Complete Oxidation Of Methane Research Articles

Complete oxidation of formaldehyde at room temperature over Ag-loaded octahedral molecular sieve synthesized from solvent-free route

Removal of formaldehyde (HCHO) has recently been attracted much attention, and completely catalytic oxidation at room temperature has been identified as one of the efficient routes for solving this problem. In this research, we show a successful preparation of Ag-loaded octahedral molecular sieve from solvent-free route (Ag/OMS-2-S), which was characterized by XRD, SEM, HRTEM, BET, XPS, ICP-OES, H2-TPR, and HCHO-TPD techniques to investigate the factors influencing the catalytic activity. Very interestingly, HCHO is completely converted into CO2 at room temperature over the Ag/OMS-2-S catalyst. To the best of our knowledge, this is the first time for complete oxidation of HCHO at room temperature over all the Ag-based catalysts. Relating to the characterizations, it is suggested that the active oxygen species play a key factor that contributes to the excellent performance of the Ag/OMS-2-S. In addition, the Ag/OMS-2-S catalyst is also very stable and selective. Combination of extraordinary activity and excellent stability of the Ag/OMS-2-S catalysts might offer an alternative way to develop new efficient catalysts for the removal of air pollutants.

Selective electrochemical oxidative coupling of methane mediated by Sr2Fe1.5Mo0.5O6-\u03b4 and its chemical stability

Efficient conversion of methane to value-added products such as olefins and aromatics has been in pursuit for the past few decades. The demand has increased further due to the recent discoveries of shale gas reserves. Oxidative and non-oxidative coupling of methane (OCM and NOCM) have been actively researched, although catalysts with commercially viable conversion rates are not yet available. Recently, {{{{{{{mathrm{Sr}}}}}}}}_2Fe_{1.5 + 0.075}Mo_{0.5}O_{6 - delta } (SFMO-075Fe) has been reported to activate methane in an electrochemical OCM (EC-OCM) set up with a C2 selectivity of 82.2%1. However, alkaline earth metal-based materials are known to suffer chemical instability in carbon-rich environments. Hence, here we evaluated the chemical stability of SFMO in carbon-rich conditions with varying oxygen concentrations at temperatures relevant for EC-OCM. SFMO-075Fe showed good methane activation properties especially at low overpotentials but suffered poor chemical stability as observed via thermogravimetric, powder XRD, and XPS measurements where SrCO3 was observed to be a major decomposition product along with SrMoO3 and MoC. Nevertheless, our study demonstrates that electrochemical methods could be used to selectively activate methane towards partial oxidation products such as ethylene at low overpotentials while higher applied biases result in the complete oxidation of methane to carbon dioxide and water.

Ag/AgCl as an efficient plasmonic photocatalyst for greenhouse gaseous methane oxidation

In this work, quasi-cube Ag/AgCl plasmonic photocatalyst was synthesized by a simple co-precipitation method and in situ photo-reduction process. The synthesized Ag/AgCl shows high efficiency and good stability in the complete oxidation of nonpolar greenhouse gas methane under the simulated sunlight irradiation. Systematic experiments and finite-difference time-domain (FDTD) simulated calculations were employed to explore the reasons for the appreciable performance improvement, and results showed that the surface plasmonic resonance (SPR) effect of Ag nanoparticles can generate strong electric field which would induce the polarization of methane molecules, hence enhancing the adsorption of methane. This work provides a new idea for exploration of other plasmonic photocatalysts in the field of nonpolar gaseous molecules photo-oxidation.

Stable Palladium Oxide Clusters Encapsulated in Silicalite-1 for Complete Methane Oxidation

Zeolite-supported metal catalysts are widely employed in a number of chemical processes, and the stability of the catalytically active species is one of the most critical factors determining the reaction performance. A good example is the Pd/zeolite catalyst, which provides high activity for methane oxidation but deactivates rapidly under the reaction conditions due to palladium nanoparticle sintering. Although coating the metals with thin shells of porous materials is a promising strategy to address the sintering of metals, it is still challenging to fix small metal particles completely inside zeolite crystals. Here, using an amine-based ligand to stabilize palladium during the zeolite synthesis, we realize the exclusive encapsulation of highly dispersed palladium oxide clusters (1.8–2.8 nm) in the microporous channels and voids of the nanosized silicalite-1 crystals. The synthesis conditions of the zeolite-supported catalyst influence the encapsulation degree and the size distribution of metal particles. Thanks to the encapsulation effect of small palladium oxide clusters, together with the inherent properties of silicalite-1 such as low acidity, high hydrophobicity, and high hydrothermal stability, the optimized Pd@silicalite-1 catalyst outperforms the traditional Pd-based catalysts prepared by wetness impregnation, exhibiting both high activity and better stability in the lean methane oxidation reaction.

