Coal gasification in CO2 atmosphere and its kinetics since 1948: A brief review

CO2 methanation is a well-known reaction that is of interest as a capture and storage (CCS) process and as a renewable energy storage system based on a power-to-gas conversion process by substitute or synthetic natural gas (SNG) production. Integrating water electrolysis and CO2 methanation is a highly effective way to store energy produced by renewables sources. The conversion of electricity into methane takes place via two steps: hydrogen is produced by electrolysis and converted to methane by CO2 methanation. The effectiveness and efficiency of power-to-gas plants strongly depend on the CO2 methanation process. For this reason, research on CO2 methanation has intensified over the last 10 years. The rise of active, selective, and stable catalysts is the core of the CO2 methanation process. Novel, heterogeneous catalysts have been tested and tuned such that the CO2 methanation process increases their productivity. The present work aims to give a critical overview of CO2 methanation catalyst production and research carried out in the last 50 years. The fundamentals of reaction mechanism, catalyst deactivation, and catalyst promoters, as well as a discussion of current and future developments in CO2 methanation, are also included.

Supported Catalysts for CO2 Methanation: A Review

The high power density, ease of transportation and storage and many years of development of internal combustion engine technologies have put liquid hydrocarbon fuels at a privileged position in our energy mix. Therefore processes that use renewable energy sources to produce liquid hydrocarbon fuels from H2O and CO2 are of crucial importance. Concentrated Solar Power (CSP) can be employed as the only energy source for the renewable production of hydrogen from water either indirectly, e.g. by supplying the electricity for electrolysis, or directly by supplying the necessary heat for thermochemically producing hydrogen. Among the various thermochemical cycles tested so far for CSP-driven hydrogen production via water splitting (WS), those based on redox-pair oxide systems, are directly adaptable to carbon dioxide splitting (CDS) and/or combined CO2/H2O splitting for the production of CO or syngas, respectively. The acknowledgement of this fact has recently revived the interest of the scientific community on such technologies. The current article presents the development, evolution and current status of CSP-aided syngas production via such redox-pair-based thermochemical cycles. At first the various redox oxide material compositions tested for water/carbon dioxide splitting are presented and their redox chemistries are discussed. Then the selection of suitable solar reactors is addressed in conjunction with the boundary conditions imposed by the redox systems as well as the heat demands, technical peculiarities and requirements of the cycle steps. The various solar reactor concepts proposed and employed for such reactions and their current status of development are presented. Finally, topics where further work is needed for commercialization of the technology are identified and discussed.

A review on solar thermal syngas production via redox pair-based water/carbon dioxide splitting thermochemical cycles

Ultramafic rocks are a major component of the oceanic lithosphere and are commonly exposed near and along slow- and ultra-spreading ridges and in other tectonically active environments The serpentinization of mantle material is a fundamental process that has significant geophysical, geochemical and biological importance for the global marine system and for subduction zone environments Mineral assemblages and textures are typically complex and reflect multiple phases of alteration, deformation and veining during emplacement, hydrothermal alteration, and weathering In this paper, we review mineralogical and geochemical consequences of serpentinization processes in oceanic upper mantle sequences in different tectonic environments and discuss the relationship between serpentinization and fluid chemistry We present phase equilibria that provide models for interpreting mineral-fluid relationships in oceanic serpentinites and allow the simultaneous evaluation of the conditions for redox, hydration and carbonation processes These models predict that serpentinization reactions are sensitive to Si content of ultramafic rocks and that serpentine phases have an upper stability limit of ∼450°C, where H 2 O-rich fluids will be dominant More pervasive serpentinization commences with olivine breakdown reactions below ∼425°C and leads to progressively more reduced fluids with decreasing temperature Our calculations indicate that carbonates may have extensive stability fields in CH4-rich fluids in Si-deficient systems and that they may be significant in generating reducing conditions If methane formation driven by serpentinization is common, its contribution to the carbon cycle in submarine biogeochemical systems may be substantial Serpentinization may thus be an important process in sustaining diverse microbial communities in subsurface and near-vent environments and has consequences for the existence of a deep biosphere

/pdf/serpentinization-of-oceanic-peridotites-implications-for-hljyokpkyi.pdf

Serpentinization of Oceanic Peridotites: Implications for Geochemical Cycles and Biological Activity

Relative importance of thermodynamic and kinetic processes in governing the chemical and isotopic composition of carbon gases in high-heatflow sedimentary basins

An oxygen-deficient Mn(II) ferrite (Mn0.97Fe2.02O3.92) was synthesized and its reactivity to reduce CO2 gas into carbon was studied at 300°C. The oxygen-deficient Mn(II) ferrite was obtained by flowing H2 gas through Mn(II) ferrite with a nearly stoichiometric composition of Mn0.97Fe2.02O4.00 at 300° C. The lattice constant of the oxygen-deficient Mn(II) ferrite (0.8505nm) is larger than that of the Mn(II) ferrite with a nearly stoichiometric composition (0.8498nm). The chemical composition of the Mn(II) ferrite changed from Mn0.97Fe2.02O4.00 to Mn0.97Fe2.02O3.92 during the H2 reduction process, indicating that the oxygen is deficient in the spinel structure of the Mn(II) ferrite. This was confirmed by Mossbauer spectroscopy and X-ray diffractometry. The efficiency of CO2 decomposition into carbon at 300°C with the oxygen-deficient Mn(II) ferrite was much lower by about 105 than that of oxygen-deficient magnetite. This is considered to be due to the difference in electron conductivity between Mn(II) ferrite and magnetite, which determines the reductivity for CO2 into carbon by donation of an electron at the adsorption site.

