Low-temperature Methane Research Articles

Amino acid-deep eutectic solvents/LaCoO3 mutualism system:Forming La-Co-C-O hybrid for low temperature methane catalytic oxidation

Low-temperature high-efficiency catalysts are key for complete methane oxidation, whereas common perovskite catalysts still have much room to improve. Herein, a unique La-Co-C-O hybrid (phase composition of La2O2CO3/LaCoO3/Co3O4) was successfully synthesized via an amino acid-deep eutectic solvent/LaCoO3 mutualism system. The C-O bond connects each phase and decreases the bond energy of active Co-O, as well as a higher Co valence state and lattice oxygen content in the hybrid. The light-off temperature of the hybrid for complete methane oxidation is 366 °C, which is 112 °C lower than the light-off temperature of LaCoO3. The high conversion rate remains in the presence of water vapour or long-term reactions. Such excellent catalytic performance of the hybrid can be attributed to the broad path of methane adsorption and C–H cleavage on acid-basic sites. This work hence provides a facile process to tailor highly active catalysts for complete methane oxidation.

Second-Sphere Lattice Effects in Copper and Iron Zeolite Catalysis.

Transition-metal-exchanged zeolites perform remarkable chemical reactions from low-temperature methane to methanol oxidation to selective reduction of NOx pollutants. As with metalloenzymes, metallozeolites have impressive reactivities that are controlled in part by interactions outside the immediate coordination sphere. These second-sphere effects include activating a metal site through enforcing an "entatic" state, controlling binding and access to the metal site with pockets and channels, and directing radical rebound vs cage escape. This review explores these effects with emphasis placed on but not limited to the selective oxidation of methane to methanol with a focus on copper and iron active sites, although other transition-metal-ion zeolite reactions are also explored. While the actual active-site geometric and electronic structures are different in the copper and iron metallozeolites compared to the metalloenzymes, their second-sphere interactions with the lattice or the protein environments are found to have strong parallels that contribute to their high activity and selectivity.

Synthesis and low temperature methane sensing performance of Pd modified In2O3 microspheres

This paper investigated the methane (CH4) gas sensing performance of Pd/In2O3 composites, fabricated by a simple solvothermal method. The morphology, composition and nanostructure of the synthesized materials were characterized and analyzed by XRD, FESEM, TEM, EDS and XPS. Compared with the pure In2O3, 6.0 at% Pd/In2O3 microspheres presented a better gas sensing performance to CH4. The response value of 6.0 at% Pd/In2O3 microspheres to 500 ppm CH4 was 15.317 at 50 °C. Besides, the sensor based on 6.0 at% Pd/In2O3 has a low detection limit (as low as 1.78 ppm). At the same time, the sensor has good selectivity, reproducibility and long-term stability. The enhanced gas sensing performance could be mainly ascribed to chemical catalysis and spillover effects of Pd nanoparticles as well as the Schottky Barrier between Pd and In2O3.

Rare Earths Modified Highly Dispersed Fibrous Ni/Kcc-1 Nanosphere Catalysts with Superb Low-Temperature Co2 Methanation Performances

Rare Earths Modified Highly Dispersed Fibrous Ni/Kcc-1 Nanosphere Catalysts with Superb Low-Temperature Co2 Methanation Performances

Enhancing the Low-Temperature Co2 Methanation Over Ni/Zro2-Al2o3 Catalyst: The Effect of Strong Metal-Support Interactions and Changes in Active Site on the Catalytic Performance

Enhancing the Low-Temperature Co2 Methanation Over Ni/Zro2-Al2o3 Catalyst: The Effect of Strong Metal-Support Interactions and Changes in Active Site on the Catalytic Performance

The High Activity of Mn2+-Rich Co-Mn-O Solid Solution Catalyst for Low-Temperature Methane Combustion

The High Activity of Mn2+-Rich Co-Mn-O Solid Solution Catalyst for Low-Temperature Methane Combustion

Insight into the role of Fe on catalytic performance over the hydrotalcite-derived Ni-based catalysts for CO2 methanation reaction

A series of Fe modified hydrotalcite-derived Ni-based catalysts (Ni3Fex-calc) were synthesized to evaluate the effect of Fe on CO2 methanation performance over Ni3-calc catalyst. The results showed that Ni3–Fe0.5-calc had superior catalytic activity with 78% CO2 conversion rate at 200 °C. The addition of moderate amount of Fe can effectively improve the reducibility, enrich the medium basic sites of Ni3-calc catalyst, and further facilitate the adsorption and activation of CO2. This resulted in the outstanding low-temperature CO2 methanation activity, as well as the enhanced resistance of carbon deposition. In-situ DRIFTS results indicated that the CO2 methanation reaction mechanism involved a progressive hydrogenation of carbonate and formate species to methane route. The formate species was the main intermediates during CO2 methanation. The introduction of Fe could significantly accelerate the hydrogenation rate of carbonates and formate species.

