制备方法对Al2O3掺杂Pt/WO3-ZrO2催化剂上正庚烷异构化反应的影响

采用恒pH法和非恒pH法制备了Al₂O₃掺杂的Pt/WO₃/ZrO₂催化剂,并用N₂吸附-脱附、X射线衍射、紫外-可见漫反射、CO化学吸附、X射线光电子能谱、²⁷Al魔角旋转核磁共振和吡啶吸附红外等技术对催化剂进行了表征.结果表明,相比于非恒pH法制备的催化剂,恒pH法制备的催化剂具有较高的比表面积和Pt分散度,在H₂气氛中产生更多的B酸位,从而表现出更高的催化正庚烷临氢异构化反应活性; 在200℃和质量空速0.9h^-1的反应条件下,正庚烷转化率达70.0%,明显高于非恒pH法制备的催化剂(43.5%).     

Surfactant effect on the conductivity behavior of CsH2PO4: Characterization by electrochemical impedance spectroscopy

Cesium dihydrogen phosphate (CDP) nanoparticles were synthesized using the surfactants cetyltrimethyl ammonium bromide (CTAB), polyoxyethylene-polyoxypropylene (F-68) and (F-68:CTAB) with molar ratio 0.06. The samples conductivity such as CDP_CTAB, CDP_F-68 and CDP_{(F-68:CTAB)0.06} was studied by impedance spectroscopy in the frequency range 0.01 Hz to 1 MHz. The Nyquist plots were drawn at different temperatures of 210, 230 and 260 °C, which are defined below transition, phase transition and above transition, respectively. The measured conductivities obey the Arrhenius relation. The influence of surfactants on conductivity are more significant at higher temperature due to grain boundary. The conductivity of CDP_CTAB increased slightly with increasing temperature to 260 °C, whereas the conductivity of other samples decreased with increasing temperature over 230 °C. The results indicated that the conductivities increase in the order of CDP_CTAB>CDP_{(F-68:CTAB)0.06}>CDP_F-68. These are in accordance to the ion exchange capacities of the samples that the surfactant shows a direct influence on the samples proton mobility. It is found that the conductivity of CsH₂PO₄ is influenced by surfactant type.     

Effect of mono-, di- and tri-ethanolammonium tetrafluoroborate protonic ionic liquids on the volatility of water, ethanol, and methanol

Vapor pressure data were measured for nine binary systems containing water, ethanol, or methanol with one of three protonic ionic liquids (PILs), viz. mono-, di- and tri-ethanolammonium tetrafluoroborate ([HMEA][BF₄], [HDEA][BF₄], and [HTEA][BF₄]), at varying temperatures and PIL-contents using a quasi-static ebulliometer. The vapor pressure data were correlated by NRTL model with an overall average absolute relative deviation (AARD) of 0.0175. It is showed that the effect of PILs on the vapor pressure lowering of solvents follows the order of [HMEA][BF₄] > [HDEA][BF₄] > [HTEA][BF₄], and the vapor pressure lowering degree follows the order of water > methanol > ethanol. Besides, the activity coefficients of solvent for binary system {solvent + PIL} at fixed PIL mole fraction of 0.10 were calculated using the regressed NRTL parameters. The results indicate that three PILs can give rise to a negative deviation from the Raoult's law for water and methanol and a positive deviation for ethanol to a varying degree, leading to the variation of relative volatility of a solvent.     

Characterization of PVdF-HFP/Nafion/AlO[OH]n composite membranes for direct methanol fuel cell (DMFC)

Poly-(vinylidene fluoride-hexafluoropropylene) (PVdF-HFP)/Nafion ionomer/aluminum oxy hydroxide nanocomposite membranes were prepared by phase inversion technique. The resultant membranes were subjected to protonic conductivity, methanol permeability, infra-red and thermogravimmetric analysis. The infra-red spectroscopic measurements revealed the presence of sulfonic acid groups in the composite membranes. The thermal stability and ionic conductivity of the polymer membranes have been greatly varied upon the addition of AlO[OH]_n. Although the PVDF-HFP/Nafion/AlO[OH]_n composite membranes have moderate protonic conductivity it has lower methanol permeability and may be considered as a candidate for DMFC applications.     

Defects in scandium doped barium zirconate studied by Sc-45 NMR

Local structure around Sc in BaZr_1 − xSc_xO_3 − δ protonic conductor has been investigated by ⁴⁵Sc MAS-NMR. The MAS-NMR spectra were consisted of several peaks, which can be assigned to Sc in different coordination environment. Compositional dependence of the spectrum was observed. The coordination environment of Sc is determined from the peak deconvolution, and the oxygen vacancy concentration and the protonic defect concentration around Sc were obtained. The present investigation suggests that oxygen vacancies preferentially located around Sc and the concentration of oxygen vacancies in the vicinity of Sc increases with increasing the Sc content. Protonic defects were found to be preferentially located around Sc at lower Sc content.     

