From CO 2 capture to synthetic methane: the emerging role of dual functional materials

Introduction

Carbon capture and utilisation (CCU) emerges as a key strategy for achieving deep reductions in greenhouse gas emissions and supporting the transition to a low-carbon economy. By capturing carbon dioxide (CO₂) from industrial processes, power generation facilities, or directly from the atmosphere, CCU enables the capture of significant quantities of CO₂ by using it as feedstock and converting it into valuable products such as fuels, chemicals or construction materials, creating a circular carbon economy that reduces dependence on fossil resources. Among the various CCU pathways (such as CO₂ mineralisation, electrochemical and thermochemical conversion into fuels and chemicals, polymer synthesis, or incorporation into construction materials), the conversion of captured CO₂ into synthetic methane has gained particular attention within the Power-to-Gas (PtG) framework. By coupling carbon utilisation with renewable energy storage, PtG offers a route to both valorise CO₂ emissions and mitigate the intermittency of renewable power sources while leveraging existing natural gas infrastructure. This process is particularly important for hard-to-abate sectors, including cement, steel, and chemical production, where direct electrification or complete process decarbonization remains challenging. When integrated with renewable energy sources, carbon utilisation pathways can further lower lifecycle emissions and contribute to net-zero targets. Consequently, CCU not only mitigates climate change by reducing atmospheric CO₂ emissions but also offers economic opportunities through the development of sustainable carbon-based products and industrial innovation.

The importance of synthetic methane lies in its compatibility with existing natural gas infrastructure, including storage, transport and distribution networks and its integration with renewable energy storage systems. Synthetic methane is produced from CO₂ through the Sabatier reaction [Equation 1] utilising catalysts based on Ni, Ru, Co, Fe, Rh, Pd, operating at atmospheric or near atmospheric pressure and temperatures ranging 100 °C–400 °C depending on the metal.

CO 2 g + H 2 g ↔ CH 4 g + 2 H 2 O g Δ H 25 ° C = − 164 kJ / mol (1)

State-of-the-art CO₂ capture and subsequent conversion to synthetic methane routes remain constrained by several techno-economic bottlenecks, being mainly the substantial energy requirements, operational complexity, and the need for discrete stages for CO₂ purification, compression, transport, and catalytic conversion (Zimmermann et al., 2020). These limitations have inspired growing interest in integrated CO₂ capture and utilisation (ICCU). The core of this process-intensified concept are the dual functional materials (DFMs), which couple CO₂ adsorption and catalytic conversion within a single reactor or integrated process units, allowing the conversion of captured CO₂ into value-added chemicals (Duyar et al., 2015).

The use of DFMs has been explored for CO₂ methanation, CO production through the Reverse Water Gas Shift (RWGS) (Yu et al., 2025) or Dry Reforming of Methane (DRM) processes and, to a lesser extent, methanol (Jeong-Potter et al., 2024; Paksoy et al., 2025) or higher-hydrocarbon synthesis. Methanation nevertheless dominates DFM research because the Sabatier reaction is technologically mature, highly selective, compatible with common capture phases, and generally operable under conditions closer to those of CO₂ capture. As a result, the benefits of integrating capture and conversion can be partially or completely offset by the addition compression, depressurization, and process complexity required to operate the system.

Dual functional materials (DFMs)

DFMs, also referred to in the literature as integrated capture and conversion materials, combine CO₂ capture sites and catalytically active phases, enabling the direct transformation of adsorbed CO₂ into value-added products such as methane, carbon monoxide, or methanol (Sun et al., 2021). Integrating capture and conversion within a single material and process reduces the energy demand and infrastructure complexity typically associated with conventional sequential schemes of CO₂ capture, storage, transport and utilisation. In addition, the ICCU enables thermal and operational coupling among CO₂ desorption, hydrogen-driven adsorbent regeneration, and catalytic reaction (Faria et al., 2025), as represented in Figure 1.

