CeO 2 nanopowders as solid sorbents for efficient CO 2 capture/release processes

Synthesis of spherical CaO pellets incorporated with Mg, Y, and Ce inert carriers for CO2 capture

Sintering and elutriation are two main problems of the calcium looping process for high-temperature CO2 capture. In the process of CO2 capture, the operation temperature is generally higher than the Taman temperature, resulting in the agglomeration and sintering of the sorbents. The traditional sorbent powers need to be granulated for practical application in a circulating fluidized bed to avoid elutriation. By using a new agar-assisted technology to granulate CaO powder incorporated with Mg, Y, and Ce inert supports, the problems of sintering and elutriation can be mitigated within one step. The incorporated inert supports are uniformly dispersed in the CaO/CaCO3 particles as an inert scaffold, and the inert scaffold is used as a skeleton to resist sintering, alleviate its agglomeration phenomenon, and keep the specific surface area to a certain extent. The Ce-incorporated CaO pellets have been proven to exhibit the best carbonation conversion and sorption capacity. The sorption capacity of 10% CeO2-incorporated CaO pellets reached 0.574 g CO2/g sorbent, more than 43% higher than that of the pure CaO pellets. In addition, the effects of the solid-liquid ratio during the preparation stage on CO2 performance were also investigated, demonstrating that a solid-liquid ratio of 1:5 was the optimal ratio to produce satisfying sorbents. The mitigated sintering and achieved spherical CaO pellets greatly promote the practical application of the calcium looping process for CO2 capture.

Synergy of Oxygen Vacancies and Base Sites for Transfer Hydrogenation of Nitroarenes on Ceria Nanorods

CeO2 nanorod based catalysts for the base-free synthesis of azoxy-aromatics via transfer hydrogenation of nitroarenes with ethanol as hydrogen donor have been synthesized and investigated. The oxygen vacancies (Ov ) and base sites are critical for their excellent catalytic properties. The Ov , i.e., undercoordinated Ce cations, serve as the sites to activate ethanol and nitroarenes by lowering the energy barrier to transfer hydrogen from α-Csp3 -H in ethanol to the nitro group coupling it to the redox reactions between Ce3+ and Ce4+ . At the same time, the base sites catalyze the condensation step to selectively produce azoxy-aromatics. The catalytic route opens a much improved way to use non-noble metal oxides without additives for the selective functional group reduction and coupling reactions.

Insight into CO selective chemisorption from syngas mixtures through Li2MnO3; a new H2 enrichment material

Li2MnO3 is able to selectively trap CO in the presence of H2 at high temperatures, favoring H2 enrichment from syngas flows.

Reduced graphene oxide -MnO2 nanocomposite for CO2 capture from flue gases at elevated temperatures

The newly prepared reduced graphene oxide-MnO₂ (rGO-MnO₂) nanocomposite has exhibited highly selective CO₂ adsorption from gaseous mixtures at elevated temperatures. The Mn²⁺ basic sites are scattered over the rGO-MnO₂ nanocomposite which produce an effective BET surface area of 710 m² g^-1 for selective CO₂ capture. The selective adsorption of CO₂ (5.87 mmol g^-1) over N₂ (0.36 mmol g^-1) and CH₄ (0.41 mmol g^-1) at 298 K/1 bar was achieved by the nanocomposite. The heat of adsorption followed a unique correlation with the quantity of CO₂ adsorbed and fits well to the Fowler-Guggenheim equation. The mechanism of CO₂ adsorption on the nanocomposite was complemented with molecular modelling and simulations. The rGO-MnO₂ have shown better CO₂ adsorption capacity of 28.5 mmol g^-1 at 323 K/20 bar as compared to zeolite derivatives, MOFs, and carbons as reported in the literature. The formation of inert frameworks with 3-6 nm porous structure in the nanocomposite thermally stabilizes to capture CO₂ repeatedly. The nanocomposite with adsorption capacity of 3.69 mmol g^-1 at 373 K/1 bar is quite close to real-life conditions for flue gas treatment.

