Dissociation Of CH Research Articles

Maximizing H2 Production from a Combination of Catalytic Partial Oxidation of CH4 and Water Gas Shift Reaction

A single-bed and dual-bed catalyst system was studied to maximize H2 production from the combination of partial oxidation of CH4 and water gas shift reaction. In addition, the different types of catalysts, including Ni, Cu, Ni-Re, and Cu-Re supported on gadolinium-doped ceria (GDC) were investigated under different operating conditions of temperature (400–650 °C). Over Ni-based catalysts, methane can easily dissociate on a Ni surface to give hydrogen and carbon species. Then, carbon species react with lattice oxygen of ceria-based material to form CO. The addition of Re to Ni/GDC enhances CH4 dissociation on the Ni surface and increases oxygen storage capacity in the catalyst, thus promoting carbon elimination. In addition, the results showed that a dual-bed catalyst system exhibited catalytic activity better than a single-bed catalyst system. The dual-bed catalyst system, by the combination of 1%Re4%Ni/GDC as a partial oxidation catalyst and 1%Re4%Cu/GDC as a water gas shift catalyst, provided the highest CH4 conversion and H2 yield. An addition of Re onto Ni/GDC and Cu/GDC caused an increase in catalytic performance because Re addition could improve the catalyst reducibility and increase metal surface area, as more of their surface active sites are exposed to reactants.

First comparison of the catalytic stability of cobalt metal, nitride and phosphide catalysts for dry reforming of methane

For the first time, the catalytic stability of cobalt metal, nitride, and phosphide phases supported on MgO was compared for dry reforming of methane. The initial CH4 conversions for Co/MgO, Co4N/MgO, and Co2P/MgO catalysts were 88.1, 87.7 and 86.0%, respectively. However, after 15 h of testing, these values gradually decreased to 69.9, 75.0 and 79.4%, respectively. The Co2P catalyst demonstrated superior stability compared to the Co and Co4N catalysts. The enhanced stability of the Co2P/MgO catalyst was attributed to its smaller particle size and a lower ratio of CH4 and CO2 dissociation rates.

Photocatalytic Oxidative Coupling of Methane to Ethane Using CO2 as a Soft Oxidant over the Au/TiO2-Vo Nanosheets.

Photocatalytic oxidative coupling of methane (OCM) offers an appealing route for converting greenhouse gas into valuable C2 hydrocarbons. However, O2, as the most commonly used oxidant, tends to result in inevitable overoxidation and waste of methane feedstock. Herein, we first report a photocatalytic OCM using CO2 as a soft oxidant for C2H6 production under mild conditions, where an efficient photocatalyst with unique interface sites is designed and constructed to facilitate CO2 adsorption and activation, while concurrently boosting CH4 dissociation. As a prototype, the Au quantum dots anchored on oxygen-deficient TiO2 nanosheets are fabricated, where the Au-Vo-Ti interface sites for CO2 adsorption and activation are collectively disclosed by in situ Kelvin probe force microscopy, quasi in situ X-ray photoelectron spectroscopy and theoretical calculations. Compared with single metal site, the Au-Vo-Ti interface sites exhibit the lower CO2 adsorption energy and decrease the energy barrier of the *CO2 hydrogenation step from 1.05 to 0.77 eV via Au-C and Ti-O dual-site bonding. The adsorbed CO2 on the photocatalyst reduces the energy barrier of *CH4 dissociation to *CH3 from 2.13 to 1.59 eV, contributing to CH4 oxidation. Additionally, in situ Fourier-transform infrared spectroscopy unveils the Au site facilitates ethane production by engaging in *CH3-Au interaction and accelerating CH3-CH3 coupling. Thus, the photocatalyst demonstrates a high C2H6 evolution rate of 2.60 mmol g-1 h-1 for OCM using CO2 as the soft oxidant, surpassing most of previously reported photocatalysts regardless of OCM and nonoxidative coupling of methane. This work highlights the importance of soft oxidants for improving oxidation reaction efficiency and provides atomic scale insight into the design of photocatalysts for CH4 conversion.

