Partial Oxidation Of Methane Research Articles

Methane partial oxidation under periodic reaction conditions on Pt/Al2O3

Exploring the impact of periodic reaction conditions on hydrogen production in methane partial oxidation on Pt/Al2O3 catalyst.

Catalytic partial oxidation of methane over oxide-ion-conductive lanthanum silicate apatites.

A lanthanum silicate La9.33Si6O26 (LSO) crystallizes in an apatite-type structure and has been known as a promising oxide-ion conductor. Here, we report the activity of LSO for catalytic partial oxidation of methane (CPOX) to synthesis gas. The LSO catalyst demonstrated relatively high catalytic activity from 500 to 700 °C, with CH4 conversion reaching 22.1% at 700 °C while retaining moderate CO and H2 selectivities of 20-60%. Notably, LSO exhibited higher CPOX activity than non-apatite-type La2SiO5 despite their similar specific surface areas. The higher CPOX activity of LSO is likely attributed to its structural superiority involving mobile oxide ions in the crystal structure. The reaction kinetic study showed that the reaction orders for methane and oxygen in the CPOX reaction over the LSO catalyst were 0.69-0.73 and 0.08-0.21, respectively. Furthermore, the small contribution of adsorbed O species generated from gas-phase O2 molecules indicated that the lattice oxygen may be involved in the reaction mechanism. The kinetic isotope effect (KIE) study using a CD4 suggested that C-H bond breaking is the rate-determining step of CPOX over LSO.

An alternative catalytic cycle for selective methane oxidation to methanol with Cu clusters in zeolites.

The partial oxidation of methane to methanol catalyzed by Cu-exchanged zeolites involves at present a three-step procedure that requires changing reaction conditions along the catalytic cycle. In this work we present an alternative catalytic cycle for selective methane conversion to methanol using as active species small Cu5 clusters supported on CHA zeolite. Periodic DFT calculations show that molecular O2 is easily activated on Cu5 clusters producing bi-coordinated O atoms able to dissociate homolytically a CH bond from CH4 and to react with the radical-like non-adsorbed methyl intermediate formed producing methanol, while competitive overoxidation to CO2 is energetically disfavored. The present mechanistic study opens a new avenue to design catalytic materials based on their ability to stabilize radical species.

Comparison of Various Hydrogen Production Technologies from Natural Gas

The article provides an overview of the present condition and immediate future potential in the realm of hydrogen energy technologies. The paper delves into the most renowned approaches for generating hydrogen from natural gas: a) Steam-Methane Reforming (SMR); b) Partial Oxidation (POX); and c) Autothermal Reforming (ATR). Nevertheless, employing these technologies on an industrial scale requires substantial R&D efforts, often on the scale of experimental ventures. The article also examines the global energy landscape, energy sources, the historical discovery of hydrogen, and the various production methods. It addresses the intricacies associated with hydrogen production technologies, with a focal point on the technology of extracting hydrogen from natural gas. Through a comparison of the benefits and drawbacks of each method and, as explicated in the concluding section of the study, several significant insights have been derived. Among the three technologies, SMR, the steam conversion process, boasts the highest hydrogen production rate. Catalytic partial oxidation of methane exhibits the swiftest reaction rate; however, it necessitates the use of pure oxygen, which poses safety concerns. The process of methane auto-thermal reforming requires no external heat and is characterized by minimal energy consumption. Steam reforming of methane emerges as an ecologically sound and scientifically promising avenue, offering high effectiveness. Nevertheless, its deployment on an industrial scale remains to be fully refined. Developing cost-effective catalysts and continuous reactor systems for methane steam conversion technology is essential to rendering it economically viable. In conclusion, there is substantial potential for advancements at hydrogen energy technologies, particularly through refining and integrating these different production methods.

(Invited) Thermo-Photo Catalysis for Energy and Environment

Thermal heterogeneous catalysis based on kinetic energy as driving force was discovered in early 1800s, and photocatalysis using potential energy as driving force was introduced in 1911. Furthermore, catalysis driven by thermal energy generated from photo energy, which is actually thermal catalysis, also has a long research history. However, only in the past decade, we developed the thermo-photo catalysis, in which the synergy of thermal and photo energies drives a catalytic process. This new type of catalysis has been explored for various processes, including (1) water splitting to hydrogen, (2) dry reforming of methane, (3) steam reforming of methane, (4) partial oxidation of methane to value-added organic compounds, and (5) hydrogenation of CO and CO2 to hydrocarbons. These findings will be discussed in this presentation with emphasis on process design and catalyst development.

