Recent trend in thermal catalytic low temperature CO2 methanation: A critical review

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.

Highly Active Ce- and Mg-Promoted Ni Catalysts Supported on Cellulose-Derived Carbon for Low-Temperature CO2 Methanation

The CO₂ methanation performance of Mg- and/or Ce-promoted Ni catalysts supported on cellulose-derived carbon (CDC) was investigated. The samples, prepared by biomorphic mineralization techniques, exhibit pore distributions correlated to the particle sizes, revealing a direct effect of the metal content in the textural properties of the samples. The catalytic performance, evaluated as CO₂ conversion and CH₄ selectivity, reveals that Ce is a better promoter than Mg, reaching higher conversion values in all of the studied temperature range (150-500 °C). In the interval of 350-400 °C, Ni-Mg-Ce/CDC attains the maximum yield to methane, 80%, reaching near 100% CH₄ selectivity. Ce-promoted catalysts were highly active at low temperatures (175 °C), achieving 54% CO₂ conversion with near 100% CH₄ selectivity. Furthermore, the large potential stability of the Ni-Mg-Ce/CDC catalyst during consecutive cycles of reaction opens a promising route for the optimization of the Sabatier process using this type of catalyst.

One-Pot Synthesis of Ni0.05Ce0.95O2−δ Catalysts with Nanocubes and Nanorods Morphology for CO2 Methanation Reaction and in Operando DRIFT Analysis of Intermediate Species

The valorization of CO2 via renewable energy sources allows one to obtain carbon-neutral fuels through its hydrogenation, like methane. In this study, Ni0.05Ce0.95O2−δ catalysts were prepared using a simple one-pot hydrothermal method yielding nanorod and nanocube particles to be used for the methanation reaction. Samples were characterized by XRD, BET, TEM, H2-TPR, and H2-TPD experiments. The catalytic activity tests revealed that the best performing catalyst was Ni0.05Ce0.95O2−δ, with nanorod morphology, which gave a CO2 conversion of 40% with a selectivity of CH4 as high as 93%, operating at 325 °C and a GHSV of 240,000 cm3 h−1 g−1. However, the lower activation energy was found for Ni0.05Ce0.95O2−δ catalysts with nanocube morphology. Furthermore, an in operando diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS) analysis was performed flowing CO2:H2 or CO:H2 mixture, showing that the main reaction pathway, for the CO2 methanation, is the direct hydrogenation of formate intermediate.

Alkali and Alkali-Earth Metals Incorporation to Ni/USY Catalysts for CO2 Methanation: The Effect of the Metal Nature

CO2 methanation is typically carried out using Ni-supported catalysts containing promoters such as alkali or alkali-earth metals to improve their properties. In this work, bimetallic Ni-based USY zeolite catalysts containing alkali (Li, K and Cs) and alkali-earth (Mg, Ca) metal compounds were prepared using the same conditions (15 wt% of metals; co-impregnation), characterized by N2 sorption, XRD, TGA, CO2 adsorption–desorption, DRS UV-Vis and H2-TPR, and finally applied in CO2 methanation reaction (86,100 mL h−1 g−1, PCO2 = 0.16 bar, H2:CO2 = 4:1). For each group, the effects of the second metal nature on the properties and performances were assessed. Alkali metals incorporation induced considerably low catalytic performances (CH4 yields < 26%), attributed to their negative impact on zeolite structure preservation. On the contrary, alkali-earth metal-containing catalysts exhibited lower structural damage. However, the formation of Ni-Mg mixed oxides in Ni-Mg/USY catalyst and CaCO3 during the reaction in Ni-Ca/USY sample could explain their performances, similar or lower than those obtained for Ni/USY catalyst. Among the studied metals, calcium was identified as the most interesting (CH4 yield of 65% at 415 °C), which was ascribed to the slight improvement of the Ni0 dispersion.

Enhancing CO2 Conversion to CO over Plasma-Deposited Composites Based on Mixed Co and Fe Oxides

The hydrogenation of CO2 to produce CO and H2O, known as reverse-water-gas shift reaction (RWGS) is considered to be an important CO2 valorization pathway. This work is aimed at proposing the thin-film catalysts based on iron and cobalt oxides for this purpose. A series of Fe–Co nanocomposites were prepared by the plasma-enhanced chemical vapor deposition (PECVD) from organic cobalt and iron precursors on a wire-mesh support. The catalysts were characterized by SEM/EDX, XPS, XRD, and Raman spectroscopy and studied for hydrogenation of CO2 in a tubular reactor operating in the temperature range of 250–400 °C and atmospheric pressure. The Co-based catalyst, containing crystalline CoO phase, exhibited high activity toward CH4, while the Fe-based catalyst, containing crystalline Fe2O3/Fe3O4 phases, was less active and converted CO2 mainly into CO. Regarding the Fe–Co nanocomposites (incl. Fe2O3/Fe3O4 and CoO), even a small fraction of iron dramatically inhibited the production of methane. With increasing the atomic fraction of iron in the Fe–Co systems, the efficiency of the RWGS reaction at 400 °C increased up to 95% selectivity to CO and 30% conversion of CO2, which significantly exceeded the conversion for pure iron–based films (approx. 9%). The superior performance of the Fe–Co nanocomposites compared to “pure” Co and Fe–based films was proposed to be explained by assuming changes in the electronic structure of the catalyst resulting from the formation of p–n junctions between nanoparticles of cobalt and iron oxides.