Photocatalytic Oxidative Coupling of Methane to Ethane Using CO2 as a Soft Oxidant Over the Au/TiO2‐Vo Nanosheets

Herein, we first report a photocatalytic OCM using CO2 as a soft oxidant for C2H6 production under mild conditions, where an efficient photocatalyst with unique interface sites is constructed to facilitate CO2 adsorption and activation, while concurrently boosting CH4 dissociation. As a prototype, the Au quantum dots anchored on oxygen‐deficient TiO2 nanosheets are fabricated, where the Au‐Vo‐Ti interface sites for CO2 adsorption and activation are collectively disclosed by in situ Kelvin probe force microscopy, quasi in situ X‐ray photoelectron spectroscopy and theoretical calculations. Compared with single metal site, the Au‐Vo‐Ti interface sites exhibit the lower CO2 adsorption energy and decrease the energy barrier of the *CO2 hydrogenation step from 1.05 to 0.77 eV via Au‐C and Ti‐O dual‐site bonding. The adsorbed CO2 reduces the energy barrier of *CH4 dissociation to *CH3 from 2.13 to 1.59 eV, contributing to CH4 oxidation. Additionally, in situ Fourier‐transform infrared spectroscopy unveils the Au site facilitates ethane production by engaging in *CH3‐Au interaction and accelerating CH3‐CH3 coupling. Thus, the photocatalyst demonstrates a high C2H6 evolution rate of 2.60 mmol g‐1 h‐1 for OCM using CO2 as the soft oxidant, surpassing most of previously reported photocatalysts regardless of OCM and nonoxidative coupling of methane.

Mg bulk and surface modification on Ni/Y2Ti2O7 catalyst for dry reforming of methane

Dry reforming of methane (DRM) can simultaneously convert two greenhouse gases, CH4 and CO2, into high value-added synthetic gas, which can effectively alleviate the energy crisis and optimize the human ecological environment. In this work, the effect of Mg addition method on the activity of the Y2Ti2O7 pyrochlore supported Ni catalysts was investigated in DRM. The H2-TPR and XPS results showed that Mg modification enhanced the interaction between Ni and Y2Ti2O7 pyrochlore support. Thus, much smaller Ni grains with better thermal stability could be achieved on the Mg doped Ni/Y2Ti2O7 catalyst, as evidenced by the XRD, H2-TPD and TEM results. CO2-assistant CH4-TPSR demonstrated that Mg surface modification can facilitate the reaction between the activated CO2∗ and the H∗ produced by CH4 dissociation. Mg incorporation increased the basic site of the Ni/Y2Ti2O7 catalyst, as evidenced by CO2-TPD-MS results, which was conducive to the adsorption and activation of CO2 to promote the removal of coke deposition. Consequently, Ni/Y1·5Mg0·5Ti2O7 and Ni–MgO/Y2Ti2O7 catalysts exhibit higher stability and more potent coke resistance than the unmodified Ni/Y2Ti2O7 sample. It is concluded that higher Ni0 dispersion and more mobile active oxygen species are the main reasons for the improvement of activity and coke resistance of the Ni/Y2Ti2O7 catalysts. In addition, in situ DRIFTS results confirmed that CO2 activation of all catalysts followed the formate intermediate species path.

Au, Ag, Pb, Pt −doped MoTe2 monolayer as a novel sensor for dissolved gases (CH4, and C2H2): A first-principles study

In this study, C2H2 and CH4 gas molecules adsorption on intrinsic MoTe2 and Au, Ag, Pb, Pt doped MoTe2 by density functional theory (DFT). The adsorption energy, bond length, charge transfer, PDOS and work function are calculated, it can be proved that Ag-MoTe2 have excellent C2H2 and CH4 adsorption performance than Au-MoTe2, Pb-MoTe2 and Pt-MoTe2. However, C2H2 gas molecule can be chemisorbed onto the doped Ag in the modified MoTe2 with a high adsorption energy of 0.923 eV, capturing approximately 0.65 e from the sensing material. Ag-MoTe2 has the better C2H2 and CH4 adsorption performance than Au-MoTe2, Pb-MoTe2 and Pt-MoTe2, as evidenced by the strong overlap of the s, p, d orbitals and the significant reduction of the energy gap from the PDOS. Therefore, suggesting that the Ag-MoTe2 could have potential application in the capture and dissociation of C2H2 and CH4.

