摘要: In this work, a Fe-doped Co3O4 OER electrocatalyst supported by an N-doped hollow nanocage carbon framework (Fe-Co3O4/NC) was successfully prepared by anion exchange and annealing in an air atmosphere strategy. XRD and HRTEM characterizations confirm that Fe the incorporation of Fe into the lattice of Co3O4. XPS characterization clarifies that the valence state of Co increases after the introduction of Fe, which originates from the electrons transfer from Co2+/Co3+ to Fe3+ and is induced by the valence electron configuration of cations. It simulates Co sites in-situ derived into CoOOH active species during the OER process, which is confirmed by the HRTEM and XPS characterization after the OER stability test. Electrochemical performance tests show that the Fe-Co3O4/NC electrocatalyst only exhibits 275 mV overpotential to achieve a current density of 10 mA/cm2 and stably maintains for 20 h at 100 mA/cm2. Together with 20% Pt/C electrocatalyst, the composed two-electrode system only needs 2.041 V applied potential to achieve 100 mA/cm2 for total water splitting in a self-made membrane electrode device, which has industrial application prospects.
摘要: We anchored atomically dispersed Fe-N4 sites on hollow N-doped carbon spheres (Fe SAs/HNCSs-800) for electrocatalytic ORR; the obtained material exhibited electrocatalytic activity and stability comparable to that of commercial Pt/C, with an onset potential of 0.925 V and a half-wave potential of 0.867 V. Aberration-corrected high-angle annular dark-field scanning transmission electron microscopy and X-ray absorption spectroscopy results confirmed the presence of highly dispersed Fe single atoms in Fe SAs/HNCSs-800. The results of experiments and theoretical calculations show that the single-atom dispersed Fe-N4 serve as the ORR active sites, and the adjacent C defects can effectively regulate the electronic structure of Fe atoms and improve the electrocatalytic ORR activity.
摘要: In this work, to better understand catalytic gasification process of direct coal liquefaction residue rich in sodium species, char structure evolution and behaviors of sodium species during gasification under CO2 atmosphere were investigated in detail by N2 adsorption and desorption, FT-IR, XRD, SEM, and Raman analyses. The results show that sodium species developed pore structure of direct coal liquefaction residue during gasification, especially expanded mesoporous structures which increased from 0.05 to 0.16 cm3/g at maximum. With the increase of gasification time, different crystalline compounds were formed in chars. Most of the mineral matters identified by XRD were calcium-containing ones, whereas no obvious sodium-containing crystalline compounds were found. This was because that most of sodium species volatilized at high temperature and the crystalline forms of sodium-containing compounds had defects. Compared with sodium species, calcium species were more prone to react with aluminosilicates, which happened to make sodium species remain active during gasification process. The ratio of (GR + VL + VR)/D rose initially and then decreased, which could be explained as the dissociation of the large aromatic and the rearrangement of small aromatic rings into large aromatic structures. Moreover, release ratio of sodium species was closely related with gasification time and 49.8% of them released in the initial stage of gasification process (within 15 min). Compared with that of direct coal liquefaction residue reloaded with water-soluble sodium species, the release ratio of sodium species in the original direct coal liquefaction residue was on a lower level (85.2% versus 89.7%).
摘要: In the present study, the kinetic behaviour and active sites evolution processes of Pt-based catalysts were investigated. It was found that highly selective hydrogen combustion could be achieved over Sn modified Pt-based catalysts in presence of both propane and propene (over 98%). The stability tests, kinetic study and catalyst characterization revealed that the existence of oxygenated species is the reason for accelerated coking reactions. The formation of graphitized cokes serving as additional unselective active sites and the oxidation of tin in PtSn alloy phases are the primary reasons causing the catalytic selectivity loss during long-run tests under propene-rich condition.
