Methanation Catalysts Research Articles

A Novel CO Methanation Catalyst System Based on Acid-Etched Natural Halloysites as Supports

A Novel CO Methanation Catalyst System Based on Acid-Etched Natural Halloysites as Supports

Ru/Al2O3 on Polymer-Derived SiC Foams as Structured Catalysts for CO2 Methanation

The catalytic methanation of CO2 via the strongly exothermic equilibrium Sabatier reaction requires the development of structured catalysts with enhanced mass- and heat-transfer features to limit hot-spot formation, avoid catalyst deactivation, and control process selectivity. In this work, we investigated the use of polymer-derived SiC open-cell foams as structured carriers onto which γ-Al2O3 was applied by either dip-coating or pore-filling methods; eventually, Ru was dispersed by impregnation. The formation of an undesired insulating SiO2 layer on the surface of the SiC struts was prevented by a pyrolysis treatment under an inert atmosphere at temperatures varying from 800 up to 1800 °C. SiC foam substrates and their corresponding structured catalysts were characterized by SEM, XRD, N2 physisorption, and compressive strength measurements, and their CO2 methanation activity was tested at atmospheric pressure in a fixed bed flow reactor operated in the temperature range from 200 to 450 °C. SiC foams obtained at intermediate pyrolysis temperatures (1000–1200 °C) showed good mechanical strength and high compatibility with the Ru/Al2O3 active catalytic overlayer.

CO2 methanation over the Ni-based catalysts supported on nano-CeO2 with varied morphologies

A series of CeO2 supports with particular morphologies (nanorods, nanocubes, nanooctas, and nanoparticles) were successfully fabricated by controlling the parameters of the hydrothermal method. The obtained nano-CeO2 materials were utilized as the supports of the Ni-based CO2 methanation catalysts prepared by the incipient impregnation method. It was found that the catalyst supported on the CeO2 nanoparticles (5Ni/NPs) exhibited much higher catalytic activity and better stability than those of catalysts with other morphological CeO2 supports. Thus, the catalytic performance of Ni/CeO2 catalysts could be facilely tuned and optimized by precisely designing the morphology of the CeO2 support. The XPS, CO2-TPD, and H2-TPR characterizing techniques showed that Ni-based catalysts supported on nano-CeO2 with varied morphologies displayed different catalytic performances. It was supposed that the typical merits, such as the abundant oxygen vacancy, medium basic sites, moderate metal-support interaction, excellent reduction ability, etc., were considered as the main origins for the enhancement of the low-temperature catalytic activities. Furthermore, the kinetic study revealed that the Ni-based catalysts supported on the nano-CeO2 with varied morphologies performed the different apparent activation energies toward CO2 methanation. The specific reaction intermediates and possible reaction pathways were carefully investigated through the in-situ DRIFTS and online TPSR techniques. Overall, this work would provide new perspectives that the roles of the morphology effect of the support ought to be emphatically considered when designing new catalysts.

Modifying Spinel Precursors for Highly Active and Stable Ni‐based CO2 Methanation Catalysts

AbstractIn CO2 methanation, spinel phases are often considered as undesirable leading to deactivation. However, they can also be considered as well‐dispersed solid solutions suitable as catalyst precursors leading to the formation of highly active and finely dispersed active sites. Though, spinels such as NiAl2O4, which form when Ni/Al2O3 supported catalysts are used, require high reduction temperatures to become active. To obtain a suitable catalyst precursor, the reducibility of such spinels must be improved so that it can be activated under conventional conditions. The undesirable spinel phase is modified by introducing manganese, known to distort the spinel structure, to form Ni0.9MnxAl2‐xO4 (0≤x≤2) as a new catalyst precursor. These exhibit significantly improved reducibility at low temperatures. By adjusting the manganese content, a methane yield of 38.7 % was achieved at 350 °C under the conditions used, which is more than twice that of the supported Ni/Al2O3 reference catalyst (SPP2080‐IMRC).