A kinetic study of nonthermal plasma pyrolysis of methane: Insights into hydrogen and carbon material production

Nonthermal plasma-assisted methane pyrolysis has emerged as a promising approach for hydrogen production under mild conditions while simultaneously yielding valuable carbon materials. Herein, we develop a plasma chemical kinetic model to elucidate the underlying reaction mechanisms involved in methane pyrolysis to hydrogen and solid carbon within a gliding arc (GA) reactor. A zero-dimensional (0D) chemical kinetics model was developed to simulate the plasma chemistry during the GA-based methane pyrolysis process, incorporating reactions involving electrons, excited species, ions, and heavy species. The model accurately predicted methane conversion and product selectivity in agreement with the experimental data. A strong correlation between hydrogen production and methane conversion was observed, primarily driven by the reaction CH4 + H → CH3 + H2, contributing 44.2% to hydrogen formation and 37.7% to methane depletion. Electron impact collisions with hydrocarbons play a secondary role, accounting for 31.1% of H2 formation. This work provides a detailed investigation into the mechanism of solid carbon formation in GA-assisted methane pyrolysis. Most of the solid carbon originates from the electron impact dissociation of C2H2 through reactions e + C2H2 → e + C2 + H2/2H and subsequent C2 condensation. C2 radicals are highlighted as the major contributors to solid carbon formation, accounting for 95.0% of the total carbon yield, which might be due to the relatively low C–H dissociation energy in C2H2. This kinetic study offers a comprehensive understanding of the mechanisms behind H2 and solid carbon formation during GA-assisted methane pyrolysis.

Insights into Photothermocatalytic Dry Reforming of Methane on Ru/La‐Al2O3 using Carbonate Species and Reactive Oxygen Species to Enhance the Fuel Production Rates and Completely Prevent Coking

AbstractPhotothermocatalytic dry reforming of methane (DRM) offers a promising strategy for converting solar energy into fuel. However, the high light intensity required for high fuel production rates and thermodynamically more favorable coking side reactions limit this strategy. Herein, a nanocomposite of La‐doped Al2O3 supporting Ru nanoparticles (NPs) (Ru/La‐Al2O3) is synthesized. At relatively low light intensity (80.2 kW m−2), Ru/La‐Al2O3 obtains high production rates of CO and H2 per gram of Ru (rRu, CO and rRu, H2, 8410.19 and 7181.94 mmol gRu−1 min−1) with light‐to‐fuel efficiency (η, 26.6%), and completely prohibits coking. In striking contrast, the reference catalyst without La doping (Ru/Al2O3) exhibits lower rRu, CO, rRu, H2, η and produces large amounts of coke. The improved photothermocatalytic performance stems from the fact that reactive oxygen species and carbonate species are involved in the oxidation of carbon species (rate‐determining steps of DRM) through two different reaction pathways, which significantly increases catalytic activity and prevents the carbon species from polymerizing into coke. Additionally, light not only enhances the DRM on Ru NPs and the oxidation reaction between carbonate species and carbon species but also promotes the dissociation of CH4 and desorption of H2, which improves the catalytic activity and product selectivity of Ru/La‐Al2O3.