Considerable progress has been made in developing DFMs for integrated CO₂ capture and methanation, resulting in a wide variety of formulations that combine adsorption and catalytic functionalities in a single material. Most DFMs are based on porous supports with surface area exceeding 200 m²/g (Bermejo-López et al., 2024), which promotes the dispersion of both adsorbent and catalytic sites, and facilitates mass transfer during cyclic operation (Zhang et al., 2024). In this context, hierarchical pore networks (integrating micro-, meso- and macroporous domains) within a single material could reconcile high adsorption capacities with efficient mass transport. Such architectures may enable rapid diffusion of reactants and products while preserving a high density of active adsorption sites. Among the supports, Al₂O₃ remains the most widely employed due to its thermal stability, tunable porosity, and favourable metal–support interactions (Danaci et al., 2016; Wang et al., 2026). However, alternative supports, including SiO₂ (Ye et al., 2021), CeO₂ (Li et al., 2026), TiO₂ (Meng et al., 2024), zeolites (Shezad et al., 2026), activated carbons, and, more recently, biochar-derived materials (Frainetti and Klinghoffer, 2024), have also attracted attention because of their ability to modify surface basicity, enhance CO₂ accessibility, improve thermal conductivity, or provide more sustainable and cost-effective material platforms.

The CO₂ capture function is commonly provided by alkali and alkaline-earth metal oxides or carbonates, including Ca, Mg, Na, K and Li-based phases (Dunstan et al., 2021). These materials typically operate within the intermediate-temperature range relevant to methanation (ca. 300 °C–450 °C), thereby enabling the direct transfer of captured CO₂ species to neighbouring catalytic sites. Among them, Na₂CO₃ and K₂CO₃ have frequently demonstrated superior methane yields compared with CaO-based systems (0.614, 0.610, 0.466 and 0.213 mmol CH₄/gDFM for Na₂O, CaO, K₂O and MgO, respectively (Sun et al., 2021)) reflecting the critical role of adsorption strength, carbonate stability and regenerability in determining overall DFM performance. More recently, amine-functionalised DFMs have emerged as promising alternatives for lower-temperature applications, where CO₂ is captured via chemisorbed amine species (McNeary et al., 2025). It has been proposed that these species may access alternative and potentially less energy-intensive hydrogenation pathways (Lian et al., 2025); however, the mechanisms governing the interaction between amine-based capture sites and methanation catalysts remain largely unresolved.

Beyond the nature of the adsorbent phase, the catalytic performance of DFMs is strongly influenced by the chemical properties of the support and the metal/support interface. Oxygen vacancies have been shown to promote CO₂ activation by stabilising bent carbonate, bicarbonate, or formate intermediates that are more reactive than gaseous CO₂ molecules (Qin et al., 2026). DRIFTS studies have concluded the formate-mediated spillover mechanism Ru-based DFMs (Proaño et al., 2019). This work shows the different CO₂ adsorption and conversion mechanism and nature of intermediate species when Na is incorporated to Ru/Al₂O₃ systems, indicating that the exact nature of the adsorbed carbonate species, the importance of oxygen vacancies, and the extent of spillover depend on the DFM architecture and formulation. A short but widely mechanistic equation showing the CO₂ adsorption-CH₄ formation mechanism; however, the atomic-scale details of the transfer and hydrogenation of intermediates should be further researched.

C O 2 → c a r b o n a t e / b i c a r b o n a t e → f o r m a t e → C O * → C H x * → C H 4 (2)

Similar mechanistic principles can be extended to a broader range of reducible oxides, including zirconia, titania, perovskites, and mixed-metal oxides. The deliberate introduction of lattice distortions, heterovalent dopants, and non-stoichiometric compositions may provide a route to develop capture-catalytic materials with enhanced activity, selectivity and interfacial stability. In addition, single-atom catalytic sites anchored on oxygen-deficient supports could provide highly efficient hydrogen activation and selective stabilisation of reaction intermediates. Within this framework, the catalytic function in DFMs is generally provided by transition metals such as Ni, Ru, Co, Fe, Rh, Pd and Fe (Arellano-Treviño et al., 2019). Noble metals, particularly Ru and Rh, typically exhibit superior methanation activity, low-temperature performance and resistance to deactivation, whereas Ni remains the most extensively investigated catalyst owing to its favourable balance between activity, availability and cost (Qin et al., 2026). Nevertheless, Ni-based systems are generally more susceptible to oxidation, sintering, and carbon deposition, especially under cyclic capture–hydrogenation conditions, thereby motivating ongoing efforts to improve their stability through support engineering, promoter incorporation, and advanced catalyst architectures.

