This paper provides a revision of the latest studies on the topic methanation, a multi-stage process where water is first converted into hydrogen in an electrolyzer, which subsequently reacts with ...carbon dioxide to produce methane. The present and future of the most common water electrolysis technologies is addressed. Critical issues to take into consideration when selecting a carbon dioxide source are evaluated. Chemical and biological approaches, together with photocatalytic configurations are discussed, analyzing pros and cons in all the cases. This paper also highlights the extensive work being done in the development of catalysts capable of selectively converting carbon dioxide into methane, as well as the different reactor configurations that can be used with this aim in any of the available methanation modalities. Relevant power-to-methane plants in Europe have been identified and assessed regarding their location, year of commissioning, capacity, technology for electrolysis and methanation type. Finally, cost issues are analyzed, highlighting economic perspectives of the power-to-methane technologies for the next decades. This document reviews all the key elements associated with the methanation process, revealing which aspects can pave the way for the large-scale implementation of this power generation model. In this sense, the gradual cost reduction of the equipment involved and the continuous increase in the efficiency of the processes are revealed as crucial aspects that can lead to a general implementation of the methanation concept on the way to a low carbon economy.
•The latest studies on Power to Methane (PtM) processes are reviewed.•Methanation systems will facilitate the transition to a low-carbon economy.•Flexible operation of PEMEC electrolyzers makes them the best option for PtM plants.•Chemical methanation have the greatest potential to be implemented on a large scale.•Biological methanation is a promising pathway for future energy storage.
To elucidate the effect of solution viscosity on the synthesis of Ni-phyllosilicate, polyacrylamide was incorporated to create a viscous aqueous medium containing of sodium metasilicate, nickel ...nitrate and NH4F. The enhanced viscosity promotes the dispersion of the initial formed crystal seeds and the growth of Ni-phyllosilicate, culminating in a Ni-rich NiPs-RT-6 of a high Ni content of up to 55.2 wt%. Residual polyacrylamide elimination was accomplished via calcination, concurrently enhancing metal-support interaction. The as-synthesized samples display a nanoflower morphology with nanospheres overlaid with numerous thin nanosheets. The relatively small Ni particles around 5.7 nm were obtained after reduction even at a very high Ni loading, owing to its strong metal-support interaction. NiPs-RT-6 achieves a CO2 conversion of 75.9% at 450 °C, 0.1 MPa, 60 L g−1·h−1, which closely approximates thermodynamic equilibrium. The turn over frequency for CO2 (TOFCO2) was substantial, calculated at 3.7 × 10−3 s−1, accompanied by activation energy (Ea) of 80.6 kJ·mol–1. In-situ Diffuse Reflectance Infrared Fourier Transform Spectroscopy (DRIFTS) further disclosed that m-HCOO– serves as a crucial intermediate following a formate reaction pathway. With its high Ni content, finely distributed Ni particles, and strong metal-support interaction, NiPs-RT-6 demonstrates promising catalytic activity in CO2 methanation.
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•The room-temperature synthesis of Ni-phyllosilicate was achieved.•A viscous solvent of polyacrylamide significantly promoted the synthesis of Ni-phyllosilicate.•The reduced Ni-phyllosilicate retained small Ni particles at a high Ni content.•Polyacrylamide improved the catalytic performance of CO2 methanation.
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•CO and CO2 methanation was investigated over supported Ni catalysts.•Ni/CeO2 catalysts showed the highest activity.•The high-surface-area ceria provides the high Ni dispersion and ...activity.•Co-precipitated Ni0.8Ce0.2Ox catalyst showed the highest specific activity.
CO and CO2 methanation was investigated over Ni catalysts supported on different supports such as γ-Al2O3, SiO2, TiO2, CeO2, and ZrO2. Among them, Ni/CeO2 was determined to be the most active for CO and CO2 methanation. These catalytic activities increased with increasing surface area of CeO2. To increase the specific catalytic activity for CO and CO2 methanation, various Ni-CeO2 catalysts with different Ni contents were prepared using co-precipitation method. The optimum Ni content was determined for both reactions. The prepared catalysts were characterized with inductively coupled plasma-atomic emission spectroscopy, N2 physisorption, temperature-programmed reduction, temperature-programmed desorption, and X-ray diffraction. The high Ni dispersion and strong CO2 adsorption appeared to be responsible for the high catalytic activity for CO and CO2 methanation. This Ni-CeO2 can be applied to the low-temperature CO and CO2 methanation reactor to achieve high single-pass conversions of CO and CO2.
