Methane Selectivity Research Articles

A promising CO2 methanation catalyst system based on modified halloysites as supports

Abstract Earth’s climate is warming due to anthropogenic emissions of greenhouse gases, especially carbon dioxide (CO2). Different reactions are allocated to mitigate the CO2 in the atmosphere. However, CO2 methanation is a pivotal research hotspot due to its ability to produce methane at low operating temperatures (200–400 °C). Halloysite nanotubes (HNTs)-based catalysts have attracted significant attention in various catalytic applications. However, Halloysite is rarely reported for thermal CO2 methanation. The selected halloysite clay was modified first using the 3-Aminopropyl triethoxy silane (NH2) as coupling agent, the resulting materials (HNTs), and then doped with Ni at different weight concentrations (5%, 10%, 20%, 40%, 50%). materials can offer high surface area and porous structure, which can improve metal dispersion. The prepared Ni/HNTs catalysts were characterized using various techniques, such as XRD, XPS, SEM, and TEM, which confirmed the existence of nanotubes and porous structures. The propensity of the prepared Ni/HNTs were evaluated to catalyse the CO2 methanation reactions at a temperature range of 250 to 500 ̊C. The catalyst containing 20 wt.% of Ni (20Ni/HNTs) showed the highest CO2 conversion at all reaction temperatures and the highest selectivity of methane at 450 °C (82%). This study paves the way for the large utilization of the HNTs as a strong support for different metals used in thermal catalytic reactions, not limited to the CO2 methanation. Graphical Abstract

Superhydrophobic and Self-Healing Porous Organic Macrocycle Crystals for Methane Purification under Humid Conditions.

Purifying methane from natural gas using adsorbents not only requires the adsorbents to possess excellent separation performance but also to overcome additional daunting challenges such as humidity interference and durability requirements for sustainable use. Herein, porous organic crystals of a new macrocycle (CaC9) with superhydrophobic and self-healing features are prepared and employed for the purification of methane (>99.99% purity) from ternary methane/ethane/propane mixtures under 97% relative humidity. The high selectivity for methane and water-resistance are attributed to the unique chemical structure of CaC9, possessing an intrinsic 4.2 Å pore along with a pore environment modified with saturated alkyl chains. Besides, CaC9 crystals exhibit a self-healing capacity to realize in situ reconstruction of porosity within 15 min. The transformation of CaC9 crystals from a nonporous state to a porous state can be easily achieved upon treatment with n-hexane vapor, thereby presenting a novel solution to enhance the sustainable separation processes of porous materials. This work introduces a novel molecular-level porous adsorbent for natural gas separation, providing a valuable impetus for designing novel adsorbents with unexpected functions.

Methane oxidation to ethanol by a molecular junction photocatalyst.

Methane, the major component of natural and shale gas, is a significant carbon source for chemical synthesis. The direct partial oxidation of methane to liquid oxygenates under mild conditions1-3 is an attractive pathway, but the molecule's inertness makes it challenging to achieve simultaneously high conversion and high selectivity towards a single target product. This difficulty is amplified when aiming for more valuable products that require C-C coupling4,5. While selective partial methane oxidation processes1-3,6-9 have thus typically generated C1 oxygenates6,7, recent reports have documented photocatalytic methane conversion to the C2 oxygenate ethanol with low conversions but good to high selectivities4,5,8-12. Here, we show that the intramolecular junction photocatalyst CTF-1 with alternating benzene and triazine motifs7,13 drives methane coupling and oxidation to ethanol with a high selectivity and much improved conversion. The heterojunction architecture not only enables efficient and long-lived separation of charges after their generation, but also preferential adsorption of H2O and O2 to the triazine and benzene units, respectively. This dual-site feature separates C-C coupling to form ethane intermediates from the sites where •OH radicals are formed and thereby avoids overoxidation. When loaded with Pt to boost performance further, the molecular heterojunction photocatalyst generates ethanol in a packed-bed flow reactor with improved conversion that results in an apparent quantum efficiency of 9.4%. We anticipate that further developing the "intramolecular junction" approach will deliver efficient and selective catalysts for C-C coupling, pertaining, but not limited, to methane conversion to C2+ chemicals.

