Catalysts For Oxidation Of Methane Research Articles

Nitrogen Vacancy-Rich C3Nx-Confined Fe–Cu Diatomic Catalysts for the Direct Selective Oxidation of Methane at Low Temperature

Nitrogen Vacancy-Rich C₃N_<i>x</i>-Confined Fe–Cu Diatomic Catalysts for the Direct Selective Oxidation of Methane at Low Temperature

Creating Atomically Iridium-Doped PdOx Nanoparticles for Efficient and Durable Methane Abatement.

The urgent environmental concern of methane abatement, attributed to its high global warming potential, necessitates the development of methane oxidation catalysts (MOC) with enhanced low-temperature activity and durability. Herein, an iridium-doped PdOx nanoparticle supported on silicalite-1 zeolite (PdIr/S-1) catalyst was synthesized and applied for methane catalytic combustion. Comprehensive characterizations confirmed the atomically dispersed nature of iridium on the surface of PdOx nanoparticles, creating an Ir4f-O-Pdcus microstructure. The atomically doped Ir transferred more electrons to adjacent oxygen atoms, modifying the electronic structure of PdOx and thus enhancing the redox ability of the PdIr/S-1 catalysts. This electronic modulation facilitated methane adsorption on the Pd site of Ir4f-O-Pdcus, reducing the energy barrier for C-H bond cleavage and thereby increasing the reaction rate for methane oxidation. Consequently, the optimized PdIr0.1/S-1 showed outstanding low-temperature activity for methane combustion (T50 = 276 °C) after aging and maintained long-term stability over 100 h under simulated exhaust conditions. Remarkably, the novel PdIr0.1/S-1 catalyst demonstrated significantly enhanced activity even after undergoing harsh hydrothermal aging at 750 °C for 16 h, significantly outperforming the conventional Pd/Al2O3 catalyst. This work provides valuable insights for designing efficient and durable MOC catalysts, addressing the critical issue of methane abatement.

A Density Functional Theory Analysis of Electrochemical Oxidation of Methane to Alcohol over High-Entropy Oxide (CoCrFeMnNi)3O4 Catalysts.

The direct conversion of methane into alcohol is a promising approach for achieving a low-carbon future, yet it remains a major challenge. In this study, we utilize density functional theory to explore the potential of the (CoCrFeMnNi)3O4 (CCFMNO) high entropy oxide (HEO) for electrochemical oxidation of methane to methanol and ethanol, alongside their competition with CO2 production. Our primary focus in this study is on thermodynamics, enabling a prompt analysis of the catalyst's potential, with the calculation of electrochemical barriers falling beyond our scope. Among all potential active sites within CCFMNO HEO, we identify Co as the most active site for methane activation when using carbonate ions as oxidants. This results in methanol production with a limiting potential of 1.4 VCHE, and ethanol and CO2 productions with a limiting potential of 1.2 VCHE. Additionally, our findings suggest that the occupied p-band center of O* on CCFMNO HEO is a potential descriptor for identifying the most active site within CCFMNO HEO. Overall, our results indicate that CCFMNO HEO holds promise as catalysts for methane oxidation to alcohols, employing carbonate ions as oxidants.

Catalytic performance of Pd catalyst supported on CeO2 or ZrO2 modified beta zeolite for methane oxidation

Two kinds of oxide-zeolite composite support, Ce-beta and Zr-beta were prepared by a simple wet impregnation method and adopted for the preparation of palladium-based catalysts for catalytic oxidation of methane. The Pd/6.8Zr-beta catalyst showed superior methane oxidation performance, achieving T50 and T90 of 417 °C and 451 °C, respectively, together with robust hydrothermal stability. Kinetic analysis has shown that incorporating Zr into the catalyst significantly enhanced its efficiency, nearly tripling the turnover frequency (TOF) for methane combustion compared to the Pd/beta catalyst. This enhanced performance was attributed to the dispersion of Zr on the zeolite surface, which not only promoted the formation of active PdO sites but also helped maintain the high Pd2+ content via facilitating the oxygen migration during the reaction, thus improving both the catalyst's activity and stability. In the Pd/8.6Ce-beta catalyst, doped CeO2 tended to aggregate in the zeolite's pores, adversely affecting the catalyst's efficiency. This aggregation promoted the formation of inactive Pd4+ species, a result of the enhanced metal-support interaction. This finding is critical for understanding the implications of dopant selection in the design of high-activity methane oxidation catalysts.

