A Study of Carbon Dioxide Capture and Catalytic Conversion to Methane using a Ruthenium, “Sodium Oxide” Dual Functional Material: Development, Performance and Characterizations

The increasing CO2 level in the atmosphere, mostly attributed to anthropogenic activities, is overwhelmingly accepted to be the main greenhouse gas responsible for climate change. Combustion of fossil fuel is claimed to be the major cause of excess CO2 emission into the atmosphere, but human society will still rely heavily on fossil fuel for energy and feedstock supplements. In order to mitigate the environment-energy crisis and achieve a sustainable developing mode, Carbon Capture, Utilization and Storage (CCUS) is an effective method and attracts considerable interests. Rather than conventional aqueous amine-based liquid absorbent, e.g. the toxic, corrosive and energy intensive monoethanolamine (MEA), solid adsorbents are preferable for CO2 capture. CO2 utilization via CO2 conversion to fuel or other value-added products is favored over CO2 storage. Also it is preferred that no transportation of captured CO2 is required. Capturing and converting CO2 to fuel, such as synthetic natural gas or CH4 is particularly useful if it is produced at the site of CO2 generation. The converted CO2 can then be recycled to the inlet of the power plant or integrated into existed fuel infrastructure eliminating any transportation. This thesis presents a study of the development, performance and characterizations of a newly discovered (second generation) dual functional material (DFM) for CO2 capture and catalytic conversion to methane in two separated steps. This material consists of Ru as the methanation catalyst and “Na2O” obtained from Na2CO3 hydrogenation as the CO2 adsorbent, both of which are deposited on the high surface area γ-Al2O3 support. The Ru, “Na2O” DFM captures CO2 from O2- and steam-containing flue gas at temperature from 250 °C to 350 °C in step 1 and converts it to synthetic natural gas (CH4) at the same temperature with addition of H2 produced from excess renewable energy (solar and/or wind energy) in step 2. The heat generated from methanation drives adsorbed CO2 to Ru by spillover from the adsorption sites and diffuse to Ru for methanation. This approach utilizes the heat in the flue gas for both adsorption and methanation therefore eliminating the need of external energy input. The second generation DFM was developed with a screening process of solid adsorbent candidates. Initial adsorption studies were conducted with powdered samples for CO2 capture capacity, methanation capability, and resistance to an O2-containing simulated flue gas feed. The new composition of DFM was then prepared with tablets for future industrial applications and scaled up to 10 grams suitable for testing in a fixed bed reactor. Parametric and 50-cycle aging studies were conducted in a newly constructed scaled-up fixed bed reactor using 10 grams of DFM tablets in the simulated flue gas atmosphere for CO2 capture. With the presence of O2 in CO2 feed gas for step 1, the Ru catalyst is oxidized but must be rapidly reduced in step 2 to the active metallic state. Parametric studies identified 15% H2 is required for stable operation with no apparent deactivation. The parametric plus 50-cycle aging studies demonstrated excellent stability of the second generation DFM. A kinetic study was also conducted for the methanation step using powdered DFM but prepared via the tablet method to minimize any mass transfer and diffusion influence on the methanation rate. An empirical rate law was developed with kinetic parameters calculated. The methanation rate of captured CO2 is highly dependent on H2 partial pressure (approaching a reaction order of 1) while essentially zero reaction order of CO2 coverage was determined. The kinetic study highlights the importance of H2 partial pressure on the methanation process. Characterizations were conducted on the ground fresh and aged (underwent parametric and aging studies) DFM tablets. BET surface area, H2 chemisorption, X-ray diffraction (XRD) pattern, transmission electron microscopy (TEM) images and scanning transmission electron microscope- energy dispersive spectroscopy (STEM-EDS) mapping were utilized to study the material changes between fresh and aged samples. From fresh to aged, similar BET surface area was measured, improved both Ru and “Na2O” dispersion, and decreased Ru cluster size was observed while no definitive proof of the nature of the sodium species was obtained via XRD. The second generation DFM containing 5% Ru, 6.1% “Na2O” / Al2O3 was shown to possess the capability of capturing CO2 from O2-containing simulated flue gas and subsequent methanation with addition of H2 produced from excess renewable energy (or from chemical processes) with twice the CO2 and CH4 capacity relative to the first generation DFM. Activity, selectivity and stability has been demonstrated for the second generation DFM. We envision swing reactors to be utilized commercially where the flue gas feed for step 1 and H2 for step 2 are throttled alternatively between each reactor for continuous operation