Passivating Lattice Oxygen in ZnO Nanocrystals to Reduce its Interactions with the Key Intermediates for a Selective Photocatalytic Methane Oxidation to Methanol

An inevitable overoxidation process is considered as one of the most challenging problems in the direct conversion of methane (CH4) to methanol (CH3OH), which is limited by the uncontrollable cracking of key intermediates. Herein, we have successfully constructed a photocatalyst, the Fe‐doped ZnO hollow polyhedron (Fe/ZnOHP), for the highly selective photoconversion of CH4 to CH3OH under mild conditions. In‐situ experiments and density functional theory calculations confirmed that the introduction of Fe was able to decrease the energy level of the O 2p orbital, which passivated the activity of lattice oxygen in ZnO nanocrystals. This passivation effect greatly weakened the interaction between *CH3 and lattice oxygen, thus facilitating the conversion of *CH3O to *CH3 intermediate rather than the direct desorption of *CH3O. As a result, Fe/ZnOHP exhibited excellent CH3OH generation rate (ca. 1009 μmol gcat−1 h‐1) and selectivity (ca. 96%) in the photocatalytic conversion of CH4 at room temperature and low pressure.

Passivating Lattice Oxygen in ZnO Nanocrystals to Reduce its Interactions with the Key Intermediates for a Selective Photocatalytic Methane Oxidation to Methanol.

Aninevitable overoxidation process is considered as one of the most challenging problems in the direct conversion of methane (CH4) to methanol (CH3OH), which is limited by the uncontrollable cracking of key intermediates. Herein, we have successfully constructed a photocatalyst, the Fe-doped ZnO hollow polyhedron (Fe/ZnOHP), for the highly selective photoconversion of CH4 to CH3OH under mild conditions.In-situ experiments and density functional theory calculations confirmed that the introduction of Fe was able to decrease the energy level of the O 2p orbital, which passivated the activity of lattice oxygen in ZnO nanocrystals. This passivation effect greatly weakened the interaction between *CH3 and lattice oxygen, thus facilitating the conversion of *CH3O to *CH3 intermediate rather than the direct desorption of *CH3O. As a result, Fe/ZnOHP exhibited excellent CH3OH generation rate (ca. 1009 μmol gcat-1 h-1) and selectivity (ca. 96%) in the photocatalytic conversion of CH4 at room temperature and low pressure.

Copper catalyzed selective methane oxidation to acetic acid using O2.

The direct transformation of methane into C2 oxygenates such as acetic acid selectively using molecular oxygen (O2) is a significant challenge due to the chemical inertness of methane, the difficulty of methane C-H bond activation/C-C bond coupling and the thermodynamically favored over-oxidation. In this study, we have successfully developed a porous aluminium metal-organic framework (MOF)-supported single-site mono-copper(ii) hydroxyl catalyst [MIL-53(Al)-Cu(OH)], which is efficient in directly oxidizing methane to acetic acid in water at 175 °C with a remarkable selectivity using only O2. This heterogeneous catalyst achieved an exceptional acetic acid productivity of 11 796 mmolCH3CO2H molCu -1 h-1 in 9.3% methane conversion with 95% selectivity in the liquid phase and can be reused at least 6 times. Our experiments, along with computational studies and spectroscopic analyses, suggest a catalytic cycle involving the formation of a methyl radical (˙CH3). The confinement of Cu-active sites within the porous MIL-53(Al) MOF facilitates C-C bond coupling, resulting in the efficient formation of acetic acid with excellent selectivity due to the internal mass transfer limitations. This work advances the development of efficient and chemoselective earth-abundant metal catalysts using MOFs for the direct transformation of methane into value-added products under mild and eco-friendly conditions.

Mn‐Doped CuO Nanostructure Films Based Gas Sensor for High Sensitive and Selective Formaldehyde Detection at a Room Temperature

AbstractThe development of an efficient gas‐sensing materials is crucial for applications in healthcare, industry, environmental monitoring, and agriculture. In this study, Mn‐doped CuO thin films were synthesized and evaluated for their gas‐sensing properties. The fabricated films exhibited a monoclinic CuO structure with (002) and (111) orientations, and their morphology reveals a uniform, spherical‐like crystalline distribution. Mn doping adjusts the optical bandgap from 2.11 eV to 2.03 eV. Compared with pure, 3% Mn‐doped CuO‐based sensor demonstrated a high response value of 82% to 20 ppm formaldehyde at room temperature with swift response and recovery times of 9 and 36 s, respectively. The high sensitivity and stability of these sensors make Mn‐doped CuO films a promising candidate for practical gas detection applications.

