Performance For Methane Combustion Research Articles

Effects of Phosphorus Addition on the Hydrophobicity and Catalytic Performance in Methane Combustion of θ-Al2O3 Supported Pd Catalysts

A series of xPθ-Al2O3 supports modified with different amounts of phosphorus element were prepared and taken as supports of palladium catalysts for methane catalytic combustion. The impacts of phosphorus additives on the hydrophobicity of Pd/xPθ-Al2O3 and its performance of methane catalytic combustion in the absence of and presence of 8% water were systematically studied. It was found that the hydrophobicity of xPθ-Al2O3 changed with the increase of phosphorus content, which had a significant effect on the activity of methane catalytic combustion. The incorporation of phosphorus replaced the hydroxyl groups on the surface of Al2O3 in the form of phosphates, thus changing the density of hydroxyl groups of Al2O3 support. TGA, NH3-TPD, IR, and XPS were employed to illustrate the process of phosphate replacement. xPθ-Al2O3 with less than 1 wt.% phosphorus content had better hydrophobicity than the unmodified θ-Al2O3 and Pd/xPθ-Al2O3, therefore had better performance for methane catalytic combustion, which was attributed to the substitution of hydroxyl groups on the surface of θ-Al2O3 by PO43− and HPO42−. However, when the phosphorus content of Al2O3 was higher than 1 wt.%, the substitution of H2PO4− began to dominate, which would lead to poorer hydrophobicity and catalytic performance. This work will guide the design of methane catalytic combustion catalysts resistant to water inhibition problem.

Nickel Oxide Nanoparticles on KIT-6: An Efficient Catalyst in Methane Combustion

KIT-6 silica with well-ordered three–dimensional (3D) mesopores has been synthesized as a support for nickel-based catalysts. Transmission Electron Microscopy (TEM) and low-angle X-ray Diffraction (XRD) analysis are used to ensure that the ordered 3D mesostructure is stable after NiO incorporation. In this study, the catalytic activities of the NiO/KIT-6 samples are investigated. Additionally, the results show that a 10 wt% NiO/KIT-6 catalyst exhibits high catalytic performance in methane combustion, with T10, T50 and T90 being only 386 °C, 456 °C and 507 °C, respectively. Hydrogen Temperature Programmed Reduction (H2-TPR) studies have shown that the interaction between NiO and KIT-6 in the 10 wt% NiO/KIT-6 catalyst is weak. Methane Temperature programmed Surface Reaction (CH4-TPSR) results show that the surface oxygen of the NiO/KIT-6 catalyst allows it to exhibit a high catalytic performance. NiO/KIT-6 catalysts exhibit superior activities to SBA-15, MCF and SiO2 support catalysts because KIT-6 has a higher surface area and ordered 3D mesopore connectivity, which is favorable for better NiO dispersion and peculiar diffusion for reactant and products. Furthermore, the used catalyst maintained an ordered mesostructure and reduction property.

Optical study of oxygen enrichment on methane combustion characteristics under high compression-ratio conditions

Natural gas is a promising fuel for IC engines with low carbon emissions, whereas its poor lean combustion performance at low load and low engine power output at high load remain a challenge for automobile manufacturers. Oxygen-enriched combustion can provide more opportunities for collisions between fuel and oxygen molecules; thus, methane combustion performance can be improved. In this work, using a high-compression-ratio optical engine, the effects of oxygen enrichment on methane combustion were comprehensively investigated, addressing the similarities and differences between high load and low load conditions. High-speed direct photography and simultaneous pressure were performed to capture detailed combustion evolutions. The results show that high oxygen concentration can greatly increase methane flame propagation speed under high energy density condition (high load). As a result, advanced combustion phase and high peak pressure are obtained by more concentrated heat release, which in turn are indicators for improvised thermal efficiencies. Under low energy density condition (low load), oxygen enrichment mainly acts as a promoter of the initial flame formation, which in turn are indicators for improvised combustion stability. A detailed comparison of flame characteristics confirms the different effects of oxygen enrichment on methane combustion under different energy density conditions. Besides, oxygen enrichment can significantly promote initial flame formation with a higher rate and lower cyclic variation, and a low degree of oxygen enrichment can also have a great effect. The current study shall give insights into the strategies for oxygen enrichment on methane engines’ performance at different loads.