The Role of Ruthenium in CO2 Capture and Catalytic Conversion to Fuel by Dual Function Materials (DFM)

Development of sustainable energy technologies and reduction of carbon dioxide in the atmosphere are the two effective strategies in dealing with current environmental issues. Herein we report a Dual Function Material (DFM) consisting of supported sodium carbonate in intimate contact with dispersed Ru as a promising catalytic solution for combining both approaches. The Ru-Na2CO3 DFM deposited on Al2O3 captures CO2 from a flue gas and catalytically converts it to synthetic natural gas (i.e., methane) using H2 generated from renewable sources. The Ru in the DFM, in combination with H2, catalytically hydrogenates both adsorbed CO2 and the bulk Na2CO3, forming methane. The depleted sites adsorb CO2 through a carbonate reformation process and in addition adsorb CO2 on its surface. This material functions well in O2- and H2O-containing flue gas where the favorable Ru redox property allows RuOx, formed during flue gas exposure, to be reduced during the hydrogenation cycle. As a combined CO2 capture and utilization scheme, this technology overcomes many of the limitations of the conventional liquid amine-based CO2 sorbent technology

The Role of Ruthenium in CO2 Capture and Catalytic Conversion to Fuel by Dual Function Materials (DFM)

Development of sustainable energy technologies and reduction of carbon dioxide in the atmosphere are the two effective strategies in dealing with current environmental issues. Herein we report a Dual Function Material (DFM) consisting of supported sodium carbonate in intimate contact with dispersed Ru as a promising catalytic solution for combining both approaches. The Ru-Na2CO3 DFM deposited on Al2O3 captures CO2 from a flue gas and catalytically converts it to synthetic natural gas (i.e., methane) using H2 generated from renewable sources. The Ru in the DFM, in combination with H2, catalytically hydrogenates both adsorbed CO2 and the bulk Na2CO3, forming methane. The depleted sites adsorb CO2 through a carbonate reformation process and in addition adsorb CO2 on its surface. This material functions well in O2- and H2O-containing flue gas where the favorable Ru redox property allows RuOx, formed during flue gas exposure, to be reduced during the hydrogenation cycle. As a combined CO2 capture and utilization scheme, this technology overcomes many of the limitations of the conventional liquid amine-based CO2 sorbent technology

Estudio DRIFTS in situ de captura de CO2 en dos pasos y metanación catalítica sobre material de doble función Ru, “Na2O”/Al2O3

6 páginasDual Function Materials (DFM) are composed of an alkali or alkaline earth CO2 adsorbent phase and a supported catalyst. It selectively captures CO2 which is then methanated using renewable H2. Both the capture and me- thanation steps are conducted at about 320 °C so no temperature swings are required allowing for continuous operation using two parallel reactors operating in tandem. This process approaches carbon neutral power generation by recycling the CH4 produced for re-combustion. This two-step process was studied by in-situ DRIFTS at 320 °C over 5%Ru-6.1%“Na2O”/Al2O3 DFM and compared with the 5%Ru/Al2O3 traditional methanation catalyst. In the DFM the Na2CO3/Al2O3 pre-curser is reduced to “Na2O” catalyzed by Ru metal. For both Ru/ Al2O3 and DFM CO2 adsorbs on Ru active sites and Al2O3 OH groups during the capture step. For DFM large amounts of CO2 absorb on the Al-O−-Na+ species forming bidentate carbonates. During the H2 reduction step (i.e., methanation step), adsorbed bicarbonates and bidentate carbonates spill over onto the Ru-support inter- face, where methanation takes place through sequential hydrogenation with formates as reaction intermediaries. Although CO2 was mainly adsorbed on the alkaline support methanation occurs over Ru, supporting the hy- pothesis that the reaction occurs at the Ru-support interface. Therefore, the multiple adsorption sites over the DFM explain the high CO2 adsorption capacity by the formation of bidentate carbonates that spill over onto the Ru-support interface, during the two-step methanation process.Los materiales de doble función (DFM) están compuestos por una fase adsorbente de CO2 alcalino o alcalinotérreo y un soporte Catalizador. Captura selectivamente el CO2 que luego se metana utilizando H2 renovable. Tanto la captura como yo- Los pasos de thanation se llevan a cabo a aproximadamente 320 °C, por lo que no se requieren cambios de temperatura, lo que permite un funcionamiento continuo. operación usando dos reactores paralelos operando en tándem. Este proceso se acerca a la energía neutral en carbono. generación mediante el reciclaje del CH4 producido para la recombustión. Este proceso de dos pasos fue estudiado por DRIFTS in situ a 320 °C sobre 5%Ru-6.1%“Na2O”/Al2O3 DFM y comparado con la metanización tradicional 5%Ru/Al2O3 Catalizador. En el DFM, el precursor Na2CO3/Al2O3 se reduce a “Na2O” catalizado por Ru metal. Tanto para Ru/ Al2O3 y DFM CO2 se adsorben en sitios activos de Ru y grupos OH de Al2O3 durante el paso de captura. Para DFM grande cantidades de CO2 se absorben en las especies Al-O−-Na+ formando carbonatos bidentados. Durante el paso de reducción de H2 (es decir, etapa de metanización), los bicarbonatos adsorbidos y los carbonatos bidentados se derraman sobre el soporte intermedio de Ru. cara, donde la metanización se lleva a cabo mediante hidrogenación secuencial con formiatos como intermediarios de la reacción. Aunque el CO2 se adsorbió principalmente en el soporte alcalino, la metanización ocurre sobre Ru, apoyando el soporte hipótesis de que la reacción ocurre en la interfaz Ru-soporte. Por lo tanto, los múltiples sitios de adsorción sobre el DFM explica la alta capacidad de adsorción de CO2 por la formación de carbonatos bidentados que se derraman sobre el Interfaz Ru-support, durante el proceso de metanización de dos pasos