Enhanced low-temperature methane oxidation over Pd supported Mn-doped NiO catalyst

This study introduces a novel catalyst system comprising Pd nanoparticles loaded onto Mn-doped NiO for the efficient oxidation of methane (CH4) at low temperatures. The loading of Pd nanoparticles onto the Mn-doped support has yielded a catalyst with exceptional activity and stability, as evidenced by the lowest T50 temperature of 276 °C and a CH4 conversion reaching 97% at 325 °C. The catalyst demonstrates optimized reaction kinetics with the lowest activation energy of 69.2 kJ mol–1. The catalyst's superior performance is attributed to the synergistic effects of the Pd/Mn-NiO composite, which include a higher Pd2+/Pd4+ ratio, increased adsorptive oxygen concentration (Oads/Ototal), and a reduced Ni3+/Ni2+ ratio. These characteristics collectively enhance the catalytic activity for CH4 oxidation. The Mars-van Krevelen mechanism underpins the oxidation process, with Pd2+ identified as the principal active site for CH4 adsorption and dissociation. Diffuse reflectance infrared Fourier transform spectroscopy coupled with mass spectrometry elucidates the pathway of surface reactive oxygen species in the formation of key intermediates, such as formates, and underscores the accelerated decomposition of carbonate facilitated by the Pd modification on the Mn-NiO surface. The findings signify a significant advancement in the development of catalysts for environmental and energy-related applications, particularly in the mitigation of CH4 emissions.

Enhanced syngas production through dry reforming of methane with Ni/CeZrO2 catalyst: Kinetic parameter investigation and CO2-rich feed simulation

Natuna's natural gas reserve, which contains 70 %–v CO2 and 30 %–v CH4, opens a prospective method for producing syngas through the dry reforming of methane (DRM). This study used the equation and determination of kinetic parameters in a fixed-bed reactor to develop the operating conditions for the DRM process. The catalyst used was 10 %Ni/CeZrO2 and followed the Langmuir-Hinshelwood mechanism, with CH4 dissociation (activation of C–H bonds) on the Ni catalyst as the rate-determining step. According to the results, the simulation and experimental data have error values of ≤ 5 % and RMSE < 0.046. This indicates that the equation and kinetic parameters used in the simulation are valid for reactor modeling. Steady-state modeling was then conducted using a 1D quasihomogeneous model. The feed composition of CO2:CH4 = 70:30 (Natuna gas field composition) has optimized results with temperature 700 °C, CH4 conversion at 92 %, CO2 conversion at 28 %, and H2/CO ratio 1.42, and carbon formation at 7.1 mgC/gcat. This study also found that a higher CO2:CH4 feed ratio could reduce carbon formation during DRM.

Enhanced coking resistance of alumina-supported cobalt nitride catalyst via doping of phosphorus for dry reforming of methane

A novel P-doped Co4N/γ-Al2O3 catalyst was firstly designed for dry reforming of methane (DRM). It was found that the use of P doping Co4N/γ-Al2O3 can enhance its coking resistance, which might be due to a decrease in CH4 dissociation ability and an increase in CO2 dissociation ability, as well as the increase of cobalt species capable of interacting with alumina.

Formation and evolution of nanobubbles in CH4-H2O-Alcohol system: Insight into the effect of alcohol chain length from molecular dynamics simulations