Polyethylene hydrogenolysis by dilute RuPt alloy to achieve H2-pressure-independent low methane selectivity

Chemical recycling of plastic waste could reduce its environmental impact and create a more sustainable society. Hydrogenolysis is a viable method for polyolefin valorization but typically requires high hydrogen pressures to minimize methane production. Here, we circumvent this stringent requirement using dilute RuPt alloy to suppress the undesired terminal C–C scission under hydrogen-lean conditions. Spectroscopic studies reveal that PE adsorption takes place on both Ru and Pt sites, yet the C–C bond cleavage proceeds faster on Ru site, which helps avoid successive terminal scission of the in situ-generated reactive intermediates due to the lack of a neighboring Ru site. Different from previous research, this method of suppressing methane generation is independent of H2 pressure, and PE can be converted to fuels and waxes/lubricant base oils with only <3.2% methane even under ambient H2 pressure. This advantage would allow the integration of distributed, low-pressure hydrogen sources into the upstream of PE hydrogenolysis and provide a feasible solution to decentralized plastic upcycling.

Effect of interlayer anions in layered double hydroxides on the photothermocatalytic CO2 methanation of derived Ni–Al2O3 catalysts

The concentration of carbon dioxide (CO2) in the atmosphere is progressively increasing due to industrial development, leading to environmental concerns such as the greenhouse effect. Consequently, it is crucial to decrease dependence on the fossil fuels and mitigate the CO2 emissions. Photothermocatalysis technology facilitates the conversion of light energy into heat energy on the surface of catalysts, thereby driving chemical reactions. This catalytic approach effectively harnesses ample solar energy, consequently reducing non-renewable energy consumption. Solar-driven CO2 methanation is an important route to simultaneously mitigate excessive carbon emissions and produce fuels. Layered double hydroxides (LDH) can be reduced at high temperature in a reductive atmosphere of a hydrogen/argon (H2/Ar) mixture to prepare metal-loaded oxide (MO) catalysts, which are widely used in CO2 hydrogenation reactions as excellent photothermal catalysts. However, there is limited study on how the interlayer anion type of LDH affects the activity of CO2 methanation. Herein, a series of LDH precursors, intercalated with various anions, were synthesized using a co-precipitation method. The LDH precursors were reduced in a H2/Ar atmosphere to acquire a group of nickel (Ni) loaded on alumina (Al2O3) catalysts, referred to as NiAl-x-MO (x ​= ​CO3, NO3, Cl, and SO4, which represents carbonate, nitrate, chloride, and sulfate anions, respectively). Energy dispersive spectrometer (EDS) elemental mapping and X-ray photoelectron spectroscopy (XPS) results revealed the presence of nitrogen (N), chlorine (Cl), and sulfur (S) species on the surfaces of NiAl–NO3-MO, NiAl–Cl-MO, and NiAl–SO4-MO catalysts, respectively. Photothermocatalytic tests were conducted on the catalysts to assess the potential influence of the residual species on CO2 methanation. Among them, the NiAl–CO3-MO catalyst demonstrated a CO2 conversion of 50.1 ​%, methane (CH4) selectivity of 99.9 ​%, along with a CH4 production rate of 94.4 ​mmol ​g−1 ​h−1. The performance of the NiAl–NO3-MO catalyst was found to be comparable to that of the NiAl–CO3-MO catalyst. In contrast, the CO2 methanation activity of the NiAl–Cl-MO and NiAl–SO4-MO catalysts were negligible. CO2 temperature programmed desorption (CO2-TPD) analysis demonstrated that the presence of N, Cl, and S species had a negligible effect on the adsorption of CO2. H2 temperature programmed desorption (H2-TPD) and density functional theory (DFT) results suggested that the strong coordination bond between residual Cl or S species and metallic Ni impeded the absorption and activation of H2, which was responsible for the low CO2 conversion. Hence, the significant role of the interlayer anion in LDH should be preferentially considered when designing LDH-derived catalysts, especially the Ni-based catalysts for hydrogenation reactions.

