-zirconia as mentioned in this paper.
Abstract: Partial oxidation of methane (POM) to synthesis gas was studied over Ru catalysts (1% (w/w)) supported on silica, alumina and ceria-zirconia. Catalyst samples were prepared by incipient wetness and ...
112 citations
TL;DR: In this paper, the authors conducted a chemical equilibrium analysis on combined CH4-reforming with CO2 and O2 (combined CORM-POM) by total Gibbs energy minimization using Lagrange's undetermined multiplier method.
109 citations
TL;DR: The results show that Au MPCs are prone to oxidation in air in the presence of halide anions, and therefore, particles made using phase transfer reagents such as tetraoctylammonium bromide must be thoroughly removed to avoid particle size growth, oxidation, and precipitation of the Au MPC.
Abstract: We report on the oxidative stability of thiol-passivated Au monolayer-protected clusters (MPCs) made via a modified Brust−Schiffrin method. A sequential oxidation of the anchored thiol groups to disulfide and sulfonate groups and the oxidation of Au atoms to Au3+ species is observed upon exposure of Au MPCs to air in the presence of halide anions. In addition, the average nanoparticle size grows via aggregation of the MPCs, leading eventually to partial oxidation of the Au MPCs and precipitation of the remaining nanoparticles from solution or to complete oxidation of the gold atoms at high halide concentrations. These results show that Au MPCs are prone to oxidation in air in the presence of halide anions, and therefore, particles made using phase transfer reagents such as tetraoctylammonium bromide must be thoroughly removed to avoid particle size growth, oxidation, and precipitation of the Au MPCs. In addition, for biological applications involving Au MPCs, care must be taken to ensure that oxidation of...
TL;DR: In this article, a multistage gliding arc discharge system was employed to investigate the effects of stage number, feed gas composition, feed flow rate, frequency, applied voltage, and electrode gap distance on the CH 4 and O 2 conversions and the product distribution.
TL;DR: In this paper, an engineered catalyst, a Rh-based monolithic catalyst with an optimized composition of 0.3%Rh/3%MgO/20%CeO2-ZrO2 supported on cordierite monolith was developed for autothermal reforming of commercial gasoline and its surrogates.
TL;DR: This work focused on particle size and structure dependent effects in methanol oxidation and decomposition, support effects and their relation to activity and selectivity, the influence of poisons such as carbon and the role of oxide and surface oxide formation on Pd nanoparticles.
Abstract: We investigated the decomposition and (partial) oxidation of methanol on Pd based catalysts in an integrated attempt, simultaneously bridging both the pressure and the materials gap. Combined studies were performed on well-defined Pd model catalysts based on ordered Al2O3 and Fe3O4 thin films, on well-defined particles supported on powders and on Pd single crystals. The interaction of Pd nanoparticles and Pd(111) with CH3OH and CH3OH/O2 mixtures was examined from ultrahigh vacuum conditions up to ambient pressures, utilizing a broad range of surface specific vibrational spectroscopies which included IRAS, TR-IRAS, PM-IRAS, SFG, and DRIFTS. Detailed kinetic studies in the low pressure region were performed by molecular beam methods, providing comprehensive insights into the microkinetics of the reaction system. The underlying microscopic processes were studied theoretically on the basis of specially designed 3-D nanocluster models containing ∼102 metal atoms. The efficiency of this novel modelling approach was demonstrated by rationalizing and complementing pertinent experimental results. In order to connect these results to the behavior under ambient conditions, kinetic and spectroscopic investigations were performed in reaction cells and lab reactors. Specifically, we focused on (1) particle size and structure dependent effects in methanol oxidation and decomposition, (2) support effects and their relation to activity and selectivity, (3) the influence of poisons such as carbon, and (4) the role of oxide and surface oxide formation on Pd nanoparticles.
TL;DR: In this article, the partial oxidation of methane over supported (ZrO2, CeO2-ZRO2) rhodium catalysts was investigated at atmospheric pressure.
Abstract: The partial oxidation of methane over supported (ZrO2, CeO2-ZrO2) rhodium catalysts was investigated at atmospheric pressure. The effect of temperature, CH4/O-2 ratio, catalyst composition and pr ...