Nanobubbles (NBs) which are gas filled cavities of nanometre dimensions present in liquids attracted increasing attention in the recent years due to their application in various fields such as chemistry, biology, medicine etc. An important aspect of NB research is the study of effect of additives on formation and evolution of these bubbles. The present study examined by applying molecular dynamics simulations, the formation and evolution of methane NBs in the CH4-H2O-Alcohol system, which is known to form during alcohol induced dissociation of CH4 hydrates in the natural gas extraction process. The effect of alcohol type and concentration on NB formation and evolution was examined through simulations of CH4-H2O-CH3OH, CH4-H2O-C2H5OH and CH4-H2O-nC3H7OH systems. The study revealed that increase in both concentration and the alkyl chain length of alcohols promoted NB formation. Alcohol molecules are found to enhance NB nucleation through accumulation near the NB-liquid interface resulting in a decrease in the surface tension (γ) at the interface. These effects become more pronounced as the alkyl chain length increases which explains the enhanced NB formation in systems containing nC3H7OH and C2H5OH compared to those containing CH3OH. The mechanism of formation and evolution of NBs is found to significantly depend on the type of alcohol present. NBs are found to nucleate at multiple locations in the systems containing nC3H7OH and C2H5OH which eventually coalesce to form a single large stable NB. In the presence of NBs which vary significantly in size, bubble growth was also found to occur through Ostwald ripening which involves transfer of CH4 from smaller NB to the larger one. In contrast, in the CH4-H2O-CH3OH system, primarily a single NB nucleated which grew in size through absorption of CH4 molecules dissolved in the liquid, rather than through coalescence or Ostwald ripening. The observed influence of alcohol type on the process of NB evolution is explained by examining the influence of alkyl chain length on γ and diffusivity of CH4 molecules. Due to the role of NBs on methane hydrate regeneration from the hydrate melt, we examined the influence of NB in the CH4-H2O-Alcohol system on the organization of water molecules (HSWs) present in the hydration shell of dissolved CH4. The value of F4 order parameter of HSWs and the number of hydrogen bonded water rings in the hydration shell of CH4 were analysed. The value of F4 order parameter indicate that the hydrophobic alkyl chain of alcohol induced hydrate like arrangement of HSWs, which is more pronounced in the case of alcohol with longer alkyl chain. However, alcohol molecules are also found to dislodge HSWs around CH4 resulting in a decrease in the number of water rings around dissolved CH4 which is not conducive to hydrate formation. These observations are consistent with the reported dual effect of alcohol on hydrate formation with alcohol promoting hydrate formation at low concentrations and inhibiting at high concentrations.

Direct methane utilization through benzene dehydroalkylation catalyzed by Co2+ sites in ZSM-5 intersections

Cobalt cations exchanged in ZSM-5 are active for the direct dehydromethylation of benzene with CH4. While toluene is the primary product, an alternate reaction pathway leads also to the formation of biphenyl and phenyltoluene. This not only diminishes the selectivity but also contributes to the deactivation of the catalyst. Temperature-programmed surface reactions show that benzene adsorbs strongly on the exchanged Co2+ cations, essentially blocking the sites for alkylation below 400 °C. At temperatures exceeding 400 °C, the partial desorption of benzene enables its reaction with CH4, leading to the formation of toluene. The formation of biphenyl is kinetically hindered, and its onset is only observed at temperatures above 450 °C. When CH4 is allowed to chemisorb on Co2+ sites prior to exposure to benzene, the formation of toluene is detected at temperatures below 400 °C. By infrared spectroscopy of benzene adsorption and UV–Vis spectroscopic characterization, we identified the existence of intersections in ZSM-5 where three H+ are in proximity. The ion exchange of a zeolite lattice Al3+ pair in such positions leads to the formation of a Co2+ site near a free Brønsted acid site. We observed a correlation between the concentration of this type of Co2+ sites and the catalytic activity of Co-ZSM-5 in benzene alkylation with CH4. This is further supported by the catalytic tests of Co-ZSM-5 materials with specifically a larger proportion of Co sites in sinusoidal channels, as a result of acidic conditions during ion exchange. Based on this, we propose that toluene formation takes place via heterolytic dissociation of CH4 on a Co2+ site at intersections followed by reaction with benzene strongly interacting with an adjacent BAS.

Growth of thick amorphous carbon films on alumina for improved tribological properties

Alumina, as a pivotal ceramic material extensively utilized in contemporary applications, the surface modification and enhancement of tribological properties are crucial. In this study, reactive magnetron sputtering was employed to deposit Ti, Si co-doped hydrogen-free (TiSi/a-C), and hydrogenated amorphous carbon films (TiSi/a-C:H) with a thickness exceeding 7 μm onto the surface of alumina ceramic substrates. Utilizing the design of the film structure, the difficulty of film-substrate adhesion was resolved by controlling the deposition time to influence the growth rate of the film, thereby enabling the reliable fabrication of thick films. The adhesion of the TiSi/a-C film exhibits the highest value, with an Lc1 value of 36.7 N. The hardness of the TiSi/a-C:H reaches a maximum of 15.2 GPa, and the hardness is closely correlated with the reaction gas utilized during its depositional process. The wear rate of amorphous carbon film decreases by 34 times compared to alumina substrate. During the dissociation of CH4 at a high hydrogen-to-carbon ratio, more hydrogen atoms are involved in the chemical reaction. The introduction of hydrogen elevates the H/E and sp3/sp2 ratios within the film, thereby favoring the generation of low-friction surfaces and refining the tribological performance of alumina ceramics.