Redox-driven surface generation of highly active Pd/PdO interface boosting low-temperature methane combustion

The supported Pd catalyst has been a benchmark for methane elimination. However, the active structures have been long under debate. Here, by the aberration-corrected high angle annular dark field scanning transmission electron microscopy, operando X-ray absorption spectroscopy and quasi in situ X-ray photoelectron spectroscopy, we revealed the two-dimensional metallic Pd bumps on the PdO surface (litchi-like structure) generated by the redox atmosphere under the lean condition as a highly active structure of the Pd/Al2O3 catalyst. The substantially increased Pd/PdO interfaces boost the methane combustion activity higher than the similar catalysts reported previously, and remarkably enhance the reaction rate by 15.5 and 10.7 times that of pure PdO or metallic Pd counterpart under lean condition at 300 °C, respectively. Density-functional theory calculations confirm the synergistic C–C bond activation of methane on the Pd/PdO interfaces. Our work provides new insight into the traditional understanding of the chemical state and particle size effects of the industrial Pd catalysts for methane oxidation.

Compositing of Co3O4 with boron nitride to promote the catalytic performance for methane oxidation

Engineering a suitable catalyst support holds great importance to ensure a high catalytic performance in heterogeneous catalysis. Herein, an advanced boron nitride nanosheet (BNNS) supported Co3O4 composite (Co3O4/BNNS) was tailor-orchestrated to serve as an active and stable catalyst for methane oxidation. BNNS helps dispersion and binding small nano Co3O4 catalyst with augmented defective structures e.g., oxygen vacancies, lattice distortion etc. This facilitates the creation of more active oxygen species on Co3O4. Meanwhile, an interfacial electronic interaction was built to maintain Co3O4 in an electron-rich state. An excellent methane oxidation performance was guaranteed for Co3O4/BNNS with methane conversion rate of 58.3 mol·gCo3O4-1·h−1, 1.9 times that of Co3O4 catalyst at reaction temperature of 366 °C and weight hourly space velocity of 40,000 mL·g−1·h−1. Moreover, a strong metal and support interaction (SMSI) was in-situ formed, resulting a BOx over-layer confined Co3O4, which promises a robust hydrothermal stability for Co3O4/BNNS catalyst. This work exemplifies the pivotal role of BNNS as an excellent support to enhance the methane oxidation performance of Co3O4 catalyst.

Copper Phosphate Nanostructures as Catalysts for the Direct Methane Oxidation

Copper Phosphate Nanostructures as Catalysts for the Direct Methane Oxidation

Investigation of catalytic methane oxidation over Ag/Co2MOx (M = Co, Ni, Cu) catalysts with varying interfacial electron transfer

Atom-doped Co3O4 catalysts loaded with Ag were examined as cost-effective catalysts for methane oxidation. The synthesized Ag/Co2NiOx catalysts exhibited distinctive surface characteristics in contrast with Ag/Co3O4 and Ag/Co2CuOx catalysts prepared using a similar method. Characterization results unveiled that Ag/Co2NiOx featured a higher presence of active surface oxygen species, lattice defects, a larger surface area, and enhanced reducibility. A methane oxidation catalytic performance followed the sequence: Ag/Co2NiOx > Ag/Co3O4 > Ag/Co2CuOx. The investigation delved into methane degradation pathways on the surfaces of three catalysts, examining their behavior under both aerobic and anaerobic atmospheres through in-situ DRIFTS analysis. Furthermore, introducing Ag showed a marked positive effect on Co-Ni mixed oxide, inducing electron transfer and a more active electron system, whereas it exhibited an inverse impact within the surface of Co-Cu mixed oxide. This work provides innovative perspectives on the development of forthcoming environmental catalysts.