Plasma-induced construction of defect-enriched perovskite oxides for catalytic methane combustion

An innovative plasma-induced strategy was employed to one-step prepare defect-enriched porous LaMnO3 and cerium-substituted LaMnO3 perovskite oxides with excellent performance in methane combustion.

Effects of direct-injected hydrogen addition on methane combustion performance in an optical SI engine with high compression-ratio

Natural gas is one of the most potential alternative fuel of clean combustion and anti-knocking property. However, slow-burning rate and obvious cyclic variations have become the major concerns for modern gas engines. Based on a high compression-ratio, optically accessible, single-cylinder spark-ignition engine, fundamental experiments were conducted to investigate the role of direct-injected hydrogen under from stoichiometric to lean combustion conditions. Synchronization measurement of in-cylinder pressure and optical flame imaging was conducted to analyze cycle-to-cycle variations, indicated thermal efficiency, and flame evolution. The results show that as the addition of direct-injected hydrogen, the cycle-to-cycle variations decrease and indicated thermal efficiency increases, with advanced combustion phase and shortened combustion duration. The combustion imaging indicates that the significant positive influence is from the direct-injected hydrogen, which promotes initial flame kernel formation and early flame propagation. Further, an empirical criterion for mass fraction burned combined with optical data was adopted for quantification and analysis of early flame evolution. It shows that the addition of direct-injected hydrogen mainly promotes the early-stage flame propagation, manifesting increased the burning rate and thermal efficiency. The results shall give useful information in the application of direct-injected hydrogen to improve natural gas engine performance while increasing flame speed and controlling cyclic variations.

Catalytic combustion of methane over a highly active and stable NiO/CeO2 catalyst

In the last decades, many reports dealing with technology for the catalytic combustion of methane (CH4) have been published. Recently, attention has increasingly focused on the synthesis and catalytic activity of nickel oxides. In this paper, a NiO/CeO2 catalyst with high catalytic performance in methane combustion was synthesized via a facile impregnation method, and its catalytic activity, stability, and water-resistance during CH4 combustion were investigated. X-ray diffraction, low-temperature N2 adsorption, thermogravimetric analysis, Fourier transform infrared spectroscopy, hydrogen temperature programmed reduction, methane temperature programmed surface reaction, Raman spectroscopy, electron paramagnetic resonance, and transmission electron microscope characterization of the catalyst were conducted to determine the origin of its high catalytic activity and stability in detail. The incorporation of NiO was found to enhance the concentration of oxygen vacancies, as well as the activity and amount of surface oxygen. As a result, the mobility of bulk oxygen in CeO2 was increased. The presence of CeO2 prevented the aggregation of NiO, enhanced reduction by NiO, and provided more oxygen species for the combustion of CH4. The results of a kinetics study indicated that the reaction order was about 1.07 for CH4 and about 0.10 for O2 over the NiO/CeO2 catalyst.

Effect of MnO2 morphology on its catalytic performance in lean methane combustion

MnO2 with nanocubes and nanorods were synthesized by a hydrothermal process, and their structures and catalytic performances in methane combustion were investigated. The activity results show that methane conversion over nanocubic MnO2 is more than 90% at 350 °C, which is much higher than that of MnO2 nanorods. N2 physisorption, XPS and H2-TPR results demonstrate that the superior catalytic performance of nanocubic MnO2 is associated with its higher BET surface area, smaller crystalline size, more surface oxygen vacancies and better low-temperature reducibility. In situ DRFIFTS results demonstrate that the carboxylates species are the main intermediate species in methane oxidation.

Effect of MOx (M = Ce, Ni, Co, Mg) on activity and hydrothermal stability of Pd supported on ZrO2–Al2O3 composite for methane lean combustion