Methane Oxidation Coupled to Selenate Reduction in a Membrane Bioreactor under Oxygen-Limiting Conditions.

Microbial methane oxidation coupled to a selenate reduction process has been proposed as a promising solution to treat contaminated water, yet the underlying microbial mechanisms are still unclear. In this study, a novel methane-based membrane bioreactor system integrating hollow fiber membranes for efficient gas delivery and ultrafiltration membranes for biomass retention was established to successfully enrich abundant suspended cultures able to perform methane-dependent selenate reduction under oxygen-limiting conditions. The microbial metabolic mechanisms were then systematically investigated through a combination of short-term batch tests, DNA-based stable isotope probing (SIP) microcosm incubation, and high-throughput sequencing analyses of 16S rRNA gene and functional genes (pmoA and narG). We confirmed that the methane-supported selenate reduction process was accomplished by a microbial consortia consisting of type-II aerobic methanotrophs and several heterotrophic selenate reducers. The mass balance and validation tests on possible intermediates suggested that methane was partially oxidized into acetate under oxygen-limiting conditions, which was consumed as a carbon source for selenate-reducing bacteria. High-throughput 16S rRNA gene sequencing, DNA-SIP incubation with 13CH4, and subsequent functional gene (pmoA and narG) sequencing results collectively proved that Methylocystis actively executed partial methane oxidation and Acidovorax and Denitratisoma were dominant selenate-reducing bacteria, thus forming a syntrophic partnership to drive selenate reduction. The findings not only advance our understanding of methane oxidation coupled to selenate reduction under oxygen-limiting conditions but also offer useful information on developing methane-based biotechnology for bioremediation of selenate-contaminated water.

Surface modification of dual-phase ceramic membrane reactor for coupling catalytic CO2 conversion with partial oxidation of methane

The oxygen transport membrane (OTM) reactor is a particularly promising process for CO2 conversion and utilization through coupling the thermochemical decomposition of CO2 with the partial oxidation of methane (POM). However, its low CO2 decomposition efficiency and poor operational stability in corrosive atmospheres are the main challenges for practical application. In this work, the porous layers of LaMO3-δ (M = Fe, Co, Ni) and Ce0.8Zr0.2O2-δ (CZ), with different functions separately, were coated on both sides of the Ce0.9Pr0.1O2-δ-Pr0.6Sr0.4Fe0.9Al0.1O3-δ (CP-PSFA) dual-phase membrane. The presence of oxygen vacancy and transition ions M with the valence of +2/+3 in the LaMO3-δ is conducive to catalyzing CO2 conversion. The LaCoO3-δ porous layer exhibits the best oxygen permeability and CO2 conversion, and the performance of POM is greatly enhanced by the in situ Ni-doped CZ porous layer. After a long-term test at 925 °C, the oxygen permeation flux of the LaCoO3-δ/CP-PSFA/CZ-Ni maintains at 0.96 mL cm−2 min−1, the conversion rate of CH4 and CO2 maintains at 23 % and 45 % respectively, and the syngas yield reaches 6.3 mL cm−2 min−1. The sandwich-like OTM reactor with functional porous layers has broad research prospects in the CO2 conversion and utilization field.

Recent Advances in the Conversion of Methane to Syngas and Chemicals via Photocatalysis

AbstractAs a primary constituent of natural gas and shale gas, direct conversion of methane has attracted significant attention due to its potential to reduce energy consumption and CO2 emissions. Compared with thermal catalysis, photocatalysis has the capacity to transcend thermodynamic constraint and enable the conversion of sustainable solar energy into chemical energy under mild reaction condition, which contributes to optimize the utilization of methane. In this review, we undertake a comparative analysis of various strategies for photocatalytic methane conversion to syngas and chemicals, including photocatalytic reforming of methane, photocatalytic partial oxidation of methane and photocatalytic coupling of methane. The distinct reaction systems with corresponding catalysts and underlying mechanisms are expounded in detail to foster a profound comprehension of solar‐driven methane conversion. Finally, the challenges and prospectives in photocatalytic methane conversion are discussed.