Selective light-driven methane oxidation to ethanol

Methane (CH4) photocatalytic upgrading to value-added chemicals, especially C2 products, is significant yet challenging due to sluggish energy/mass transfer and insufficient chemical driven-force in single photochemical process. Herein, we realize solar-driven CH4 oxidation to ethanol (C2H5OH) on crystalline carbon nitride (CCN) modified with Cu9S5 and Cu single atoms (Cu9S5/Cu-CCN). The integration of photothermal effect and photocatalysis overcomes CH4-to-C2H5OH conversion bottlenecks, with Cu9S5 as a hotspot to convert solar-energy to heat. In-situ characterizations demonstrate that Cu single atoms play as electron acceptor for O2 reduction to ·OOH/ · OH, while Cu9S5 acts as hole acceptor and site for CH4 adsorption, C − H activation, and C − C coupling. Theoretical calculations demonstrate that Cu9S5/Cu-CCN reduces C − C coupling energy barrier by stabilizing ·CH3 and ·CH2O. Impressively, C2H5OH productivity reaches 549.7 μmol g–1 h–1, with selectivity of 94.8% and apparent quantum efficiency of 0.9% (420 nm). This work provides a sustainable avenue for CH4 conversion to value-added chemcials.

Co-Electrolysis of H2O and CO2 at Intermediate Temperatures with Protonic Ceramic Cell Reactors

Co-electrolysis of H2O and CO2 in protonic ceramic membrane reactors (PCMRs) is considered a promising approach to convert CO2 into value-added products, but also a way to in-situ store green hydrogen from intermediate temperature (400-600 oC) H2O electrolysis in the form of chemicals or fuels.1 In such PCMRs, steam is split (oxygen evolution reaction-OER) over the anodic electrode (positrode) while the protons created are subsequently transported through the ceramic electrolyte to the cathodic electrode (negatrode) where they react with CO2. This system exhibits significant challenges regarding the choice of the electrocatalysts’ components at both sides of the ceramic membrane. For instance, the highly oxidizing environment of the anodic steam electrolysis rules out the state-of-art Ni-based ceramometallic (cermet) electrodes, whereas the CO2 electrocatalyst environment should be appropriately tuned to achieve high selectivity to the desired products.2 Herein, we have synthesized, characterized and evaluated the performance of promising mixed ionic-(protons, oxygen ions) electronic conducting oxides (perovskites and misfit layered oxides) for use as anodes for OER. The as synthesized electrode systems were firstly characterized with several physicochemical methods (XRD, TPR, TGA, XPS) and then deposited on Ni-cermet supported half-cells for the electrocatalytic studies (EIS, LSV, CP). The results have shown that several candidate materials could allow > 80% faradaic efficiencies, while a significant number of protons reacted with CO2 towards primarily CO and less towards CH4. Interestingly, the distribution of the products showed a strong dependence on the operation temperature and current density with methane selectivity to be improved at lower operation temperatures and high current densities. The latter is practically results in higher ratios of H2/CO2 which is expected to enhance methane yields.References Vøllestad, R. Strandbakke, M. Tarach, D. Catalán-Martínez, M.-L. Fontaine, D. Beeaff, D. R. Clark, J. M. Serra, T. Norby;Mixed proton and electron conducting double perovskite anodes for stable and efficient tubular proton ceramic electrolysers; Nature Materials 2019, 18, 752-759.Duan, R. Kee, H. Zhu, N. Sullivan, L. Zhu, L. Bian, D. Jennings, R. O’Hayre,“Highly efficient reversible protonic ceramic electrochemical cells for power generation and fuel production”, Nature Energy 2019, 4, 230-240.J. Martin, ChemCatChem.

Tailored pore-confined single-site iron(III) catalyst for selective CH4 oxidation to CH3OH or CH3CO2H using O2

