Catalytic Combustion Of Methane Research Articles

Reaction mechanism insights into CH4 catalytic oxidation on Pt13 cluster: A DFT study

Catalytic combustion of methane is an efficient and environment-friendly combustion method that can effectively reduce air pollutant emissions. To uncover the reaction mechanism of methane catalytic oxidation, density functional theory (DFT) calculation was performed on Pt13 cluster with the B3LYP method. Combining thermodynamic parameters with dynamics parameters, the optimal paths for CH4 activation and CO2 formation are CH4* → CH3* → CH2* → CH* → CHOH* → COH* and CH* → CHOH* → CHO* → CO* → COOH* → CO2*, respectively. In addition, the presence of H2O in the reactants changed the reaction path from CH4* → CH3* → CH2* → CH*+O* → CHO* → CO*+O* → CO2* to CH4* → CH3* → CH2* → CH*+OH* → CHOH* → CHO* → CO*+OH* → COOH* → CO2*, thus leading to the rate-determine step (RDS) changes from CO*+O* → CO2* to CH3* → CH2*. The energy barrier of the RDS with H2O is 1.19 eV, much lower than that of the RDS without H2O (1.31 eV), indicating that the presence of H2O in the reactants is beneficial to the catalytic oxidation of CH4.

Combined silicon carbide and zirconia open cell foams for the process intensification of catalytic methane combustion in lean conditions: Impact on heat and mass transfer

For catalytic process intensification, a series of open cell foams (OCFs) made of silicon carbide (SiC) and zirconia (Zir) with pore density of 30 ppi coated with 3 wt% PdO/Co3O4 as catalyst were combined together and tested toward methane oxidation in lean conditions. In each combination, the SiC OCF was positioned in the reactor on the inlet side of the reactant gases followed by the Zir OCF. The reactor was fed at different weight hourly space velocities (WHSV, 30 and 90 NL h−1 gcat−1) and inlet methane concentrations (0.5 and 1 vol%). The best results are obtained with the combination where two supports of same length but with different thermal conductivity (higher at the inlet of the reactor, SiC, and lower at the outlet, Zir) are used in series. For all OCF combinations, mass transfer effects were evaluated using the characteristic resistances (kinetic, internal and external mass transfer). The external and internal heat transfer effects were analyzed using the Mears and Anderson criteria. Furthermore, a comparison in terms of volumetric heat transfer coefficient and heats of removal/reaction was performed.

Experimental and numerical study of catalytic combustion and pore-scale numerical study of mass diffusion in high porosity fibrous porous media

Pore structure has a significant effect on transport phenomena inside porous media. This effect can be considered in simulations by using suitable transport coefficients. Some correlations are reported in the literature, which can be applied for simple pore geometries. In the present study, a pore-scale simulation approach is presented to determine mass diffusion coefficient considering molecular and Knudsen diffusion in a fibrous porous medium as a complex porous geometry. The methodology is employed for species in catalytic combustion of Methane inside a fibrous porous structure. The effect of Solid Volume Fraction (SVF), fibers orientation, and diameter are discussed in different temperatures. It is found that SVF plays the dominant role in mass diffusion, specifically above 600K. Mass diffusion coefficients obtained in the present study and flow permeability, conduction and radiation heat transfer coefficients from the previous study are used to simulate methane combustion inside the fibrous structure on the macro scale. An experimental setup is developed for validation. The results indicated that the simulation could well predict the temperature distribution, also 6.4% error in estimating the Methane conversion rate was observed. Due to the low Peclet number, the concentration of CH4 and O2 decreased unexpectedly before entering the catalytic zone.

Highly Active PdO/Mn3O4/CeO2 Nanocomposites Supported on One Dimensional Halloysite Nanotubes for Photoassisted Thermal Catalytic Methane Combustion

AbstractIn this work, we have successfully triggered the aqueous auto‐redox reactions between reductive Ce(OH)3 and oxidative MnO4−/Pd2+ ions to form PdO/Mn3O4/CeO2 (PMC) nanocomposites. PMC could spontaneously self‐assemble into compact encapsulation on the surface of halloysite nanotubes (HNTs) to form the final one dimensional HNTs supported PMCs (HPMC). It is identified that there exists strong synergistic effects among the components of PdO, Mn3O4, and CeO2, and hence HPMC could show excellent performance on photoassisted thermal catalytic CH4 combustion that its light‐off temperature was sharply reduced to be 180 °C under visible light irradiation. Based on detailed studies, it is found that the catalytic reaction process well follows the classic MVK mechanism, and adsorption/activation of O2 into active oxygen species (O*) should be the rate‐determining step for CH4 conversion.