Mesoporous configuration effects on the physicochemical features of hierarchical ZSM-5 supported cobalt oxide as catalysts in methane partial oxidation

Hierarchical porous system has become a prevalent method to overcome the diffusion limitation of conventional zeolites. Two types of mesopores characterized as intra-crystalline (mesopores in the zeolite pore wall) and inter-crystalline mesopores (meso-sized voids between nano-zeolite aggregates) could be formed in the synthesis of hierarchical zeolites. In an attempt to investigate the influence of mesopores structure on the physicochemical properties of hierarchical ZSM-5, specifically cobalt oxide impregnated ZSM-5 zeolite samples with intra- and inter-crystalline mesopores were synthesized through two different synthesis strategies. Analysis of the physicochemical properties of the as-modified hierarchical ZSM-5 catalysts were carried out using SEM, TEM, XPS, and H2-TPR which showed distinct features given by the two mesopores configurations. Co-oxide impregnated on ZSM-5 with inter-crystalline mesopores was dominated by Co(II) species, while Co-oxide/ZSM-5 showed a fair amount of Co(III) and Co(II). Furthermore, analysis of the catalytic activity was conducted using methane partial oxidation as a model reaction. With a variation in reaction time, various types of oxygenated products, i.e. methanol, formaldehyde, formic acid, and a small trace of carbon dioxide were observed. Catalytic results suggested that the Co-oxide/ZSM-5 material with inter-crystalline mesopores configuration is more active for the methane partial oxidation reaction compared to the Co-oxide/ZSM-5 with intracrystalline mesopores. This was confirmed by the formation of formaldehyde rather than methanol as the major product in the brief reaction time of 30 min.

Nitrogen-doped carbon particles with distinctive ethylene adsorption selectivity for efficient ethylene/acetylene separation

Separation of ethylene/acetylene (C2H4/C2H2) mixtures with C2H4-selective adsorbents is of economics and energy efficiency to purify crude C2H2 from methane pyrolysis or partial oxidation (POX) process. Herein, a systematic study was carried out to investigate the structural properties and C2H4/C2H2 separation performance of novel nitrogen-doped carbon particles, as well as the mechanism of preferentially adsorbing C2H4 over C2H2 through the Grand Canonical Monte Carlo (GCMC) simulations. The nitrogen-doped carbon particles derived from coconut shell and metronidazole present regular particle sizes centering at 710 μm and excellent crushing strength of 89 N. Well-developed microporosity with pore dimension mainly ranging in 0.54–0.68 nm, and fine-tuning surface chemistry with abundant nitrogen-containing species (pyridinic N, pyrrolic N and graphitic N) were observed in nitrogen-doped carbon particles. Interestingly, nitrogen-doped carbon particles exhibit preferential adsorption of C2H4 over C2H2, and the IAST-predicted selectivity of 1.5-N-CP reaches as high as 5.2 for C2H4/C2H2 (1/9) mixture at 1.0 bar and 25 °C. Remarkably, the separation stability and recyclability with complete separation for C2H4/C2H2 were well maintained during cyclic dynamic breakthrough experiments. GCMC simulation results demonstrate that the graphitic N with great binding energy (−22.61 kJ/mol for C2H4 and −19.87 kJ/mol for C2H2) favors the adsorption of both C2H4 and C2H2. The pore dimension ranging 0.54–0.68 nm, together with pyridinic N and pyrrolic N species significantly enhance the separation of C2H4/C2H2 through the large difference in adsorption interactions between C2H4 and C2H2. Therefore, the nitrogen-doped carbon particles have the excellent application accessibility in purifying C2H2 from C2H4/C2H2 mixture.

Photodriven Methane Conversion on Transition Metal Oxide Catalyst: Recent Progress and Prospects.

Methane as the main component in natural gas is a promising chemical raw material for synthesizing value-added chemicals, but its harsh chemical conversion process often causes severe energy and environment concerns. Photocatalysis provides an attractive path to active and convert methane into various products under mild conditions with clean and sustainable solar energy, although many challenges remain at present. In this review, recent advances in photocatalytic methane conversion are systematically summarized. As the basis of methane conversion, the activation of methane is first elucidated from the structural basis and activation path of methane molecules. The study is committed to categorizing and elucidating the research progress and the laws of the intricate methane conversion reactions according to the target products, including photocatalytic methane partial oxidation, reforming, coupling, combustion, and functionalization. Advanced photocatalytic reactor designs are also designed to enrich the options and reliability of photocatalytic methane conversion performance evaluation. The challenges and prospects of photocatalytic methane conversion are also discussed, which in turn offers guidelines for methane-conversion-related photocatalyst exploration, reaction mechanism investigation, and advanced photoreactor design.

Partial Methane Oxidation to Methanol on Ru-Porphyrins - on the Role of Non-Innocent Ligands and Spin Crossover.