Engineering the underlying surface to manipulate the growth of 2D perovskites for highly efficient solar cells

status: publishe

Determination of fluoride component in the multifunctional refining flux used for recycling aluminum scrap

In this paper, the optimum fluoride component in the multifunctional refining flux used for recycling aluminum scrap was determined. Theoretical analysis of solid fluxing shows that strong stripping ability of oxide layer on aluminum surface for the flux and appropriate interfacial tensions between Al melt / inclusion (σM-I), flux / inclusion (σF-I), and flux / Al melt (σF-M) are indispensable for making the flux achieve the properties of covering, drossing, and cleaning simultaneously. In term of four preliminarily selected fluoride salts, i.e., KF, AlF3, K3AlF6 and KAlF4, the results of interfacial tension measurements indicates that, combined addition of A-type fluoride (KF) and B-type fluoride (AlF3, K3AlF6 and KAlF4) to equimolar NaCl-KCl can just offset the shortage of single addition of KF which means worsening the separating effect of flux from melt surface and weakening the wettability of flux on the inclusions due to the lower σF-M and the higher σF-I respectively. Additionally, coalescence behaviors of aluminum droplets in molten fluxes reveals that, KF, K3AlF6 or KAlF4 possesses stronger stripping ability of oxide layer, while the stripping ability of oxide layer for AlF3 is weaker. Ultimately, the combination of KF with K3AlF6 or/and KAlF4 is ascertained to be an optimum selection for fluoride component in the multifunctional refining flux

Effect of reinforcement types on the ball milling behavior and mechanical properties of 2024Al matrix composites

In this paper, 2024 Al matrix composites reinforced by nanocrystalline high-entropy alloy particles (NC-HEAp), SiC particles, and coarse-grained high-entropy alloy particles (CG-HEAp) were fabricated via powder metallurgy, and a comparative study of different reinforcements was deeply conducted. The results showed that reinforcement types significantly influenced the morphology of composite powders, and the grain size and interfacial condition of composites. After ball milling, irregular granular NC-HEA-Al and SiC–Al composite powders were produced while the CG-HEA-Al composite powders exhibited flake shapes, and particle size of NC-HEAp sharply decreased and was significantly smaller than the other two reinforcements. The Cu-rich diffusion layer, a high dislocation density, and a thin oxide layer were formed in the interfaces of NC-HEA-Al, SiC–Al, and CG-HEA-Al composites, respectively. The NC-HEA-Al composite possessed the highest strength due to the best effect of grain refinement, while the SiC–Al composite displayed better ductility attributed to higher work hardening rate after the yield stage than that of the NC-HEA-Al composite. The CG-HEA-Al composites showed the least attractive mechanical properties, related to a poor interface bonding and pre-existing cracks in CG-HEAp. Furthermore, the differences in strengthening mechanisms of the three composites were also discussed. This work provides guidelines for designing metal matrix composites fabricated by powder metallurgy