Promoters based on Ce, La, Zr, Mg, and alkali metals have been incorporated into DFMs to modify the physicochemical environment of the catalytic sites. Depending on their chemical state and loading, these promoters can enhance surface basicity and CO₂ activation, improve oxygen mobility and metal reducibility, promote metal dispersion, strengthen resistance to sintering, and modify the formation and stability of carbonate and formate intermediates. Their function should, however, be distinguished from that of the primary capture phase (Sun et al., 2019). Although species such as Mg, Na, or K may act as CO₂ sorbents when incorporated at relatively high loadings, they may also behave as catalytic promoters at lower concentrations by modifying the properties of the active metal, support, or metal–support interface. The resulting effect therefore depends strongly on promoter loading, composition, preparation method, and operating conditions (Pu et al., 2025; Zheng et al., 2025).

The beneficial effect of promoter incorporation is illustrated by a Ru-promoted Ni-based DMF containing 1 wt% Ru, 10 wt% Ni, and 6.1 wt.%Na₂O/Al₂O₃, which maintained a CO₂ capture capacity of 0.52 mmol/g DFM and CH₄ yield of 0.38 mmol/g DFM, after 20 cycles of capture/methanation cycles at 320 °C, demonstrating how promoter incorporation can complement support engineering and advanced catalyst architectures to improve the activity and durability of Ni-based DFMs.

DFMs limitations

Beyond these intrinsic material considerations, the transition of DFMs for CO₂ methanation from laboratory-scale demonstrations to robust process implementation is still limited by several interrelated bottlenecks (Figure 2). Excessive or poorly controlled interactions between CO₂ adsorption sites and methanation-active phases may compromise CO₂ uptake, catalytic activity, methane selectivity, or regeneration efficiency, while realistic operating environments containing steam, oxygen, or acidic impurities can promote sintering, oxidation, poisoning, or irreversible carbonate formation (Omodolor et al., 2020; Zhang et al., 2024). These degradation pathways are rarely independent: metal sintering reduces the density of accessible hydrogenation sites while simultaneously altering the local basicity of the support, so that adsorption capacity and catalytic activity decline in a coupled rather than additive manner. Additional constraints emerge when DFMs are shaped into structured or pelletised forms (Faria et al., 2023), where heat and mass-transfer limitations become particularly relevant due to the highly exothermic nature of the Sabatier reaction; local temperature gradients within pellets or coated structures can accelerate deactivation, broaden methane selectivity towards undesired by-products, and reduce overall process controllability (Tsiotsias et al., 2025). Taken together, these effects show that intrinsic material performance and macroscopic transport phenomena cannot be optimised independently of one another.

Therefore, the optimisation of DFMs must move beyond intrinsic adsorption and catalytic performance towards integrated criteria that include cyclic durability, impurity tolerance, mechanical stability, shaping, reactor configuration, dynamic operation with renewable H₂ supply, and techno-economic and life-cycle performance (Hussain et al., 2026). Addressing these interrelated material, reactor, and process-level limitations will be decisive in determining whether DFM-based CO₂ capture and methanation can progress from a promising process-intensification strategy to a technically robust and scalable PtG platform (Figure 2).

Novel materials design

From a formulation and synthesis perspective, addressing these limitations requires a transition from empirical formulation strategies towards the rational design of integrated adsorption–reaction architectures. Rather than treating adsorbents and catalysts as independent components simply co-located within the same solid, future DFMs should be conceived as engineered reaction environments in which CO₂ capture, intermediate transport and hydrogenation are deliberately organised across multiple length scales, from the atomic arrangement of active sites to the macroscopic geometry of the shaped material. Particular attention should be devoted to the design of adsorption/catalysis interfaces, across which captured CO₂ species must transfer efficiently towards methanation-active sites. The spatial arrangement of adsorption and catalytic domains needs to strike a delicate balance between proximity and separation: domains must lie close enough to enable rapid intermediate migration and conversion, yet sufficiently segregated to avoid active-site blockage, excessive carbonate stabilisation, undesired metal–support interactions, or competitive adsorption between CO₂ and reaction intermediates. This design viewpoint opens the door to advanced architectures such as core–shell systems, in which a protective or promotional shell limits metal sintering while preserving site accessibility (Li et al., 2014; Gac et al., 2018; Yan et al., 2025), hierarchically porous structures that improve reactant accessibility while decoupling transport length scales from the size of the active sites (Wang et al., 2024; Skoda et al., 2026), compositional-gradient materials, and compartmentalised or spatially resolved domains capable of independently tuning local basicity, redox state and hydrogen availability (Estevez et al., 2026).

