Showing papers on "Partial oxidation published in 2014"

Dynamic Methane Partial Oxidation Using a Fe2O3@La0.8Sr0.2FeO3-δ Core–Shell Redox Catalyst in the Absence of Gaseous Oxygen

Abstract: Chemical looping reforming partially oxidizes methane into syngas through cyclic redox reactions of an active lattice-oxygen (O2–) containing redox catalyst. The avoidance of direct contact between methane and steam and/or gaseous oxygen has the potential to eliminate the energy consumption for generating these oxidants, thereby increasing methane conversion efficiency. This article investigates redox catalysts comprised of iron oxide core covered with lanthanum strontium ferrite (LSF) shell. The iron oxide core serves as the primary source of lattice-oxygen, whereas the LSF shell provides an active surface and facilitates O2– and electron conductions. These core–shell materials have the promise to provide higher selectivity for methane conversion with lower solid circulation rates than traditional redox catalysts. Methane oxidation by this catalyst exhibits four distinct regions, i.e. deep oxidation; competing deep and selective oxidation; selective oxidation with autoactivation; and methane decompositio...

Synthesis, characterisation and performance evaluation of spinel-derived Ni/Al2O3 catalysts for various methane reforming reactions

Abstract: The catalytic performance of bulk nickel aluminate catalysts synthesised by co-precipitation (NiAl 2 O 4 -CP) and co-dissolution (NiAl 2 O 4 -D) was examined for various methane reforming reactions, namely partial oxidation, steam reforming and oxidative steam reforming. The calcined and reduced spinels were thoroughly characterised by a wide number of analytical techniques including WDXRF , N 2 physisorption, XRD, UV–visible–NIR DRS, XPS, TEM, H 2 -TPR and NH 3 -TPD. The characterisation results of the calcined samples at 850 °C showed that nickel aluminate phase was mainly obtained on the NiAl 2 O 4 -CP near-surface together with a small NiO excess. By contrast, a large amount of NiO phase was formed on NiAl 2 O 4 -D and deposited on the spinel surface. The reduction at 850 °C of the two samples produced monodispersed Ni particles (10.6 nm) in the NiAl 2 O 4 -CP while larger metallic nickel (17.7 nm) was deposited on the NiAl 2 O 4 -D. In the three investigated reforming reactions the NiAl 2 O 4 -CP catalyst proved to be highly active, stable and resistant toward carbon deposition. Moreover, the performances of the NiAl 2 O 4 -CP catalyst appeared to be generally comparable with that of a commercial 1%Rh/Al 2 O 3 catalyst. The difference in catalytic behaviour between the two nickel aluminates was related to the Ni dispersion, its particle size and its capacity to minimise the acid character of the alumina by covering a large part of its surface.

Fe2O3@LaxSr1−xFeO3 Core–Shell Redox Catalyst for Methane Partial Oxidation

Abstract: Efficient and environmentally friendly conversion of methane into syngas is a topic of practical relevance for the production of hydrogen, chemicals, and synthetic fuels. At present, methane-derived syngas is produced primarily through the steam methane reforming processes. The efficiencies of such processes are limited owing to the endothermic steam methane reforming reaction and the high steam to methane ratio required by the reforming catalysts. Chemical looping reforming represents an alternative approach for methane conversion. In the chemical looping reforming scheme, a solid oxygen carrier or “redox catalyst” is used to partially oxidize methane to syngas. The reduced redox catalyst is then regenerated with air. The cyclic redox operation reduces the steam usage while simplifying the heat integration scheme. Herein, a new Fe2O3@LaxSr1−xFeO3 (LSF) core–shell redox catalyst is synthesized and investigated. Compared with several other commonly investigated iron-based redox catalysts, the newly developed core–shell redox catalyst is significantly more active and selective for syngas production from methane. It is also more resistant toward carbon formation and maintains high activity over cyclic redox operations.

Partial Oxidation of Methane to Methanol Using Bismuth-Based Photocatalysts

Abstract: Bismuth-based photocatalysts, Bi2WO6, BiVO4, and coupled Bi2WO6/TiO2–P25, have been synthesized by a facile hydrothermal method, characterized, and evaluated for the first time for the selective photooxidation of methane to methanol. Several conditions were used in order to better comprehend the reaction mechanism. The obtained BiVO4 is, among the others, the most promising photocatalyst for this reaction, displaying higher CH3OH selectivity and being more stable than the others. When Bi2WO6 was coupled with TiO2, the methane conversion increased; however, overoxidation of CH4 to CO2 predominates. A similar effect is observed when electron scavengers such as O2 or Fe3+ were introduced in the photoreactor as a result of the formation of highly oxidant radicals.