A Novel Preparation of Mn/NiCo2O4 Catalyst with High Catalytic Activity on Methane

In this paper, a Mn/NiCo2O4 catalyst was prepared for the complete oxidation of low-concentration methane. When the ratio of Mn: Co is 1:4, the catalyst has the best catalytic activity, and the best methane conversion temperature Feis 400 °C. In addition, the catalytic activity remains stable during the long-term reaction, showing adequate thermal stability. The catalyst is grown on FeCrAl alloy by hydrothermal method to complete the catalytic oxidation of methane. In the catalysis process, the Mn/NiCo2O4-FeCrAl catalyst is energized and the current is directly passed through the alloy substrate to generate Joule heat, reaching the optimal catalytic temperature for complete oxidation of methane.

Highly effective La-deficient La1-xCexMnO3 mixed oxides for the complete oxidation of methane

La-deficient La1-xCexMnO3 mixed oxides, obtained by selective dissolution in 1 ​M nitric acid, were employed in methane complete oxidation. The majority of the La cations in these perovskites were removed, resulting in increased specific surface areas, better reducibility and greater activity. Incorporation of a small amount of Ce stabilized the structure and a perovskite phase persisted in La-deficient La1-xCexMnO3 mixed oxides after 12 ​h of acid dissolution. La0.95Ce0.05MnO3 after the acid treatment exhibited satisfactory catalytic activity, with T50 and T90 values of 365 and 459 ​°C, respectively, which was even comparable to that previously reported 1% Pd/Al2O3 catalysts. And it showed excellent long-term activity even in the presence of CO2 and H2O.

Electrochemical Oxidative Coupling of Methane to Produce Higher Hydrocarbons Using Sr2Fe1.5Mo0.5O6-Δ Electrocatalysts

Efficient conversion of methane to value added products such as olefins and aromatics has been in pursuit for the past several decades. The demand has increased further due to the recent discoveries of shale gas reserves (1). Oxidative and non-oxidative coupling of methane (OCM and NOCM) has been actively researched although commercially viable conversion rates have not been achieved with any catalyst yet. Electrochemical OCM is gaining attention due to its ability to control the oxide ion flux that will help reduce the over-oxidation of methane while also helping to activate methane. Recently, (SFMO-075Fe) has been reported to activate methane with a C2 product selectivity of 82.2% (2). However, alkaline earth metal-based materials are known to suffer chemical instability in carbon rich environments at elevated operating temperatures. Hence, we evaluated the chemical stability of SFMO-075Fe and SFMO in carbon rich conditions at temperatures relevance for EC-OCM. SFMO-075 showed wonderful methane activation properties but suffered poor chemical stability as observed in thermogravimetric and powder XRD measurements. XPS and XRD measurements revealed that SrCO3 as the major product along with MoC when SFMO is exposed to methane at 900°C. We further found that methane could be selectively activated towards partial oxidation products such as ethylene at low overpotentials while higher applied biases results in complete oxidation of methane to carbon dioxide and water. We report in this presentation our findings with SFMO along with potential benefits of EC-OCM for methane activation. References Schwach, X. Pan, and X. Bao, “Direct Conversion of Methane to Value-Added Chemicals over Heterogeneous Catalysts: Challenges and Prospects,” Chem. Rev., 117, 8497, 2017.Zhu, S. Hou, X. Hu, J. Lu, F. Chen, and K. Xie, “Electrochemical conversion of methane to ethylene in a solid oxide electrolyzer,” Nat. Commun., 10, 1173, 2019.

Influence of NOx on the activity of Pd/θ-Al2O3 catalyst for methane oxidation: Alleviation of transient deactivation

Alumina supported Pd catalyst (Pd/Al2O3) is active for complete oxidation of methane, while often suffers transient deactivation during the cold down process. Herein, heating and cooling cycle tests between 200 and 900°C and isothermal experiments at 650°C were conducted to investigate the influence of NOx on transient deactivation of Pd/θ-Al2O3 catalyst during the methane oxidation. It was found that the co-fed of NO alleviated transient deactivation in the cooling ramp from 800 to 500°C, which was resulted from the in situ formation of NO2 during the process of methane oxidation. Over the Pd/θ-Al2O3, thermogravimetric analysis and O2 temperature programmed oxidation measurements confirmed that transient deactivation was due to the decomposition of PdO particles and the hysteresis of Pd reoxidation, while the metal Pd entities were less active for methane oxidation than the PdO ones. CO pulse chemisorption and scanning transmission electron microscopy characterizations rule out the NO2 effect on Pd size change. Powder X-ray diffraction and X-ray photoelectron spectroscopy characterizations were used to obtain palladium status of Pd/θ-Al2O3 before and after reactions, indicating that in lean conditions at 650°C, the presence of NO2 increases the content of active PdO on the catalyst surface, thus benefits methane oxidation. Homogeneous reaction between CH4, O2, and NOx may be partially responsible for the alleviation above 650°C. The interesting research of alleviation in transient deactivation by NOx, the components co-existing in exhausts, are of great significance for the application.