A deeper understanding of structure–function relationships, spanning textural properties, basicity, metal dispersion, metal–support interactions, redox behaviour and interfacial chemistry, should guide the development of next-generation DFMs. Hierarchical porosity can improve reactant accessibility and intermediate transport without sacrificing volumetric capacity, while tailored interfaces can enhance hydrogen activation, facilitate carbon transfer from adsorbed carbonate/bicarbonate species towards the metallic phase, and suppress competing deactivation pathways such as coke deposition or irreversible support carbonation (Shezad et al., 2026; Skoda et al., 2026). For hybrid and amine-containing DFMs, particular emphasis should be placed on elucidating the formation and reactivity of amine-bound CO₂ species, their participation in hydrogenation pathways, and their stability under repeated thermal and chemical cycling, since oxidative and thermal degradation of amines remains one of the principal barriers to long-term operation (Selvam et al., 2026; Deo et al., 2025; McNeary et al., 2025).

Ultimately, future materials design should move beyond maximising isolated performance metrics, such as adsorption capacity or CH₄ yield measured under single-cycle, idealised conditions, and instead focus on controlling the dynamic behaviour of active sites, adsorbed intermediates and interfacial phenomena under realistic operating conditions. Emerging synthesis techniques, including templating strategies, additive manufacturing, and self-assembly approaches, may allow unprecedented control over these complex pore structures (Kreitz et al., 2020). Apart from advanced synthesis methodologies, advanced characterisation, including in situ and in operando will be essential for establishing the mechanistic design principles required to engineer truly integrated, rather than merely combined, DFMs. The integration of experimental studies with multiscale computational tools, including density functional theory, microkinetic modelling, reactor-scale simulations, high-throughput screening, and machine learning, could support the rational design of DFMs. As an example, AI/machine learning-guided methodologies have been used recently to discover optimized CO₂ hydrogenation catalysts for jet fuel range hydrocarbons production, highlighting ML as a tool for materials discovery and development (Santos et al., 2026). This combined approach could enable the identification of optimal sorbent/catalyst/promoter–support combinations and help translate mechanistic understanding into predictive design rules, rather than relying solely on iterative composition-by-composition screening. In our view, the next major advance in DFM development will not arise from independently optimising the sorbent and catalyst, but from engineering the interface that governs the transfer and conversion of captured CO₂ species using advanced characterisation and data-driven and machine learning-guided methodologies.

Beyond materials design

At the level of testing and performance assessment, the field would benefit from more standardised, application-relevant protocols that capture the intrinsic dynamic nature of ICCU operation. Beyond reporting CO₂ adsorption capacity and methane yield under simplified, single-pass conditions, future studies should systematically evaluate cyclic stability over hundreds rather than tens of cycles, methane productivity per unit mass and per unit time, overall carbon balance, H₂ utilisation efficiency, regeneration energy requirements, impurity tolerance (Cimino et al., 2022), and resistance to steam-induced deactivation. Testing protocols should also incorporate realistic gas compositions and CO₂ concentrations representative of flue-gas, biogas, or Direct Air Capture (DAC) streams, together with controlled humidity, oxygen traces, and potential acidic contaminants, particularly when DFMs are intended for flue-gas or biogas-upgrading applications, where such species are present and difficult to remove. The evaluation of DFMs should further incorporate kinetic descriptors and heat-management indicators, supported by operando or in situ characterisation tools capable of tracking the evolution of adsorbed species, reaction intermediates, and active sites during repeated capture/hydrogenation cycles.

Finally, future research on scale-up and process implementation must bridge the persistent gap between powder-based proof-of-concept studies and structured reactor configurations suitable for continuous or semi-continuous operation. This requires explicitly addressing heat- and mass-transfer limitations, pressure drop, mechanical attrition, thermal conductivity, reactor packing, flow distribution, and the management of the exothermicity of the Sabatier reaction, which, if left unaddressed, can compromise both selectivity and material lifetime at larger scales. DFM design should therefore be coupled with reactor engineering from the early development stage, explicitly considering whether the material is destined for fixed beds, structured beds, coated monoliths, fluidised systems or modular PtG units, since each configuration imposes distinct constraints on particle size, mechanical strength and thermal management. Emerging manufacturing routes, such as 3D-printed or additively manufactured structured supports with tailored internal geometries, offer a promising means of decoupling heat-removal capacity from bed pressure drop, and merit closer integration with DFM formulation strategies. At the same time, scale-up studies should integrate techno-economic assessment, life-cycle analysis, and dynamic operation scenarios that reflect the intermittency of renewable hydrogen and electricity supply, rather than relying on idealised, steady-state assumptions. Only by combining material optimisation with reactor design, process control and system-level analysis will it become possible to establish whether DFM-based CO₂ methanation can offer a genuine advantage, in terms of efficiency, capital cost or operational simplicity, over conventional sequential capture-and-conversion routes.

