Stabilization of NaNO3-Promoted Magnesium Oxide for High-Temperature CO2 Capture

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.

Encapsulation of Phase-Changing Eutectic Salts in Magnesium Oxide Fibers for High-Temperature Carbon Dioxide Capture: Beyond the Capacity-Stability Tradeoff

Eutectic mixture (EM)-promoted MgO sorbents exhibit high CO₂ sorption capacities but  experience a significant decrease in uptake after multiple sorption-regeneration cycles due to EM movement and redistribution at high temperatures. Encapsulation of a pseudoliquid, phase-changing EM promoter with MgO may thus prevent the loss of active interface by confining the EM within a fixed area inside a MgO shell. In this work, we successfully embedded an EM composed of KNO₃ and LiNO₃ in a MgO fiber matrix via core-shell electrospinning. The synthesized sorbent achieved relatively high and steady sorption capacities, maintaining a stable uptake of ∼20 wt % after 25 sorption-regeneration cycles. The sorbent was also characterized using various techniques including in situ transmission electron microscopy (TEM) to describe its morphology, from which it was confirmed that the eutectic salt existed in distributed hollow pockets within the MgO fiber matrix and stayed confined within these fixed areas, favorably limiting its movement and redistribution when exposed to high temperatures where it exists in the liquid form. The EM may also be described as a glue that holds the fiber together, while MgO acts as a protective shell that prevents structural changes and rearrangement caused by EM movement, allowing the sorbent to retain its cyclic stability after multiple cycles and demonstrating its potential for industrial use after further improvement. Thus, the microencapsulation of a phase-changing EM material with pure MgO metal oxide was successfully achieved and might be explored for various material applications.

Exfoliated Ni-Al LDH 2D nanosheets for intermediate temperature CO2 capture

CO₂ capture is projected as one of the pragmatic approaches to deal with the global warming phenomenon. Adsorption-based CO₂ capture is considered an economically attractive option to reduce CO₂ emission. The success of the adsorption-based capture primarily relies on adsorbents and thus a variety of adsorbents have been investigated in the literature. We here report a high surface area (210.2 m²/g) exfoliated Ni-Al LDH nanoplatelet as a promising candidate for CO₂ capture at an intermediate temperature of 200 °C applicable to integrated gasification combined cycle (IGCC) and sorption enhanced water gas shift (SEWGS) reactions. The materials were well characterized by PXRD, TGA, FTIR, TEM, ICP-OES, and N₂ adsorption surface area, and pore size distribution techniques. A unique nanoflower morphology comprising of exfoliated LDH platelets of ca. 5 layer thickness was obtained. The CO₂ capture capacity (0.66 mmol/g) of the exfoliated Ni-Al LDH nanoplatelet is comparable to that of the widely reported Mg-Al LDH-derived mixed oxides and MgO-based adsorbents. Provided that Ni-Al and other transition metal LDH materials are known to exhibit superior catalytic properties for CO₂ methanation, this work could pave the way for development of dual-functional materials for CO₂ capture and conversion.