Materials and logistics for carbon dioxide capture, storage and utilization

The efforts to curtail carbon dioxide presence in the atmosphere are a strong function of the available technologies to capture, store and usefully utilize it. Materials with adequate CO₂ sorption kinetics that are both effective and economical are of prime importance for the whole capture system to be built around. This work identifies such materials that are currently used in CO₂ adsorption beds/columns at different global locations, along with their vital operational parameters, logistics and costs. Three main classes of materials currently in use to that end are discussed in detail here, namely solid sorbents, advanced solvents membrane systems. These materials are then compared in terms of their potential CO₂ uptake, operating parameters and ease of use and implementation of the respective technology. Tabular data are appended to each technology covered with the most relevant advantages and disadvantages. With such comprehensive survey of the recent state-of-the-art materials, recommendations are also made to facilitate the selection of systems based on their CO₂ yield, price and suitability to the geographical location.

Silica-Supported Nitrogen-Enriched Porous Benzimidazole-Linked and Triazine-Based Polymers for the Adsorption of CO2

Two crystalline and five amorphous benzimidazole polymers (BINP) were synthesized and conjugated to porous silica via amine and aldehyde-based materials by a simple reflux procedure. The resulting polymers were subject to thermal analysis for monitoring and quantification of the adsorption and desorption of CO₂. All the polymers were capable of adsorbing CO₂ from a flowing stream of only 80 mL/min at 25 °C. The adsorbed CO₂ onto the polymers were effectively desorbed at room temperature, illustrating the potential application of such polymers for repeated adsorption/desorption of CO₂. The CO₂ adsorption capacities of these polymers were dependent upon their nitrogen content, specific surface area, and pore size. The available nitrogen atoms for binding to the carbon of CO₂ via tetrel bonds also plays an important role in the capture of this gas. Minimal and much lower CO₂ adsorption was also noted with two crystalline polymers, compared to the five amorphous counterparts. Intermolecular hydrogen bonding and π-π interaction effectively prevented the polymer N sites of the crystalline polymers from interacting with polarized CO₂ molecules.

Trends in Solid Adsorbent Materials Development for CO2 Capture

A recent report from the United Nations has warned about the excessive CO₂ emissions and the necessity of making efforts to keep the increase in global temperature below 2 °C. Current CO₂ capture technologies are inadequate for reaching that goal, and effective mitigation strategies must be pursued. In this work, we summarize trends in materials development for CO₂ adsorption with focus on recent studies. We put adsorbent materials into four main groups: (I) carbon-based materials, (II) silica/alumina/zeolites, (III) porous crystalline solids, and (IV) metal oxides. Trends in computational investigations along with experimental findings are covered to find promising candidates in light of practical challenges imposed by process economics.

An in situ FTIR study of the plasma- and thermally-driven reaction of isopropyl alcohol at CeO2: evidence for a loose transition state involving Ce3+?

This paper reports on the thermally-driven and non-thermal plasma-driven reaction of IsoPropyl Alcohol (IPA) on ceria (CeO₂) with the aim to investigate the differences between plasma catalytic interactions and the analogous thermal reactions.

Structure Design of Low-Temperature Regenerative Hyperbranched Polyamine Adsorbent for CO2 Capture

A novel low-temperature regenerative hydroxy-functionalized hyperbranched polyamine adsorbent (0.16OH-HBPA) for CO₂ capture was readily prepared using glutaraldehyde to cross-link amino-terminated hyperbranched polymers (HBP) and functionalized with glycidol, followed by the reduction of the imino groups of 0.16OH-HBPA to alkyl aminos using NaBH₄. Here, the HBP has been prepared through the one-pot reaction between pentaethylenehexamine and methyl acrylate. The as-prepared 0.16OH-HBPA adsorbent showed a high adsorption capacity (4.05 mmol/g) for CO₂ (concentration, 10%) in the presence of water at 25 °C, and the alkyl amino utilization efficiency reached 73%. More importantly, the CO₂-adsorbed 0.16OH-HBPA showed excellent regenerative performance at low temperatures (85 °C, under pure CO₂ gas) due to the introduced hydroxyl that can cooperatively adsorb CO₂ via the amino groups to form stable carbamic acid. This process suppressed the formation of open-chain urea and cyclic urea and could overcome the disadvantages of high regeneration temperatures (≥90 °C, under pure inert gas) of CO₂-adsorbed traditional solid amine adsorbents.