Chemical looping beyond combustion: production of synthesis gas via chemical looping partial oxidation of methane

Abstract: The recent surge in natural gas reserves has revived interest in the development of novel processes to convert natural gas into valuable chemical feedstocks. In the present work, we are applying “chemical looping”, a technology that has found much attention as a clean combustion technology, towards selective partial oxidation of methane to produce synthesis gas (CLPOM). By tailoring the composition of NixFe1−x–CeO2 oxygen carriers and carefully controlling the supply of oxygen, i.e., the extent of the carrier reduction and oxidation in redox cycles, the reactivity and selectivity of these carriers for partial oxidation was optimized. Addition of a small amount of Ni to iron oxides allowed the combination of the high reactivity of Ni for methane activation with the good syngas selectivity of iron oxides. An optimized carrier with the composition of Ni0.12Fe0.88–CeO2 demonstrated excellent stability in multi-cycle CLPOM operation and high syngas yields with a H2:CO ratio of ∼2 and minimal carbon formation. Finally, a simplified fixed-bed reactor model was used to assess the thermal aspects of operating the process in a periodically operated fixed-bed reactor. We found that the process is highly sensitive to the degree of carrier utilization, but that maximum temperatures can be easily controlled in CLPOM via control of the active metal content and oxygen utilization in the carriers. Overall, chemical looping partial oxidation of methane emerges as an attractive alternative to conventional catalytic partial oxidation, enabling the use of low-cost transition metal oxides and air as oxidant, and resulting in inherently safe reactor operation by avoiding mixed methane/air streams.

Hydrogen production from simple alkanes and oxygenated hydrocarbons over ceria-zirconia supported catalysts: Review

Abstract: The use of ceria–zirconia based catalysts in hydrogen production from simple alkanes and oxygenated hydrocarbons for the processes of steam reforming (SR), autothermal reforming (‘ATR’), catalytic partial oxidation (‘CPO’), and dry reforming (‘DR’) is reviewed in this paper. Along with preparation methods, the effects of operating conditions like molar steam to carbon ratio, oxygen to carbon ratio, and temperature on the performance of hydrogen production from methane, acetic acid, ethanol, and glycerol were examined. SR and ATR of these feedstocks over ceria–zirconia supports have been widely investigated. In comparison the utilization of these supports in the CPO and DR processes has been investigated mainly for methane as compared to oxygenated hydrocarbons. Ce-rich supports were reported to be effective in hydrogen production from SR and ATR of ethanol and glycerol and in steam methane reforming (SMR) in the ‘low’ temperature range (500–600 °C), whereas zirconium-rich supports exhibited higher catalytic activity in the ‘high’ temperature range (700–800 °C). In the case of DR, Ce-rich supports were effective at high temperatures i.e. above 700°C. The methods of preparation of the supports/catalyst are shown to affect the surface area (catalyst/support), crystallite size of (active metal/support), reducibility and dispersion of the active metal, thus affecting performance of the catalyst.

Electrocatalytic selective oxidation of glycerol to tartronate on Au/C anode catalysts in anion exchange membrane fuel cells with electricity cogeneration

Abstract: Sustainable cogeneration of tartronate (high yield of 61.8%) and electrical energy (1527 J, 12 h) has been achieved from direct electrocatalytic oxidation of glycerol on Au/C in a 5 cm2 anion exchange membrane-direct glycerol fuel cells (AEM-DGFCs). The electrode structure and reaction conditions exhibited strong effects on the anode potential, which can be tuned to OH groups of glycerol while minimizing over-oxidation of the secondary OH and C C bond cleavage, thereby promoting the tartronate production. The relatively low activity of partial oxidation products (glycerate, tartronate, mesoxalate) on Au/C revealed in half cell indicates that the tartronate generation in AEM-DGFCs is through direct adsorbed C3 intermediates oxidation. Mass transport of reactants and reaction intermediates governed by the operational conditions was also found to play a critical role in regulating reaction rate and the desired products selectivity. Furthermore, Au/C prepared via aqueous phase reduction method (Au/C-AQ) was compared with organic phase nanocapsule method (Au/C-NC), and it shows the residual surfactants have little effect on the tartronate yield.

