Oxidative Conversion Of Methane Research Articles

Highly and stably dispersed Pt catalysts supported over La1−xSrxAlO3−0.5x perovskite for oxidative methane activation and their structures

Catalytic activity for oxidative methane conversion (partial oxidation of methane) over Pt catalyst supported on La1−xSrxAlO3−0.5x was investigated. Pt/La0.7Sr0.3AlO2.85 showed higher and more stable hydrogen yield than Pt/α-Al2O3 did. Pt/La0.7Sr0.3AlO2.85 showed higher catalytic activity for steam reform of methane even in an oxidative atmosphere, which was attributable to high Pt dispersion in the oxidative reaction atmosphere. Pt dispersion over La0.8Sr0.2AlO2.9 or La0.7Sr0.3AlO2.85 increased concomitantly with increasing calcination temperature in air. This phenomenon was not observed by aging in He flow. From structural analyses using XRD, XPS, EXAFS, and XANES, the interaction or coordination between Pt and surface oxygen (Os) was observed. This coordination was weakened in a reductive atmosphere and regenerated in an oxidative atmosphere. This interaction or coordination between the Pt and La1−xSrxAlO3−0.5x contributed to high Pt dispersion in an oxidative atmosphere and to high catalytic activity for the partial oxidation of methane.

Structure and size effects on the catalytic properties of complex metal oxide compositions in the oxidative conversion of methane

Results are given for a study of the effects of structure and size on the characteristics of catalysts derived from oxides of transition metals (Mn, Fe, Ni, Co, Cu) and aluminum and zirconium oxides modified by rare earth oxides, yttrium oxide, and scandium oxide as well as samples doped by platinum group metals (Pt, Pd) on their catalytic properties in the oxidative conversion of methane by means of partial and extensive oxidation, steam, dry, and oxy-dry-steam conversion (tri-reforming) of methane.

Mechanism of oxidative conversion of methane to synthesis gas at short contact times

New stable heat-resistant high-performance catalysts for a new generation of selective production of synthesis gas from methane have been developed, the relationship of physical and chemical characteristics of catalysts and their catalytic properties was identified and the mechanism of the process was proposed.

New selective catalysts of oxidative conversion of methane to synthesis gas

ISSN 00125016, Doklady Physical Chemis try, 2011, Vol. 441, Part 2, pp. 233–236. © Pleiades Publishing, Ltd., 2011.Original Russian Text © A.G. Dedov, A.S. Loktev, G.N. Mazo, L.S. Leonova, D.A. Komissarenko, Yu.A. Mamaev, M.S. Kaluzhskikh, O.A. Shlyakhtin, E.P. Kuznetsova,M.N. Kartasheva, I.I. Moiseev, 2011, published in Doklady Akademii Nauk, 2011, Vol. 441, No. 5, pp. 635–638.

Methane activation and partial oxidation on free gold and palladium clusters: Mechanistic insights into cooperative and highly selective cluster catalysis

The catalytic activation, dehydrogenation, and direct oxidative conversion of methane into more valuable products such as larger hydrocarbons, alcohols, aldehydes etc. are of considerable industrial interest. To investigate the energetics and kinetics of elementary bond-breaking and bond-formation processes, free metal clusters can serve as versatile catalytic model systems. In this context, temperature dependent reactions of small cationic gold clusters Au(x)+ with methane as well as a mixture of methane and molecular oxygen have been performed in an octopole ion trap under multi-collision conditions and compared with the corresponding reactions on palladium clusters Pd(x)+ (x = 2-4). Binding energies of methane to all investigated cluster cations are determined from kinetic measurements via statistical analysis. Furthermore, among the gold clusters, the dimer Au2+ is found to be able to dehydrogenate methane and to convert it into ethylene in a highly selective catalytic reaction. In contrast, all investigated palladium clusters activate methane under non-selective formation of a variety of dehydrogenated products. Most interestingly, methane dehydrogenation is observed for Pd(x)+ and Au2+ only, if a cluster specific 'critical number' of methane molecules is pre-adsorbed. This emphasizes the importance of cooperative coadsorption effects in the dehydrogenation process on these clusters. Finally, the reaction between Au2+ and both O2 and CH4 yields a low temperature product of the stoichiometry Au2(C3H8O2)+ that clearly contains activated O2 and dehydrogenated methane indicating a possible C-O bond formation process. The palladium dimer Pd2+ on the other hand exhibits only the mere coadsorption of molecular oxygen and non-dehydrogenated methane.