Capture and Reuse of Carbon Dioxide (CO2) for a Plastics Circular Economy: A Review

Plastic production has been increasing at enormous rates. Particularly, the socioenvironmental problems resulting from the linear economy model have been widely discussed, especially regarding plastic pieces intended for single use and disposed improperly in the environment. Nonetheless, greenhouse gas emissions caused by inappropriate disposal or recycling and by the many production stages have not been discussed thoroughly. Regarding the manufacturing processes, carbon dioxide is produced mainly through heating of process streams and intrinsic chemical transformations, explaining why first-generation petrochemical industries are among the top five most greenhouse gas (GHG)-polluting businesses. Consequently, the plastics market must pursue full integration with the circular economy approach, promoting the simultaneous recycling of plastic wastes and sequestration and reuse of CO2 through carbon capture and utilization (CCU) strategies, which can be employed for the manufacture of olefins (among other process streams) and reduction of fossil-fuel demands and environmental impacts. Considering the previous remarks, the present manuscript’s purpose is to provide a review regarding CO2 emissions, capture, and utilization in the plastics industry. A detailed bibliometric review of both the scientific and the patent literature available is presented, including the description of key players and critical discussions and suggestions about the main technologies. As shown throughout the text, the number of documents has grown steadily, illustrating the increasing importance of CCU strategies in the field of plastics manufacture.

Low temperature methanation of CO2 over an amorphous cobalt-based catalyst

CO2 methanation is an important reaction in CO2 valorization. Because of the high kinetic barriers, the reaction usually needs to proceed at higher temperature (>300 °C). High-efficiency CO2 methanation at low temperature (<200 °C) is an interesting topic, and only several noble metal catalysts were reported to achieve this goal. Currently, design of cheap metal catalysts that can effectively accelerate this reaction at low temperature is still a challenge. In this work, we found that the amorphous Co-Zr0.1-B-O catalyst could catalyze the reaction at above 140 °C. The activity of the catalyst at 180 °C reached 10.7 mmolCO2 gcat -1 h-1, which is comparable to or even higher than that of some noble metal catalysts under similar conditions. The Zr promoter in this work had the highest promoting factor to date among the catalysts for CO2 methanation. As far as we know, this is the first report of an amorphous transition metal catalyst that could effectively accelerate CO2 methanation. The outstanding performance of the catalyst could be ascribed to two aspects. The amorphous nature of the catalyst offered abundant surface defects and intrinsic active sites. On the other hand, the Zr promoter could enlarge the surface area of the catalyst, enrich the Co atoms on the catalyst surface, and tune the valence state of the atoms at the catalyst surface. The reaction mechanism was proposed based on the control experiments.

Barium promoted Ni/Sm2O3 catalysts for enhanced CO2 methanation

Low temperature CO₂ methanation is a favorable pathway to achieve high selectivity to methane while increasing the stability of the catalysts. A Ba promoted Ni/Sm₂O₃ catalyst was investigated for CO₂ methanation at atmospheric pressure with the temperature ranging from 200–450 °C. 5Ni–5Ba/Sm₂O₃ showed significant enhancement of CO₂ conversion particularly at temperatures ≤ 300 °C compared to Ni/Sm₂O₃. Incorporation of Ba into 5Ni/Sm₂O₃ improved the basicity of the catalysts and transformed the morphology of Sm₂O₃ from random structure into uniform groundnut shape nanoparticles. The uniformity of Sm₂O₃ created interparticle porosity that may be responsible for efficient heat transfer during a long catalytic reaction. Ba is also postulated to catalyze oxygen vacancy formation on Sm₂O₃ under a reducing environment presumably via isomorphic substitution. The disappearance of a high temperature (∼600 °C) reduction peak in H₂-TPR analysis revealed the reducibility of NiO following impregnation with Ba. However, further increasing the Ba loading to 15% formed BaNiO₃–BaNiO_2.36 phases which consequently reduced the activity of the Ni–Ba/Sm₂O₃ catalyst at low temperature. Ni was suggested to segregate from BaNiO₃–BaNiO_2.36 at high temperature thus exhibiting comparable activity with Ni/Sm₂O₃ at 450 °C.