Zr0.5Al0.5O1.75 (ZA) was modified by metal oxide (Ce, Co, Ni or Mg oxide) via double solvent method. The Pd nanoparticles were supported on the modified ZA and then tested for methane lean combustion. The textural, structural and redox properties, surface Pd oxidation states and stability of the samples were investigated systematically. The modified catalysts were aged in the 750 °C humid air (10 vol.% water vapor) for 10 h, namely aging treatment. It was found that the activity and hydrothermal stability of the Pd/ZA catalyst was enhanced after the addition of NiO, MgO or Co3O4. Particularly, the Pd/NiO/Zr0.5Al0.5O1.75 (Pd/NiO/ZA) catalyst exhibited the best performance for methane combustion in the presence of water vapor, regardless of aging treatment. X-ray diffraction (XRD) patterns showed that the presence of spinel phase in the Pd/NiO/ZA. CO-chemisorption results demonstrated the highest Pd dispersion on the fresh and aged Pd/NiO/ZA. H2-temperature-programmed reduction (H2-TPR) measurements indicated that the Pd/NiO/ZA catalyst possessed the best reducibility regardless of aging treatment. X-ray photoelectron spectroscopy (XPS) analysis and temperature-programmed oxidation (TPO) experiments revealed that the Pd/NiO/ZA catalyst possessed the highest active phase PdO content and stability. Consequently, the Pd/NiO/ZA catalyst would be promisingly applied to exhaust after-treatment for lean-burn natural gas vehicles.

High thermal-stability ceria synthesized via thermal-hydrolysis route and methane-combustion performance

Enhancement of the thermal stability of a catalyst is an efficient way to improve the catalytic activity of a catalytic reaction performed at high temperature. In this study, cerium oxide (ceria, CeO2) with a high thermal stability was synthesized by controlling the agglomeration of the primary particles via the thermal hydrolysis of ceric nitrate, accompanied by testing for the catalytic combustion of methane (CH4). The specific surface area of this material after calcination at 1,173K for 5 h was 50m2/g, which was much higher than that of the two reference materials (ceria made via precipitation of cerous nitrate using aqueous ammonia at 4.1m2/g, and the Japan reference catalyst JRC-CEO-1 at 1.4m2/g). The ceria made via thermal hydrolysis showed high crystallinity and a much higher pore volume, which resulted in excellent thermal resistance. For O2 conversion in ceria, catalyzed CH4 combustion at 923 K, the ceria created in this study demonstrated higher activity than that for either reference. The high CH4 combustion performance was due to the high specific surface area and to a superior oxygen storage capacity (OSC) even after a combustion test.

Low-temperature combustion of methane using PdO/Al2O3 catalyst: Influence of crystalline phase of Al2O3 support

Palladium oxide (PdO) catalysts supported on various alumina supports (θ-, δ-, κ-, η-, and γ-Al2O3) were prepared and the effect of the crystalline phases of the supports on the catalytic performance in methane combustion was investigated. Among the catalysts examined, the PdO/θ-Al2O3 catalyst, which showed the lowest reduction temperature in the temperature-programmed reduction of methane and the highest oxygen capacity in methane pulse experiments, exhibited the highest CH4 conversion and stability for methane combustion. However, all the catalysts were deactivated because of the growth of PdO particles and strong adsorption of water vapor.

Dextrose-aided hydrothermal preparation with large surface area on 1D single-crystalline perovskite La0.5Sr0.5CoO3 nanowires without template: Highly catalytic activity for methane combustion

Single-crystalline nanowires of perovskite-type oxides (PTOs) La0.5Sr0.5CoO3 were synthesized via a dextrose-assisted hydrothermal route (DHR) and/or l-Lysine. The physicochemical properties of the materials were characterized by means of XRD, BET, HRSEM, HRTEM, SAED, ICP-AES, H2-TPR, and O2-TPD techniques. It is found that the single-crystalline sample (LSCO-2) derived at temperature of 170°C with a dextrose/l-Lysine volumetric ratio of 0.3/1.0 of new nanowire DHR possessed a high surface oxygen concentration and the best low-temperature reducibility, and a high surface area (17.7m2g−1) from nitrogen sorption analysis which exhibited much better than that observed with the corresponding perovskites synthesized by conventional process for polycrystalline La0.5Sr0.5CoO3 catalyst. The average width and length of the nanowires are 5–10nm and 2μm, respectively. Among the LSCO samples, the LSCO-2 sample showed the best performance for methane combustion, giving the T10%, T50%, and T90% of 249, 461 and 702°C at GHSV=30,000ml/(hgcat), respectively. After running at 800°C for 50h, the nanowire DHR (LSCO-2) showed a higher stability and activity than the nanoparticles (LSCO-4) counterpart. It indicated that the good catalytic performance of LSCO-2 was related to higher surface area/energies, and better low-temperature reducibility, as well as to the different adsorbed oxygen species concentration.