Catalytic oxidation of 1,2-dichlorobenzene over Ca-doped FeOx hollow microspheres

Abstract: Novel Ca-doped FeOx hollow microspheres were successfully prepared using carbon microspheres as templates. The as-prepared catalysts were characterized by FAAS, XRD, N2 adsorption/desorption, SEM, TEM, H2-TPR and XPS. The catalytic activities of the samples were evaluated by catalytic oxidation of 1,2-dichlorobenzene (o-DCB). The results showed that the molar ratios of Ca/(Ca + Fe) in the hollow microspheres and their morphologies significantly affected their catalytic performances. The low-temperature catalytic activity decreased in the order of FeCa10 > FeCa20 > Fe2O3 > FeCa5, in well agreement with the sequence of their reducibility. The optimal FeCa10 catalyst exhibited not only excellent catalytic activity, water-resistant performance and stability but also lower apparent activation energy (21.6 kJ/mol). In situ FTIR measurements revealed the acetate and formate species were the partial oxidation products, which could be subsequently oxidized to form CO2. It is concluded that the excellent catalytic performance of FeCa10 catalyst might be attributed to the combined effects of several factors such as small crystallite size, high surface active oxygen concentration, good low-temperature reducibility and the synergic effect between CaO and Fe3O4. It is reasonable for us to believe that such Ca-doped FeOx hollow microspheres are promising catalysts for the elimination of chlorinated volatile organic pollutants.

Thermodynamic Analysis of Syngas Production via the Solar Thermochemical Cerium Oxide Redox Cycle with Methane-Driven Reduction

Abstract: The present work considers the convergence of two approaches for syngas production: solar fuels via the cerium oxide (ceria) redox cycle and the partial oxidation of methane. The chemical thermodynamics of the ceria–methane system reveal that coupling the reduction of ceria to the partial oxidation of methane enables isothermal cycling at temperatures as low as 1223 K with the additional production of high-quality syngas during the reduction step. The equilibrium non-stoichiometry of the oxidation step has a substantial impact on the conversion of the oxidizer to fuel, with important implications for cycle efficiency. A model of the process thermodynamics is used to evaluate the efficiency of the cycle and its sensitivity to oxidation non-stoichiometry, temperature, and concentration ratio. Reduction with methane enables significant gains in efficiency over other proposed approaches, with plausible solar-to-fuel efficiencies reaching 40% without any heat recovery.

The Oxidation of Rhenium and Identification of Rhenium Oxides During Catalytic Partial Oxidation of Ethylene: An In-Situ XPS Study

Abstract: Rhenium is catalytically active for many valuable chemical reactions, and consequently has been the subject of scientific investigation for several decades. However, little is known about the chemical identity of the species present on rhenium surfaces during catalytic reactions because techniques for investigating catalyst surfaces in-situ - such as near-ambient-pressure X-ray pho- toemission spectroscopy (NAP-XPS) - have only recently become available. In the current work, we present an in-situ XPS study of rhenium catalysts. We examine the oxidized rhenium species that form on a metallic rhenium foil in an oxidizing atmosphere, a reducing atmosphere, and during a model catalytic reaction (i.e. the partial-oxidation of ethylene).

Partial Oxidation of Methane to Syngas Over γ-Al2O3-Supported Rh Nanoparticles: Kinetic and Mechanistic Origins of Size Effect on Selectivity and Activity

Abstract: A series of supported Rh/γ-Al2O3 catalysts with an overall metal loading of 0.005 wt % was synthesized by impregnation of γ-Al2O3 with a toluene solution containing colloidally prepared well-defined (1.1, 2.5, 2.9, 3.7, and 5.5 nm) Rh nanoparticles (NP). The size of NP was not found to change after their deposition on γ-Al2O3 and even after performing partial oxidation of methane (POM) to synthesis gas at 1073 K for 160 h on stream. Apparent CO formation turnover rates and CO selectivity strongly decrease with an increase in this size. Contrarily, the overall scheme of POM is size-independent, i.e. CO and H2 are mainly formed through reforming reactions of CH4 with CO2 and H2O at least under conditions of complete oxygen conversion. The size effect on the activity and selectivity was related to the kinetics of interaction of CH4, O2, and CO2 with Rh/γ-Al2O3 as concluded from our microkinetic analysis of corresponding transient experiments in the temporal analysis of products reactor. The rate constants of...

A CO2-stable reduction-tolerant Nd-containing dual phase membrane for oxyfuel CO2 capture

Abstract: We report a novel CO2-stable reduction-tolerant dual-phase oxygen transport membrane 40 wt% Nd0.6Sr0.4FeO3−δ–60 wt% Ce0.9Nd0.1O2−δ (40NSFO–60CNO), which was successfully developed by a facile one-pot EDTA–citric sol–gel method. The microstructure of the crystalline 40NSFO–60CNO phase was investigated by combined in situ X-ray diffraction (XRD), scanning electron microscopy (SEM), back scattered SEM (BSEM), and energy dispersive X-ray spectroscopy (EDXS) analyses. Oxygen permeation and long-time stability under CO2 and CH4 atmospheres were investigated. A stable oxygen flux of 0.21 cm3 min−1 cm−2 at 950 °C with undiluted CO2 as sweep gas is found which is increased to 0.48 cm3 min−1 cm−2 if the air side is coated with a porous La0.6Sr0.4CoO3−δ (LSC) layer. All the experimental results demonstrate that the 40NSFO–60CNO not only shows good reversibility of the oxygen permeation fluxes upon temperature cycling, but also good phase stability in a CO2 atmosphere and under the harsh conditions of partial oxidation of methane to synthesis gas up to 950 °C.