CO2 Methanation: Nickel-Alumina Catalyst Prepared by Solid-State Combustion.

The development of solvent-free methods for the synthesis of catalysts is one of the main tasks of green chemistry. A nickel–alumina catalyst for CO2 methanation was synthesized by solid-state combustion method using hexakis-(imidazole) nickel (II) nitrate complex. Using X-ray Powder Diffraction (XRD), Transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS), and Hydrogen temperature-programmed reduction (H2-TPR), it was shown that the synthesized catalyst is characterized by the localization of easily reduced nickel oxide on alumina surface. This provided low-temperature activation of the catalyst in the reaction mixture containing 4 vol% CO2. In addition, the synthesized catalyst had higher activity in low-temperature CO2 methanation compared to industrial NIAP-07-01 catalyst, which contained almost three times more hard-to-reduce nickel–aluminum spinel. Thus, the proposed approaches to the synthesis and activation of the catalyst make it possible to simplify the catalyst preparation procedure and to abandon the use of solvents, which must be disposed of later on.

Experimental study of effect of slickwater fracturing on coal pore structure and methane adsorption

Driven by high pressure, slickwater may intrude into the pores of coal seams, causing changes in the pore structure, and ultimately affecting the flow of Coalbed Methane (CBM). In this study, slickwater prepared with different concentrations of polyacrylamide (PAM) is used to soak coal samples from Inner Mongolia under high pressure to explore the effect of slickwater fracturing on coal seam pores. To study the evolution characteristics of the pore structure of coal samples treated with slickwater, low temperature nitrogen adsorption experiments and methane adsorption experiments are combined. The experimental results show that under the action of external pressure, slickwater invades the pore structure of coal, resulting in a significant decrease in pore volume and specific surface area. Furthermore, with the increase of the pressure and viscosity of the slickwater, the slickwater residue blocks the micropores in the coal pore structure more severely. The damage to methane adsorption by residue is more serious than that to nitrogen adsorption, reflecting that more residue remains in the micropores of coal samples. The development of a gel breaker suitable for slickwater can promote the degradation of PAM polymer molecules and the reduction of residual liquid viscosity after fracturing, and improve the flowback effect. This may be an effective way to reduce reservoir damage.

Facile synthesis of palladium incorporated NiCo2O4 spinel for low temperature methane combustion: Activate lattice oxygen to promote activity

While palladium-based catalysts are effective in low-temperature methane combustion, their high cost and scarcity render them unsuitable to fulfil the growing demand. The design of improved catalysts which can more efficiently utilize this precious metal is required. Here, by using a facile one-pot thermal decomposition method Pd-NiCo2O4 spinel catalysts with a unique structure are obtained, in which the majority of Pd incorporated into the bulk spinel structure of NiCo2O4 with limited highly dispersed PdOx species on the surface at an atomic scale. The robust 1 %Pd-NiCo2O4 spinel catalyst exhibits comparable activity in methane oxidation to that of the conventional incipient wetness impregnation 2 %Pd/NiCo2O4. Theoretical calculations and catalyst characterizations (SEM, HRTEM, XRD, XPS, XAS, ICP-OES, etc.) revealed that the enhanced activity is mainly originated from having the O p-band center closer to the Fermi level, with Pd ions incorporated into the bulk NiCo2O4via substituting for the octahedral coordinated Ni3+/Co3+.