Direct oxidation of methane to valuable oxygenates like alcohols and acetic acid under mild conditions poses a significant challenge due to high C‒H bond dissociation energy, facile overoxidation to CO and CO2 and the intricacy of C−H activation/C−C coupling. In this work, we develop a multifunctional iron(III) dihydroxyl catalytic species immobilized within a metal-organic framework (MOF) for selective methane oxidation into methanol or acetic acid at different reaction conditions using O2. The active-site isolation of monomeric FeIII(OH)2 species at the MOF nodes, their confinement within the porous framework, and their electron-deficient nature facilitate chemoselective C‒H oxidation, yielding methanol or acetic acid with high productivities of 38,592μmolCH3OHgFe−1h−1\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$38,592\\,\\upmu {{{\\rm{mol}}}}_{{{{\\rm{CH}}}}_{3}{{\\rm{OH}}}}{{{{\\rm{g}}}}_{{{\\rm{Fe}}}}}^{-1}{{{\\rm{h}}}}^{-1}$$\\end{document} and 81,043μmolCH3CO2HgFe−1h−1\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$81,043\\,\\upmu {{{\\rm{mol}}}}_{{{{\\rm{CH}}}}_{3}{{{\\rm{CO}}}}_{2}{{\\rm{H}}}}{{{{\\rm{g}}}}_{{{\\rm{Fe}}}}}^{-1}{{{\\rm{h}}}}^{-1}$$\\end{document}, respectively. Experiments and theoretical calculations suggest that methanol formation occurs via a FeIII-FeI-FeIII catalytic cycle, whereas CH3CO2H is produced via hydrocarboxylation of in-situ generated CH3OH with CO2 and H2, and direct CH4 carboxylation with CO2.

Metal-organic frameworks based on pyrazolates for the selective and efficient capture of formaldehyde

Indoor air pollution is one of the major threads in developed countries, notably due to high concentrations of formaldehyde, a harmful molecule difficult to eliminate. Addressing this purification challenge while adhering to the principles of sustainable development requires the use of innovative, advanced sustainable materials. Here we show that by combining state-of-the-art spectroscopic techniques with density-functional theory molecular simulations, we have developed an advantageous mild chemisorption synergistic mechanism using porous metal (III or IV) pyrazole- di-carboxylate based metal-organic framework (MOF) to trap formaldehyde in a reversible manner, without incurring significant energy penalties for regeneration. A straightforward, environmentally friendly, and scalable synthesis protocol was established for the porous, water-stable aluminum pyrazole dicarboxylate known as Al-3.5-PDA or MOF-303, capable of functioning as a highly efficient and reusable filter. It demonstrates selectivity and high storage capacity for formaldehyde under conditions typical of severe indoor use, such as in housing or vehicle cockpits, including varying VOC mixtures and concentrations, humidity, and temperature, without any accidental release. Furthermore, we have successfully regenerated this sorbent using a simple domestic protocol, ensuring the material reusability for at least 10 cycles.

Effective synergistic interaction between InZnZrOx ternary metal oxides and SAPO-34 molecular sieve catalysts for CO2 hydrogenation to light olefins

The synergistic interaction of metal oxides with molecular sieves is essential for the catalytic hydrogenation of carbon dioxide (CO2) into light olefins (C2=–C4=) over bifunctional tandem catalysts. Herein, a series of In2O3-doped InZnZrOx (IZZ) ternary metal oxides was prepared and physically mixed with SAPO-34. The bifunctional catalyst was used in the direct conversion of CO2 to light olefins. The relationship between IZZ oxide structures prepared using different methods and the catalytic performance of bifunctional catalysts was investigated. Moreover, the migration of InOx in ternary metal oxides was revealed. Results revealed that for IZZ oxides prepared via precipitation coating and impregnation, InOx species migrated to the SAPO-34 surface during thermocatalytic reaction due to the dispersion of In2O3 on the ZnZrOx surface and its weak interaction with ZnZrOx. This led to the neutralization of acid centers on SAPO-34 by InOx, thereby destroying the synergistic interaction between the oxides and SAPO-34, resulting in a large amount of unneeded methane and poor light olefin selectivity. However, the co-precipitated IZZ-CP oxides exhibited a ternary solid solution structure and inhibited the migration of InOx. This enhanced CO2 and H2 activation, affording more formate (HCOO*) and methoxide (CH3O*) intermediates that strengthened the synergistic interaction between the oxides and molecular sieves. After optimizing the In2O3 doping amount in IZZ-CP oxide and the reaction conditions, the IZZ-CP/SAPO-34 bifunctional catalyst achieved 17.9 % CO2 conversion, 80.1 % C2=–C4= selectivity, only 7.6 % methane and 44.6 % CO selectivity. It also maintained excellent catalytic stability without significant deactivation after continuous reaction for 80 h.

