Combining CO2 capture and catalytic conversion to methane

Comprehensive investigation of isotherm, RSM, and ANN modeling of CO2 capture by multi-walled carbon nanotube

Chemical vapor deposition was used to produce multi-walled carbon nanotubes (MWCNTs), which were modified by Fe-Ni/AC catalysts to enhance CO2 adsorption. In this study, a new realm of possibilities and potential advancements in CO2 capture technology is unveiled through the unique combination of cutting-edge modeling techniques and utilization of the recently synthesized Fe-Ni/AC catalyst adsorbent. SEM, BET, and FTIR were used to analyze their structure and morphology. The surface area of MWCNT was found to be 240 m2/g, but after modification, it was reduced to 11 m2/g. The modified MWCNT showed increased adsorption capacity with higher pressure and lower temperature, due to the introduction of new adsorption sites and favorable interactions at lower temperatures. At 25 °C and 10 bar, it reached a maximum adsorption capacity of 424.08 mg/g. The optimal values of the pressure, time, and temperature parameters were achieved at 7 bar, 2646 S and 313 K. The Freundlich and Hill models had the highest correlation with the experimental data. The Second-Order and Fractional Order kinetic models fit the adsorption results well. The adsorption process was found to be exothermic and spontaneous. The modified MWCNT has the potential for efficient gas adsorption in fields like gas storage or separation. The regenerated M-MWCNT adsorbent demonstrated the ability to be reused multiple times for the CO2 adsorption process, as evidenced by the study. In this study, a feed-forward MLP artificial neural network model was created using a back-propagation training approach to predict CO2 adsorption. The most suitable and efficient MLP network structure, selected for optimization, consisted of two hidden layers with 25 and 10 neurons, respectively. This network was trained using the Levenberg-Marquardt backpropagation algorithm. An MLP artificial neural network model was created, with a minimum MSE performance of 0.0004247 and an R2 value of 0.99904, indicating its accuracy. The experiment also utilized the blank spreadsheet design within the framework of response surface methodology to predict CO2 adsorption. The proximity between the Predicted R2 value of 0.8899 and the Adjusted R2 value of 0.9016, with a difference of less than 0.2, indicates a high level of similarity. This suggests that the model is exceptionally reliable in its ability to predict future observations, highlighting its robustness.

The Need for Flexible Chemical Synthesis and How Dual-Function Materials Can Pave the Way

Since climate change keeps escalating, it is imperative that the increasing CO₂ emissions be combated. Over recent years, research efforts have been aiming for the design and optimization of materials for CO₂ capture and conversion to enable a circular economy. The uncertainties in the energy sector and the variations in supply and demand place an additional burden on the commercialization and implementation of these carbon capture and utilization technologies. Therefore, the scientific community needs to think out of the box if it is to find solutions to mitigate the effects of climate change. Flexible chemical synthesis can pave the way for tackling market uncertainties. The materials for flexible chemical synthesis function under a dynamic operation, and thus, they need to be studied as such. Dual-function materials are an emerging group of dynamic catalytic materials that integrate the CO₂ capture and conversion steps. Hence, they can be used to allow some flexibility in the production of chemicals as a response to the changing energy sector. This Perspective highlights the necessity of flexible chemical synthesis by focusing on understanding the catalytic characteristics under a dynamic operation and by discussing the requirements for the optimization of materials at the nanoscale.

Flexible NiRu Systems for CO2 Methanation: From Efficient Catalysts to Advanced Dual-Function Materials

CO₂ emissions in the atmosphere have been increasing rapidly in recent years, causing global warming. CO₂ methanation reaction is deemed to be a way to combat these emissions by converting CO₂ into synthetic natural gas, i.e., CH₄. NiRu/CeAl and NiRu/CeZr both demonstrated favourable activity for CO₂ methanation, with NiRu/CeAl approaching equilibrium conversion at 350 °C with 100% CH₄ selectivity. Its stability under high space velocity (400 L·g^-1·h^-1) was also commendable. By adding an adsorbent, potassium, the CO₂ adsorption capability of NiRu/CeAl was boosted, allowing it to function as a dual-function material (DFM) for integrated CO₂ capture and utilisation, producing 0.264 mol of CH₄/kg of sample from captured CO₂. Furthermore, time-resolved operando DRIFTS-MS measurements were performed to gain insights into the process mechanism. The obtained results demonstrate that CO₂ was captured on basic sites and was also dissociated on metallic sites in such a way that during the reduction step, methane was produced by two different pathways. This study reveals that by adding an adsorbent to the formulation of an effective NiRu methanation catalyst, advanced dual-function materials can be designed.

