Mechanism of high-temperature CO2 sorption on lithium zirconate

A theoretical study on CO2 at Li4SiO4 and Li3NaSiO4 surfaces

Lithium silicates have attracted great attention in recent years due to their potential use as high-temperature (450-700 °C) sorbents for CO₂ capture. Lithium orthosilicate (Li₄SiO₄) can theoretically adsorb CO₂ in amounts up to 0.36 g CO₂ per g Li₄SiO₄. The development of new Li₄SiO₄-based sorbents is hindered by a lack of knowledge of the mechanisms ruling CO₂ adsorption on Li₄SiO₄, especially for eutectic mixtures. In this work, the structural, electronic, thermodynamic and CO₂ capture properties of monoclinic phases of Li₄SiO₄ and a binary (Li₃NaSiO₄) eutectic mixture are investigated using density functional theory. The properties of the bulk crystal phases as well as of the relevant surfaces are analysed. Likewise, the results for CO₂-lithium silicates indicate that CO₂ is strongly adsorbed on the oxygen sites of both sorbents through chemisorption, causing an alteration not only in the chemical structure and atomic charges of the gas, as reflected by both the angles and bond distances as well as atomic charges, but also in the cell parameters of the Li₄SiO₄ and Li₃NaSiO₄ systems, especially in Li₄SiO₄(001) and Li₃NaSiO₄(010) surfaces. The results confirm strong adsorption of CO₂ molecules on all the considered surfaces and materials followed by CO₂ activation as inferred from CO₂ bending, bond elongation and surface to CO₂ charge transfer, indicating CO₂ chemisorption for all cases. The Li₄SiO₄ and Li₃NaSiO₄ surfaces may be proposed as suitable sorbents for CO₂ capture in wide temperature ranges.

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.

Non-isothermal reaction mechanism and kinetic analysis for the synthesis of monoclinic lithium zirconate (m-Li2ZrO3) during solid-state reaction

Non-isothermal reaction mechanism and kinetic analysis for the synthesis of monoclinic lithium zirconate (m-Li2ZrO3) were investigated by processing of TG-DTA, along with XRD, DLS, and HRTEM. For this purpose, the solid-state reaction of Li2CO3 with ZrO2 was carried out by TG-DTA at different heating rates (10, 20, and 30 °C/min) from room temperature to 1100 °C. The thermal data was used to calculate the kinetic parameters by two types of isoconversional methods: Flynn-Wall-Ozawa (FWO) and Kissinger-Akahira-Sunose (KAS). The reaction mechanism was determined by the model-fitting method, applying the Coats-Redfern (CR) approximation to the different solid-state reaction models. The results confirmed the formation of pure m-Li2ZrO3, consists of semispherical particles of about 490 nm, using a very short reaction time. The average activation energy obtained by FWO and KAS methods were 274.73 and 272.50 kJ/mol, respectively. It was found that the formation of m-Li2ZrO3 from Li2CO3 with ZrO2 is governed by the three-dimensional diffusion mechanism. Based on these results, a microscopic reaction model of the formation of m-Li2ZrO3 was proposed.

New approach to consecutive CO oxidation and CO2 chemisorption using Li2CuO2 ceramics modified with Na- and K-molten salts

The addition of alkali carbonates to Li₂CuO₂ improved the CO oxidation and the subsequent CO₂ with a high ratio of captured/released CO₂. Materials modified with a single carbonate presented the best enhancement for the removal of both CO_X.

Industrial carbon dioxide capture and utilization: state of the art and future challenges

This review covers the sustainable development of advanced improvements in CO₂ capture and utilization.

Ultrafast Carbon Dioxide Sorption Kinetics Using Morphology-Controllable Lithium Zirconate

It was reported that the main obstacle of Li₂ZrO₃ as high-temperature CO₂ absorbents is the very slow CO₂ sorption kinetics, which are ascribed to the gradual formation of compact zirconia and carbonate shells along with inner unreacted lithium zirconate cores; accordingly, the "sticky" Li⁺ and O^2- ions have to travel a long distance through the solid shells by diffusion. We report here that three-dimensional interconnected nanoporous Li₂ZrO₃ exhibiting ultrafast kinetics is promising for CO₂ sorption. Specifically, nanoporous Li₂ZrO₃ (LZ-NP) exhibited a rapid sorption rate of 10.28 wt %/min with an uptake of 27 wt % of CO₂. Typically, the k₁ values of LZ-NP (kinetic parameters extracted from sorption kinetics) were nearly 1 order of magnitude higher than the previously reported conventional Li₂ZrO₃ reaction systems. Its sorption capacity of 25 wt % within ∼4 min is 2 orders of magnitude faster than those obtained using spherical Li₂ZrO₃ powders. Furthermore, nanoporous Li₂ZrO₃ exhibited good stability over 60 absorption-desorption cycles, showing its potential for practical CO₂ capture applications. CO₂ adsorption isotherms for Li₂ZrO₃ absorbents were successfully modeled using a double-exponential equation at various CO₂ partial pressures.