A Method for the Accurate Quantification of Gas Streams by Online Mass Spectrometry.

The accuracy of the online quantification of gaseous effluents from catalytic reactors by mass spectrometry (MS) is rarely addressed by researchers despite the extensive use of the technique. MS results are strongly sensitive to both the operation conditions of the reactor and to the state of the instrument. Therefore, most studies use them as qualitative descriptors of the performance of catalytic reaction systems. The purpose of this work was to develop an accurate method for the quantification of gaseous effluents from catalytic reactors. For this purpose, the mathematical expressions from the so-called external and internal standard calibration methods for MS were coupled to the typical metrics used for studying catalytic reactions, namely, conversion, selectivity, and carbon mass balances. The catalytic combustion of methane was selected as a model reaction to test the developed approach. The accuracy of the developed method was validated by comparison with results obtained in a separate reaction system coupled online to a gas chromatograph. The closure of the carbon mass balance was used as control metrics allowing for the assessment of the physical meaning of the method. In general, the internal standard method of calibration was found to be best for the accurate quantification of gaseous streams by online mass spectrometry. In general, the results of this investigation may be of use to researchers in the field of catalysis as well as to research workers using mass spectrometry for various purposes.

Methane combustion over palladium catalyst within the confined space of MFI zeolite

Isolated cationic Pd species encapsulated in MFI zeolite, i.e., Pd@MFI, have been successfully prepared via in situ hydrothermal route followed by oxidative treatment. The as-prepared Pd@MFI samples are investigated as promising catalysts in the reaction of methane combustion. Typically, Pd@H-ZSM-5 shows remarkable activity in methane catalytic combustion with a low apparent activation energy value of 70.7 kJ/mol as well as good catalytic stability even in excess water vapor. Detailed characterization results demonstrate the strong interaction between Pd sites and zeolite framework in Pd@ZSM-5 and the efficient stabilization of isolated Pd sites by zeolite thereof. Spectroscopy analyses reveal that the presence of Brønsted acid sites is beneficial to methane adsorption and its subsequent activation on adjacent Pd sites, constructing cooperation between Brønsted acid sites and Pd sites within the confined space of MFI zeolite toward high-efficiency methane catalytic combustion. The reaction mechanism of methane combustion catalyzed by Pd@H-ZSM-5 model catalyst is finally discussed.

Enhancing oxygen activation on high surface area Pd-SnO2 solid solution with isolated metal site catalysts for catalytic CH4 combustion

A facile strategy of redox hydrothermal is developed to prepare highly dispersed Pd on SnO2 support as insertion compound or alloy with high surface area. By means of this method, the interaction between Pd and SnO2-x can be strengthened and results in synergistic effect between Pd center and the surrounding sites of the SnO2-x, which induces consequence changes in the physicochemical properties of the catalysts and, as a consequence, their catalytic performance and stability. The as-synthesized 3%Pd-SnO2 catalyst exhibits a remarkable reactivity of 14.34 × 104 mmol∙gcat-1∙s−1 and good stability for catalytic methane combustion, due to the high surface density of Pdδ+ species and oxygen vacancies. This later provides more active oxygen species and also to stabilize the highly dispersed Pdδ+ species which are active for the dissociative adsorption of methane. With correlation of structure and reactivity, it is revealed that such highly dispersed Pd species work synergistically with oxygen vacancy of the support to promote CH4 oxidation. This synergistic interaction also prevents catalyst deactivation which is of high interest for the future development of new generation of combustion catalysts.