From micro- to nano-size catalytic membrane hydrogenation reactors with accumulated hydrogen

Preconditions and prospects of development of the new generation nano-sized membrane reactors are studied in this work. In such reactors hydrogenation reactions will be performed for the first time in the pores of ceramic membranes actively employing hydrogen which is preliminarily adsorbed in mono- and multilayered oriented carbon nanotubes with graphene walls (OCNTG) formed on the inner surface of pores. It is shown with the use of microfiltration membranes “TRUMEM” ( D average ˜ 130 nm) that reactions of CO oxidation (over a Cu 0,03Ti 0,97O 2 ± δ catalyst) and oxidative conversion of methane to synthesis gas and light hydrocarbons (over La + Ce/MgO) are significantly intensified when membranes are used. Almost the same value of methane conversion as in a flow reactor is reached in a membrane catalytic module at temperatures which are lower by 100–170 °C. Investigation of hydrogen adsorption, storage and desorption regularities in nano-sized membrane reactors was performed via forming of OCNTG in the pores of ultrafiltration membranes “TRUMEM” ( D average = 50 nm and 90 nm) and their saturation with hydrogen under 10–13 MPa. It is found that the amount of adsorbed hydrogen reached 14.0% of OCNTG weight. Adsorption of hydrogen in OCNTG is characterized for the first time by thermogravimetric analysis (TGA) coupled with mass-spectrometric analysis. Hydrogen desorption under atmospheric pressure occurs at ˜175 °C. Adsorptivity to hydrogen of three carbon structures, nanocrystallites of pyrocarbon (NCP), their superposition, and OCNTG, is studied. It is found that this property is characteristic only for the latter structure. A new effect of hydrogen variation of performance (HVP) is found: hydrogen adsorbed in OCNTG affects the transport properties of membranes decreasing their performance on liquids 4–26-fold which confirms high activity of hydrogen indirectly, the dissociative mechanism of hydrogen adsorption being probably the basis.

Peculiarities of oxidative coupling of methane in redox cyclic mode over Ag–La 2O 3/SiO 2 catalysts

Properties of Ag–La 2O 3/SiO 2 catalysts in oxidative coupling of methane (OCM) carried out in redox cyclic mode were studied. Methane and air were injected as separate and alternating pulses, and the oxidative conversion of methane proceeded due to participation of mobile lattice oxygen of the catalysts. It was found that joint action of Ag and La 2O 3 in OCM could give considerable synergetic effect. Such catalysts as 3%Ag–10%La 2O 3/SiO 2 and 6%Ag–10%La 2O 3/SiO 2 exhibited high efficiency in the OCM reaction performed in the redox cyclic mode. In the case of 3%Ag–10%La 2O 3/SiO 2, the yield of C 2 hydrocarbons reached about 30% at C 2 selectivity close to 60%. Active sites which were responsible for OCM reaction were generated during reduction of silver by the injected methane. OCM selectivity increased remarkably if a small amount of hydrogen was injected over the catalyst before the methane pulse.

New nanosized catalytic membrane reactors for hydrogenation with stored hydrogen: Prerequisites and the experimental basis for their creation

The prerequisites and prospects for creating a new generation of nanosized membrane reactors are considered. For the first time, hydrogenation reactions take place in ceramic membrane pores with hydrogen adsorbed beforehand in mono- and multilayered oriented carbon nanotubes with graphene walls (OCNTGs) formed on the internal pore surface. It is shown for Trumem microfiltration membranes with D avg ∼130 nm that oxidation reactions of CO on a Cu0.03Ti0.97O2 ± δ catalyst and the oxidative conversion of methane into synthesis gas and light hydrocarbons on La + Ce/MgO are considerably enhanced when they occur in membranes. Regularities of hydrogen adsorption, storage, and desorption in nanosized membrane reactors are investigated through OCNTG formation in Trumem ultrafiltration membrane pores with D avg = 50 and 90 nm and their saturation with hydrogen at a pressure of 10–13 MPa. It is shown that the amount of adsorbed hydrogen reaches 14.0% of OCNTG mass. Using thermogravimetric analysis in combination with mass-spectrometric analysis, hydrogen adsorption in OCNTG is first determined and its desorption is found to proceed at atmospheric pressure at a temperature of ∼175°C. It is shown that adsorbed hydrogen affects the transport properties of the membranes, reducing their efficiency with respect to liquids by 4–26 times. This is indirect confirmation of its high activity, due apparently the dissociative mechanism of adsorption.