TL;DR: In this article, NiO catalysts have been applied for combined steam and carbon dioxide reforming of methane to produce synthesis gas (H2/CO = 2), and a nano-sized Ni/Mgo-Al2O3 catalyst has been successfully developed for the target reaction.
Abstract: Various supported Ni catalysts have been applied for combined steam and carbon dioxide reforming of methane to produce synthesis gas (H2/CO = 2). Highly active and stable nano-sized Ni/Mgo–Al2O3 catalyst has been successfully developed for the target reaction. The high activity and stability is due to beneficial effects of MgO such as enhanced steam adsorption, basic property, nano-sized NiO crystallite size and strong interaction between Ni and support.
TL;DR: In this article, mixed oxides of nickel, magnesium and aluminum were prepared by precursors hydrotalcite type and were substituted by lanthanum or cerium using the method of anion exchange.
Abstract: Mixed oxides of nickel, magnesium and aluminum were prepared by precursors hydrotalcite type and were substituted by lanthanum or cerium using the method of anion exchange. The catalysts were characterized by X-Ray Photoelectronic Spectroscopy (XPS); Energy Dispersive X-Ray Spectroscopy (EDS); Surface Area Method BET; X-Ray Diffraction (XRD); Temperature Programmed Reduction (TPR) and Catalytic Tests. Analysis of the mixed oxides suggests that the hydrotalcite type precursor after thermal treatment lead a good dispersion of nickel forming the periclase (Ni, Mg)O replaced by cations of Al 3+ and spinel structure (Ni,Mg)Al 2 O 4 . The catalysts were tested in the partial oxidation of methane and the results showed that the catalysts promoted with lanthanum and cerium led to a reduction in the velocity of the carbon formation.
TL;DR: In this article, three reactors with varying designs were used for autothermal reforming of an alkane mixture and of commercial desulphurised Jet A-1, and the long-term stability of the three reactors revealed that it is decisive to posses a highly sophisticated educt and fuel evaporation technology in combination with a homogeneous mixing of the educts.
TL;DR: It was found that very small Pd particles on Fe(3)O(4) show a strongly modified adsorption behavior, characterized by atypically weak CO adsorptive behavior and a characteristic CO stretching frequency around 2130 cm(-1).
Abstract: Combining scanning tunneling microscopy (STM), IR reflection absorption spectroscopy (IRAS) and molecular beam (MB) techniques, we have investigated particle size effects on a Pd/Fe3O4 model catalyst. We focus on the particle size dependence of (i) CO adsorption, (ii) oxygen adsorption and (iii) Pd nanoparticle oxidation/reduction. The model system, which is based on Pd nanoparticles supported on an ordered Fe3O4 film on Pt(111), is characterized in detail with respect to particle morphology, nucleation, growth and coalescence behavior of the Pd particles. Morphological changes upon stabilization by thermal treatment in oxygen atmosphere are also considered. The size of the Pd particles can be varied roughly between 1 and 100 nm. The growth and morphology of the Pd particles on the Fe3O4/Pt(111) film were characterized by STM and IRAS of adsorbed CO as a probe molecule. It was found that very small Pd particles on Fe3O4 show a strongly modified adsorption behavior, characterized by atypically weak CO adsorption and a characteristic CO stretching frequency around 2130 cm−1. This modification is attributed to a strong interaction with the support. Additionally, the kinetics of CO adsorption was studied by sticking coefficient experiments as a function of particle size. For small particles it is shown that the CO adsorption rate is significantly enhanced by the capture zone effect. The absolute size of the capture zone was quantified on the basis of the STM and sticking coefficient data. Finally, oxygen adsorption was studied by means of MB CO titration experiments. Pure chemisorption of oxygen is observed at 400 K, whereas at 500 K partial oxidation of the particles occurs. The oxidation behavior reveals strong kinetic hindrances to oxidation for larger particles, whereas facile oxidation and reduction are observed for smaller particles. For the latter, estimates point to the formation of oxide layers which, on average, are thicker than the surface oxides on corresponding single crystal surfaces.
TL;DR: In this article, a predictive microkinetic model for CH4 (C1) partial oxidation, combustion, and reforming, as well as oxygenate (CH3OH and CH2O) decomposition and oxidation on platinum, consisting of 104 elementary-like steps.