Effect of partial substitution of Zn2+ with Co2+ on catalytic methane combustion performance of Zn1-xCoxGa2O4 (x=0, 0.1, 0.3) microspheres

The modified ZnGa2O4 microspheres were prepared by the conventional hydrothermal method and used to catalyze methane combustion reaction. Because Co2+ and Zn2+ have similar ion radii, so it seems that the Zn2+ at the tetrahedral (Td) position of ZnGa2O4 was partially replaced by Co2+ to adjust the oxygen distribution, and finally the Zn1-xCoxGa2O4 (x = 0.1, 0.3) microspheres catalysts was obtained. X-ray photoelectron spectroscopy (XPS) analysis exhibited that Co3+ were present in the Zn1-xCoxGa2O4 (0.1, 0.3) samples, and interstitial oxygen were formed to maintain electrical neutrality. Oxygen temperature programmed desorption (O2-TPD) profiles showed that there was only one oxygen species desorption from ZnGa2O4 sample, while the Zn1-xCoxGa2O4 (0.1, 0.3) samples had two oxygen desorption peaks, that is the first one is surface adsorbed oxygen, the second is lattice oxygen. The catalytic methane combustion performance of the samples indicated that the partial substitution of Co2+ for Zn2+ in ZnGa2O4 can effectively improve its activity.

Low-temperature combustion of methane over graphene templated Co3O4 defective-nanoplates

Transition metal oxides are the potential catalysts to replace noble-metal based catalyst for the catalytic combustion of methane due to the tolerable reactivity and low cost. However, these catalysts are challenged by the low temperature reactivity. Herein, the surface defective Co3O4 nanoplates are realized through a facile co-precipitation and thermal reduction method with the association of GO. The resultant catalysts (CoGO50) demonstrate a superior low-temperature reactivity for the methane oxidation to CO2 and H2O in comparison with the common Co3O4 catalyst. The reliable stability of CoGO50 catalyst was proved by 80 h testing with intermittent feeding of water vapor. The experimental analysis demonstrates that the presence of a small amount of GO significantly affects the catalysts in surface valence state, active oxygen species and surface oxygen vacancies through reacting with the cobalt oxide as a reductant. Moreover, GO plays as 2D confine template to form smaller and thinner nanoplates. This work provides a facile method to control the surface properties of catalyst not only for Co3O4 based catalysts but also for wider solid catalysts.

Oxygen Vacancies and Lewis Acid Sites Synergistically Promoted Catalytic Methane Combustion over Perovskite Oxides.

An in-depth understanding of the surface properties-activity relationship could provide a fundamental guidance for the design of highly efficient perovskite-based catalysts for the control of anthropogenic methane emission. Herein, both oxygen vacancies and Con+ Lewis acid sites were purposely introduced on ordered macroporous La0.8Sr0.2CoO3 monolithic catalysts by one-step reduction and selective etching in oxalic acid, and their synergistic effect on methane combustion was investigated. Combined with experimental and theoretical investigations, we revealed that the positively charged Con+ Lewis acid sites and single-electron-trapped oxygen vacancies (Vo·) formed an active pair, which enabled an effective localized electron cloud shift from Vo· to Con+. The characteristic electronic effect modulates surface electronic properties and coordination structures, thus resulting in superior oxygen activation capacity, lattice oxygen mobility, and reducibility, as well as favorable CH4 interaction and oxidation. Our work not only gives insights into surface properties-activity relationships on perovskite for hydrocarbon combustion but also sheds substantial light on future environmental catalyst design and modulation for hydrocarbon pollutants elimination.

Irregularly Shaped NiO Nanostructures for Catalytic Lean Methane Combustion

Irregularly Shaped NiO Nanostructures for Catalytic Lean Methane Combustion

Catalytic combustion of methane conducted on La–B–O–C (B[dbnd]Co, Mn, Fe) composites: The effects of B-sites cation properties

The novel La–B–O–C composites were fabricated as catalysts for methane catalytic combustion at low temperature, and considering the effect of newly C–O bond on B-site ions as active sites, three metal ions (Co, Mn, Fe) were selected for experiment. XRD, N2-physisorption, XPS and H2-TPR measurements were used to characterize the physicochemical properties of catalysts, which showed that the newly established C–O–B bond reduced the ionic valence of the B-site, and the redox capacities were increased or decreased to different degrees, respectively. Catalytic tests showed that T50 of La–Co–C–O composites (LC-C) and La–Fe–C–O composites (LF-C) are 377 °C and 482 °C, much lower than that of unmodified catalyst, respectively. But T50 of La–Mn–C–O composites (LM-C) increases to 507 °C from 493 °C. The superior performance of LC-C could be attributed to the high oxygen vacancies and enhanced redox property, and the better performance of LF-C was mainly benefited from the increase in lattice oxygen. For LM-C, the sacrifice of Mn4+ weakened the catalytic activity. There are more obvious mechanistic differences for different B-site elements in the La–B–O–C. The study will bring innovative insights into the design of excellent composites catalysts for methane oxidation.