摘要: Direct synthesis of liquefied petroleum gas from syngas via Fischer-Tropsch synthesis route was systematically investigated over a nano-level core@shell catalyst. We introduced an incorporation of FeMg catalyst into mesoporous silica shell, with a further modification of Cu particles on the silica surface. The modified Cu/FeMg@SiO2 nano core-shell catalysts were synthesized by the combination of co-precipitation, modified sol-gel and facile impregnation methods. The as-synthesized catalysts’ physicochemical property was characterized by XRD, TEM, N2 adsorption-desorption, H2-TPR, XPS and CO2-TPD techniques. The catalytic performance of Cu/FeMg@SiO2 catalyst shows a high CO conversion of 96.6%, rather low CO2 selectivity of 21.9% and considerable LPG selectivity of 37.9%. The catalytic results indicate that the SiO2 shell restrains the formation of CH4 and contributes to increasing long-chain products. Meanwhile, the enhanced CO conversion of Cu/FeMg@SiO2 was ascribed to the active metal Cu dispersed on SiO2 shell, which also promoted olefin hydrogenation and cracking of C5+ hydrocarbons products. The proposed catalyst preparation method will provide a new strategy for the synthesis of nano level catalyst with combinations of metal- and zeolite-based catalyst.
摘要: Using pseudo-boehmite and ultrafine copper hydroxide as the raw materials with n(Cu/Al) = 1∶3, the effects of ball milling medium on the Cu-Al spinel sustained release catalysts prepared via the solid-state reaction method are explored. The obtained catalysts are characterized by XRD, BET, and H2-TPR techniques, and their catalytic properties in methanol steam reforming (MSR) are evaluated. The results demonstrate that Cu-Al spinel solid solution can be synthesized by both dry and wet mechanical ball milling methods, and more Cu2 + ions are found to be incorporated into the spinel lattice through the latter method. The crystalline sizes of as-synthesized spinels are similar; however, the specific surface areas and pore volumes are different as well as their reduction properties. Compared with the dry milling method, the wet ball milling method can facilitate the solid phase reaction, generating catalysts with solely spinel crystalline phase, higher specific surface area, and larger pore volume. Furthermore, catalysts derived from the wet milling method demonstrate improved catalytic activity and stability, and lower CO selectivity in MSR. The highest activity is obtained over CuHAl-Ac-950 prepared using ethanol (95%) as the ball milling medium.
摘要: La2O3 as a catalyst is used for oxidative coupling of methane (OCM) reactions due to its excellent stability and high C2 selectivity, but poor activity on methane dissociation limits its wide application. Different valence metals are doped on the La2O3(001) surface to improve the methane conversion activity, and the activation of methane on metal-doped La2O3(001) surfaces has been investigated via the density functional theory (DFT) calculations. The relationship between the valence states of doped metals and the methane conversion activities shows that doping low valence metals (Li, Na, K, Mg, Ca, Sr and Ba) and equivalent metals (Al, Ga, In) can significantly improve the conversion activity of methane. Among them, the activation energy of methane on the Li-La2O3(001) surface is the lowest, which is only 13.0 kJ/mol. However, doping of high valence metals (Zr, Nb, Re and W) cannot improve the CH4 dissociation activity. Furthermore, the relationships between surface oxygen vacancy formation energies, acid-base properties and the activation energies of CH4 have also been investigated. The results show that with the increase of metal valence state, the oxygen vacancy formation energy increases, while the dissociation activity of CH4 decreases. The introduction of alkali and alkaline earth metals increases the alkalinity of La2O3(001) surface, and the alkalinity of La2O3(001) doped with the alkali metal is stronger than that with the alkaline earth metal, exhibiting higher dissociation activity of CH4. Our research may provide a guide for improving methane conversion activity on La2O3 catalysts.
摘要: 本论文基于传统聚合物基炭材料合成原理，通过选择合适结构的前驱体分子，在聚合过程中分子水平锚定Co原子，同时引入TiO2纳米颗粒，再经高温焙烧后制得一种双金属氮氧化物（ComTinOxNy）-Co单原子（Co-NC）复合催化剂。该催化剂在酸性（Eonset = 0.755 V vs. RHE，0.5 mol/L H2SO4; 0.760 V vs. RHE，0.1 mol/L HClO4）、中性（Eonset = 0.787 V vs. RHE，0.1 mol/L PBS）、碱性（Eonset = 0.880 V vs. RHE，0.1 mol/L KOH）电解液中的氧气还原（ORR）性能（pH = 0−13）均优于纯氮杂碳纳米管、氮杂碳纳米管负载的金属氮氧化物和Co单原子催化剂，表明，ComTinOxNy与Co单原子的协同效应使得复合催化剂具有更好的ORR活性，同时复合催化剂的稳定性和选择性显著优于商品Pt/C催化剂。这为开发高性能低成本氧气还原电催化剂提供了新的思路。