Zr-Doped NiO Nanoparticles for Low-Temperature Methane Combustion

The development of efficient and stable non-noble metal-based catalysts for low-temperature methane combustion is extremely important and still a profound challenge. Herein, high-performance Ni1–xZrxO2−δ solid solution nanocatalysts were prepared through a homogeneous co-precipitation strategy, where the hydrolysis of CO32– was controlled to facilitate the dispersion and interaction of Ni and Zr components. The structural and surface properties of nanocatalysts were facilely tuned by modulating the Zr doping content. An optimized incorporation of Zr into the NiO lattice endowed the Ni0.89Zr0.11O2−δ nanocatalyst with a small crystallite size, large specific surface area, and simultaneously increased surface acidic–basic sites. Moreover, abundant active Ni2+ and surface oxygen species were generated due to the promoted conversion of Ni3+ to Ni2+, which played pivotal roles in the adsorption/activation of methane and further oxidation of reaction intermediates to CO2. Consequently, Ni0.89Zr0.11O2−δ exhibited an excellent low-temperature activity, high CO2 selectivity, and superior catalytic stability under both dry and wet conditions.

Elucidating the layer-number impact of MoS2 on the adsorption and hydrogenation of CO

MoS2 is an attractive sulfur-resistant catalyst for directly converting sulfur-containing syngas to high value-added chemicals. However, the effect of the layered structure on the catalytic activity for CO hydrogenation reactions is far from clear. Herein, MoS2/carbon composite catalysts with 1–8 stacking layers in MoS2 crystallites are synthesized, and the impact of the layer numbers on the catalytic performance is probed for the low-temperature methanation of sulfur-containing syngas. The results indicate that the turnover frequency of CO methanation increases from 2.4 × 10-3 to 3.7 × 10-3 s−1 with decreasing layer numbers of MoS2 crystallites from 8.3 to 1.1. This result is thoroughly explained by the fact that the higher ratio of rim sites in MoS2 crystallites with fewer layer numbers enhances the catalytic activity, which originates from the facilitated activation of CO and H2. These understandings are important for the rational design and development of more efficient MoS2-based catalysts for CO hydrogenation.

Fabrication of surface oxygen vacancies on NiMnAl-LDO catalyst by high-shear mixer-assisted preparation for low-temperature CO2 methanation

Low-temperature performance of non-noble metal Ni-based catalysts in CO2 methanation still faces great challenges. A series of NiMnAl-LDO (layered double oxides) catalysts with different processing conditions were prepared using the high-shear mixer-assisted method. The FH-C (80 °C) catalyst exhibited high activity in low-temperature CO2 methanation, and CO2 conversion and CH4 selectivity reached 85% and 97% at 200 °C. Characterization results show that the strong shear force of the high-shear mixer can improve the dispersion of the catalyst and reduce the particle size of the catalyst. The high-shear mixer treatment increases the CO2 chemisorption and the number of strongly basic sites on the catalyst. The main reason for the low-temperature activity of the catalyst is that the high-shear mixer increases the number of oxygen vacancies in the catalyst. In situ infrared probes into the surface species and intermediate products of the catalyst, confirming that formate is an intermediate product of the CO2 methanation reaction. Density functional theory calculations demonstrated that increasing the content of oxygen vacancies is beneficial for increasing the CO2 adsorption capacity of the catalyst and reducing the reaction energy barrier of CO2 → COOH*.

Material characterization of Au/Ni nanocatalyst for low-temperature carbon dioxide methanation

The nanocatalyst for the carbon oxide methanation process is used, among others, in environmental protection, chemical industry, and renewable energy sources. The use of a suitable catalyst allows a chemical reaction to be carried out between unreacted gaseous substrates. The most frequently studied monometallic catalysts are: Ni, Ru, Rh, Pt, Au, Cu, Fe. Bimetallic nanocatalysts are equally popular. Their catalytic properties differ from those of pure component metals. Numerous studies indicate a positive effect in catalysts containing particles: Au-Ag, Au-Pt, Au-Pd, Pd-Ni, Pd-Cu. A review of the literature indicates that examples of the use of metal nanoparticles of spherical shape deposited on a nickel substrate in the methanation process are known, but so far no attempt has been shown in publications to produce a catalyst based on gold nanoparticles with developed surface in the form of spiky (nanourchins, nanostars) on a nickel base as presented in the article. Gold nanourchins are deposited on a nickel substrate in the form of a nickel molecular mesh. The prepared nanocatalyst has been subjected to structural analysis using a transmission electron microscope (TEM). Scanning Electron Microscopic (SEM) images were taken with a Zeiss Supra 35. Qualitative studies of chemical composition were also performed using the Energy Dispersive Spectrometer (EDS). Based on the TEM results, the appearance of the X-ray diffraction pattern was computer modelled. A nanocatalyst was obtained with a high coverage of the nickel molecular mesh surface with gold nanoparticles not exceeding 50 nm in diameter.