Utilization of High Entropy Alloy (Co–Cu–Fe–Mn–Ni) and Support (CeO2) Interaction for CO2 Conversion into Syngas

AbstractHere metal support interaction (MSI) is demonstrated in a high entropy alloy (HEA: CoCuFeMnNi) supported CeO2. The HEA behaves as an active dry reforming catalyst only when it is supported over CeO2 oxide, clearly demonstrating MSI. Based on spectroscopic and microscopic observations, it is envisaged that the substitutional effect is the one that causes the lattice oxygen activation, an important active species during DRM reaction. Transient studies are performed to understand the surface chemistry of the interaction between methane and CO2 in the presence of a catalyst, which results in a methane decomposition first to generate hydrogen and carbon and followed by a CO2 reaction to give CO using deposited carbon. The experimental observations are further proven by mechanistic study with DFT calculations which show a major contribution of H‐assisted CO2 dissociation and pre‐H2 releasing carbon depositing CH4 dissociation and a minor contribution of pre‐CO releasing H2 formation. This MSI moves the d‐band center of the Co atoms of CoCuFeMnNi/CeO2 to the closest position of the Fermi level as compared to the isolated nanoparticles. This study can be taken as a proof of concept to demonstrate that MSI can be generated in the HEA/CeO2 catalysts for a generic heterogeneous gas phase reaction.

Dry reforming of methane over Ni5 nanocluster supported on double perovskite surface − A DFT study

The opportunity for efficient hydrogen extraction from natural gas through perovskite-supported Ni5 nanocluster has been investigated using first-principles calculations. The reaction dynamics of dry reforming of methane (DRM) has been studied, and all the elementary steps are assessed to locate the transition states. The obtained results demonstrate a high affinity of CH4 and CO2 towards the supported nanocluster as predicted by reasonably large adsorption energies. Chromium and Molybdenum on the perovskite surface play an essential role, in conjunction with Nickel, in methane CH bond activation. Ni2Cr and Ni2Mo are identified as the sites where methane reaction begins and ends, or vice versa. The dissociation of CO2 is also facilitated by the nanocluster, with the rate-limiting step in the two pathways being CH4 dissociation. The study suggests that decorating the anode with Ni-nanoclusters can effectively promote hydrogen extraction from hydrocarbon fuels in solid-oxide fuel cells.

Computational modeling of CH4 and CO2 adsorption on monolayer graphenylene: Implications for optoelectronic properties and hydrogen production

Graphenylene (GP) is a two–dimensional carbon allotrope with a hexagonal lattice structure containing periodic pores. The unique arrangement of GP offers potential applications in electronics, optoelectronics, energy storage, and gas separation. Specifically, its advantageous electronic and optical properties, make it a promising candidate for hydrogen production and advanced electronic devices. In this study, we employ a computational chemistry–based modeling approach to investigate the adsorption mechanisms of CH4 and CO2 on monolayer GP, with a specific focus on their effects on optical adsorption and electrical transport properties at room temperature. To simulate the adsorption dynamics as closely as possible to experimental conditions, we utilize the self–consistent charge tight–binding density functional theory (SCC–DFTB). Through semi–classical molecular dynamics (MD) simulations, we observe the formation of H2 molecules from the dissociation of CH4 and the formation of CO + O species from carbon dioxide molecules. This provides insights into the adsorption and dispersion mechanisms of CH4 and CO2 on GP. Furthermore, we explore the impact of molecular adsorption on optical absorption properties. Our results demonstrate that CH4 and CH2 affects drastically the optical adsorption of GP, while CO2 does not significantly affect the optical properties of the two–dimensional material. To analyze electron transport, we employ the open–boundary non–equilibrium Green's function method. By studying the conductivity of GP and graphene under voltage bias up to 300 mV, we gain valuable insights into the electrical transport properties of GP under optical absorption conditions. The findings from our computational modeling approach might contribute to a deeper understanding of the potential applications of GP in hydrogen production and advanced electronic devices.