The partial oxidation reaction of CH4 led to the formation of CH3 OH in the presence of Ru-porphyrin oxo complexes (denoted as POR, POR-O and POR-OH where in the case of the last two, oxygen atom and the OH group were attached to the active site, respectively), in which Ru was present on different oxidation states. The simulations were performed based on Density Functional Theory (DFT) with extended geometric and electronic structure analyses of each reaction step. Moreover, the reaction pathways were investigated in different spin states. The Spin Crossover (SCO) phenomenon was found to play an important role in the kinetics of the reaction in the presence of POR and POR-O. Harmonic Oscillator Model of Aromaticity (HOMA) index was applied for different spin states to estimate the aromaticity changes of the pyrrole rings in the Ru-porphyrin complexes. In order to characterize the nature of bonding, the Natural Bond Orbitals (NBO) analysis including the Wiberg Bond Index (WBI) and Natural Population Analysis (NPA) was carried out. Finally, the Non-Covalent Interactions (NCI) index was employed to gain insight into interactions between the components of the reaction. It was found that the non-covalent interactions cannot be neglected in the studied reaction paths.

Electron-Delocalization-Stabilized Photoelectrocatalytic Coupling of Methane by NiO-Polyoxometalate Sub-1 nm Heterostructures.

The oxidative coupling of methane to C2 oxygenates merits great scientific and technological potential yet remains a challenge due to its inferior selectivity. Subnanomaterials (SNMs) with "p-n-p-n"-type heteroconstructions feature enhanced external field coupling properties and tunable electronic structures, serving as promising catalysts for the selective partial oxidation of methane. Here we develop NiO-polyoxometalate (POM) subnanocoils with a thickness of 1.8 nm, showing excellent catalytic activity toward photoelectrochemical coupling of methane into a C2 product under mild conditions (1 bar, 25 °C) with a notable productivity (up to 4.48 mmol gcat-1 h-1) and a high selectivity (>99%). Under photoelectrochemical coupling, C-H bonds can be activated by NiO, and the resulted *COOH intermediates are stabilized by the delocalized electrons in POM clusters. The contiguous active sites of NiO and POM at the molecular level allow the in situ coupling of *COOH into oxalate. This work points out an economic way for the oxidation of methane under mild conditions and may enlighten the design of functional SNMs from fundamental standpoints.

Mechanism of the noncatalytic oxidation of soot using in situ transmission electron microscopy

Soot generation is a major challenge in industries. The elimination of soot is particularly crucial to reduce pollutant emissions and boost carbon conversion. The mechanisms for soot oxidation are complex, with quantified models obtained under in situ conditions still missing. We prepare soot samples via noncatalytic partial oxidation of methane. Various oxidation models are established based on the results of in situ transmission electron microscopy experiments. A quantified maturity parameter is proposed and used to categorize the soot particles according to the nanostructure at various maturity levels, which in turn lead to different oxidation mechanisms. To tackle the challenges in the kinetic analysis of soot aggregates, a simplification model is proposed and soot oxidation rates are quantified. In addition, a special core-shell separation model is revealed through in situ analysis and kinetic studies. In this study, we obtain important quantified models for soot oxidation under in situ conditions.

Calcium-looping coupling methane partial oxidation and dry reforming process for integrated CO2 capture and conversion: Regulable H2/CO molar ratio and excellent coke deposition-resistant

Calcium-looping coupling methane partial oxidation and dry reforming process for integrated CO2 capture and conversion: Regulable H2/CO molar ratio and excellent coke deposition-resistant

Methane against Methanol: The Tortoise and the Hare of the Oxidation Race.

The selective partial oxidation of methane to methanol has been a major chemistry challenge over the past several decades. The reason for this is that the weaker C-H bond of the desired product (methanol) is readily activated by the same catalyst used to activate the stronger C-H bond of methane. Quantum chemical calculations reveal how hydrogen-bonding interactions with the catalyst as well as other electronic and geometric effects slow the unwanted methanol oxidation reaction. Thus, the oxidation of methane (the tortoise in Aesop's fable) becomes faster than methanol (Aesop's hare), increasing the selectivity toward the desired product. Activation barriers are calculated for two different mechanisms (2+2 and radical), and reaction rates for the oxidation of the two molecules are obtained using semiclassical instanton theory to include tunneling effects for the proton transfers. The tunneling effects are shown to accelerate all reactions substantially but do not dramatically affect the selectivity.