Feasibility of switchable dual function materials as a flexible technology for CO2 capture and utilisation and evidence of passive direct air capture

The feasibility of a Dual Function Material (DFM) with a versatile catalyst offering switchable chemical synthesis from carbon dioxide (CO₂) was demonstrated for the first time, showing evidence of the ability of these DFMs to passively capture CO₂ directly from the air as well. These DFMs open up possibilities in flexible chemical production from dilute sources of CO₂, through a combination of CO₂ adsorption and subsequent chemical transformation (methanation, reverse water gas shift or dry reforming of methane). Combinations of Ni Ru bimetallic catalyst with Na₂O, K₂O or CaO adsorbent were supported on CeO₂-Al₂O₃ to develop flexible DFMs. The designed multicomponent materials were shown to reversibly adsorb CO₂ between the 350 and 650 °C temperature range and were easily regenerated by an inert gas purge stream. The components of the flexible DFMs showed a high degree of interaction with each other, which evidently enhanced their CO₂ capture performance ranging from 0.14 to 0.49 mol kg^-1. It was shown that captured CO₂ could be converted into useful products through either CO₂ methanation, reverse water-gas shift (RWGS) or dry reforming of methane (DRM), which provides flexibility in terms of co-reactant (hydrogen vs. methane) and end product (synthetic natural gas, syngas or CO) by adjusting reaction conditions. The best DFM was the one containing CaO, producing 104 μmol of CH₄ per kg_DFM in CO₂ methanation, 58 μmol of CO per kg_DFM in RWGS and 338 μmol of CO per kg_DFM in DRM.

Mechanistic insights into the CO2 capture and reduction on K-promoted Cu/Al2O3 by spatiotemporal operando methodologies

Integrated CO2 capture and conversion processes bring the promise of drastic abatement of CO2 emission together with its valorisation to chemical building blocks such as CH4 and CO.

CO2 Capture at Medium to High Temperature Using Solid Oxide-Based Sorbents: Fundamental Aspects, Mechanistic Insights, and Recent Advances

Carbon dioxide capture and mitigation form a key part of the technological response to combat climate change and reduce CO₂ emissions. Solid materials capable of reversibly absorbing CO₂ have been the focus of intense research for the past two decades, with promising stability and low energy costs to implement and operate compared to the more widely used liquid amines. In this review, we explore the fundamental aspects underpinning solid CO₂ sorbents based on alkali and alkaline earth metal oxides operating at medium to high temperature: how their structure, chemical composition, and morphology impact their performance and long-term use. Various optimization strategies are outlined to improve upon the most promising materials, and we combine recent advances across disparate scientific disciplines, including materials discovery, synthesis, and in situ characterization, to present a coherent understanding of the mechanisms of CO₂ absorption both at surfaces and within solid materials.

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.

Sepiolite-based adsorbents for carbon dioxide capture

Sepiolite and the sepiolite-based materials were studied in terms of carbon dioxide adsorption. The pore structure and the surface characterization of the obtained materials were specified based on adsorption-desorption isotherms of nitrogen measured at –196oC and carbon dioxide at 0oC. The specific surface area (SSA) was calculated according to the BET equation. The pore volume was estimated using the DFT method. Pristine sepiolite has shown the following value of SSA and CO2 uptake at 0oC – 105 m2/g and 0.27 mmol/g, respectively. The highest value of these parameters was found for material obtained by KOH activation of mixture sepiolite and molasses (MSEP2) – 676 m2/g and 1.49 mmol/g. Sample MSEP2 also indicated the highest value of total pore volume and micropores volume with a diameter up to 0.8 nm.