Abstract: Hydrogen production from fuel processing and its utilization in fuel cell technology is recognized as a promising route to future power generation. Reliable chemistry models are necessary to improve the hydrogen generation processes via optimal reactor design. With this objective, here, we present a predictive microkinetic model for CH4 (C1) partial oxidation, combustion, and reforming, as well as oxygenate (CH3OH and CH2O) decomposition and oxidation on platinum, consisting of 104 elementary-like steps. A hierarchical multiscale approach is used in the parameter estimation of bottom-up mechanism building. Thermodynamic consistency is ensured in the C1 mechanism. Important kinetic parameters are identified via sensitivity analysis for various experimental systems, using diverse operating conditions, and only a limited number of important kinetic parameters are refined (four for CH4). The C1 mechanism is extensively validated against several additional experimental data and is observed to be fairly predict...
TL;DR: In this article, a novel Cu/ZnO-CNTs (carbon nano-tubes) nano-catalyst was prepared by a chemical reduction and wet impregnation method, and was applied to catalyze the steam reforming reaction of methanol.
Abstract: A novel Cu/ZnO-CNTs (carbon nano-tubes) nano-catalyst was prepared by a chemical reduction and wet impregnation method, and was applied to catalyze the steam reforming reaction of methanol. If one uses CNT as the support, the CNTs should be pre-treated by nitric acid and sulfuric acid at 60 °C for 24 h to create defects on its surface; the hydrophilicity of CNTs was improved by adding a suitable amount of ethanol. The catalysts were characterized by TEM, XRD, FTIR and TGA. A good dispersion of Cu nano-particles on the surface of CNTs with particle size about 10 nm is identified by TEM analysis. Using 23 wt% Cu80ZnO20-CNTs as the catalyst, we obtained the hydrogen yield for steam reforming of methanol of 83% at 280 °C and near 100% at temperatures higher than 320 °C with 1.5 of molar ratio of water to methanol. The higher hydrogen production (larger than 400mmol/(s kg cat)), higher selectivity of CO2 and lower CO concentration were also observed.
TL;DR: The partial and total oxidation of methanol on clean and oxygen-precovered Cu(110) has been studied by periodic density functional theory calculations within the generalized gradient approximation, demonstrating that the specific structure of oxygen on copper plays an important role in both the partial and the total oxidation.
Abstract: The partial and total oxidation of methanol on clean and oxygen-precovered Cu(110) has been studied by periodic density functional theory calculations within the generalized gradient approximation. Reaction paths including the geometry and the energetics of several reaction intermediates and the activation barriers between them have been determined, thus creating a complete scheme for methanol oxidation on copper. The calculations demonstrate that the specific structure of oxygen on copper plays an important role in both the partial and the total oxidation of methanol. For lower oxygen concentrations on the surface, the partial oxidation of methanol to formaldehyde is promoted by the presence of oxygen on the surface through the removal of hydrogen in the form of water, which prevents the recombinative desorption of methanol. At larger oxygen concentrations, the presence of isolated oxygen atoms reduces the C−H bond breaking barrier of adsorbed methoxy considerably, thus accelerating the formation of form...
TL;DR: In this article, the partial oxidation of methane to synthesis gas due to CH 4 + 1/2 0 2 → CO + 2H 2 was investigated in a permselective membrane reactor using perovskite hollow fibers for the selective separation of oxygen from air.
Abstract: Two consecutive model reactions of the type A - B→ C are studied in two kinds of catalytic membrane reactors. The partial oxidation of methane to synthesis gas due to CH 4 + 1/ 2 0 2 → CO + 2H 2 was investigated in a novel type of permselective membrane reactor using perovskite hollow fibers for the selective separation of oxygen from air. Partial hydrogenations were studied in a pore-through-flow membrane reactor as a special type of a catalytic membrane contactor. The catalytically functionalized pores of the membrane provide a medium with defined contact times for the cofeed of hydrogen and an unsaturated hydrocarbon, and the attempts of the scale-up of the successful laboratory experiments to the pilot scale are reported.
TL;DR: Detailed reaction model which describes the oxygen exchange and the processes at the catalyst more precisely is discussed and correlations are drawn between structure, oxygen dynamics and the catalytic performance in terms of activity, selectivity and long-term stability.
