摘要: Two different ranks of coals (Ximeng lignite, L and Xishan bituminous coal, B) and biomass (cornstalk, C) were selected to investigate effects of heating rate and pressure on structure and oxidation reactivity of chars from pyrolysis. The chars were prepared in a two-step pressurized fixed bed reactor at 900℃ from slow pyrolysis and fast pyrolysis under a range of pressures (0.1-2.0 MPa), which were marked as SC and FC, respectively. Specific surface area, surface morphology, and aromaticity of chars were characterized. Isothermal thermogravimetry was performed to study oxidation reactivity of chars. Results indicate that the char yields of three samples are distinctly varied and pyrolysis pressure and heating rate influence them through different residence time and diffusion rate of volatiles varying with different raw materials. The yields of chars from fast pyrolysis are all lower than those from slow pyrolysis and they increase slightly with increasing pyrolysis pressure from atmospheric pressure to 2.0 MPa. The specific surface areas of L-FC and B-FC are larger than that of L-SC and B-SC. However, the specific surface area of C-FC is smaller than that of C-SC. The morphology of FC is all rougher than that of SC. The aromaticity of B-SC is higher than that of B-FC, while that of L-SC and C-SC is lower than that of L-FC and C-FC derived from pressurized pyrolysis. The evolution of char structure at low heating rate and high pressure results generally in poor reactivity of char. The reactivity of cornstalk char is much higher than that of coal char, which should be correlated to the dispersion and concentration of inorganic matters in the char which is affected by heating rate and pressure.
摘要: Density functional theory calculations were used to investigate CO2 adsorption behaviors on Fetet1-and Feoct2-terminated surface of Fe3O4 (111). The results indicated that on the Fetet1-terminated surface, the linear CO2 is favored at 1/5 monolayer (ML), whereas the bent CO2 bonded to surface O, i.e. carbonate structure, becomes possible at higher coverage. On the Feoct2-terminated surface, the bent CO2 is favored; both carbonate and carboxylate structure are formed at both 1/6 and 1/3 ML. Meanwhile, the Fetet1-terminated Fe3O4(111) surface has weak coverage effects, whereas the Feoct2-terminated Fe3O4(111) surface has strong coverage effects; the Feoct2-terminated surface is thermodynamically more favorable than the Fetet1-terminated surface for CO2 adsorption.
摘要: Fuel desulfurization is an appealing topic for the chemical industry since severe environmental regulations regarding SO2 emissions have been legislated in many countries. In order to reduce the amount of sulfur-containing compounds in fuels, responsible for high SOx emission levels, a green chemistry approach is compulsory. In this paper, vanadium salen and salophen complexes were used in the oxidation of a model aromatic sulfide, such as dibenzothiophene (DBT), in the presence of H2O2 as green oxidant. The oxidative process was successfully coupled with the extraction of the oxidized compounds by ionic liquids. The system resulted highly selective for sulfide oxidation, showing poor reactivity toward the oxidation of alkenes and allowing a significant reduction of S content in a model benzine. To note, the use of microwave in place of standard heating allowed to obtain 98% of DBT oxidation and almost complete sulfur extraction in the model fuel in 1000 s. For these reasons, this system was considered an easy, rapid and clean process to achieve fuel desulfurization.
摘要: The main objective of this paper was to characterize the voltammetric profiles of the Pt/C, Pt/C-ATO, Pd/C and Pd/C-ATO electrocatalysts and study their catalytic activities for methane oxidation in an acidic electrolyte at 25℃ and in a direct methane proton exchange membrane fuel cell at 80℃. The electrocatalysts prepared also were characterized by X-ray diffraction (XRD) and transmission electron microscopy (TEM). The diffractograms of the Pt/C and Pt/C-ATO electrocatalysts show four peaks associated with Pt face-centered cubic (fcc) structure, and the diffractograms of Pd/C and Pd/C-ATO show four peaks associated with Pd face-centered cubic (fcc) structure. For Pt/C-ATO and Pd/C-ATO, characteristic peaks of cassiterite (SnO2) phase are observed, which are associated with Sb-doped SnO2 (ATO) used as supports for electrocatalysts. Cyclic voltammograms (CV) of all electrocatalysts after adsorption of methane show that there is a current increase during the anodic scan. However, this effect is more pronounced for Pt/C-ATO and Pd/C-ATO. This process is related to the oxidation of the adsorbed species through the bifunctional mechanism, where ATO provides oxygenated species for the oxidation of CO or HCO intermediates adsorbed in Pt or Pd sites. From in situ ATR-FTIR (Attenuated Total Reflectance-Fourier Transform Infrared) experiments for all electrocatalysts prepared the formation of HCO or CO intermediates are observed, which indicates the production of carbon dioxide. Polarization curves at 80℃ in a direct methane fuel cell (DMEFC) show that Pd/C and Pt/C electroacatalysts have superior performance to Pd/C-ATO and Pt/C-ATO in methane oxidation.