Selective CH functionalization of methane, ethane, and propane by a perfluoroarene iodine(III) complex.

Abstract: Direct partial oxidation of methane, ethane, and propane to their respective trifluoroacetate esters is achieved by a homogeneous hypervalent iodine(III) complex in non-superacidic (trifluoroacetic acid) solvent. The reaction is highly selective for ester formation (>99%). In the case of ethane, greater than 0.5 M EtTFA can be achieved. Preliminary kinetic analysis and density functional calculations support a nonradical electrophilic CH activation and iodine alkyl functionalization mechanism.

The origin of high activity but low CO2 selectivity on binary PtSn in the direct ethanol fuel cell

Abstract: The most active binary PtSn catalyst for direct ethanol fuel cell applications has been studied at 20 °C and 60 °C, using variable temperature electrochemical in situ FTIR. In comparison with Pt, binary PtSn inhibits ethanol dissociation to CO(a), but promotes partial oxidation to acetaldehyde and acetic acid. Increasing the temperature from 20 °C to 60 °C facilitates both ethanol dissociation to CO(a) and then further oxidation to CO2, leading to an increased selectivity towards CO2; however, acetaldehyde and acetic acid are still the main products. Potential-dependent phase diagrams for surface oxidants of OH(a) formation on Pt(111), Pt(211) and Sn modified Pt(111) and Pt(211) surfaces have been determined using density functional theory (DFT) calculations. It is shown that Sn promotes the formation of OH(a) with a lower onset potential on the Pt(111) surface, whereas an increase in the onset potential is found upon modification of the (211) surface. In addition, Sn inhibits the Pt(211) step edge with respect to ethanol C–C bond breaking compared with that found on the pure Pt, which reduces the formation of CO(a). Sn was also found to facilitate ethanol dehydrogenation and partial oxidation to acetaldehyde and acetic acid which, combined with the more facile OH(a) formation on the Pt(111) surface, gives us a clear understanding of the experimentally determined results. This combined electrochemical in situ FTIR and DFT study provides, for the first time, an insight into the long-term puzzling features of the high activity but low CO2 production found on binary PtSn ethanol fuel cell catalysts.

Nitrogen-doped carbon nanotubes decorated silicon carbide as a metal-free catalyst for partial oxidation of H2S

Abstract: Hierarchical metal-free catalyst based on the CVD synthesis of nitrogen-doped carbon nanotubes decorated silicon carbide (N-CNTs/SiC) macroscopic host structure has been prepared. The catalyst was evaluated in the partial oxidation of H 2 S by oxygen into elemental sulfur in a fixed-bed reactor. The catalytic results indicate that the N-CNTs/SiC catalyst exhibits an extremely high desulfurization performance even under severe reaction conditions such as low temperature, high space velocity and at low O 2 -to-H 2 S molar ratio. The high desulfurization performance was attributed to the high effective surface area of the catalyst along with a short diffusion length associated with the nanoscopic dimension of the carbon nanotubes. The N-CNTs/SiC catalyst also displays a high stability as a function of time on stream which could be attributed to the strong anchoring of the nitrogen doping within the carbon matrix. The extrudates shape of the SiC support allows the direct macroscopic shaping of the catalyst for use in conventional fixed-bed reactor without facing problems linked with catalyst handling, transportation and pressure drop across the catalyst bed as encountered with nanoscopic carbon-based catalyst.

Selective Monooxidation of Light Alkanes Using Chloride and Iodate

Abstract: We describe an efficient system for the direct partial oxidation of methane, ethane, and propane using iodate salts with catalytic amounts of chloride in protic solvents. In HTFA (TFA = trifluoroacetate), >20% methane conversion with >85% selectivity for MeTFA have been achieved. The addition of substoichiometric amounts of chloride is essential, and for methane the conversion increases from 20%. The reaction also proceeds in aqueous HTFA as well as acetic acid to afford methyl acetate. 13C labeling experiments showed that less than 2% of methane is overoxidized to 13CO2 at 15% conversion of 13CH4. The system is selective for higher alkanes: 30% ethane conversion with 98% selectivity for EtTFA and 19% propane conversion that is selective for mixtures of the mono- and difunctionalized TFA esters. Studies of methane conversion using a series of iodine-based reagents [I2, ICl, ICl3, I(TFA)3, I2O4, I2O5, (IO2)2S2O7, (IO)2SO4] indicated that the chloride enhancement is not li...