Supported La1−x Ce x MnO3 perovskite catalysts: preparation, characterization and catalytic performance in methane combustion

A serials of La1−xCexMnO3 (x = 0, 0.2, 0.4, 0.6 and 0.8) catalysts have been prepared via a sol-gel process using citric acid as a chelating agent. The phase composition and morphology of the catalysts are characterized by XRD, SEM and TEM. La1−xCexMnO3/γ-Al2O3/cordierite catalyst has also been prepared by immersion process using cordierite honeycomb ceramic as carrier and γ-Al2O3 as support agents. The effect of Ce-doping on the structure of perovskite and catalytic property of methane combustion is explored. The results show that with the increase of Ce substitution, the crystal structure of perovskite changes from the tetragonal system to the orthorhombic system and when the x is equal to 0.2, the catalytic property in methane combustion is the best.

Catalytic performance in methane combustion of rare-earth perovskites RECo0.50Mn0.50O3 (RE: La, Er, Y)

RECo0.50Mn0.50O3 perovskites (RE: La, Y, Er) have been prepared by an auto-combustion method and calcined at 700°C, 850°C and 950°C. YCo0.50Mn0.50O3 forms at temperatures as low as 700°C, much lower than those required in solid-state ceramic synthesis. All materials show adequate specific surface when calcined at 700°C. ErCo0.50Mn0.50O3, which has the largest surface area, shows the lowest activity due to the presence of segregated phases, while YCo0.50Mn0.50O3, which reaches the perovskite structure at lower temperatures, exhibits the highest catalytic activity. The catalytic activity, evaluated from the total combustion of methane, can be related to the presence of the perovskite structure, an adequate surface area and the reducibility of the material. At the calcination temperatures of 850°C and 950°C, at which the surface area and crystalline degrees are almost the same for the La-, Y- and Er-systems, no differences in the catalytic activity were detected. The catalytic activity, higher for materials calcined at lower temperatures, is progressively lost due to sintering processes occurring at higher calcinations temperatures, as confirmed by SEM observations.

Structure properties and catalytic performance in methane combustion of double perovskites Sr2Mg1−xMnxMoO6−δ

The double perovskite oxides Sr2Mg1−xMnxMoO6−δ (x=0, 0.2, 0.5, 0.8 and 1), formerly applied as anode materials for solid oxide fuel cells, were investigated as catalysts for the methane combustion. The mixed oxides were prepared by sol–gel procedures, followed by annealing under reducing atmosphere of 5% H2 in nitrogen. The structure properties of these oxides were characterized in detail by X-ray diffraction, X-ray photoelectron spectroscopy and X-ray absorption spectroscopy. The catalytic property was strongly influenced by the Mn substitution and the optimized activity was observed for Sr2Mg0.5Mn0.5MoO6−δ. The relation between catalytic performance and degree of Mn substitution was examined with regard to the structure and surface characteristics of the mixed oxides, which was discussed in view of the presence of oxygen vacancies and may be correlated with the Mn-relating surface lattice oxygen species.

Surface properties and catalytic performance in methane combustion of La0.7Sr0.3Fe1−Ga O3− perovskite-type oxides

Abstract The perovskite-type oxides La0.7Sr0.3Fe1−yGayO3−δ (y = 0, 0.3, 0.5, 0.7 and 1), usually applied as oxygen-permeable membrane materials, were investigated as catalysts for the catalytic combustion of methane. The structure and properties of these catalysts were characterized by XRD, BET, XPS and TPR techniques. The catalytic activities were strongly influenced by the Fe contents of the mixed oxides, which was examined in relation to the structure and surface characteristics and may be correlated with their surface oxygen species and redox properties. The optimized catalytic performance was observed for La0.7Sr0.3Fe0.7Ga0.3O3−δ with the highest methane conversion of 91% at 600 °C and the thermal stability test was also described.