Low temperature CO₂ methanation on 5Ni–5Ba/Sm₂O₃ is a favorable pathway to achieve high selectivity to methane while increasing the stability of the catalysts.

Understanding the opportunities of metal–organic frameworks (MOFs) for CO2 capture and gas-phase CO2 conversion processes: a comprehensive overview

The rapid increase in the concentration of atmospheric carbon dioxide is one of the most pressing problems facing our planet.

Bimetallic Ni-Based Catalysts for CO2 Methanation: A Review

CO₂ methanation has recently emerged as a process that targets the reduction in anthropogenic CO₂ emissions, via the conversion of CO₂ captured from point and mobile sources, as well as H₂ produced from renewables into CH₄. Ni, among the early transition metals, as well as Ru and Rh, among the noble metals, have been known to be among the most active methanation catalysts, with Ni being favoured due to its low cost and high natural abundance. However, insufficient low-temperature activity, low dispersion and reducibility, as well as nanoparticle sintering are some of the main drawbacks when using Ni-based catalysts. Such problems can be partly overcome via the introduction of a second transition metal (e.g., Fe, Co) or a noble metal (e.g., Ru, Rh, Pt, Pd and Re) in Ni-based catalysts. Through Ni-M alloy formation, or the intricate synergy between two adjacent metallic phases, new high-performing and low-cost methanation catalysts can be obtained. This review summarizes and critically discusses recent progress made in the field of bimetallic Ni-M (M = Fe, Co, Cu, Ru, Rh, Pt, Pd, Re)-based catalyst development for the CO₂ methanation reaction.

Promising Catalytic Systems for CO2 Hydrogenation into CH4: A Review of Recent Studies

The increasing utilization of renewable sources for electricity production turns CO2 methanation into a key process in the future energy context, as this reaction allows storing the temporary renewable electricity surplus in the natural gas network (Power-to-Gas). This kind of chemical reaction requires the use of a catalyst and thus it has gained the attention of many researchers thriving to achieve active, selective and stable materials in a remarkable number of studies. The existing papers published in literature in the past few years about CO2 methanation tackled the catalysts composition and their related performances and mechanisms, which served as a basis for researchers to further extend their in-depth investigations in the reported systems. In summary, the focus was mainly in the enhancement of the synthesized materials that involved the active metal phase (i.e., boosting its dispersion), the different types of solid supports, and the frequent addition of a second metal oxide (usually behaving as a promoter). The current manuscript aims in recapping a huge number of trials and is divided based on the support nature: SiO2, Al2O3, CeO2, ZrO2, MgO, hydrotalcites, carbons and zeolites, and proposes the main properties to be kept for obtaining highly efficient carbon dioxide methanation catalysts.

Aqueous Miscible Organic LDH Derived Ni-Based Catalysts for Efficient CO2 Methanation

Converting CO2 to methane via catalytic routes is an effective way to control the CO2 content released in the atmosphere while producing value-added fuels and chemicals. In this study, the CO2 methanation performance of highly dispersed Ni-based catalysts derived from aqueous miscible organic layered double hydroxides (AMO-LDHs) was investigated. The activity of the catalyst was found to be largely influenced by the chemical composition of Ni metal precursor and loading. A Ni-based catalyst derived from AMO-Ni3Al1-CO3 LDH exhibited a maximum CO2 conversion of 87.9% and 100% CH4 selectivity ascribed to both the lamellar catalyst structure and the high Ni metal dispersion achieved. Moreover, due to the strong Ni metal–support interactions and abundant oxygen vacancy concentration developed, this catalyst also showed excellent resistance to carbon deposition and metal sintering. In particular, high stability was observed after 19 h in CO2/H2 reaction at 360 °C.

Ru and Ni—Privileged Metal Combination for Environmental Nanocatalysis

Privileged structures is a term that is used in drug design to indicate a fragment that is popular in the population of drugs or drug candidates that are in the application or investigation phases, respectively. Privileged structures are popular motifs because they generate efficient drugs. Similarly, some elements appear to be more efficient and more popular in catalyst design and development. To indicate this fact, we use here a term privileged metal combination. In particular, Ru-based catalysts have paved a bumpy road in a variety of commercial applications from ammonia synthesis to carbon (di)oxide methanation. Here, we review Ru/Ni combinations in order to specifically find applications in environmental nanocatalysis and more specifically in carbon (di)oxide methanation. Synergy, ensemble and the ligand effect are theoretical foundations that are used to explain the advantages of multicomponent catalysis. The economic effect is another important issue in blending metal combinations. Low temperature and photocatalytic processes can be indicated as new tendencies in carbon (di)oxide methanation. However, due to economics, future industrial developments of this reaction are still questionable.