A high temperature gas flow environment for neutron total scattering studies of complex materials

We present the design and capabilities of a high temperature gas flow environment for neutron diffraction and pair distribution function studies available at the Nanoscale Ordered Materials Diffractometer instrument at the Spallation Neutron Source. Design considerations for successful total scattering studies are discussed, and guidance for planning experiments, preparing samples, and correcting and reducing data is defined. The new capabilities are demonstrated with an in situ decomposition study of a battery electrode material under inert gas flow and an in operando carbonation/decarbonation experiment under reactive gas flow. This capability will aid in identifying and quantifying the atomistic configurations of chemically reactive species and their influence on underlying crystal structures. Furthermore, studies of reaction kinetics and growth pathways in a wide variety of functional materials can be performed across a range of length scales spanning the atomic to the nanoscale.

Alkali Metal CO2 Sorbents and the Resulting Metal Carbonates: Potential for Process Intensification of Sorption-Enhanced Steam Reforming

Sorption-enhanced steam reforming (SESR) is an energy and cost efficient approach to produce hydrogen with high purity. SESR makes it economically feasible to use a wide range of feedstocks for hydrogen production such as methane, ethanol, and biomass. Selection of catalysts and sorbents plays a vital role in SESR. This article reviews the recent research aimed at process intensification by the integration of catalysis and chemisorption functions into a single material. Alkali metal ceramic powders, including Li₂ZrO₃, Li₄SiO₄ and Na₂ZrO₃ display characteristics suitable for capturing CO₂ at low concentrations (<15% CO₂) and high temperatures (>500 °C), and thus are applicable to precombustion technologies such as SESR, as well as postcombustion capture of CO₂ from flue gases. This paper reviews the progress made in improving the operational performance of alkali metal ceramics under conditions that simulate power plant and SESR operation, by adopting new methods of sorbent synthesis and doping with additional elements. The paper also discusses the role of carbonates formed after in situ CO₂ chemisorption during a steam reforming process in respect of catalysts for tar cracking.

Mechanisms of absorption and desorption of CO2 by molten NaNO3-promoted MgO

We present details of the mechanism of absorption and desorption of carbon dioxide by molten NaNO₃-promoted MgO and their implications for the applications of alkali nitrate-promoted MgO absorbents with many repeated absorption and desorption cycles.

Alkali-Doped Lithium Orthosilicate Sorbents for Carbon Dioxide Capture

New alkali-doped (Na2 CO3 and K2 CO3 ) Li4 SiO4 sorbents with excellent performance at low CO2 concentrations were synthesized. We speculate that alkali doping breaks the orderly arrangement of the Li4 SiO4 crystals, hence increasing its specific surface area and the number of pores. It was shown that 10 wt % Na2 CO3 and 5 wt % K2 CO3 are the optimal additive ratios for doped sorbents to attain the highest conversions. Moreover, under 15 vol % CO2 , the doped sorbents present clearly faster absorption rates and exhibit stable cyclic durability with impressive conversions of about 90 %, at least 20 % higher than that of non-doped Li4 SiO4 . The attained conversions are also 10 % higher than the reported highest conversion of 80 % on doped Li4 SiO4 . The performance of Li4 SiO4 is believed to be enhanced by the eutectic melt, and it is the first time that the existence of eutectic Li/Na or Li/K carbonate on doped sorbents when absorbing CO2 at high temperature is confirmed; this was done using systematical analysis combining differential scanning calorimetry with in situ powder X-ray diffraction.

Synthesis of Lithium Metal Oxide Nanoparticles by Induction Thermal Plasmas

Lithium metal oxide nanoparticles were synthesized by induction thermal plasma. Four different systems—Li–Mn, Li–Cr, Li–Co, and Li–Ni—were compared to understand formation mechanism of Li–Me oxide nanoparticles in thermal plasma process. Analyses of X-ray diffractometry and electron microscopy showed that Li–Me oxide nanoparticles were successfully synthesized in Li–Mn, Li–Cr, and Li–Co systems. Spinel structured LiMn₂O₄ with truncated octahedral shape was formed. Layer structured LiCrO₂ or LiCoO₂ nanoparticles with polyhedral shapes were also synthesized in Li–Cr or Li–Co systems. By contrast, Li–Ni oxide nanoparticles were not synthesized in the Li–Ni system. Nucleation temperatures of each metal in the considered system were evaluated. The relationship between the nucleation temperature and melting and boiling points suggests that the melting points of metal oxides have a strong influence on the formation of lithium metal oxide nanoparticles. A lower melting temperature leads to a longer reaction time, resulting in a higher fraction of the lithium metal oxide nanoparticles in the prepared nanoparticles.