Effect of noble metal addition over active Ru/TiO2 catalyst for CO selective methanation from H2 rich-streams

Selective CO methanation from H2-rich stream has been regarded as a promising route for deep removal of low CO concentration and catalytic hydrogen purification processes. This work is focused on the development of more efficient catalysts applied in practical conditions. For this purpose, we prepared a series of catalysts based on Ru supported over titania and promoted with small amounts of Rh and Pt. Characterization details revealed that Rh and Pt modify the electronic properties of Ru. The results of catalytic activity showed that Pt has a negative effect since it promotes the reverse water gas shift reaction decreasing the selectivity of methanation but Rh increases remarkably the activity and selectivity of CO methanation. The obtained results suggest that RuRh-based catalyst could become important for the treatment of industrial-volume streams.

Highly active Ni/CeO2/SiO2 catalyst for low-temperature CO2 methanation: Synergistic effect of small Ni particles and optimal amount of CeO2

CO2 methanation is of great significance to CO2 utilization. However, it is challenging to prepare Ni-based catalysts with superior low-temperature activity via a simple method. In this work, a highly active Ni/CeO2/SiO2 catalyst is developed by a combustion-impregnation method, and the synergistic effect of active sites for H2 and CO2 activation are studied. The research results show that highly dispersed Ni particles (6 nm) are obtained by this method with an instantaneous reaction. As a result of the increased number of Ni active sites, the catalyst exhibits improved catalytic activity. Moreover, addition of CeO2 promoter further improves the low-temperature activity. First, it enhances the catalyst reducibility, creating more Ni active sites for H2 dissociation. Second, the surface oxygen vacancies formed on CeO2 facilitate CO2 activation. Therefore, the best performance of 63% CO2 conversion and 99% CH4 selectivity at 250 °C is achieved on the Ni-5Ce catalyst with small Ni particles and optimal amount of CeO2 promoter. With higher CeO2 content, Ni-7.5Ce catalyst displays decreased catalyst reducibility and catalytic activity. Therefore, it can be concluded that a proper ratio between both types of sites is crucial for CO2 methanation.

The effect of Ru-Ru coordination numbers on CO2 methanation over Ru supported catalyst

CO2 methanation might be an efficient way to reduce the greenhouse effect and solve the energy problems. The supported Ru catalysts are one of the most widely used methanation catalysts, but the effect of the Ru particles' micro-morphology on the CO2 methanation was rarely studied theoretically. The Run/Ru(0001) (n = 1, 2, 3, 4) was built for modeling the defected Ru sites with low Ru-Ru coordination numbers (CN = 3, 4, 5, and 5.5) in the present work. On the Run/Ru(0001) (n = 1, 2, 3, 4), the most favored pathway for CH4 formation is the COH route: CO2 → CO → COH → C → CH → CH2 → CH3 → CH4. Based on the microkinetic modeling results, we find the selectivity for CH4 increases when the CN of Ru increases from 3 to 5.5, and the selectivity is almost 100% over Ru4/Ru(0001). However, the selectivity for CO is the opposite, that is, the Ru ensemble with lower CN is favorable for CO formation. This study reveals the strong relationship between the Ru-Ru CN and the CO2 methanation reactivity/selectivity and finds the model catalysts with about fiver Ru-Ru CN exhibit the best methanation property. Consequently, metal nanoparticles with more fractions of five-coordinated Ru-Ru configurations would be beneficial for CO2 methanation.

Ni/M/SiO2 catalyst (M=La, Ce or Mg) for CO2 methanation: Importance of the Ni active sites