Ni–CaZrO3 with perovskite phase loaded on ZrO2 for CO2 methanation

CO2 methanation has emerged as a promising strategy for the greenhouse gas CO2 utilization and storage of hydrogen. However, achieving low temperature activity and high temperature stability remains challenging due to the sintering of Ni-based catalysts. To address these limitations, this study introduces a Ni–CaZrO3 catalyst featuring a perovskite phase supported on ZrO2, prepared via citrate complexation and impregnation methods. In this approach, a perovskite-type oxide (PTO) of CaZrO3 forms through a solid reaction on the surface of ZrO2 with impregnated CaO. The formation of CaZrO3 on Ni/ZrO2 restrains the ZrO2 support aggregation and reduces the particle size of Ni nanoparticles (NPs), thereby enhancing the activity for CO2 methanation. The interaction between Ni–CaZrO3, and ZrO2 effectively confines the Ni NPs and CaZrO3, enhancing the sintering resistance of Ni–CaZrO3. This leads to excellent stability of the resulting catalyst for CO2 methanation. The Ni–CaZrO3/ZrO2 catalyst achieves 85% CO2 conversion and maintains 100% methane selectivity at 300 °C, demonstrating the prolonged stability over 100 h at 550 °C. Notably, the loading of CaZrO3 in a perovskite phase on ZrO2 via solid surface reaction represents an interesting and valuable route, which could be extended to loading other PTOs for industrial applications.

Support induced effects on the activity and stability of Ga2O3 based catalysts for the CO2-assisted oxidative dehydrogenation of propane

The influence of the support nature (Al2O3, TiO2, SiO2) on the activity and stability of supported Ga2O3 (10 wt%) catalysts was investigated for the production of propylene through the CO2-assisted oxidative dehydrogenation of propane (CO2-ODP). Catalytic activity was found to be higher when gallium oxide was dispersed on alumina support which was characterized by the highest acid site density and moderate surface basicity. Below 650 °C propylene yield increased in the order Ga2O3-TiO2<Ga2O3-SiO2<Ga2O3-Al2O3, which was modified as Ga2O3-Al2O3<Ga2O3-TiO2<Ga2O3-SiO2 for higher reaction temperatures. Propylene selectivity decreased with increasing reaction temperature followed by an increase of ethylene and methane selectivity implying that the side reactions of propane hydrogenolysis and propane/propylene decomposition were facilitated at higher temperatures hindering the CO2-ODP reaction. Gallium oxide catalysts supported on TiO2 and SiO2 exhibited sufficient stability for 30-35 hours on stream at 660 and 710 οC, contrary to Ga2O3-Al2O3 which although was stable at 710 οC it was gradually deactivated when the reaction was taking place at 600 °C. Temperature programmed oxidation experiments showed that carbon deposition was favored over Ga2O3-Al2O3 catalyst when the reaction was conducted at low temperature, which may be related to the higher surface acidity of this sample and be responsible for its deactivation with time. SEM images and elemental mapping obtained from both the freshly prepared and used Ga2O3-MxOy samples showed that Ga and M (M: Si, Ti, Al) were uniformly present even after prolonged catalyst interaction with the reaction mixture. EDS analysis indicated that carbon formation was accelerated with increasing reaction temperature.

Preparation of Sustainable Ni/SiO2 Catalysts from Rice Husk by Different Methods for CO2 Methanation.

Silicon dioxide (SiO2) from rice husk can be extracted and be used as support for Ni-based catalysts. The impregnation method (IM) is usually used for preparing Ni/SiO2 catalysts, but its catalytic activity in CO2 hydrogenation to CH4 remains unsatisfactory. In this work, we explored alternative preparation methods, using ammonia evaporation method (AEM) and hydrothermal method (HM) to prepare the catalysts. The results showed that the catalysts prepared by AEM and HM were significantly superior to that prepared by IM. Notably, the catalyst synthesized by AEM from sustainable silica exhibited the best performance, achieving 81.69 % CO2 conversion and over 99 % methane selectivity at low reaction temperature of 300 °C. The characterization techniques indicate that the Ni/SiO2-AEM catalyst can form nickel phyllosilicate with lamellar structure, leading to better Ni dispersion and higher specific surface area. Furthermore, the results of in-situ DRIFTS have revealed the potential catalytic mechanism over Ni/SiO2 catalysts, indicating that it involves pathways with both the CO* and HCOO* as the key intermediates.