Sulfur resistance and stability of yttrium-stabilized binary Co-Cu and Ni-Cu composites with zirconium dioxide in the oxidative conversion of methane

Binary Co-Cu and Ni-Cu composites with YSZ have demonstrated rather high thermal resistance (up to 1000 °C) and stability in the extensive oxidation of methane. The tendency of the nickel–copper composites to carbon deposition depends on the amount of nickel introduced. The higher stability was found for the sample with active phase containing 4% Ni, 16% Cu. The sulfur resistance of the palladium-doped Ni–Cu composite is attributed to the formation of an adsorbed [PdO·SO2] complex. TPHR data indicated that the oxygen in this sample is less reactive in methane oxidation.

Catalytic activity of neodymium substituted zinc ferrites for oxidative conversion of methane

The catalytic behavior for oxidative conversion of methane in large oxygen excess (methane combustion) and in reducing conditions (oxidative coupling of methane) was comparatively investigated for the first time over pure and neodymium substituted zinc ferrites prepared by combustion method. The catalytic activity proved to be strongly related to the oxide structure, to the specific defects created by substitution as well as to the composition of the reaction mixture. The neodymium substituted ferrites (ZnFe 1.75Nd 0.25O 4, ZnFe 1.5Nd 0.5O 4 and ZnFeNdO 4) exhibited high activity for methane combustion but low activity for coupling reaction. On the other hand, the pure zinc ferrite (ZnFe 2O 4) and ZnNd 2O 4 were active to catalyze methane coupling whereas the activity for methane combustion was low. The catalytic activity of the oxides and the reaction mechanism on simple and mixed oxides is discussed in light of the experimental results.

Role of rare-earth element oxides in catalysts for the oxidative conversion of methane based on Ni/Al2O3

It has been established that oxides of the rare-earth elements with moderate redox potentials (La2O3, CeO2) increased the activity and working stability of Ni-Al2O3/cordierite catalysts in the reactions of deep and partial oxidation of methane. In the presence of the (NiO + La2O3 + Al2O3)/cordierite catalyst the process of carbon dioxide conversion of methane can be intensified by introduction of oxygen into the reaction gas mixture which decreases the temperature to achieve high conversion to 75–100 °C and has practically no effect on selectivity with respect to H2.

Effect of platinum, palladium and rhodium on the activity and sulfur resistance of catalysts based on ZrO2 in the oxidative conversion of methane

A study was carried out on the effect of noble metals (Pd, Pt, and Rh) on the activity and sulfur resistance of a Cu-Ni-Ce oxide composite on yttrium-stabilized zirconium in the oxidation of methane by oxygen. The enhancement in activity in the deep oxidation of methane, which is greatest for the pallaldium sample, is related to the oxidation-reduction properties of the composites. The platinum catalyst displayed greatest sulfur resistance, which may be attributed to the mechanism for the oxidation of SO2 on platinum-group metals.

Oxidative conversion of methane to syngas on metallic Ni monolith with Mg promotion

A MgO-promoted metallic nickel monolith was prepared from nickel sponge by sintering, acid treating and loading. The catalytic performances on the monolithic catalysts, unpromoted and promoted by MgO, were studied in the partial oxidation and oxidative steam and CO2 reformings of methane to syngas.

Oxidative conversion of C1–C3 alkanes by vanadium oxide catalysts. DFT results and their accuracy

AbstractElementary steps in the oxidative conversion of methane, ethane, and propane by supported vanadium oxide species are studied by density functional theory, specifically B3LYP. Two models are adopted, namely OV(OH)3 and OVSi7O12H7, which yield similar energy profiles. The initial and rate‐determining step is hydrogen abstraction. Within the C1–C3 series, energy barriers and reaction energies follow the same trend as the CH bond strength in the different alkanes. For methane, only methanol formation is possible whereas for ethane and propane, oxidative dehydrogenation yields the corresponding alkenes. Single point CCSD(T)/TZVP calculations are used to assess the B3LYP error. For the barrier of the initial hydrogen abstraction the B3LYP error is larger than usual, −40 to −60 kJ/mol. With the non‐hybrid BP86 and PBE functionals even larger errors occur and the potential energy surface is qualitatively different. © 2008 Wiley Periodicals, Inc. Int J Quantum Chem, 2008

La-promoted Na2WO4/Mn/SiO2 catalysts for the oxidative conversion of methane simultaneously to ethylene and carbon monoxide