Unidentical Twins: Geometrically Similar but Chemically Distinct Metal-Free Sites in Boron Oxide for Methane Oxidation to HCHO, CO and CO2.

Metal-free boron-based catalysts such as boron oxide (B2O3) and boron nitride (h-BN) are promising catalysts for methane oxidation to HCHO and CO. The B2O3 catalyst contains various probable boron sites (B1 to B6), which may be responsible for methane oxidation. In this work, we utilized density functional theory to compare two relevant geometrically identical boron sites (B2 and B4) for their reactivities. The two sites are explored in-detail for the conversion of methane to formaldehyde (M2F), carbon monoxide and carbon dioxide. The B4 site activates the methane C-H bond easily as compared to the B2 site. In M2F conversion, the rate-determining step for the B2 site is the co-activation of dioxygen and methane, whereas over the B4 site, formaldehyde formation is the rate-determining step. The computationally-determined RDS for the B4 site coincides well with the reported experiments. It is further revealed that this site also prefers the formation of CO over CO2, which is in-line with the experiments in literature. It is also shown through orbital analysis that methanol formation does not occur during methane oxidation. We employed descriptors such as condensed Fukui functions and global electrophilicity index to chemically distinct these twin sites.

Integrated 1D Simulation of Aftertreatment System and Chemistry-Based Multizone RCCI Combustion for Optimal Performance with Methane Oxidation Catalyst

This paper presents a comprehensive investigation into the design of a methane oxidation catalyst aftertreatment system specifically tailored for the Wärtsilä W31DF natural gas engine which has been converted to a reactivity-controlled compression ignition NG/Diesel engine. A GT-Power model was coupled with a predictive physical base chemical kinetic multizone model (MZM) as a combustion object. In this MZM simulation, a set of 54 species and 269 reactions as chemical kinetic mechanism were used for modelling combustion and emissions. Aftertreatment simulations were conducted using a 1D air-path model in the same GT-Power model, integrated with a chemical kinetic model featuring 15 catalytic reactions, based on activation energy and species concentrations from combustion outputs. The latter offered detailed exhaust composition and exhaust thermodynamic data under specific operating conditions, effectively capturing the intricate interactions between the investigated aftertreatment system, combustion, and exhaust composition. Special emphasis was placed on the formation of intermediate hydrocarbons such as C2H4 and C2H6, despite their concentrations being lower than that of CH4. The analysis of catalytic conversion focused on key species, including H2O, CO2, CO, CH4, C2H4, and C2H6, examining their interactions. After consideration of thermal management and pressure drop, a practical choice of a 400 mm long catalyst with a density of 10 cells per cm2 was selected. Investigations of this catalyst’s specification revealed complete CO conversion and a minimum of 89% hydrocarbon conversion efficiency. Integrating the exhaust aftertreatment system into the air path resulted in a reduction in engine-indicated efficiency by up to 2.65% but did not affect in-cylinder combustion.

Highly productive V/Zn-SiO2 catalysts for the selective oxidation of methane

The production of formaldehyde on industrial scale requires huge amounts of energy due to the involvement of reforming processes in combination with the demand in the megaton scale. Hence, a direct route for the transformation of (bio)methane to formaldehyde would decrease costs and puts less pressure on the environment. Herein, we report on the use of zinc modified silicas as possible support materials for vanadium catalysts and the resulting consequences for the performance in the selective oxidation of methane to formaldehyde. After optimization of the Zn content and reaction conditions, a remarkably high space-time yield of 12.4 kgCH2O·kgcat−1·h−1 was achieved. As a result of the extensive characterization by means of UV–vis, Raman, XANES and NMR spectroscopy it was found that vanadium is in the vicinity of highly dispersed zinc atoms which promote the formation of active vanadium species as supposed by theoretical calculations. This work presents a further step of catalyst development towards direct industrial methane conversion which may help to overcome current limitations in the future.