The hydrogenation of CO2 to methane with renewable H2 can mitigate the greenhouse effect and realize the sustainable energy production. The SiO2 supported Ni catalysts were prepared via a simple combustion-impregnation method. Highly dispersed Ni particles were obtained, accompanied by increased H2 and CO2 adsorption capacity. And the Ni active sites and the catalyst adsorption capacity to H2 and CO2 were modified by different promoters (La, Ce, or Mg). La and Ce were conducive to Ni dispersion and catalyst reducibility, bringing in more active sites and further enhanced catalytic activity at low temperatures. Conversely, the slight agglomeration of Ni particles and reduced catalyst reducibility were found on the catalyst with Mg, resulting from the formation of solid solution. Moreover, Mg atoms were prone to enrich on the surface of catalyst, which may cover part of Ni active sites and make them inaccessible. Therefore, though the largest H2 and CO2 adsorption capacity were achieved on the catalyst with Mg, it displayed the poor catalytic performance. Hence, the importance of the Ni active sites on the low-temperature activity of catalyst in CO2 methanation was confirmed in this work. Besides, the increased CO2 activation ability benefiting from the promoter could facilitate the catalytic activity at low temperatures. The fundamental findings in this work may help develop an efficient Ni-based catalyst for CO2 methanation at low temperatures.

Ru/HxMoO3-y with plasmonic effect for boosting photothermal catalytic CO2 methanation

Utilizing localized surface plasmon resonance (LSPR) effect of catalysts to facilitate photothermal catalysis of CO2 to CH4 is an attractive strategy for mitigating CO2 emissions. Herein, we demonstrate that Ru/HxMoO3-y synthesized via H-spillover exhibits plasmonic absorption in the visible-near-infrared (Vis-NIR) region, achieving a CH4 yield of 20.8 mmol/gcat/h (520 mmol/gRu/h) with 100 % selectivity in the CO2 methanation under Vis-NIR light irradiation at 140 °C. Irradiation with Vis-NIR light substantialy increases the CH4 yield (~ 4.7 fold) compared with that under dark conditions. The abundant surface oxygen vacancies provide active sites for CO2 adsorption and activation. In situ infrared spectroscopic analysis reveals that photothermal catalytic CO2 methanation follows *CO pathway. This work represents a simple strategy for developing a plasmonic catalyst for efficient photothermal catalytic CO2 methanation.

Ru–Ni/GA-MMO composites as highly active catalysts for CO selective methanation in H2-rich gases

CO selective methanation (CO-SMET) is as an ideal H2-rich gases purification measurement for proton exchange membrane fuel cell system. Herein, the graphene aerogel-mixed metal oxide (GA-MMO) supported Ru–Ni bimetallic catalysts are exploited for CO-SMET in H2-rich gases. The results reveal that a three-dimensional network structure GA-MMO aerogel with higher specific surface area, better thermal stability and more defects or structural disorders is formed when MMO:GO mass ratio is in the range of 1–4. After loading of Ru, more NiO are reduced to metallic Ni by hydrogen spillover effect, and thus obviously enhances the reactivity. The GA-MMO supported Ru–Ni catalyst exhibits more excellent metal dispersion, reducibility, stronger CO adsorption and activation than the MMO supported Ru–Ni catalyst, thereby resulting in better catalytic performance and stability. This work offers new insights into the construction of highly active catalyst for the efficient generation of high-quality H2 from H2-rich gases.

The Impact of Support Material of Cobalt‐Based Catalysts Prepared by Double Flame Spray Pyrolysis on CO2 Methanation Dynamics

AbstractMethanation is capable of chemical storage of fluctuating renewable energy, which requires fundamental understanding of the dynamics of the kinetic processes taking place on the catalyst surface. In order to elucidate the impact of the catalyst support on the dynamics, Co‐based model catalysts were synthesized via double flame spray pyrolysis (DFSP) differing only in the support materials. In particular, Co nanoparticles of identical particle size distributions are supported on SiO2, TiO2 and SiO2‐TiO2 mixtures by independent formation of the support and the active metal by means of DFSP. The transient catalyst behavior was studied by step changes of the feed gas composition and the analysis of the reactor response with high temporal resolution, according to the periodic transient kinetics method. It was revealed that H2O adsorption strongly depends on the support with increasing sorption capacity from SiO2, via SiO2‐TiO2 to TiO2. The storage of H2O on the support induces a sorption‐enhancement effect and thereby promotes the transient CH4 formation rate for Co/TiO2 catalysts. Transient experiments before and after a steady‐state operation period under CO2 methanation reveal an unchanging reaction mechanism, while changes in selectivity towards CH4 and CO are observed together with a certain degree of deactivation. Hence, the support material was identified to play a major role in activity, selectivity and deactivation behavior for supported Co catalysts in CO2 methanation.