Abstract: The major objective of this research project was to reach a microscopic understanding of the structure, function and dynamics of V-Mo-(W) mixed oxides for the partial oxidation of acrolein to acrylic acid. Different model catalysts (from binary and ternary vanadium molybdenum oxides up to quaternary oxides with additional tungsten) were prepared via a solid state preparation route and hydrochemical preparation of precursors by spray-drying or crystallisation with subsequent calcination. The phase composition was investigated ex situ by XRD and HR-TEM. Solid state prepared samples are characterised by crystalline phases associated to suitable phase diagrams. Samples prepared from crystallised and spray-dried precursors show crystalline phases which are not part of the phase diagram. Amorphous or nanocrystalline structures are only found in tungsten doped samples. The kinetics of the partial oxidation as well as the catalysts' structure have been studied in situ by XAS, XRD, temperature programmed reaction and reduction as well as by a transient isotopic tracing technique (SSITKA). The reduction and re-oxidation kinetics of the bulk phase have been evaluated by XAS. A direct influence not only of the catalysts' composition but also of the preparation route is shown. Altogether correlations are drawn between structure, oxygen dynamics and the catalytic performance in terms of activity, selectivity and long-term stability. A model for the solid state behaviour under reaction conditions has been developed. Furthermore, isotope exchange experiments provided a closer image of the mechanism of the selective acrolein oxidation. Based on the in situ characterisation in combination with micro kinetic modelling a detailed reaction model which describes the oxygen exchange and the processes at the catalyst more precisely is discussed.
TL;DR: In this article, an X-ray image of the R 2 O 3 (Rh) was used to determine the structural changes of the catalyst in a micro-reactor with a fixed-bed of 2.5 Wt% Rh/Al O 3.
TL;DR: In this article, multi-noble metal particles on Al2O3 were prepared in one step by flame spray pyrolysis (FSP) of the corresponding noble metal precursors dissolved in methanol and acetic acid (v/v 1:1) or xylene.
Abstract: Mono and multi-noble metal particles on Al2O3 were prepared in one step by flame spray pyrolysis (FSP) of the corresponding noble metal precursors dissolved in methanol and acetic acid (v/v 1:1) or xylene. The noble metal loading of the catalysts was close to the theoretical composition as determined by WD-XRF and LA-ICP-MS. The preparation method was combined with high-throughput testing using an experimental setup consisting of eight parallel fixed-bed reactors. Samples containing 0.1‐5 wt% noble metals (Ru, Rh, Pt, Pd) on Al2O3 were tested in the catalytic partial oxidation of methane. The ignition of the reaction towards carbon monoxide and hydrogen depended on the loading and the noble metal constituents. The selectivity of these noble metal catalysts towards CO and H2 was similar under the conditions used (methane: oxygen ratio 2:1, temperature from 300 to 500 8C) and exceeded significantly those of gold and silver containing catalysts. Selected catalysts were further analysed using XPS, BET, STEM-EDXS and XANES/EXAFS. The catalysts exhibited generally a specific surface area of more than 100 m 2 /g, and were made up of ca. 10 nm alumina particles on which the smaller noble metal particles (1‐2 nm, partially oxidized state) were discernible. XPS investigation revealed an enrichment of noble metals on the alumina surface of all samples. The question of alloy formation was addressed by STEM-EDXS and EXAFS analysis. In some cases, particularly for Pt‐Pd and Pt‐Rh, alloying close to the bulk alloys was found, in contrast to Pt‐Ru being only partially alloyed. In situ X-ray absorption spectroscopy on selected samples was used to gain insight into the oxidation state during ignition and extinction of the catalytic partial oxidation of methane to hydrogen and carbon monoxide. # 2006 Elsevier B.V. All rights reserved.
TL;DR: In this article, the reactivity of planar model catalysts for CO hydrogenation and methanol partial oxidation were examined by sum frequency generation (SFG) vibrational spectroscopy and by polarization-modulation IRAS at pressures ranging from ultrahigh vacuum to ∼1 bar.
TL;DR: In this article, the results of photooxidation of 1-pentanol over niobium oxides calcined at various temperatures were judged, and the selectivity to partial oxidation products correlates to the amount of Lewis acid sites from FT-IR spectra of pyridine and NH 3 adsorbed niibium oxide catalysts.
TL;DR: In this paper, a probe consisting of a thin quartz capillary and a thermocouple was moved with sub-mm resolution through the catalyst/heat shield stack to sample the gases into a mass spectrometer and measure temperature.