Abstract A series of La-promoted 5 wt% Na2WO4/2 wt% Mn/SiO2 catalysts were prepared by varying the impregnation sequence and the concentration of La promoter, and their catalytic performance for the oxidative conversion of methane was investigated in a micro-quartz-tube reactor. The catalysts were characterized by X-ray photoelectron spectroscopy (XPS) and X-ray diffraction (XRD). It was found that the existence of Mn ions was in favor of the dispersion of La species on the catalyst, and the addition of La promoter could increase the dispersion of Na2WO4, which enriched the amount of surface oxygen species connected with the metal atoms. This oxygen species was found to be active for the oxidative coupling of methane to C2 hydrocarbons. The selectivity and yield of C2 hydrocarbons with a C2H4/CO ratio of 1/1 reached the optimized value of about 56% and 25%, respectively, at 800 °C, over the 5 wt% Na2WO4/2 wt% La–2 wt% Mn/SiO2 catalyst prepared by co-impregnation of La and Mn.

Oxidative Conversion of Methane

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Influence of the composition of composites based on Y-and Sc-stabilized zirconium dioxide on catalytic properties in the oxidative conversion of methane

The effect of the composition of composites based on Y-and Sc-stabilized zirconium dioxide doped with CeO2 and transition metal (Cu, Co, Ni) oxides on catalytic properties in the oxidative conversion of methane was studied. The activity of the composites correlated with the quantity and mobility of oxygen in them.

Preparation of mesostructured barium sulfate and its application in methane activation

Barium sulfate with lamellar and tubular microstructure was developed through a surfactant templating route under different synthesis conditions. Lamellar barium sulfate was synthesized through direct combination of Ba 2+ and SO 4 2 − in an aqueous solution containing sodium dodecyl benzene sulfonate (SDBS). Agglomerate barium sulfate nanotubes were obtained by the reaction of Ba 2+ and CaSO 4 in the SDBS aqueous solution. Preparation of regular single barium sulfate nanotubes was achieved by the controlled hydrolysis of dimethyl sulfate in an aqueous solution containing Ba 2+ and SDBS. As revealed by transmission electron microscopy characterization, the tube wall thickness was 7–8 nm, and the inner diameter was about 6 nm. When such mesostructured barium sulfate was loaded with VOSO 4 and sulfuric acid (100%), it performed excellently in catalyzing oxidative conversion of methane to methanol using molecular oxygen. The conversion proceeded at a relatively lower temperature (under 250 °C) than over general solid catalysts, and the selectivity to methanol remained high when methane conversion increased to an acceptable level. When the reaction proceeded stably, the one-pass conversion of methane was about 30%, and the selectivity to methanol could reach 50%.

Ceramic membranes modified with catalytic oxide films as ensembles of catalytic nanoreactors

Hybrid catalytic membrane systems have been produced by modifying porous ceramic membranes with metal oxide films. A two-layer cermet membrane consisting of a flexible stainless steel layer and an overlying porous TiO2 ceramic layer and a ceramic titanium carbide membrane are examined. The membrane surfaces have been modified by the alkoxide method using colloidal organic solutions of metal complex precursors. Producing a tetragonal single-phase ZrO2/Y2O3 coating on the cermet surface increases the abrasion strength of the ceramic layer. CO oxidation and the oxidative conversion of methane into synthesis gas and light hydrocarbons can be markedly intensified by modifying the membrane channels with Cu0.03Ti0.97O2±δ and La + Ce/MgO catalysts, respectively. A method has been developed for depositing, onto the geometrical surface of a membrane, a film of the new single-phase oxide P0.03Ti0.97O2±δ with an anatase structure and uniform pores of mean diameter 〈d〉 ∼ 2 nm. Blocks of zeolite-like silicalite can be formed on the surface of the phosphorus-titanium oxide film. The resulting hybrid membrane is characterized by an anisotropic permeability depending on the flow direction. This property has an effect on conversion and selectivity in the nonoxidative dehydrogenation of methanol.

Low-temperature selective oxidation of methane to ethane and ethylene over BaCO 3/La 2O 3 catalysts prepared by urea combustion method

A series of BaCO 3/La 2O 3 catalysts have been prepared using urea combustion method, and tested their activity in oxidative conversion of methane to ethane and ethylene below 600 °C. For 5% BaCO 3/La 2O 3 catalyst, under integral conditions, CH 4 conversion of 31.8% with C 2 selectivity of 45.9% have been obtained at 320 °C. With the increase of BaCO 3 contents, CH 4 conversion and C 2 selectivity are improved. The temperature profiles of reactor have been described and found that the distribution of hot spots on catalyst bed is related to the low-temperature activity of catalyst.