Insight into the Dynamic Nature of the Pt-CeO2 Interface in Dry Reforming of Methane.

Single-atom catalysts (SACs) are attractive in one-carbon (C1) chemistry because of their high atom efficiency. However, it is a great challenge for understanding the dynamic roles of SACs under operating conditions. Here, isolated Pt atoms trapped on defective CeO2 surface are investigated by experiments, especially operando techniques, which offers basic understanding of the nature and dynamic evolution of the Pt-CeO2 interface in dry reforming of methane (DRM). The Pt-Olattice configuration is highly active for CH4 dissociation at the expense of the Olattice atoms, which in turn promotes the H-assisted dissociation of CO2. The transformation of Pt atoms between positive and metallic states is driven by the DRM reaction, which is essential for rendering highly efficient catalysis. The dynamic evolution of Pt atoms favors to eliminate the reactive intermediates, such as carbonates and formates. The dynamic nature of the Pt-CeO2 interface in the DRM reaction shows a similar picture to the Yin and Yang transformation in ancient Chinese Tai Ji wisdom.

Nanoscale structural transformations in LaFeO3 oxygen carriers for enhanced reactivity in chemical looping combustion

The push for decarbonization necessitates the development of clean and efficient energy conversion technologies. Among these, the chemical looping platform has emerged as a promising approach, albeit with challenges such as high operating temperatures. This necessitates the design of high-performance chemical looping carriers. In this study, we explore the potential of nanosized oxygen carriers, noted for their high reactivity, for the chemical looping combustion of methane (CH4). LaFeO3, a widely investigated perovskite-type mixed metal oxide known for its effectiveness as an oxygen carrier, is examined. Nanosized LaFeO3 is synthesized by embedding LaFeO3 onto mesoporous silica matrix (LFO-SBA15), and its reactivity is benchmarked against bulk-scale LaFeO3 supported on SiO2 (LFO-SiO2). The nanosized carrier demonstrates a ∼ 1000% improvement in reactivity compared to the bulk carrier. This enhancement is attributed to the formation of a highly reactive cubic phase of LaFeO3 at the nanoscale, in contrast to the orthorhombic phase present in bulk-scale LaFeO3. This finding is supported by density functional theory calculations, which reveal that the cubic phase of LaFeO3 facilitates the formation of oxygen vacancies and lowers the energy barrier for CH4 dissociation. This work highlights the potential of nanosized LaFeO3 for the chemical looping combustion of CH4, providing valuable guidance for the rational design and development of high-performance chemical looping carriers.

Synergistic effect of Ru single atom and nanoparticle on photothermal methane dry reforming reaction

Dry reforming of methane is indeed an attractive pathway for converting greenhouse gases into syngas. However, owing to the strong-endothermic nature of this reaction, high reaction temperature is commonly involved which causes high energy consumption, catalytic deactivation by sintering of active species, and/or coke formation. Herein, a RuSA+NP/TiO2 composite catalyst consisting of uniformly dispersed Ru nanoparticles (RuNP) and Ru single atoms (RuSA) on TiO2 sheet is fabricated. This catalyst demonstrates remarkable syngas generation rates of 1380 mmol g-1h−1 for CO and 933 mmol g-1h−1 for H2 at 500 °C under light irradiation. It is concluded that the presence of Ru single atoms modulates the electronic structure of catalyst, reducing energy barrier in the DRM process. Additionally, the electron-deficient Ru nanoparticles provide effective sites for CH4 dissociation. Light irradiation is found to reduce the apparent activation energy (Ea) of DRM and enhance durability of catalyst by retarding coking process.