Composite protonic solid electrolytes in the CsHSO4-SiO2 system

Transport, thermal and structural properties of the composite solid electrolytes (1 −x)CsHSO₄---xSiO₂ (where x = 0–0.8) were investigated. The composites were prepared by mechanical mixing of components followed by heating at temperatures near CsHSO₄ melting point (483 K). The dependence of low temperature phase conductivity on x has a maximum with a value 2.5 orders of magnitude higher than that of pure CsHSO₄ and conductivity is governed by protons. Heterogeneous doping is shown to change markedly the thermodynamic parameters of the ionic component. The phase transition temperature CsHSO₄ in the composites decreases from 414 to 350 K with the increase of the content of heterogeneous additive SiO₂ from 0 to 0.7. As x raises CsHSO₄ the amorphization takes place and the relative change of ionic conductivity at phase transition diminishes, the phase transition becomes diffusive and disappears for the 0.2CsHSO₄---0.8SiO₂ composite.     

Synthesis of the sulfonated condensed polynuclear aromatic (S-COPNA) resins as strong protonic acids

The mixture (PXG/PR=1.00) of pyrene (PR) and p-xylylene glycol (1,4-benzenedimethanol) (PXG) in the presence of 5 wt % of p-toluenesulfonic acid (TsOH) was heated at 140 °C for 45 min under nitrogen to give the highly viscous condensed polynuclear aromatic (COPNA) resin. It was converted into an infusible and insoluble solid by further heating at 300 °C for 1 h. The obtained material was treated with fuming sulfuric acid at 80 °C for 15 h under nitrogen to give the sulfonated COPNA resin. The similar acidic resin was prepared by the reaction of phenanthrene or naphthalene with PXG in the presence of TsOH followed by sulfonation. The performance of the sulfonated polymers as the strong protonic acids was evaluated.     

Synthesis of photocatalytic active fibrous titania by the solvothermal reactions

Abstract

Fibrous titania was synthesized by the solvothermal reactions of H₁Ti₄O₉ nH₂in different media. H₂Ti₄O₉·nH₂O transformed in steps to H₂Ti₈O₁₇, monoclinic TiO_z, anatase and rutile. The phase transformation temperature and microstructure of the products changed significantly depending on the heating environment. The critical temperature at which anatase appeared in liquid media was much lower than that in air. The titania fibers consisted of nanocrystals of TiO₂. The crystallite size and crystallinity of titania decreased with decreasing the dielectric constant of the reaction medium. Consequently, the photocatalytic activity of titania changed with heat treatment media in the following sequence: ethanol, methanol > water > air, i.e., fibrous titania possessing excellent photocatalytic activity could be obtained by the solvothermal reactions using alcohol such as methanol and ethanol. Titania powders crystallized by the solvothermal reaction in methanol also possessed excellent thermal stability.     

聚N-甲基苯胺的质子酸掺杂

聚N-甲基苯胺(PMAn)可用酸碱进行可逆的掺杂及反掺杂。掺杂使电导增大。掺杂过程在本质上是链的质子化过程,与阴离子无关。用FTIR、UV-VIS、ESR表征了掺杂前后结构的变化。结果表明,掺杂后链上来偶电子增加,电子及电荷更加离域化,并与电导率增大相吻合。PMAn的导电载流子可能是离域化的阳离子自由基。     

Perovskite-based nanocomposites as high-performance air electrodes for protonic ceramic cells

Hydrogen (H₂) is regarded as an important energy carrier to achieve a clean and sustainable future. In particular, protonic ceramic cells (PCCs) as promising energy conversion technologies have received rapidly increasing attention for the production and use of H₂, showing higher energy efficiencies at reduced temperatures than oxygen-ion-conducting counterparts. Nevertheless, the sluggish kinetics of air electrodes for oxygen reduction/evolution reactions has become one of the main obstacles to achieving high-efficiency PCCs. Therefore, the key point to realizing the commercialization of PCCs is the development of high-performance air electrodes. Particularly, perovskite-based nanocomposites received increasing interests as high-efficiency air electrodes for PCCs recently due to the synergistic effect and strong interaction between various phases with different functionalities at nanoscale. Herein, the advances of this area in 2020–2022 are mainly reviewed by highlighting the superiorities, design strategies, and remaining challenges of perovskite-based nanocomposites as air electrodes for PCCs at reduced temperatures.