Progress on sorption-enhanced reaction process for hydrogen production

Concerns about the environment and fossil fuel depletion led to the concept of “hydrogen economy”, where hydrogen is used as an energy carrier. Nowadays, hydrogen is mostly produced from fossil fuel resources by natural gas reforming, coal gasification, as well as the water-gas-shift (WGS) reaction involved in these processes. Alternatively, bioethanol, glucose, glycerol, bio-oil, and other renewable biomass-derived feedstocks can also be employed for hydrogen production via steam reforming process. The combination of steam reforming and/or WGS reaction with

Regeneration mechanisms of high-lithium content zirconates as CO2capture sorbents: experimental measurements and theoretical investigations

During absorption/desorption cycles, lithium-rich zirconates (Li₈ZrO₆and Li₆Zr₂O₇) will be consumed and will not be regenerated. Their primary regeneration product is in the form of Li₂ZrO₃. This result indicates that among known lithium zirconates, Li₂ZrO₃is the best sorbent for CO₂capture.

Water steam effect during high CO2 chemisorption in lithium cuprate (Li2CuO2) at moderate temperatures: experimental and theoretical evidence

Li₂CuO₂ is able to chemisorb high quantities of CO₂ in the presence of water steam at low temperatures.

Oxidative CO2 reforming of methane in La0.6Sr0.4Co0.8Ga0.2O3-δ (LSCG) hollow fiber membrane reactor

CO2 utilization in catalytic membrane reactors for syngas production is an environmentally benign solution to counter the escalating global CO2 concerns. In this study, integration of a La0.6Sr0.4Co0.8Ga0.2O3-δ (LSCG) hollow fiber membrane reactor with Ni/LaAlO3-Al2O3 catalyst for the oxidative CO2 reforming of methane (OCRM) reaction was successfully tested for 160 h of reaction. High CH4 and CO2 conversions of ca. 94% and 73% were obtained with O2 flux ca. 1 mL·min(-1)·cm(-2) at 725 °C for the 160-h stability test. Surface temperature programmed desorption studies of the membrane were conducted with H2, CO, and CO2 as probe gases to facilitate understanding on the effect of H2 and CO product gases as well as CO2 reactant gases on the membrane surface. Scanning electron microscopy-energy dispersive X-ray (SEM-EDX), X-ray photoelectron spectroscopy (XPS), and Fourier transform infrared (FTIR) analysis of the postreacted membrane after 160-h stability tests suggests Sr-enriched phases with the presence of adsorbed carbonate and hydrogenated carbon. This shows the subsequent reactant spillover on the membrane surface from the catalyst bed took place due to the reaction occurring on the catalyst. However, XRD analysis of the bulk structure does not show any phase impurities, thus confirming the structural integrity of the LSCG hollow fiber membrane.

CO₂ sorbents with scaffold-like Ca-Al layered double hydroxides as precursors for CO₂ capture at high temperatures

A highly stable high-temperature CO₂ sorbent consisting of scaffold-like Ca-rich oxides (Ca-Al-O) with rapid absorption kinetics and a high capacity is described. The Ca-rich oxides were prepared by annealing Ca-Al-NO₃ layered double hydroxide (LDH) precursors through a sol-gel process with Al(O(i)P)₃ and Ca(NO₃)₂ with Ca(2+)/Al(3+) ratios of 1:1, 2:1, 4:1, and 7:1. XRD indicated that only LDH powders were formed for Ca(2+)/Al(3+) ratios of 2:1. However, both LDH and Ca(OH)₂ phases were produced at higher ratios. Both TEM and SEM observations indicated that the Ca-Al-NO₃ LDHs displayed a scaffold-like porous structure morphology rather than platelet-like particles. Upon annealing at 600 °C, a highly stable porous network structure of the CaO-based Ca-Al-O mixed oxide (CAMO), composed of CaO and Ca₁₂Al₁₄O₃₃, was still present. The CAMO exhibited high specific surface areas (up to 191 m(2)g(-1)) and a pore size distribution of 3-6 nm, which allowed rapid diffusion of CO₂ into the interior of the material, inducing fast carbonation/calcination and enhancing the sintering-resistant nature over multiple carbonation/calcination cycles for CO₂ absorption at 700 °C. Thermogravimetric analysis results indicated that a CO₂ capture capacity of approximately 49 wt% could be obtained with rapid absorption from the porous 7:1 CAMO sorbents by carbonation at 700 °C for 5 min. Also, 94-98% of the initial CO₂ capture capability was retained after 50 cycles of multiple carbonation/calcination tests. Therefore, the CAMO framework is a good isolator for preventing the aggregation of CaO particles, and it is suitable for long-term cyclic operation in high-temperature environments.