Simulation Study of Ceramic Fibrous Structured Catalysts for CO2 Methanation—Enhancement of the Performance and Comparison to Pellet Catalysts

Simulation Study of Ceramic Fibrous Structured Catalysts for CO2 Methanation—Enhancement of the Performance and Comparison to Pellet Catalysts

Strong Interaction over Ru/Defects‐Rich Aluminium Oxide Boosts Photothermal CO2 Methanation via Microchannel Flow‐Type System

AbstractThe CO2 methanation is an important component of the “power to gas” strategy, and the Ru‐Al2O3 catalyst is considered to be a state‐of‐the‐art catalyst for this reaction. Conventional Ru‐Al2O3 is prepared by wet impregnation. Due to weak interactions between Ru and the Al2O3, construction of a controllable interface between the metal and the substrate is still challenging. In this work, a UV pulse laser is used to controllably construct ultra‐small Ru nanoparticles on defects‐rich Al2O3‐x‐L in situ grown on Al foil (Ru‐Al2O3‐x‐L) for effective photothermal CO2 methanation. The catkin‐like fluff Al2O3‐x‐L efficiently traps light to ensure the light adsorption of Ru‐Al2O3‐x‐L. The defects in Al2O3‐x‐L efficiently anchors Ru. A Strong‐Metal‐Support‐Interaction (SMSI) effect is constructed between the ultra‐small Ru nanoparticles and the Al2O3‐x‐L. The Ru‐Al2O3‐x‐L exhibits remarkable photothermal catalytic performance (CH4 yield of 12.35 mol gRu−1 h−1) in the closed batch system. Then an innovative flow reactor is established based on the one‐piece Ru‐Al2O3‐x‐L microchannel catalyst. Thanks to local pressure on the edge of the microchannels, the CH4 yield is further enhanced to 14.04 mol gRu−1 h−1. Finally, an outdoor setup demonstrates the feasibility of photothermal CO2 methanation (CH4 yield of 18.00 mmol min−1). This work provides novel perspectives for the construction of multi‐level micro/nanostructures integrated catalysts for photothermal CO2 methanation.

3D printed co-precipitated Ni-Al CO2 methanation catalysts by Binder Jetting: Fabrication, characterization and test in a single pellet string reactor

The Binder Jetting 3D printing technique was used to fabricate spherical Ni-Al CO2 methanation catalysts from co-precipitated catalyst precursor powder. Catalysts with different nickel loadings were prepared by varying the molar Ni/Al ratio (1/1, 2/1, 3/1, 5/1) during precipitation or the amount of admixed precursor powder (10, 20, 30 wt.%) for printing. XRD and TG analysis revealed phase composition and reducibility characteristics analogous to conventionally prepared Ni-Al catalysts. TEM displayed nickel particle sizes as small as 3.9 nm with a Ni dispersion of up to 13.4 % determined by H2 chemisorption. Moreover, meso- and macroporous catalyst pellets were generated with a specific surface area of up to 192 m2∕gcat. The catalysts NiAl11–20, NiAl21–20 and NiAl51–20 were exemplarily tested in a single pellet string reactor where CO2 conversions of up to 99 % and a high selectivity towards CH4 was observed at ptot = 9 bar upon reaching thermodynamic equilibrium.