Regulating Au coverage for the direct oxidation of methane to methanol

The direct oxidation of methane to methanol under mild conditions is challenging owing to its inadequate activity and low selectivity. A key objective is improving the selective oxidation of the first carbon-hydrogen bond of methane, while inhibiting the oxidation of the remaining carbon-hydrogen bonds to ensure high yield and selectivity of methanol. Here we design ultrathin PdxAuy nanosheets and revealed a volcano-type relationship between the binding strength of hydroxyl radical on the catalyst surface and catalytic performance using experimental and density functional theory results. Our investigations indicate a trade-off relationship between the reaction-triggering and reaction-conversion steps in the reaction process. The optimized Pd3Au1 nanosheets exhibits a methanol production rate of 147.8 millimoles per gram of Pd per hour, with a selectivity of 98% at 70 °C, representing one of the most efficient catalysts for the direct oxidation of methane to methanol.

Mesoporous Ceria and Ceria‐Praseodymia as High Surface Area Supports for Pd‐based Catalysts with Enhanced Methane Oxidation Activity

AbstractIn recent years, Pd/CeO2 materials have proven to be effective catalysts for the total oxidation of methane. In this work, three different synthesis routes were used to prepare high specific surface area supports, consisting of pure CeO2 and 10 at% Pr‐doped ceria (Ce90Pr10). Nano‐structured spheres were obtained with a microwave‐assisted synthesis, dumbbell‐like particles were produced through a urea‐based hydrothermal method, and ordered mesoporous oxides were prepared by using SBA‐15 as hard‐template. The six materials were then impregnated with 2 wt% Pd, calcined at 500 °C, and comprehensively characterized. All the samples retained their high surface area after impregnation (75–110 m2 g−1), allowing a good dispersion of palladium. No significant structural or morphological differences were observed upon Pr doping, but a higher Pd oxidation state was induced by Pr‐doped supports. However, all Pd/CeO2 and Pd/Ce90Pr10 catalysts exhibited similar activity for dry methane oxidation below 500 °C, regardless of the synthesis technique and of the Pr presence: they all achieved almost complete CH4 oxidation at 400 °C, showing a really remarkable improvement with respect to analogous low surface area supports. A promoting role of Pr was instead noticed in wet conditions, thanks to its ability to counteract water‐induced deactivation phenomena.

Research progress in single-atom catalysts for the selective oxidation of methane

Research progress in single-atom catalysts for the selective oxidation of methane

Cold plasma activated Ni0/Ni2+ interface catalysts for efficient electrocatalytic methane oxidation to low-carbon alcohols

To stabilize Ni0/Ni2+ during the CH4OR process, herein, we have successfully developed a general oxidation strategy for the direct synthesis of transition metal oxides by O2 cold plasma treatment of Ni0, including NiO, to generate a Ni0/Ni2+-on-Cu interface.

Stabilizing Pd–cerium oxide–aluminum oxide catalysts for methane oxidation by reduction pretreatments

Pd–CeO2 based catalysts are state-of-the-art for methane oxidation, but deactivate due to Pd nanoparticle growth at high temperature.

Tailored Platinum Group Metal/Spinel Oxide Catalysts for Dynamically Enhanced Methane Oxidation.

A combined experimental and molecular modeling study identifies a family of spinel oxides that in combination with PGM (platinum group metals) provide enhanced methane oxidation activity. With a reduction in greenhouse gas (GHG) emissions urgently needed, there is renewed interest in the use of natural gas vehicles (NGVs) and engines (NGEs) for transportation, commerce, and industrial applications. NGVs and NGEs emit less CO2 than their petroleum-derived counterparts but may emit uncombusted methane, an even more potent GHG. For stoichiometric engines, methane oxidation catalysts containing PGM and spinel oxide in layered architectures offer increased methane oxidation activity and lower light-off temperatures (T50). The reducible spinel oxide has direct and indirect roles that are effectively described by the bulk oxygen vacancy formation energy (Evac). We apply density functional theory (DFT) to identify several earth-abundant, cobalt-rich spinel oxides with favorable Evac, shown to correlate with dynamic oxygen storage capacity (DOSC) and CO and H2 oxidation activity. We experimentally rank-order the DFT-identified spinel oxides in combination with Pt+Pd for their methane oxidation activity measurements, under both time-invariant and modulated feed conditions. We show good agreement between the activity and the DFT-computed reducibility of the spinel oxide. The findings suggest spinel reducibility is a key factor in achieving enhanced low-temperature methane conversion, enabled through a balance of methane activation on the PGM sites and subsequent oxidation of the intermediates and byproducts on spinel oxides. In agreement with its computationally predicted Evac, NiCo2O4 was confirmed to have the highest DOSC and lowest T50 among the tested spinel samples.