Recent trends, current challenges and future prospects for syngas-free methane partial oxidation

Recent trends, current challenges and future prospects for syngas-free methane partial oxidation

A-site vacancy induced electronic engineering of perovskite for synergistic modulation of redox activity and magnetocaloric effect

Realizing “Power to Syngas” by electrifying chemical reactors via induction heating is one of the key enabling technologies to decarbonize the chemical industry. Nevertheless, developing catalysts for the induction heating process that can simultaneously serve as magnetic susceptors under high-temperature conditions remains challenging. Herein, we formulate a A-site vacancy induced electronic engineering strategy and, accordingly, synthesize a series of LaFe0.5Al0.5O3 perovskite catalysts with different amounts of La vacancies (VLa) (LFAO, 1.5 M-LFAO, and 3 M-LFAO). In this way, we tune both the redox activity and the magnetocaloric effect (MCE) of perovskite and, for the first time, achieve induction heating methane partial oxidation coupled with CO2 splitting for syngas production. Compared with the reported catalysts, the 3 M-LFAO had not only superior syngas and CO yields (101.84 L·kg cat−1/54.96 L kg cat−1) but also a great MCE (875 °C). Spectroscopic investigations and DFT calculations rationalize these observations and demonstrate that the VLa cause a unique Fe4+–O2-–Fe3+ configuration in perovskite, accounting for an upshift of Fe 3d and O 2p band centers and therefore enhancing redox activity and MCE. This work deepens the understanding of the relationship between catalysis and MCE and unlocks the novel guidance to design induction heating chemical processes.

Solution combustion derived nanoalloys: Robust and efficient catalyst systems for partial oxidation of methane

Noble metals like Pt, Pd, Ir, Os, and Ru showed excellent performance for catalytic conversion of methane to syngas by catalytic partial oxidation of methane (CPOM), nevertheless, monometallic catalysts always suffer either from partial deactivation due to coke oxidation or hotspot formation inside the reactor tube wall. Therefore, a series of bimetallic catalysts of Pd–Pt, Pt–Ru, and Pd–Ru supported on ceria have been prepared by a unique facile solution combustion method (SCS) to stabilize the metallic particles as nanoalloys and understand the intermetallic synergy to improve both catalyst conversion and lifetime. All the catalysts were characterized by XRD, BET, TPR, XPS, HRTEM, and RAMAN to delineate the structure-function relationship. DFT study has been carried out to explain the H2/CO selectivity discrepancy between bimetallic and monometallic catalysts. XPS and Raman studies confirm a strong interaction between active metals and support to facilitate the synergistic effect during the reaction. The strong interaction and higher dispersion of nano-particles of active metals could enhance active sites for the efficient conversion of methane to syngas. HRTEM proves the nanoalloy formation of these bimetallic catalysts, which improved the reaction thermodynamics of the newly prepared catalyst systems.

The role of TiO2:SnO2 heterojunction for partial oxidation of methane by photoelectrocatalytic process at room temperature

Partial Oxidation of Methane into hydrocarbons using photoelectrochemical routes is attractive from a sustainability point of view owing to the possibility of using renewable energy (i.e., solar illumination) to activate this stable molecule. However, the process demands the development of novel catalysts that can promote methane activation and oxidation in a controlled manner to increase energy conversion efficiency. Herein, we demonstrated that semiconductor heterostructures improved charge separation compared to the individual materials alone. A more effortless transfer between bands favors the separation of the electron-hole (e−/h+) pairs generated by the photoelectrocatalytic system and prevents them from recombining. This process produces reactive oxygens, essential to driving methane oxidation conversion of the C–H bond cleavage. TiO2:SnO2 semiconductor heterojunction catalysts in film shape were investigated for methane oxidation via a photoelectrocatalytic process. The methane oxidation reactions were carried out in an inflow and sealed electrochemical system for 1 h. Liquid-state nuclear magnetic resonance revealed methanol and acetic acid as the main liquid products, where the TiO2:SnO2 heterojunction exhibited better performance with values of 30 and 8 µmol.cm−2.h−1, respectively. Compared to their materials alone, the superior performance of the TiO2:SnO2 heterojunction is attributed to the formation of heterostructure type II that enables a more effortless transfer between bands, facilitating the separation of the generated e−/h+ pairs under UV-Vis irradiation. The outcomes achieved here will motivate further studies for developing semiconductor heterojunction structure catalysts in photoelectrocatalysis to partially oxidize methane into valuable chemicals.