Catalytic Methane Combustion on the Hydrothermally Synthesized MnO2 Nanowire Catalysts

Catalytic Methane Combustion on the Hydrothermally Synthesized MnO₂ Nanowire Catalysts

Electrophoretic coating for steam methane micro‐reformer: Optimum voltage and time, channel design, and substrate type

Following our previous simulation study, in this study manufacturing of previously simulated micro-reformer was carried out in order to study intensifying steam methane reforming. SUS 310 was selected as the base material and a copper gasket was used for sealing. Because of simplicity and being straightforward, the electrophoretic deposition method was used for the first time to coat a commercial Nickel-based reforming catalyst onto reaction plates. All reaction plates had the dimensions of 21 × 20 mm and at most 3 mm depth. S310 was used for anode and S304 for cathode. Reduction of catalyst was performed at 650°C. Five cm quartz packing was used to preheat feed before entering the micro-reformer. In the first part, after investigating important variables of voltage and coating time in the range of 1 to 4 minutes and 100 to 140 V, optimum conditions were found to be 120 V and 1.5 minute, respectively, which gave 5.1 mg/cm2 surface density. At optimum condition, micro-reformer had better performance than packed-bed reactor even at low weight hourly space velocities. In the second part of the study, three channel designs, that is, parallel, splitting-jointing, and pin-hole were designed, manufactured, and mounted into the micro-reformer. Based on specific methane conversion, splitting-jointing had marginally better performance than parallel channels. This finding was contrary to the simulation results. This difference originates from two reasons: (a) monolayer assumption in the simulation was not real because of inherent porosity in the EPD coated layer; (b) a gap of 0.2 mm between the micro-reformer casing and the reaction plate would appear if temperature exceeded 650°C and this gap caused flow by pass-through channels. At the third and final part, copper substrate was coated and compared with S310 substrate. Results did not show so much better methane conversion because dimension were very small, which means temperature along the depth or length did not vary considerably. Stability analysis, reducing the channel sizes, redesigning the micro-reformer to add endothermic reaction (such as methane catalytic combustion) section will be our next studies.

Synthesis of Highly Dispersed Palladium Nanoparticles Supported on Silica for Catalytic Combustion of Methane

Palladium nanoparticles supported on silica catalysts (Pd/SiO2) were prepared by wet impregnation (WI), dry impregnation (DI), strong electrostatic adsorption (SEA), and charge-enhanced dry impregn...

Intensification of ultra-lean catalytic combustion of methane in microreactors by boundary layer interruptions – A computational study

Oxidation of an ultra-lean mixture of methane and air over a platinum catalyst at the constant temperature of 1000 K is investigated numerically in several microreactor configurations featuring different hydrodynamics. These include a straight microchannel with the catalyst coated on the walls and a few wavy microchannels with continuous and discretised catalytic coating. The surface generated CO2 is selected as the indicator of catalytic activity and is evaluated along the catalytic surfaces and the outlet of reactor. It is shown that separation and reattachment of the boundary layer significantly alters the catalytic activity by modifying the structure of concentration boundary layer. Comparison of a strategically coated wavy microchannel with a straight microchannel, with accounting for the residence time, yields an increase of up to 400% in the production rate of CO2. It is argued that the observed hydrodynamic effects upon catalytic activities could help designing highly improved catalytic microreactors.

Total Oxidation of Methane on Oxide and Mixed Oxide Ceria-Containing Catalysts

Methane, discovered in 1766 by Alessandro Volta, is an attractive energy source because of its high heat of combustion per mole of carbon dioxide. However, methane is the most abundant hydrocarbon in the atmosphere and is an important greenhouse gas, with a 21-fold greater relative radiative effectiveness than CO2 on a per-molecule basis. To avoid or limit the formation of pollutants that are dangerous for both human health and the atmospheric environment, the catalytic combustion of methane appears to be one of the most promising alternatives to thermal combustion. Total oxidation of methane, which is environmentally friendly at much lower temperatures, is believed to be an efficient and economically feasible way to eliminate pollutants. This work presents a literature review, a statu quo, on catalytic methane oxidation on transition metal oxide-modified ceria catalysts (MOx/CeO2). Methane was used for this study since it is of great interest as a model compound for understanding the mechanisms of oxidation and catalytic combustion on metal oxides. The objective was to evaluate the conceptual ideas of oxygen vacancy formation through doping to increase the catalytic activity for methane oxidation over CeO2. Oxygen vacancies were created through the formation of solid solutions, and their catalytic activities were compared to the catalytic activity of an undoped CeO2 sample. The reaction conditions, the type of catalysts, the morphology and crystallographic facets exposing the role of oxygen vacancies, the deactivation mechanism, the stability of the catalysts, the reaction mechanism and kinetic characteristics are summarized.