Computational Study of Zn Single-Atom Catalysts on In2O3 Nanomaterials for Direct Synthesis of Acetic Acid from CH4 and CO2

The direct conversion of methane and carbon dioxide will be a promising way to alleviate the greenhouse gas effect and reduce the dependency on traditional fossil fuels. In this study, the catalytic transformation of methane and carbon dioxide to acetic acid with a 100% atomic economy effect over the zinc single-atom catalyst supported on In2O3 nanomaterial with surface oxygen vacancy (Zn1/In2O3–x) was investigated by using density functional theory calculations, including dissociative adsorption of methane, C–C bond coupling, acetate species protonation, and desorption of acetic acid. The results indicate that the Zn single atom is beneficial to the dissociation of methane and the stabilization of methyl by forming the Zn–CH3 species. Besides, carbon dioxide can be adsorbed on the surface of the catalyst and activated further owing to the presence of surface oxygen vacancy. The facile C–C coupling of co-adsorbed methyl and carbon dioxide is realized by the synergistic mode combining the Zn single atom and surface oxygen vacancy following the Langmuir–Hinshelwood mechanism, in which a Zn–C–C moiety is formed in the transition state. The subsequently formed acetate species is bonded with Zn strongly and undergoes a protonation process to form acetic acid which also interacts strongly with the Zn single atom, resulting in desorption of acetic acid being the rate-determining step of the whole reaction. The insights in this work would be useful to clarify the reaction mechanism of producing acetic acid from methane and carbon dioxide over the Zn1/In2O3–x single-atom catalyst, which could provide a sufficient way to design efficient catalysts for methane and carbon dioxide conversion.

Cu supported on various oxides as a candidate catalyst for dry methane reforming in DIR-SOFCs systems

A series of Cu-support systems were tested as potential candidates for DIR-SOFC (Direct Internal Reforming SOFC) catalysts towards a dry reforming of methane (DRM). The various supports (α-Al2O3, CeO2, ZrO2, SrTiO3) with comparable specific surface area (SSA), and additionally γ-Al2O3 with SSA an order of magnitude larger than that of the other supports has been applied. The obtained Cu-support systems were characterized in terms of structure (XRD, XPS), microstructure (SEM), redox properties (TPR/TPOx), and next their catalytic activity and selectivity in DRM reaction were tested. All Cu-support materials show catalytic activity in DRM reaction, but only activity of Cu–SrTiO3 is high (due to the incorporation of Cu into SrTiO3 structure). The catalytic activity of other materials depends on the copper oxidation state (Cu2+ and Cu+). The highest catalytic activity in DRM process was obtained for Cu–AlO(OH) catalyst thanks to an order of greater SSA than in the case of other systems.

Effect of Fe and La on the Performance of NiMgAl HT-Derived Catalysts in the Methanation of CO2 and Biogas

Bulk Ni-based catalysts derived from hydrotalcite-type (HT) compounds show enhanced stability in the hydrogenation of CO2 into CH4, in comparison to their supported counterparts. The composition of the parent hydrotalcite determines the Ni loading and particle size, as well as the basicity of the catalysts. In this work, a comparison between the effect of Fe and La on the performance of NiMgAl HT compounds (Ni/Mg/Al = 25/50/25 atomic ratio) calcined at 600 °C is investigated. After a reduction pretreatment at 750 °C, both promoters enhance the activity in the low-temperature range; however, the La-containing catalyst reaches a better CH4 productivity rate at high oven temperature (i.e., 200 L gNi–1 h–1 at 325 °C). Although the formation of the NiFe alloy improves the activity, lanthanum keeps smaller Ni0 particles and provides a higher basicity to the mixed oxide than Fe. The activity of the NiMgLaAl catalyst can be further tailored by increasing the Ni loading from 25.6 wt % (Ni25Mg50La5Al20) to 44.6 wt % (Ni50Mg25La5Al20). Lastly, the feasibility of HT-derived catalysts in the direct methanation of clean biogas is proved.