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•The effect of promoter was evaluated for CO and CO2 methanation.•Mn, Ce, Mg, V, and Zr are beneficial for both CO and CO2 methanation activity.•CO2 methanation is related to the Ni ...dispersion and relevant CO2 adsorption.•Ni-V/Al@Al2O3 with the highest Ni dispersion is the best for CO methanation.•The promotional effect of Mn is remarkable for both CO and CO2 methanation.
Effects of metal promoter on CO and CO2 methanation were examined over Ni-M (M = Mn, Ce, Zr, Mg, K, Zn, or V)/Al@Al2O3 catalysts prepared by the co-impregnation method. Ni-M (M = Mn, Ce, or Zr)/γ-Al2O3 catalysts were also investigated for comparison. The prepared catalysts were characterized with a variety of techniques such as N2 physisorption, CO2 chemisorption, H2 chemisorption, temperature-programmed reduction with H2 (H2-TPR), temperature-programmed desorption of CO2 (CO2-TPD), X-ray diffraction (XRD), high-resolution transmission electron microscopy (HRTEM), X-ray photoelectron spectroscopy (XPS), and in-situ diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS). Among different promoters, Mn, Ce, Mg, V, and Zr are beneficial to enhance both CO and CO2 methanation activity due to the improvement of the Ni dispersion. The Ni-V/Al@Al2O3 catalyst performs the highest CO methanation activity due to the largest Ni sites. However, it is not the best one for CO2 methanation among tested catalysts because of the much decrease in CO2 adsorption capacity. The promotional effect of Mn is the most remarkable for both CO and CO2 methanation. On the other hand, the negative effect of K and Zn was observed on both CO and CO2 methanation by the small number of active Ni sites and the decrease in the amount of basic sites. The CO2 methanation mechanism over Ni-Mn/Al@Al2O3 catalyst is elucidated by the transform route: adsorbed carbonate species – formate species – methane under hydrogenation process.
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•CO2 methanation follows the formate pathway on Ni/c-ZrO2.•The CO2* adsorbed states on the Ni/ZrO2 interface are hydrogenated to CH4.•The CO2* adsorbed states at Ni sites convert CO ...without further conversion to CH4.•ZrO2 improves Ni reducibility, and promotes H2O formation via H-spillover effect.•Y3+ doping stabilizes cubic ZrO2 support and improves the Ni/ZrO2 catalyst.
The CO2 methanation mechanism was studied via combined in-situ FTIR and DFT calculations on the cubic ZrO2 supported Ni catalyst. The formation and evolution of CO2 initial adsorbed species were addressed. The bicarbonates produced from CO2 reacting with surface OH sites are transformed to the CO2* adsorbed state on the Ni/ZrO2 interface (CO2*-interface) that are hydrogenated to CH4. The CO2 adsorbed states (CO2*-Ni) generated from CO2 reacting with surface Ni sites are hydrogenated to CO* as a byproduct rather than an intermediate for methanation. The formate pathway is dominated for methanation on Ni/ZrO2, in which bidentate formates hydrogenation to H2COO* is the rate-determining step with the activation energy of 1.01 eV. The presence of ZrO2 support improves the electron mobility and reducibility of Ni, and induces H-spillover effect to promote H2O* formation. Y3+ doping into the support of Ni/ZrO2 stabilizes the c-ZrO2 phase and promote methanation activity of the catalyst.
The performance of nickel supported on lanthana-modified hydroxyapatite (HAP) catalysts is investigated in the CO2 methanation. The addition of La (1–6.6 wt%) leads to a surface enrichment following ...a sequential multilayer deposition model. Moreover, La addition systematically improves the dispersion of Ni particles and their reducibility, which in turn increases spectacularly the amounts of basic sites and their thermal stability. Such physicochemical changes impact positively on the activity of the catalysts in CO2 methanation. The estimated turnover frequency (TOF) suggest that the small Ni particles are the most efficient. The latter seem to provide a large density of very active defects on Ni-La2O3 interface. The optimized catalyst proves to be highly resistant to deactivation during 100 h time-on-stream (TOS). The samples were also assayed as dual function materials (DFMs) for CO2 adsorption and methanation. A scheme is proposed to describe the different steps involved in a CO2 adsorption/hydrogenation cycle.
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•The performance of Ni/La(x)/HAP catalysts is investigated in CO2 capture and methanation.•Lanthana addition leads to a surface enrichment following a sequential multilayer deposition model.•The presence of lanthana enhances the surface basicity, the dispersion of Ni particles and their reducibility.•Ni/La(x)/HAP catalysts show a high activity and prove to be competitive with reference materials in CO2 methanation.•The optimized catalyst demonstrates a high resistance to deactivation during 100 h TOS.