Pd-Promoted Co2NiO4 with lattice Co[sbnd]O[sbnd]Ni and interfacial Pd[sbnd]O activation for highly efficient methane oxidation

Nowadays, developing advanced Pd-based catalysts with highly efficient catalytic activity and long-term stability still presents profound challenges. Here, we prepare a novel Pd-Co2NiO4 catalysts with PdOx species simultaneously embedded into Co2NiO4 lattice and decorated on Co2NiO4 surface in high dispersion. The Pd-Co2NiO4 catalysts shows the attractive activity and excellent stability for methane complete oxidation. Based on the experimental and theoretical analysis, the enhanced methane oxidation activity of Pd-Co2NiO4 catalysts is mainly ascribed to two factors. PdOx species incorporated into Co2NiO4 lattice modulates effectively the electronic structure of catalysts, which promotes the electron transfer between Co 3d-O 2p hybrid orbital and Ni eg orbital in Co2NiO4 and thus benefits the activation of adjacent lattice O in CoONi hybridization, resulting in the rapid migration and activation of lattice oxygen in Co2NiO4 support (Factor I). In addition, the deposition of PdOx species on the Co2NiO4 surface tunes the metal-support interface interactions and promotes the activation of PdO bonds, giving rise to more facile CH4 activation ability (Factor Ⅱ). Collectively, the enhanced catalytic properties of the Pd-Co2NiO4 catalysts originated from the activation of lattice oxygen in the Pd-regulated CoONi hybridization and decorated PdOx sites. This study presented here not only gives further insight into the metal-support electronic interaction, but paves the promising way for the rational fabrication of next-generation environmental catalysts.

Confinement of subnanometric PdCo bimetallic oxide clusters in zeolites for methane complete oxidation

• A strategy of encapsulating PdCo clusters into MFI zeolite channels is developed. • PdCo clusters (0.4–0.6 nm) are encapsulated into sinusoidal channels of MFI zeolite. • Co improves the activity of surface oxygen and modulates electronic state of Pd. • PdCo@MFI exhibits high activity and H 2 O-resistance stability for CH 4 combustion. Supported Pd-based catalysts are widely used for various catalytic transformations, but steam-induced sintering remains a critical issue for industrial application. Here, we report a strategy of encapsulating PdCo bimetallic oxide clusters (0.4–0.6 nm) into sinusoidal channels of MFI zeolite used for methane complete oxidation. The introduction of Co species promotes the activation of surface oxygen species and modulates electronic state of Pd species, effectively enhancing the catalytic performance with the lowest temperature of CH 4 complete conversion obtained at 435 °C in the presence of steam. Meanwhile, the PdCo particle size and catalytic activity are remained on PdCo@MFI after 20 h at 420 °C in the presence of steam, much more stable than that of reference catalysts (PdCo/ZSM-5, drop 19% and PdCo/Al 2 O 3 , drop 22%). The strategy of confining bimetallic clusters into zeolites to enhance the activity and stability broadens the avenue to designing better catalysts for methane complete oxidation.

Operando characterisation of alumina-supported bimetallic Pd–Pt catalysts during methane oxidation in dry and wet conditions

Near ambient pressure x-ray photoelectron spectroscopy (NAP-XPS) was used to study the chemical states of a range of alumina-supported monometallic Pd and bimetallic Pd–Pt nanocatalysts, under methane oxidation conditions. It has been suggested before that for optimal complete methane oxidation, palladium needs to be in an oxidised state. These experiments, combining NAP-XPS with a broad range of characterisation techniques, demonstrate a clear link between Pt presence, Pd oxidation, and catalyst activity under stoichiometric reaction conditions. Under oxygen-rich conditions this behaviour is less clear, as all of the palladium tends to be oxidised, but there are still benefits to the addition of Pt in place of Pd for complete oxidation of methane.

