燃料化学学报最新文献

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.

A series of silicon spheres supported cobalt catalysts were prepared by incipient wetness impregnation followed by decomposition under treatment of glow discharge plasma with different intensities. The catalysts were characterized by X-ray powder diffraction, N₂ physical adsorption-desorption, H₂ temperature-programmed reduction, transmission electron microscope and Fourier-Transform Infrared spectroscopy. The Fischer-Tropsch synthesis performance were tested on a fixed bed reactor. The influence of plasma treatment on cobalt dispersion, reducibility and cobalt-support interaction were analyzed and discussed. The results showed that the plasma-treated catalysts had better catalytic performance than the calcined sample. The Co/SP-P650W catalyst showed the highest reaction activity due to the proper cobalt dispersion and higher cobalt reducibility.

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 promote 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.

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.

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.

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.

Comparing the composite TiO₂ prepared by hydrothermal sol gel method and microwave-assisted sol gel method, the microwave-assisted sol gel method with shorter time and better crystallinity was finally used to prepare ZnO-TiO₂ materials with different composite ratios. The specific surface area, pore volume and pore size of ZnO-TiO₂ composite are significantly larger than those of TiO₂. The surface acidity of ZnO-TiO₂ composite is stronger. The band structure is conducive to the efficient separation of electrons and holes, and the catalytic reduction activity and selectivity are stronger. The best composite ratio of ZnO and TiO₂ is optimized to be 0.2 through photocatalytic denitration experiments. For NOx with an initial concentration of 6.83 mg/m³, under the light source condition irradiated by 65 W energy-saving lamp, the visible photocatalytic removal efficiency is as high as 85%. When the NO_x concentration is increased to 13.67 mg/m³ and the ammonia nitrogen ratio is 1:1, the denitration efficiency is as high as 96%, which is 43% higher than that of pure TiO₂. According to mechanism analysis, the whole reaction can be divided into adsorption and photocatalysis. Adsorption is the speed control step of the reaction. NO is oxidized to NO₂ under the action of adsorbed oxygen, and photogenerated electrons can further reduce NO₂ to N₂. After NH₃ is introduced, NH₃ and photogenerated electrons work together to improve NO_x removal efficiency.

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.

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 (G_R + V_L + V_R)/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%).

Ash content is an important factor affecting the quality and combustion performance of biochar. In this paper, a method of ash removal from biomass is proposed by carbonization followed by CO₂-enhanced water leaching. The effects of the carbonization temperature of bagasse, the temperature and time of CO₂-enhanced water leaching on the deashing were investigated. The results show that the deashing rate firstly increases and then decreases with the carbonization temperature, while the opposite trend is obtained with increasing the water leaching temperature and time. For bagasse biochar carbonized at 300 °C, the deashing rate reaches 57% at the water leaching temperature of 40 °C for 4 h. Compared with water leaching without carbonization, the proposed method can increase the content of fixed carbon and the char yield by 7% and 3%, respectively. It is because in the process of deashing, CO₂ diffuses and dissolves into water to form carbonic acid which reacts with part of metal salts to form water-soluble salts, resulting in the removal rate of K, Na and Ca up to above 50%, and part removal of calcite and dolomite. Also, the proposed process shows higher deashing efficiency and universality, but the deashing degree is closely related to the ash composition and kinds in biochar. As to peanut shell and poplar, the deashing rate exceeds 30% by carbonization at 300 °C and CO₂-enhanced water leaching at 40 °C for 4 h.