A considerable amount of works were focused on the formation mechanism of calcium ferrite phases during the iron ore sintering process, especially under various O2 content atmospheres at temperatures higher than 1100°C. But little attention has been paid on reactions between CaO and iron oxides in CO–CO2 atmospheres at lower temperatures. In this study, the solid state reaction mechanisms between CaO and Fe3O4 under CO–CO2 atmospheres at 800°C–1100°C were revealed by using XRD, VSM, etc. The results indicated that Ca2Fe2O5 was easily formed under 5–50 vol% CO/(CO+CO2) atmosphere above 850°C via the reaction of 6CaO + 2Fe3O4 +CO2 = 3Ca2Fe2O5 + CO and the reaction would be promoted with increasing the roasting temperature. In the CO–CO2 atmosphere, Fe3O4 is easily oxidized to Fe2O3 in the presence of CaO because CO2 components act as oxidative medium for the oxidation of Fe2+ to Fe3+.
Chemical vapor transport (CVT) process is a simple and efficient method for synthesizing nano-SnO products, and previous references reveal that the CVT process is characterized as high temperature and long synthesis time. Our previous studies indicated that SnO 2 was easily reduced to solid-state SnO and then volatilized as gaseous SnO under certain CO-CO 2 atmosphere, so that a novel CVT process under CO-CO 2 atmosphere was proposed in the present work. The nano-SnOs synthesized by the CVT under 15 vol% CO/(CO + CO 2 ) atmosphere were characterized using XRD , SEM, TEM, XPS , etc. The results showed that tetragonal structure nano-SnO diskette and sphere with uniform granularity of 50–100 nm were obtained with high purity. During the CVT process, CO-CO 2 mixed gases could reduce SnO 2 to SnO and act as a CVT medium to take away the newly formed gaseous SnO, resulting in the decrease of the partial pressure of SnO. In addition, the nano-SnOs could enhance the SCR deNOx activity of activated carbon (AC), and both the reaction temperature window of AC and the NO conversion were increased if the AC was coated by nano-SnOs.
Kai Ma,Yao Luo,Jietao Wang,Xu Chang,Tong Liu,Yao Wang,Mingyue Ding
Developing robust fuel electrodes with high catalytic activity and stability under CO/CO 2 atmospheres is critical for reversible solid oxide fuel cells (RSOFCs). Here, we report a novel A-site-deficient perovskite Sr 1.95 Fe 1.5 Mo 0.3 Ni 0.2 F 0.1 O 6-δ (SFMNF) synthesized via electrospinning, combining Ni 2+ (B-site cation) and F - (anion) co-doping to enhance CO 2 electrolysis and syngas oxidation performance. Physicochemical characterization reveals that F-doping lowers the crystallization temperature, increases oxygen vacancy concentration, and strengthens CO 2 chemisorption. Reduction under H 2 induces exsolution of Ni 3 Fe alloy nanoparticles. The SFMNF electrode achieves a current density of 233 mA cm -2 at 1.3 V and 750°C in CO:CO 2 =2:1 atmosphere, with 36.2% higher activity than the pre-reduced state. Electrochemical impedance and distribution of relaxation time analyses identify CO 2 adsorption/dissociation as the rate-limiting step. The cell demonstrates exceptional durability over 50 redox cycles and 85-hour of operation without carbon deposition. This work highlights dual doping as an effective strategy to tailor perovskite properties for efficient CO 2 utilization in RSOFCs.
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