A Latent La-Co-C-O Hybrid Derived from an Amino Acid-Deep Eutectic Solvent/Perovskite LacoO <sub>3</sub> Mutualism System: Adjustment of the Co-O Bond for Complete Methane Oxidation

A Latent La-Co-C-O Hybrid Derived from an Amino Acid-Deep Eutectic Solvent/Perovskite LacoO <sub>3</sub> Mutualism System: Adjustment of the Co-O Bond for Complete Methane Oxidation

Structure and performance of zeolite supported Pd for complete methane oxidation

The influence of zeolite support materials and their impact on CH4 oxidation activity was studied utilizing Pd supported on H-beta and H-SSZ-13. A correlation between CH4 oxidation activity, Si/Al ratio (SAR), the type of zeolite framework, reduction-oxidation behaviour, and Pd species present was found by combining catalytic activity measurements with a variety of characterization methods (operando XAS, NH3-TPD, SAXS, STEM and NaCl titration). Operando XAS analysis indicated that catalysts with high CH4 oxidation activity experienced rapid transitions between metallic- and oxidized-Pd states when switching between rich and lean conditions. This behaviour was exhibited by catalysts with dispersed Pd particles. By contrast, the formation of ion-exchanged Pd2+ and large Pd particles appeared to have a detrimental effect on the oxidation-reduction behaviour and the conversion of CH4. The formation of ion-exchanged Pd2+ and large Pd particles was limited by using a highly siliceous beta zeolite support with a low capacity for cation exchange. The same effect was also found using a small-pore SSZ-13 zeolite due to the lower mobility of Pd species. It was found that the zeolite support material should be carefully selected so that the well-dispersed Pd particles remain, and the formation of ion-exchanged Pd2+ is minimized.

Optimisation of bimetallic Co-Ni supported catalysts for oxidation of methane in natural gas vehicles

This work deals with the extensive study of supported bimetallic Co-Ni catalysts for the complete oxidation of methane. The simultaneous incorporation of nickel and cobalt was found to enhance the redox properties by favouring the formation of nickel cobaltite-like species and partially inhibiting the interaction between Co3O4 and alumina. In turn, this resulted in an increase of the amount of Co3+ cations in the catalysts, which led to a more notable presence of active lattice oxygen species in the samples. When the nickel loading was increased, the generation of less active NiO was observed. The improvement of the redox properties resulted in a promotion of the specific reaction rate and a shift of around 50 °C in the T50 value over the bimetallic catalysts. The most active catalyst (25Co-5Ni) was found to be relatively stable during prolonged operation times, but suffered an appreciable and irreversible deactivation in the presence of water vapour.

Chlorine-promoted perovskite nanocomposite as a high-performance oxygen transfer agent for chemical looping methane-assisted CO2 splitting

Metal oxide-mediated CO2 splitting with the assistance of methane (aka chemical looping dry reforming of methane) is a novel and attractive approach for CO2 utilization. Herein, we demonstrate that doping and tailoring the redox window of strontium ferrite (SrFeO3-δ)-calcium oxide nanocomposites are effective strategies to improve the performance of chemical looping reforming. The oxygen storage capacity of this redox material is about 0.82 mol O/kg. Chlorine promotes coking in the reduction step; the tailored window not only suppresses complete oxidation of methane but also enhances CO2 transformation in a fixed-bed reactor. At 980 °C, the carbon efficiency is as high as 99%, very close to the equilibrium value. In this case, no recycling or downstream separation is needed, making the proposed scheme more efficient. In addition, both the yield of CO and the productivity of syngas remain stable over 10 redox cycles. This exceptional redox performance makes the chloride-promoted SrFeO3-δ-based nanocomposites a highly competitive and cost-effective chemical looping material.

Nickel-magnesium mixed oxide catalyst for low temperature methane oxidation

A series of nickel-magnesium mixed oxides (NiMg) of varying molar ratios, Ni9Mg, Ni2Mg, NiMg, NiMg2 and NiMg9, were synthesized using the co-precipitation technique. These materials were prepared as possible lower cost alternatives to Pd-based methane oxidation catalysts. The NiMg catalysts were characterized by means of X-ray diffraction (XRD), photoelectron spectroscopy (XPS) and H2-temperature programmed reduction (H2-TPR). Their activity for complete methane oxidation was investigated using temperature programmed oxidation. Ni9Mg was found to be the most active catalyst of the series. Characterization results showed that most of the materials formed solid solutions of the NixMg1-xO type. The activity of the Ni9Mg was attributed to its highest surface area and highest oxygen mobility. It was further tested and aged in simulated natural gas engine exhaust that contained 10 vol% water vapor. The results were compared to a reference 1 wt% Pd/Al2O3 methane oxidation catalyst tested under the same conditions. Ni9Mg exhibited approximately 94% methane conversion after 40 h of aging which was higher than that of the Pd-based reference catalyst with methane conversion below 80% after only 16 h of aging. Ni9Mg is thus proposed as a promising alternative to PGM-based catalysts for complete methane oxidation.