Guidelines to prepare active, selective, and stable supported metal catalysts for CO2 methanation with hydrogen

Catalytic thermal hydrogenation of CO2 to CH4 with renewably produced H2 is one of the routes to reduce the CO2 concentration in the atmosphere. In this respect, various catalysts have been developed. Among them, 5% Ru-loaded Al2O3 [Ru(5%)-Al2O3] has shown the highest performance, at 300 °C, in terms of the intrinsic reaction rate and the turnover frequency (TOF), which were 38 mmolCH4 g−1h−1 and 1188 h−1, respectively. The CH4 selectivity of the catalyst was 95%. Despite of the above and other achievements, the developments of the catalysts that exhibit higher performances should be continued. This work now reports that 1% Ru-loaded ETS-10 [Ru(1%)-ETS-10] and 1% Ru-loaded TiO2 [Ru(1%)-TiO2] give the intrinsic reaction rates of 329 and 266 mmolCH4 g−1h−1, TOFs of 3321 and 2684 h−1 with the CH4 selectivities of 85.8 and 97.9%, respectively. In particular, Ru(1%)-ETS-10 is superior to Ru(1%)-TiO2 in terms of the stability (stable for more than 130 h). The analyses of the above three catalysts suggested the guidelines to prepare high performance catalysts, which are the support should be microporous materials and should possess the capability to introduce metal ions into the support by cation exchange so that they can be activated to metal nanoparticles by reduction, the support should be able to stabilize the metal nanoparticles, the active metal catalysts should be 2–5 nm sized three-dimensional (3D) Rux nanoparticles, the loading level of Rux nanoparticles should be 1%, the support should have the affinity to capture CO2 so that the catalyst can have the dual functionality of CO2 capture and CO2 reduction, the Rux nanoparticles should be highly basic, and the prepared Rux nanoparticles should not be poisoned by CO.

Iron promoted MOF-derived carbon encapsulated NiFe alloy nanoparticles core-shell catalyst for CO2 methanation

The highly ordered and designable properties of MOFs make them competitive precursors to constructing high-performance catalysts for CO2 methanation, however, only a few studies have investigated the facilitation effect of promoters. Herein, a series of carbon encapsulated NiFe alloy nanoparticles core-shell catalysts (NixFe@C, x refers to the ratio of Ni to Fe) were successfully prepared by a method of pyrolyzing Ni-MOF-74 after impregnation in Fe3+ solution for CO2 hydrogenation to CH4, and their composition and structural characteristics were explored in detail by PXRD, N2 adsorption/desorption measurements, TEM, and XPS, etc. Fe-doped catalysts exhibited significantly enhanced CO2 methanation activity compared to the monometallic Ni catalysts, especially Ni7Fe@C, which reached 72.3 % CO2 conversion with CH4 selectivity of 99.3 % at 350 °C, and showed a CO2 conversion of 53.3 % at 300 °C, twice that of Ni@C. The specific effects of the Fe addition on the composition and structure of the catalysts were also investigated via a combination of experiments and DFT calculations, which indicates that appropriate incorporation of Fe was conducive to promoting the dispersion of metal particles and the adsorption ability of CO2 and CO, and thus resulted in significantly improved catalytic performance. This work provides a promising route for the rational design of MOF-derived CO2 methanation catalysts and makes a new attempt to investigate the influence of promoters.

High-performance Ni/OMA catalyst achieved by solid-state grinding – A case study of CO methanation

The development of methanation catalysts with a high catalytic activity at low temperatures and a long-term durability at high temperatures is still challenged by the conflicting constraint on the catalyst design. In this work, Ni(NO3)2·6H2O. and ordered mesoporous alumina (OMA) containing different amounts of the P123 template were co-ground to prepare Ni/OMA catalysts. Results indicate that NiO was embedded in the meso-channels of OMA via the solid-state grinding. Moreover, the metal particle size, dispersion and reducibility of the catalyst can be easily regulated by the amount of the residual P123 template in OMA, which can be simply controlled by changing the treatment temperature of the OMA precursor. The optimized 15Ni/OMA-120 with a high dispersion and small size of metallic Ni showed high low-temperature catalytic activity with TOF of 31.5 h−1 and STY of 319.1 molCH4 gcat h−1 at 340 °C, but also demonstrated good anti-sintering and coke-resistance performance with a time-on-stream of 150 h long-term durability at 600 °C, which is comparable with the counterpart 15Ni-OMA prepared by traditional wet-process of one-pot evaporation induced self-assembly.