Understanding the reversible and irreversible deactivation of methane oxidation catalysts

Catalytic oxidation is a promising technology for controlling methane emissions from natural gas engines, but fast and severe deactivation prevents implementation. We investigated a commercial Pd on alumina oxidation catalyst under realistic conditions and identified two deactivation phenomena: fast, reversible inhibition and slow, irreversible loss of active sites. The loss of active sites occurs only during methane conversion, fortunately a brief oxygen cut-off is enough to regenerate the catalyst. Both types of deactivation increase the reduction temperature of PdO. From 36 kinetic experiments we propose a simple kinetic model encompassing both types of deactivation. The inhibition is confirmed to be due to water coverage of the active sites whereas dispersion of Pd on the surface is the cause of the irreversible loss of active sites. The new insight shows a pathway toward designing more durable catalysts for complete methane oxidation.

Palladium Catalysts for Methane Oxidation: Old Materials, New Challenges.

ConspectusMethane complete oxidation is an important reaction that is part of the general scheme used for removing pollutants contained in emissions from internal combustion engines and, more generally, combustion processes. It has also recently attracted interest as an option for the removal of atmospheric methane in the context of negative emission technologies. Methane, a powerful greenhouse gas, can be converted to carbon dioxide and water via its complete oxidation. Despite burning methane being facile because the combustion sustains its complete oxidation after ignition, methane strong C-H bonds require a catalyst to perform the oxidation at low temperatures and in the absence of a flame so as to avoid the formation of nitrogen oxides, such as those produced in flares. This process allows methane removal to be obtained under conditions that usually lead to higher emissions, such as under cold start conditions in the case of internal combustion engines. Among several options that include homo- and heterogeneous catalysts, supported palladium-based catalysts are the most active heterogeneous systems for this reaction. Finely divided palladium can activate C-H bonds at temperatures as low as 150 °C, although complete conversion is usually not reached until 400-500 °C in practical applications. Major goals are to achieve catalytic methane oxidation at as low as possible temperature and to utilize this expensive metal more efficiently.Compared to any other transition metal, palladium and its oxides are orders of magnitude more reactive for methane oxidation in the absence of water. During the last few decades, much research has been devoted to unveiling the origin of the high activity of supported palladium catalysts, their active phase, the effect of support, promoters, and defects, and the effect of reaction conditions with the goal of further improving their reactivity. There is an overall agreement in trends, yet there are noticeable differences in some details of the catalytic performance of palladium, including the active phase under reaction conditions and the reasons for catalyst deactivation and poisoning. In this Account we summarize our work in this space using well-defined catalysts, especially model palladium surfaces and those prepared using colloidal nanocrystals as precursors, and spectroscopic tools to unveil important details about the chemistry of supported palladium catalysts. We describe advanced techniques aimed at elucidating the role of several parameters in the performance of palladium catalysts for methane oxidation as well as in engineering catalysts through advancing fundamental understanding and synthesis methods. We report the state of research on active phases and sites, then move to the role of supports and promoters, and finally discuss stability in catalytic performance and the role of water in the palladium active phase. Overall, we want to emphasize the importance of a fundamental understanding in designing and realizing active and stable palladium-based catalysts for methane oxidation as an example for a variety of energy and environmental applications of nanomaterials in catalysis.

Transition-Metal-Promoted Cu-SSZ-13 Catalysts for Continuous Selective Oxidation of Methane to Methanol Using Molecular Oxygen

Transition-Metal-Promoted Cu-SSZ-13 Catalysts for Continuous Selective Oxidation of Methane to Methanol Using Molecular Oxygen