Conventional hydrothermal process versus microwave-assisted hydrothermal synthesis of La1−xAgxMnO3+δ (x = 0, 0.2) perovskites used in methane combustion

Abstract A study on the synthesis of La 1− x Ag x MnO 3+ δ ( x = 0, 0.2) using a microwave process (MWhyd) has been carried out by comparing the heating time and reaction temperature with the same factor under conventional thermal process (CHhyd). Experiments have been conducted using the hydrothermal method at medium pressure ( T = 200 °C, P = 20 atm) followed by a thermal treatment of the precursor at 700 °C (10 h). Structural and physico-chemical properties of the catalysts were investigated using X-ray diffraction (XRD), BET sorption, temperature-programmed reduction or desorption, mass spectrometry (TPR-MS and TPD-MS), and X-ray photoelectron spectroscopy (XPS). While CHhyd and MWhyd powder catalysts exhibited the same XRD patterns indexed as pure perovskite structure, their surface physico-chemical properties were found to be strongly influenced by the preparation method. The effect of the nature of oxygen species, their amount and mobility, evidenced by temperature programmed experiments, on the catalytic properties in methane combustion in the presence and in the absence of hydrogen sulphide has been studied. MWhyd-La 0.8 Ag 0.2 MnO 3+ δ catalysts were found to exhibit a much better performance in methane combustion together with higher resistance to sulphur poisoning than CHhyd catalysts.

Catalytic Combustion of Methane over Cobalt–Magnesium Oxide Solid Solution Catalysts

A series of cobalt–magnesium oxide solid solution catalysts (CoMgO) have been prepared using urea combustion methods, and characterised by X-ray diffraction (XRD) and laser Raman (LR). The catalytic activities for methane combustion have been tested in a continuous-flow microreactor. The Co content has a significant effect on the activity of the cobalt–magnesium oxide solid solution catalysts. The catalysts containing 5 and 10% Co have the lowest light-off temperature in methane combustion. In the preparation of cobalt–magnesium oxide solid solution catalysts, higher urea to metal ratio favors the formation of the catalysts with smaller crystal particles and leads to a better catalytic performance for methane combustion. Addition of lanthanum nitrate to the solution of Co and Mg nitrate depressed the formation of the cobalt–magnesium oxide solid solution and decreased the activity of the catalysts for methane combustion. The cobalt–magnesium oxide solid solution catalysts are very stable when the calcination or reaction temperature is no more than 900°C. However, the catalytic activity decreases rapidly after high temperature (>1000°C) calcination, possibly due to sintering of the catalyst and thus decrease of the surface area.

Reverse Microemulsion-Mediated Synthesis and Structural Evolution of Barium Hexaaluminate Nanoparticles

Nanocrystalline barium hexaaluminate has been successfully synthesized through the use of a reverse microemulsion as a medium for controlled hydrolysis and polycondensation of barium and aluminum alkoxides. The nanoparticles derived were characterized with electron microscopy, X-ray diffraction, and nitrogen adsorption analysis. This novel material possessed a well-defined particle morphology and an ultrahigh surface area, and exhibited excellent catalytic performance in methane combustion. Its structural evolution was found to be strongly dependent on synthesis parameters, such as water/alkoxide ratio and aging period. Powder recovery and drying techniques also had an important impact on particle agglomeration and structural development. Through the unique synthesis approach described, barium hexaaluminate with superb thermal stability was achieved, with surface areas in excess of 100 m{sup 2}/g retained even after calcination at 1,300 C.

Surface properties and catalytic performance in methane combustion of Sr-substituted lanthanum manganites

Perovskite type La 1 − x Sr x MnO 3 ( x = 0–0.5) oxides were prepared by the amorphous citrate process, characterised by X-ray diffraction, oxygen desorption, temperature-programmed reduction, infrared and X-ray photoelectron spectroscopic techniques, and tested for methane combustion within the 473–1073 K temperature range. Since catalyst activity was found to depend strongly on BET areas and to a lesser extent, on the degree of substitution ( x), intrinsic activities were computed for La 1 − x Sr x MnO 3 catalyst series. Among the compositions investigated, the degree of substitution x = 0.2 showed the highest intrinsic activity within the temperatures explored. Characterisation techniques made possible to correlate catalytic performance with the structural characteristics of the oxides. The stability of Mn 4+ is probably the most important parameter, but excess of oxygen and atomic surface composition should also be taken into account.

Pd-Pt bimetallic catalyst supported on SAPO-5 for catalytic combustion of diluted methane in the presence of water vapor

The examination of the combustion of a trace amount of methane over Pd‐ion‐exchanged silicoaluminophosphate‐5 (Pd‐SAPO‐5) at low temperature in the presence of water vapor reveals that water vapor strongly depresses methane combustion and causes a significant decrease in catalytic activity with time. The newly prepared bimetallic catalyst Pd–Pt‐SAPO‐5, on the other hand, shows higher performance for methane combustion under similar conditions.