Looking ahead, the maturation of DFM technology will likely depend less on the discovery of new active-phase chemistries than on the field’s ability to integrate materials design, reaction engineering and systems-level analysis within a single, iterative design loop. We argue that DFM performance should be evaluated under realistic cyclic and reactor-relevant conditions, rather than primarily through isolated values of CO₂ adsorption capacity or methane yield. The DFMs that ultimately reach pilot- and commercial-scale PtG deployment are unlikely to be those that maximise a single laboratory metric, but rather those engineered, tested and benchmarked against the variable, impure and dynamic conditions that characterise real renewable-energy-driven operation.

Summary

Within the broader landscape of emerging CCU technologies, including CO₂ mineralisation, electrochemical and thermochemical conversion, polymer synthesis, and the production of renewable fuels and chemicals, DFMs have attracted considerable attention due to their capacity to bridge CO₂ capture and conversion within a single process unit. This integrated approach not only simplifies process design but also creates new opportunities to develop energy-efficient routes for producing renewable fuels and chemicals.

The published literature demonstrates that DFM performance emerges from the coupled design of the support, capture phase, catalytic sites, and their interfacial proximity under cyclic operating conditions. In our view, this is the central point that the field has yet to fully assume: the bottleneck limiting DFM development is no longer the discovery of new individual sorbents or catalysts operating independently or isolated, but the efficiency of the boundary connecting them. Performance gains from new active phases have begun to show diminishing returns whenever capture and conversion functionalities remain effectively decoupled rather than mechanistically coupled. We argue that the next meaningful step forward will come from understanding and engineering the transfer, transformation, and release of captured CO₂ species across this boundary, rather than from further optimising either component in isolation.

Within this interfacial challenge, we consider the case of amine-functionalised DFMs to be particularly significant, and arguably the most consequential open question for the field. Unlike conventional alkaline or alkaline-earth capture phases, amine-based sites can chemisorb CO₂ under milder conditions, potentially enabling integrated capture and methanation at lower temperatures. Lowering the operating temperature window of DFMs without sacrificing methanation activity would represent a fundamental advance, as it would decouple ICCU from the narrow 300 °C–450 °C range imposed by alkali/alkaline-earth carbonate chemistry while simultaneously reducing process energy requirements. Achieving this requires understanding interactions between amine–CO₂ chemisorbed species and neighbouring hydrogenation sites, and whether these species can access genuinely distinct, lower-barrier reaction pathways rather than simply mimicking carbonate-mediated routes at lower efficiency. This mechanistic question remains largely unresolved, and meaningful advances will be contingent upon addressing this jointly with the oxidative and thermal degradation of amine species under repeated cycling, which remains one of the principal barriers to sustained operation. In our opinion, the field would benefit from treating mechanistic understanding and stability as a single design problem, rather than pursuing reactivity gains that cannot be sustained over realistic operating lifetimes.

Should these challenges be resolved, we believe the potential of DFMs would extend well beyond synthetic methane production. A material platform capable of efficient capture–conversion coupling at lower temperatures would be well positioned to operate directly on dilute CO₂ streams, such as those characteristic of DAC, where the same low-temperature amine chemistry that benefits CO₂ methanation is already the basis of most current capture approaches; whether this advantage translates directly into integrated capture-and-conversion performance remains, to our knowledge, an open question rather than a demonstrated outcome. More directly supported by the present analysis is the prospect of operating across a wider, more flexible range of conditions, accommodating intermittent renewable H₂ supply, variable feed humidity, and fluctuating thermal duty, without the structural and energetic compromises that high-temperature DFMs currently demand. In our opinion, this operational flexibility, rather than incremental gains in CH₄ yield, is what will ultimately determine whether DFMs evolve from a laboratory-scale process-intensification concept into a genuinely deployable platform technology for carbon capture and utilisation.

Correction note

A correction has been made to this article. Details can be found at: 10.3389/fenve.2026.1981638.

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Footnotes

Edited by: Isidro A. Pérez, University of Valladolid, Spain

Reviewed by: Vishwajit Chavda, Kyungpook National University, Republic of Korea