An Integrated Carbon Dioxide Capture and Methanation Process

Reducing the ever-growing level of CO_(2)in the atmosphere is critical for the sustainable development of human society in the context of global warming.Integration of the capture and upgrading of CO_(2)is,therefore,highly desirable since each process step is costly,both energetically and economically.Here,we report a CO_(2)direct air capture(DAC)and fixation process that produces methane.Low concentrations of CO_(2)(∼400 ppm)in the air are captured by an aqueous solution of sodium hydroxide to form carbonate.The carbonate is subsequently hydrogenated to methane,which is easily separated from the reaction system,catalyzed by TiO2-supported Ru in the aqueous phase with a selectivity of 99.9%among gas-phase products.The concurrent regenerated hydroxide,in turn,increases the alkalinity of the aqueous solution for further CO_(2)capture,thereby enabling this one-ofits-kind continuous CO_(2)capture and methanation process.Engineering simulations demonstrate the energy feasibility of this CO_(2)DAC and methanation process,highlighting its promise for potential largescale applications.

Highly active sites of low spin Fe^(Ⅱ)N_(4)species:The identification and the ORR performance

Over recent years,catalytic materials of Fe-N-C species have been recognized being active for oxygen reduction reaction(ORR).However,the identification of active site remains challenging as it generally involves a pyrolysis process and mixed components being obtained.Herein Fe_(3)C/C and Fe_(2)N/C samples were synthesized by temperature programmed reduction of Fe precursors in 15%CH_(4)/H_(2)and pure NH_(3),respectively.By acid leaching of Fe_(2)N/C sample,only single sites of FeN_(4)species were presented,providing an ideal model for identification of catalytic functions of the single sites of FeN_(4)in ORR.A correlation was conducted between the concentration of Fe^(Ⅱ)N_(4)in low spin state by Mossbauer spectra and the kinetic current density at 0.8 V in alkaline media,and such a structure-performance correlation assures the catalytic roles of low spin Fe^(Ⅱ)N_(4) species as highly active sites for the ORR.

Preparation and characterization of pure SiC ceramics by high temperature physical vapor transport induced by seeding with nano SiC particles

High temperature physical vapor transport(HTPVT) was employed to grow polycrystalline SiC ceramics with high density and purity, induced by nano SiC particles as seeds. The obtained SiC ceramics were identified as 6 H-SiC with a mainly preferred orientation along the(0 0 0 6) plane, and an obvious refinement of grain size was demonstrated for the SiC seeds. Mean grain sizes of the obtained SiC ceramics were112 μm and 314 μm, by using the SiC seeds with the mean particle size of 50 nm and 500 nm, respectively,which were obviously smaller than that of the seed-free sample(960 μm). The samples obtained with the seeds also demonstrated enhanced flexural strength and hardness, attributing to the reduced mean grain size. Furthermore, SiC ceramics without seeds via HTPVT exhibited a high thermal conductivity of242 W·(m·K)^-1 at room temperature due to the highly preferred orientation. While the degree of preferred orientation of seed-induced samples was lower, the thermal conductivity of SiC ceramics induced by seeding still maintained at least 200 W·(m·K)^-1 at room temperature, this level was much higher than most other methods. Therefore, seed-induced method appears to be an effective way to control structures and behavior of SiC ceramics through HTPVT.