Predicting the Catalytic Activity of Surface Oxidation Reactions by Ionization Energies

Developing a descriptor to understand the reactivity of a catalyst is critical in achieving the rational design of heterogeneous catalysts. Ideally, the descriptor should be simple, predictive, as ...

The interplay between the suprafacial and intrafacial mechanisms for complete methane oxidation on substituted LaCoO3 perovskite oxides

The rational design of efficient catalysts can be guided by identifying proper descriptors that can rationalize and predict the catalytic behavior. This study presents the feasibility of using the relative positions of the O p-band center and the B-site metal cation d-band center as an activity descriptor for methane oxidation over LaCoO3 perovskite oxides. Experiments on B-site-substituted LaFexCo1−xO3 perovskite oxides revealed that the relative positions of the two band centers governed the catalytic comportment. The suprafacial model-driven catalysts with negative relative position values exhibited high activity at low temperatures. Conversely, the intrafacial model-driven catalysts with positive relative position values showed superior activity at high temperatures. These findings were found to be effective for catalytic performance prediction on the A-site substituted La1−xSrxCoO3 perovskite oxides. This work hence showcases a promising principle to design highly active perovskite catalysts suitable for oxidation reactions.

Catalytic performance of Pd catalyst supported on Zr:Ce modified mesoporous silica for methane oxidation

Catalytic oxidation of methane is critical for exhaust after-treatment systems where cold-start emissions and lean combustion still pose serious challenges. In this work, the effect of support materials on the complete catalytic oxidation of methane over palladium is studied in dry and wet conditions. A series of metal oxides (CeO2, ZrO2, n-SiO2) and mixed metal oxides (Zr0.65Ce0.35O2, Zr0.33Ce0.33/n-Si0.33O2, Zr0.66Ce0.17/n-Si0.17O2) supported Pd catalysts were synthesized, characterized and tested for methane oxidation. Pd/n-SiO2 was found to be highly active catalyst with the lowest initial (T10%) and final (T100%) conversion temperatures as compared to Pd supported on CeO2 and ZrO2. Methane combustion over mixed oxide supports, prepared with different ratios of Zr:Ce:Si, showed improved catalytic performance. Catalyst with equal ratios of Zr:Ce:Si (Pd/Zr0.33Ce0.33/n-Si0.33O2) showed similar performance to that of Pd/n-SiO2 with approximately ~8 (±2) °C higher light-off temperature. Additionally, cyclic wet (8 vol% H2O) and dry reactions were performed to evaluate the hydrothermal stability and activity regeneration when switching from wet to dry conditions. Optimal addition of ZrO2 and CeO2 to n-SiO2 resulted in higher stability of palladium catalyst over wide ranges of temperatures (350–600 °C). Catalysts were characterized by various analytical techniques, including TEM, XRD, XRF, N2-BET, O2-TPD, and CO chemisorption. TEM results demonstrate that mixed oxide support stabilized Pd nanoparticles, and n-SiO2 encapsulation prevented sintering and deactivation. Activity tests and characterization results demonstrate overall superior catalytic properties of Pd supported on Zr0.33Ce0.33/n-Si0.33O2. This catalyst can be quite promising for practical applications due to its high activity for total methane oxidation and excellent thermal stability.

Experimental study on honeycomb reactor using methane via chemical looping cycle for solar syngas

The chemical looping process on honeycomb reactor for solar syngas is experimentally studied in this work, which is the key reaction of the liquid sunshine production process. The honeycomb reactor realizes the integration of oxygen carrier and reaction chamber. NiO is placed in the reactor as oxygen carrier and methane is introduced as fuel gas. The results show that, with the development of process, the major reaction in the reactor gradually changed from methane complete oxidation to methane partial oxidation. During the process, the methane conversion and outlet syngas concentration is affected by the methane flow and fractional oxidation. Under the optimal operating conditions, the methane conversion can be maintained more than 95% and the concentration of outlet syngas can be around 90%. Compared with non-honeycomb fixed bed reactor, the methane conversion increases by more than 20 percent point and the concentration of outlet syngas increases by about 10 percent point. In addition, oxygen carrier in honeycomb reactor shows excellent cyclic stability in 30 times experiments.