Highly dispersed Ni-Ce catalyst over clay montmorillonite K10 in low-temperature CO2 methanation

The Carbon Capture and Utilization (CCU) option can be an efficient solution for CO2 emission mitigation. To this end, we have investigated the carbon dioxide methanation at low temperatures. Highly active, selective, stable, low-cost catalysts are required for energy and carbon balance benefits. Supported nickel-based catalysts result as the most studied and promising candidates showing a good compromise between performance and low preparation costs. The catalyst design role is key to obtaining the best performance, requiring many experiments and optimisation procedures. Herein, the enhanced Montmorillonite MK10-supported Ni(0)Ce(III) catalyst, prepared by consecutive hydrothermal and electrostatic adsorption methods followed by reduction under hydrogen flow, was used in batch CO2 methanation, exhibiting 76 % of CO2 conversion with 100 % CH4 selectivity after 3 h. The catalytic system reveals very high robustness preserving the same activity and selectivity for at least 5 reaction cycles if compared with γ-Al2O3-supported Ni(0)Ce(III) catalyst, the latter showing the same activity but only in the first cycle. EDX, XPS, SEM, TPD, TPR, and BET characterisation techniques were used to elucidate and evaluate the potential synergistic effect of the active metal centre-promoter-support interfaces, highlighting their role in the activity and robustness of the catalyst, comparing the same effect using different alumina and silicate solid supports. The effects of the reaction conditions on the methane yield and selectivity were also evaluated.

Synergetic effect of iron and tungsten on molybdenum‐doped HZSM‐5 zeolite in catalytic methane dehydroaromatization

AbstractMethane dehydroaromatization is a viable route for production of carbon and valuable petrochemicals. Unlike Fischer–Tropsch and methanol synthesis processes which have been scaled up to commercial level, development of methane dehydroaromatization to commercial level has been hampered by various challenges. In this work, a 5.4 wt. % trimetallic (Fe‐W‐Mo/HZSM‐5) catalyst has been synthesized, characterized, and applied in catalytic methane dehydroaromatization reaction. A gas chromatograph was used to analyze both liquid and gaseous products from the reactor. Based on 0.0013 moles of reacted methane after 240 min time on stream at 750, GHSV 960 mlg‐1cath‐1, and atmospheric pressure, a 5.4% Mo/HZSM‐5 catalyst recorded 7.9% methane conversion, 10.6% C2 hydrocarbon selectivity, 51.8% benzene selectivity, 9.8% toluene selectivity and 27.8% coke selectivity. Doping Mo/HZSM‐5 with Fe reduced methane conversion by 4.0%, increased C2 hydrocarbon selectivity by 1.7%, reduced benzene selectivity by 6.2% and increased toluene and coke selectivity by 1.8% and 2.8% respectively. Doping Mo/HZSM‐5 with W increased methane conversion by 7.3%, reduced C2 hydrocarbon selectivity by 2.1%, reduced benzene selectivity by 7.6% and increased toluene and coke selectivity by 0.3% and 9.4% respectively. When iron and tungsten were loaded onto Mo/HZSM‐5, catalytic activity of the tri‐metallic catalyst in methane conversion reduced by 2.0%, C2 hydrocarbon selectivity increased by 2.7%, benzene selectivity reduced by 3.1%, toluene selectivity reduced by 3.7%, and coke selectivity increased by 4.1%. Therefore, this present work demonstrates that metal synergy in a tri‐metallic catalyst plays a role in methane conversion and selectivity towards useful hydrocarbons.

Engineering nanoparticle structure at synergistic Ru-Na interface for integrated CO2 capture and hydrogenation

The development of dual functional material for cyclic CO2 capture and hydrogenation is of great significance for converting diluted CO2 into valuable fuels, but suffers from kinetic limitation and deactivation of adsorbent and catalyst. Herein, we engineered a series of RuNa/γ-Al2O3 materials, varying the size of ruthenium from single atoms to clusters/nanoparticles. The coordination environment and structure sensitivity of ruthenium were quantitatively investigated at atomic scale. Our findings reveal that the reduced Ru nanoparticles, approximately 7.1 nm in diameter with a Ru-Ru coordination number of 5.9, exhibit high methane formation activity and selectivity at 340 °C. The Ru-Na interfacial sites facilitate CO2 migration through a deoxygenation pathway, involving carbonate dissociation, carbonyl formation, and hydrogenation. In-situ experiments and theoretical calculations show that stable carbonyl intermediates on metallic Ru nanoparticles facilitate heterolytic C–O scission and C–H bonding, significantly lowering the energy barrier for activating stored CO2.