Crude glycerol as a raw material for the liquid phase oxidation reaction

Abstract: In the present work, crude and partially purified glycerol fractions received from large biodiesel production plant were used as a raw material in the catalytic partial oxidation process. Before using, each fractions were carefully characterized in order to identify and quantify the major contaminants. Depending on the purification degree, the weight concentration of glycerol in the different fractions varied from 40.3% to 98.2%, the methanol content did not exceed 29.1%, mineral salts (determined as ash) varied from 0.03% 6.6%, while the residual organic matter (non-glycerol and non-methanol, named here MONG-NM) was between 0.7% and 22.1%. The reaction of glycerol oxidation was carried out in the liquid phase over a commercial 1 wt.% Pt/Al 2 O 3 catalyst. The effect of each identified impurity type was independently studied, both in the presence and absence of base in the reaction mixture. The results indicated that MONG-NM is the most problematic compound, as it strongly hinders the reaction. As the post-reaction analysis of spent catalyst (Elemental Analysis and XPS) showed practically negligible leaching of platinum and lack of important changes in its oxidation state, the most probable explanation for observed decrease in glycerol conversion is blocking of glycerol access to the catalyst active sites by adsorbed heavy-weight components of MONG-NM. An attempt of regeneration and reusing of spent catalyst proved that such poisoning can be reversed by simple washing of catalyst with organic solvent enable to dissolve hydrophobic fatty acid derivatives. The mineral salts also have a detrimental effect on the glycerol oxidation process, but much tinier than that of MONG-NM. In contrast, the presence of methanol in the feed promoted the process reactivity, which was attributed to improved oxygen solubility in the methanol–water solutions (at least in the analysed range of methanol concentrations ≤5 wt.%).

Direct oxidation of methane to methanol on Fe–O modified graphene

Abstract: Introduction of functional groups to graphene can be used for the rational design of catalysts for the oxidation of hydrocarbons to alcohols. We have employed the PBE-D2 level of theory to study the direct oxidation of CH4 to CH3OH on a Fe–O active site generated on graphene by the decomposition of nitrous oxide (N2O) over Fe-embedded graphene. Restricted and unrestricted spin state of systems were also taken into account. The calculations show that FeO/graphene provides excellent reactivity for the oxy-functionalization of methane to methanol. The oxygen-centered radicals (O−˙) on the catalyst can activate the strong C–H bond of methane leading to its homolytic cleavage. The C–H bond activation requires an energy of 17.5 kcal mol−1, which is comparable with the barrier on traditional effective catalysts. Comparing the molecular adsorption complex, the formation of the iron coordinated fragments of C–H bond activation on the graphene support is found to be less energetically stable than on the Fe sites in the zeolite support. As a result, the conversion of the grafted species to the methanol product in the second step of the reaction is much more facile than for Fe-exchanged zeolite catalysts. An activation energy of 16.4 kcal mol−1 is required to yield the methanol product. Fe–O modified graphene materials could be promising catalysts for the partial oxidation of methane with N2O as an oxidant.

Partial oxidation of methane over bifunctional catalyst I. In situ formation of Ni0/La2O3 during temperature programmed POM reaction over LaNiO3 perovskite

Abstract: The transformation of perovskite to an oxide-supported metal during reaction of partial oxidation of methane (POM) has been very often cited in literature as the “reduction” of the perovskite, without any detailed mechanism. In this work, the in situ transformation of initial LaNiO3 perovskite to Ni0/La2O3 was studied under flowing CH4/Ar and CH4 + O2/Ar (POM mixture) in temperature-programmed conditions. The catalyst was characterized before, during and after these experiments using X-ray diffraction (XRD), thermogravimetric analysis (TGA) and high resolution transmission electron microscopy (HRTEM/EDS) with Fast Fourier Transform (FFT) and Reverse FFT. Total oxidation of methane over LaNiO3 and lanthanum oxide (La2O3), as well as formation of syngas over the resulting Ni0/La2O3 catalysts, were studied for interpreting the three-step evolution of LaNiO3 to Ni0/La2O3, and evidencing NiO demixing from perovskite. A new global kinetic model of POM process over the final bifunctional Ni0/La2O3 catalyst was described.