CO2 decomposition with oxygen-deficient Mn(II) ferrite

The CO2 decomposition into carbon with the rhodium-bearing activated magnetite (Rh-AM) was studied in comparison with the activated magnetite (AM). The Rh-AM and the AM were prepared by flowing hydrogen gas through the rhodium-bearing magnetite (Rh-M) and the magnetite (M), respectively. The rate of activation of the Rh-M to the Rh-AM was about three times higher than that of the M to the AM at 300 °C. The reactivity for the CO2 decomposition into carbon with the Rh-AM (70% CO2 was decomposed in 40 min) was higher than that with the AM (30% in 40 min) at 300 °C. The Rh-M was activated to the Rh-AM at a lower temperature of 250 °C, and the Rh-AM decomposed CO2 into carbon at 250 °C. On the other hand, the M was little activated at 250 °C.

Carbon dioxide decomposition into carbon with the rhodium-bearing magnetite activated by H2-reduction

The reduction of CO2 to carbon was studied in oxygen-deficient Mn(II)-bearing ferrites (MnxFe3-xO4-δ, O⩽x⩽1, δ>0) at 300 °C. They were prepared by reducing Mn(II)-bearing ferrites with H2 gas at 300°C. The oxygen-deficient Mn(II)-bearing ferrites showed a single phase with a spinel structure having an oxygen deficiency. The decomposition reaction of CO2 to carbon was accompanied by oxidation of the oxygen-deficient Mn(II)-bearing ferrites. The decomposition rate slowed when the Mn(II) content in the Mn(II)-bearing ferrites increased. A Mossbauer study of the phase changes of the solid samples during the H2 reduction and CO2 decomposition indicated the following. Increases in the Mn(II) content lowered the electron conductivity of the Mn(II)-bearing ferrites. Increases in the oxygen deficiency, δ, contributed to an increase in electron conductivity and suggested that electron conduction due to the electron hopping determines the reductivity of CO2 to carbon by the donation of an electron at adsorption sites.

Reactivity of oxygen-deficient Mn(II)-bearing ferrites (MnxFe3-xO4-δ, O⩽x⩽1, δ>0) toward CO2 decomposition to carbon

CO2 decomposition reaction into carbon was studied at 300 °C using the H2-reduced Zn(II)-bearing ferrite which consisted of the Zn(II) oxide and the active wustite. The H2-reduced Zn(II)-bearing ferrite was prepared from Zn(II)-bearing ferrite by the reduction with H2 gas at 300 °C. The wustite (FeδO) in the H2-reduced Zn(II)-bearing ferrite had a higher δ value (δ=0.97, active wustite) than those of the normal wustites (0.90 570 °C). The decomposition reaction of CO2 proceeds in two steps: (1) CO2 reduction to CO, and (2) CO decomposition into carbon. In the initial stage, the reduction of CO2 into CO takes place, accompanying both the oxidation of the active wustite to the slightly oxidized wustite, and the transformation of active wustite and Zn(II) oxide into the Zn(II)-bearing ferrite. After the reaction of the initial stage attains equilibrium of an apparent state of rest, the adsorbed CO is decomposed into carbon, associated with the transformation of the slightly oxidized wustite and the Zn(II) oxide into the Zn(II)-bearing ferrite.

Decomposition of CO2 and CO into carbon with active wüstite prepared from Zn(II)-bearing ferrite

The adsorption isotherm and the enthalpy of adsorption of CO2 on oxides of oxygen-deficient magnetite have been studied by adsorption techniques. Oxygen-deficient magnetite was prepared by flowing H2 gas through magnetite powder at 300 °C. Adsorption of CO2 onto oxygen-deficient magnetite was studied in the temperature range 150–300 °C. We found that the adsorption can be expressed by the Langmuir dissociative isotherm for three fragments: one carbon atom and two oxygen ions. Deposition of carbon after the adsorption reaction suggests that reduction of surface carbon seems to be involved in the adsorption reaction. The high reactivity for the reduction of CO2 to carbon is considered to come from such a reactive site where an electron is readily donated to the carbon of the CO2 molecule and the oxygen in the CO2 molecule is readily incorporated into a lattice point in the form of O2–. Electron hopping between the Fe2+ and Fe3+ ions in the spinel structure of the magnetite would facilitate the donation of an electron at the adsorption site. The distorted spinel structure of the surface of the H2-reduced magnetite, where the oxygen site is defected, would facilitate the incorporation of the oxygen of CO2.

M. Tabata

Papers

CO2 decomposition with oxygen-deficient Mn(II) ferrite

Carbon dioxide decomposition into carbon with the rhodium-bearing magnetite activated by H2-reduction

Reactivity of oxygen-deficient Mn(II)-bearing ferrites (MnxFe3-xO4-δ, O⩽x⩽1, δ>0) toward CO2 decomposition to carbon

Decomposition of CO2 and CO into carbon with active wüstite prepared from Zn(II)-bearing ferrite

Adsorption of CO2 on oxygen-deficient magnetite : adsorption enthalpy and adsorption isotherm