Zeolite-Supported Ni Catalysts for CO2 Methanation: Effect of Zeolite Structure and Si/Al Ratio

The urgent need to reduce CO2 emissions requires the development of efficient catalysts for the conversion of CO2 into chemicals and fuels. In this study, a series of nickel catalysts supported on ITQ-2 and ZSM-5 zeolites have been prepared, characterized and tested in the hydrogenation reaction of CO2 towards methane. Specifically, two ITQ-2 and two ZSM 5 zeolites with different aluminum content have been studied. For both types, the higher Si/Al ratio of the material, the more active the catalyst due probably to its higher hydrophobicity. The largest difference was found for the ITQ-2 samples, being the CO2 conversion for the sample with a greater Si/Al ratio 50 points higher at 350 °C. Comparing both zeolite structures, while similar catalytic results were obtained with the samples with lower Si/Al ratio, a distinctly higher activity was found for the ITQ-2 zeolite without aluminum, pure silica. Therefore, this result suggests that the presence of aluminum is of particular relevance. Among the studied materials, the catalyst supported on the delaminated ITQ-2 zeolite without Al was the most active catalyst. Its higher activity was mainly attributed to the smaller crystallite size of nickel supported on the large external surface area presented by this zeolite.

The Role of Alkali and Alkaline Earth Metals in the CO2 Methanation Reaction and the Combined Capture and Methanation of CO2

CO2 methanation has great potential for the better utilization of existing carbon resources via the transformation of spent carbon (CO2) to synthetic natural gas (CH4). Alkali and alkaline earth metals can serve both as promoters for methanation catalysts and as adsorbent phases upon the combined capture and methanation of CO2. Their promotion effect during methanation of carbon dioxide mainly relies on their ability to generate new basic sites on the surface of metal oxide supports that favour CO2 chemisorption and activation. However, suppression of methanation activity can also occur under certain conditions. Regarding the combined CO2 capture and methanation process, the development of novel dual-function materials (DFMs) that incorporate both adsorption and methanation functions has opened a new pathway towards the utilization of carbon dioxide emitted from point sources. The sorption and catalytically active phases on these types of materials are crucial parameters influencing their performance and stability and thus, great efforts have been undertaken for their optimization. In this review, we present some of the most recent works on the development of alkali and alkaline earth metal promoted CO2 methanation catalysts, as well as DFMs for the combined capture and methanation of CO2.

Sustainable Carbon as Efficient Support for Metal-Based Nanocatalyst: Applications in Energy Harvesting and Storage

Sustainable activated carbon can be obtained from the pyrolysis/activation of biomass wastes coming from different origins. Carbon obtained in this way shows interesting properties, such as high surface area, electrical conductivity, thermal and chemical stability, and porosity. These characteristics among others, such as a tailored pore size distribution and the possibility of functionalization, lead to an increased use of activated carbons in catalysis. The use of activated carbons from biomass origins is a step forward in the development of more sustainable processes enhancing material recycling and reuse in the frame of a circular economy. In this article, a perspective of different heterogeneous catalysts based on sustainable activated carbon from biomass origins will be analyzed focusing on their properties and catalytic performance for determined energy-related applications. In this way, the article aims to give the reader a scope of the potential of these tailor-made sustainable materials as a support in heterogeneous catalysis and future developments needed to improve catalyst performance. The selected applications are those related with H2 energy and the production of biomethane for energy through CO2 methanation.

Three-Dimensional Mesoporous Ni-CeO2 Catalysts with Ni Embedded in the Pore Walls for CO2 Methanation

Mesoporous Ni-based catalysts with Ni confined in nanochannels are widely used in CO2 methanation. However, when Ni loadings are high, the nanochannels are easily blocked by nickel particles, which reduces the catalytic performance. In this work, three-dimensional mesoporous Ni-CeO2-CSC catalysts with high Ni loadings (20−80 wt %) were prepared using a colloidal solution combustion method, and characterized by nitrogen adsorption–desorption, X-ray diffraction (XRD), transmission electron microscopy (TEM) and H2 temperature programmed reduction (H2-TPR). Among the catalysts with different Ni loadings, the 50% Ni-CeO2-CSC with 50 wt % Ni loading exhibited the best catalytic performance in CO2 methanation. Furthermore, the 50% Ni-CeO2-CSC catalyst was stable for 50 h at 300° and 350 °C in CO2 methanation. The characterization results illustrate that the 50% Ni-CeO2-CSC catalyst has Ni particles smaller than 5 nm embedded in the pore walls, and the Ni particles interact with CeO2. On the contrary, the 50% Ni-CeO2-CP catalyst, prepared using the traditional coprecipitation method, is less active and selective for CO2 methanation due to the larger size of the Ni and CeO2 particles. The special three-dimensional mesoporous embedded structure in the 50% Ni-CeO2-CSC can provide more metal–oxide interface and stabilize small Ni particles in pore walls, which makes the catalyst more active and stable in CO2 methanation.