Global opportunities and challenges on net-zero CO2 emissions towards a sustainable future

Artistic representation of CO2 emissions from various sources into the atmosphere, and its consequence on the global climatic conditions.

CO2 Hydrogenation to Methanol with Ga- and Zn-Doped Mesoporous Cu/SiO2 Catalysts Prepared by the Aerosol-Assisted Sol-Gel Process*

The preparation of copper-based heterogeneous catalysts dedicated to the hydrogenation of CO₂ to methanol typically relies on multi-step procedures carried out in batch. These steps are precisely tailored to introduce the active phase (Cu) and the promoters (e. g., zinc, gallium) onto a preformed support to maximize catalyst performance. However, each process step can be associated with the formation of waste and with the consumption of energy, thereby negatively impacting the environmental performance of the overall catalyst preparation procedure. Here, a direct and continuous production process is proposed for the synthesis of efficient catalysts for the CO₂ -to-methanol reaction. Gallium- and zinc-promoted mesoporous Cu-SiO₂ catalysts were prepared in one step by the aerosol-assisted sol-gel process. The catalysts consisted of spherical microparticles and featured high specific surface area and pore volume, with interconnected pores of about 6 nm. A strong promoting effect of Ga and Zn was highlighted, boosting the selectivity for methanol at the expense of CO. Upon calcination, it was shown that Cu species (initially trapped in the silica matrix) underwent a migration towards the catalyst surface and a progressive sintering. After optimization, the catalysts obtained via such direct, continuous, simple, and scalable route could compete with the best catalysts reported in the literature and obtained via multi-step approaches.

Hydrogenation of Carbon Dioxide to Methanol over Non-Cu-based Heterogeneous Catalysts

The increasing atmospheric CO₂ level makes CO₂ reduction an urgent challenge facing the world. Catalytic transformation of CO₂ into chemicals and fuels utilizing renewable energy is one of the promising approaches toward alleviating CO₂ emissions. In particular, the selective hydrogenation of CO₂ to methanol utilizing renewable hydrogen potentially enables large scale transformation of CO₂ . The Cu-based catalysts have been extensively investigated in CO₂ hydrogenation. However, it is not only limited by long-term instability but also displays unsatisfactory catalytic performance. The supported metal-based catalysts (Pd, Pt, Au, and Ag) can achieve high methanol selectivity at low temperatures. The mixed oxide catalysts represented by M_a ZrO_x (M_a =Zn, Ga, and Cd) solid solution catalysts present high methanol selectivity and catalytic activity as well as excellent stability. This Review focuses on the recent advances in developing Non-Cu-based heterogeneous catalysts and current understandings of catalyst design and catalytic performance. First, the thermodynamics of CO₂ hydrogenation to methanol is discussed. Then, the progress in supported metal-based catalysts, bimetallic alloys or intermetallic compounds catalysts, and mixed oxide catalysts is discussed. Finally, a summary and a perspective are presented.

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.

Transition Metal Dichalcogenides for the Application of Pollution Reduction: A Review

The material characteristics and properties of transition metal dichalcogenide (TMDCs) have gained research interest in various fields, such as electronics, catalytic, and energy storage. In particular, many researchers have been focusing on the applications of TMDCs in dealing with environmental pollution. TMDCs provide a unique opportunity to develop higher-value applications related to environmental matters. This work highlights the applications of TMDCs contributing to pollution reduction in (i) gas sensing technology, (ii) gas adsorption and removal, (iii) wastewater treatment, (iv) fuel cleaning, and (v) carbon dioxide valorization and conversion. Overall, the applications of TMDCs have successfully demonstrated the advantages of contributing to environmental conversation due to their special properties. The challenges and bottlenecks of implementing TMDCs in the actual industry are also highlighted. More efforts need to be devoted to overcoming the hurdles to maximize the potential of TMDCs implementation in the industry.