Polyol-pretreated SBA-16 supported Ni-Fe bimetallic catalyst applied in CO methanation at low temperature

• Polyols were used to pretreat the mesoporous silica molecular sieve SBA-16 to adjust the surface groups. • Bimetallic Ni-Fe catalysts with polyol-pretreated support were obtained. • The mechanism of how the polyols influence the surface SiOH groups and thus the metal particles distribution was figured out. • Catalysts with polyol-pretreated support lowered the minimum temperature for CO complete conversion to 230 °C from 290 °C. Polyols were used to pretreat the mesoporous silica molecular sieve SBA-16 and thus supported bimetallic Ni-Fe catalyst was prepared in order to address the low activity of CO methanation at lower temperature. The characterization of the pretreated support and catalysts indicated that the residual polyols release heat during combustion, which could provide energy for the decomposition of metal precursors, lowering the decomposition temperature and reducing the metal particle size. More importantly, the pretreatment of support with polyols could increase the isolated silicon hydroxyl, and strengthen the metal-support interaction, thus obtaining smaller metal particles. The smaller metal particles promoted the dissociation of reactant gas, as a result, Ni-Fe bimetallic catalyst with polyol-pretreated support could lower the minimum temperature for CO complete conversion from 290 °C to 230 °C while keeping CH 4 selectivity above 90%. Catalysts with polyol-pretreated support provide a new possibility for low-temperature CO methanation technology.

Preparation, Characterization, and Activity of Pd/PSS-Modified Membranes in the Low Temperature Dry Reforming of Methane with and without Addition of Extra Steam.

The external surface of a commercial porous stainless steel (PSS) was modified by either oxidation in air at varying temperatures (600, 700, and 800 °C) or coating with different oxides (SiO2, Al2O3, and ZrO2). Among them, PSS-ZrO2 appears as the most suitable carrier for the synthesis of the Pd membrane. A composite Pd membrane supported on the PSS-ZrO2 substrate was prepared by the electroless plating deposition method. Supported Ru catalysts were first evaluated for the low-temperature methane dry reforming (DRM) reaction in a continuous flow reactor (CR). Ru/ZrO2-La2O3 catalyst was found to be active and stable, so it was used in a membrane reactor (MR), which enhances the methane conversions above the equilibrium values. The influence of adding H2O to the feed of DRM was investigated over a Ru/ZrO2-La2O3 catalyst in the MR. Activity results are compared with those measured in a CR. The addition of H2O into the feed favors other reactions such as Water-Gas Shift (RWGS) and Steam Reforming (SR), which occur together with DRM, resulting in a dramatic decrease of CO2 conversion and CO production, but a marked increase of H2 yield.

Bed packing configuration and hot-spot utilization for low-temperature CO2 methanation on monolithic reactor

The revival of CO2 methanation (Sabatier reaction) as part of the large-scale Power-to-Gas technology has stimulated the development of novel reactor concepts for better heat management due to its exothermic nature. The generation of hot-spots in fixed bed reactors could reduce methane yield, accelerate catalyst deactivation, and potentially cause thermal runaway. However, hot-spots could be utilized to achieve outstanding CO2 methanation performance at low temperatures and high gas flow rate in monolithic reactors, whereas strategic bed packing configurations could boost the performance of low-activity catalytic beds. We prepared NiFe catalysts derived from in-situ grown layered double hydroxides via urea hydrolysis on washcoated cordierite honeycomb substrate with varying activities. Temperature profiles by both experimental and computational fluid dynamic (CFD) studies revealed hot-spot formation along catalytic beds. Hot-spots increased the catalytic beds’ temperature due to high thermal conductivity of cordierite monolith, thus accelerated the reaction. The monolithic reactor with a single-monolith bed exhibited a methane yield of 16.5% at 250 °C, which was significantly increased to 80.4% on the reactor with three-monolith bed of the same catalyst at similar reaction condition with a constant ratio of catalyst mass to gas flow rate. A combined low-high activity monolithic bed was proposed which demonstrated high methane yield and excellent stability. Interestingly, the methane yields were higher at a gas flow rate of 1500 mL/min than that at 500 mL/min, again ascribed to the beneficial effect of hot-spot formation on monolithic reactors. Therefore, strategic bed packing configuration plays an important role in the optimization of monolithic methanation reactors, and hot-spot formation could be exploited to achieve excellent CO2 methanation performance at low temperatures.