Catalytic methane combustion in plate-type microreactors with different channel configurations: An experimental study

This paper presents an experimental study on the catalytic methane combustion (CMC) in plate-type microreactors with wall-coated Pt/γ-Al2O3 catalyst. Firstly, the influence of different operational conditions and coating properties on the CMC in the straight parallel-channel microreactor has been investigated. A specific catalyst loading of 57.6 g m−2 was found to yield the highest methane conversion over 3.5 wt% Pt/γ-Al2O3. A higher or lower loading tended to decrease the methane conversion due to either the limited internal diffusion through the thicker coating layer or insufficient active sites in the thinner coating layer. Then, the above microreactor was compared with other five different geometries, including cavity, double serpentine microchannels, obstacled microchannels, meshed circuit and vascular network. The double serpentine microchannel geometry presented the highest methane conversion (especially at a relatively low mixture flow rate) due to the appropriate control over the residence time and catalyst coating surface area.

Parametric study of methane catalytic combustion in a micro-channel reactor: Effects of porous washcoat properties

A washcoat resolved numerical model of catalytic micro combustor fueled by methane is developed. Detailed gas phase mechanism and alumina dioxide supported Pt-based surface mechanism are adopted. This model proves to capture flow, temperature and species fields precisely including impermeable flow and products accumulation in porous washcoat layer. The novelty and superiority of this research compared to traditional modeling method in which instantaneous diffusion onto catalytic wall is assumed lies in that: it is possible to investigate effects of porous washcoat properties with this full-scale numerical model. Computational results show that homogeneous reactions (HR) are impaired and heterogeneous reactions (HTR) are strengthened as channel confinement increases. Da number analysis reveals that the micro combustor works under a mixed controlled mode in which catalytic reaction rate and internal mass diffusion rate are comparable. When washcoat layer thickness increases from 15 μm to 75 μm, overall catalyst usage roughly decreases from 0.34 to 0.05. It is concluded washcoat thickness can’t be too thin in order to maintain HTR intensity and too thick since catalyst usage is extremely low. Porous washcoat properties impact combustion characteristics in a similar mechanism: modifying effective mass diffusion coefficient. In general, increasing porosity, average pore diameter and decreasing tortuosity will enhance HTR and impair HR. In real application, these parameters can be utilized to modify combustion temperature, emission performance and stability operation map.

Exploring halloysite nanotubes as catalyst support for methane combustion: Influence of support pretreatment

Catalytic combustion of methane is considered an environmentally friendly route for energy generation owing to the high H/C ratio of methane and low CO2 emissions compared to other hydrocarbons fuels. The utilization of heterogeneous catalysts permits combustion at lower temperatures compared with thermal combustion. Herein, we developed new catalysts of palladium-supported halloysite nanotubes (HNTs) for methane combustion. This was performed via chemical modification of HNTs using four different species i.e. H2SO4 (HNTs-H2SO4), NaOH (HNTs-NaOH), sodium dodecyl sulfate (HNTs-SDS), and cetyltrimethylammonium bromide (HNTs-CTAB). After chemical modification, Pd was deposited on the pretreated HNTs and the impact of chemical treatment on the morphology, crystal structure, textural properties, and methane oxidation activity was studied. All catalysts based on chemically modified HNTs exhibited enhanced catalytic performance towards methane combustion compared to Pd-supported on pristine HNTs, in particular, Pd/alkali-treated HNTs (Pd/HNTs-NaOH) revealed the highest catalytic activity towards methane combustion with the temperature of complete conversion (T100) equals 385 °C and activation energy of 79.15 kJ mol−1. Furthermore, the same sample displayed enhanced stability compared to other counterparts. This was assigned to the confinement of Pd nanoparticles at the inner surface which enhances the catalyst-support interaction, increases the number of surface active sites, and enhances the resistance to sintering at high temperatures.