The advances and challenges of power-to-methane, especially the methanation process, including operation parameters, catalyst categories and roles, and reaction/deactivation mechanisms, are discussed ...in detail.
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Power-to-methane (P2M) processes, by converting electricity from renewable energy to H2 and then into other high value-added and energy-intense chemicals in the presence of active catalysts, have become an effective solution for energy storage. However, the fluctuating electricity from intermittent renewable energy leads to a dynamic composition of reactants for downstream methanation, which requires an excellent heterogeneous catalyst to withstand the harsh conditions. Based on these findings, the objective of this review is to classify the fundamentals and status of CO/CO2 methanation and identify the pathways in the presence of various catalysts for methane production. In addition, this review sheds insight into the future development and challenges of CO2 or CO methanation, including the deactivation mechanisms and catalyst performance under dynamically harsh conditions. Finally, we elaborated on the advantages and development prospects of P2M, and then we summarized the current stage and ongoing industrialization projects of P2M.
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•The ultrathin Ni-phyllosilicate was successfully synthesized by ball milling method.•H2O2 played a crucial role of pore-forming reagent to create defects in Ni-phyllosilicate.•Nickel ...acetylacetonate was the optimal nickel salt precursor to form Ni-phyllosilicate.•Metal utilization rate was significantly improved owing to the ultrathin defect-rich structure.•The optimum catalyst exhibited enhanced low-temperature activity for CO2 methanation.
To address the problems of low metal utilization rate and poor low-temperature activity of the nickel phyllosilicate catalysts for CO2 methanation, this work prepared ultrathin defect-rich Ni-phyllosilicate through ball milling method in the presence of H2O2 modifier, which simultaneously created active sites with more quantity and higher quality. The instantaneous temperature and high pressure derived from the collision and friction of grinding balls provided driving force for the Ni-phyllosilicate synthesis, and the shear force destroyed the interlayer forces to construct the ultrathin layers. H2O2 molecule could insert the layers and dissociate to O2 bubbles, whose cavitation effect created holes and defects in the nickel phyllosilicate nanosheets and SiO2 spheres. H2O2 amount was crucial for the defect construction and the optimum Ni-AA-1H catalyst possessed the ultrathin nanosheet of 0.68 nm and high Ni dispersion of 15.6 %, whose TOFCO2 reached 3.76 × 10−2 s−1 at 160 °C. The in-situ DRIFTS results confirmed the enhanced low-temperature activity and the HCOO− reaction pathway over Ni-AA-1H for CO2 methanation. Nickel precursor effect was also investigated, and nickel acetylacetonate was determined as the optimal one compared with nickel acetate and nickel chloride, owing to the high steric effect of CH3COCHCOCH3− group and strong basicity environment during ball milling process.
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•Ni-M (La, Ce, Fe or Co)/ZrO2-clays show excellent catalytic activity for CO and CO2 methanation.•La, Ce, Fe or Co promotes NiO dispersion and enhance the thermal stability of ...catalyst.•Cerium doped catalyst shows superior catalytic activity to other elements for CO methantion.•Ion doped catalyst shows superior catalytic activity to other elements for CO2 methantion.•High performance is resulted from synergy of doped element, ZrO2 modified clays and nickel species.
The metal (La, Ce, Fe or Co) doped nickel catalysts supported on zirconia modified clays have been prepared by the incipient wetness impregnation method. The zirconia modified clays have a new mesoporous structure with zirconia nanoparticles highly dispersed on the partly damaged clay layers and have been prepared in one pot by the hydrothermal treatment. The catalytic performances of the catalysts for CO and CO2 methanation have been investigated. The catalysts have been characterized by X-ray diffraction (XRD), transmittance electron microscopy (TEM), H2 temperature-programmed reduction (H2-TPR), nitrogen adsorption-desorption, and thermogravimetry and differential thermal analysis (TG-DTA). It is found that small amount of La, Ce, Co or Fe in the nickel catalyst supported on the zirconia modified clays promote the dispersion of NiO nanoparticles, increase the quantity of the reduced active nickel species in the catalyst and enhance the thermal stability for CO and CO2 methanation. The addition of La or Ce in the catalysts is beneficial to CO methanation, and Ce is superior to the other three elements for this reaction. The addition of Fe and Co is beneficial to CO2 methanation, and Fe is superior to the other three elements for CO2 methanation. The metal doped catalysts exhibit excellent stability for both CO and CO2 methanation. The outstanding catalytic performance of the catalyst is resulted from the synergistic effect of doped metal, zirconia on the clay layers, the mesopores on support, as well as the active nickel species.