Electron reservoir enhances methane conversion on Zn dimer supported by N doped graphene: A DFT study

Catalytic conversion of methane to commodity chemicals is highly desired. With methods of density functional theory (DFT) computations, we investigated methane conversion to methanol (MCM) with H2O2 as oxidant over Zn dimer supported by amino nitrogen and pyridinic nitrogen co-doped porous graphene (Zn2@NPG). The facile oxidation of Zn dimer gives rise to the formation of reactive site toward methane activation. The CH3-H bond cleavage with 0.24 eV energy barrier is directly followed by the formation of methanol and regeneration of Zn2@NPG. Further analysis revealed that Zn dimer is strongly stabilized and positive charged by sharing 4 s electrons with N atoms, which ensures high-stability and good electronic conductivity of the Zn2@NPG. Amino N atom exhibits efficient electronic transfer with Zn dimer by forming two Zn-N bonds, endowing its function as an electron reservoir. Amino N as an electron donator promotes oxidation of Zn dimer and as an electron acceptor facilitates deoxidation of Zn dimer and methane conversion. The combined effect of Zn dimer and amino N atoms endows Zn2@NPG with excellent electronic structure for high activity in catalyzing MCM. This work opens a new door to accomplish low-temperature methane conversion on bi-atom catalysts (BACs).

Deciphering the role of Ni particle size and nickel-ceria interfacial perimeter in the low-temperature CO2 methanation reaction over remarkably active Ni/CeO2 nanorods

The structure sensitivity of CO2 methanation was explored over nickel particles (10–25 nm) supported on CeO2 nanorods. An optimum Ni particle size of 20 nm was revealed, with the corresponding sample demonstrating remarkable activity, i.e., 187 μmol CH4 g−1 s−1 and 92 % CH4 yield at 275 °C, which is among the highest ever reported. Notably, the intrinsic activity on the basis of the exposed Ni sites or Ni-ceria perimeter is largely independent of the Ni size, showcasing that neither the exposed Ni sites nor the Ni-ceria interface can be employed as activity descriptors. A compromise between the length of the metal-support perimeter and the competitive presence of larger Ni particles is necessary for the optimum activity. On the grounds of a structure-sensitivity analysis, the superior activity of larger Ni particles could be attributed to the presence of under-coordinated step and kink sites, instead of largely inactive terrace sites.

Screening Transition Metals (Mn, Fe, Co, and Cu) Promoted Ni-Based CO2 Methanation Bimetal Catalysts with Advanced Low-Temperature Activities

The Ni monometallic catalyst usually exhibits poor CO₂ methanation activity, although its low cost is beneficial for conducting large-scale application in industries. Herein, the transition metal (Mn, Fe, Co, and Cu)-doped Ni-based bimetallic catalysts loaded on mesoporous Ce₀.₈Zr₀.₂O₂ solid solution were prepared to address this challenge in CO₂ methanation. We found that the Co-doped catalysts exhibited much higher activity than the corresponding counterparts. Therefore, the relationship between the Co/Ni ratio and activity was further investigated to acquire the optimum ratio. The obtained catalysts were characterized by various measurements. The results demonstrated that doping the second transition metals could promote Ni dispersion and strengthen metal–support interaction. Resultantly, serious agglomeration of the metallic active sites was successfully inhibited. Besides, we also carried out the in situ diffuse reflectance infrared spectroscopy and online temperature-programmed surface reaction of CO₂ methanation to study the possible reaction intermediates and pathways over the Ni–Co bimetallic catalysts. A dynamic study was also conducted to further study the effect of the doped transition metals on the apparent activation energies. Besides, the present research also revealed that the Ni–Co synergistic effect significantly improved the low-temperature activity by regulating the reaction intermediates. As a result, the Ni–Co bimetallic catalysts supported by mesoporous Ce₀.₈Zr₀.₂O₂ solid solution were considered as a series of promising and efficient low-temperature CO₂ methanation catalysts.