Catalytic dehydrogenation of ethylbenzene with carbon dioxide: promotional effect of antimony in supported vanadium–antimony oxide catalyst

Alumina-supported vanadium oxide, VO_x/Al₂O₃, and binary vanadium–antimony oxides, VSbO_x/Al₂O₃, have been tested in the ethylbenzene dehydrogenation with carbon dioxide and characterized by S_BET, X-ray diffraction, X-ray photoelectron spectroscopy, hydrogen temperature-programmed reduction and CO₂ pulse methods. VSbO_x/Al₂O₃ exhibited enhanced catalytic activity and especially on-stream stability compared to VO_x/Al₂O₃ catalyst. Incorporation of antimony into VO_x/Al₂O₃ increased dispersion of active VO_x species, enhanced redox properties of the systems and formed a new mixed vanadium–antimony oxide phase in the most catalytically efficient V_0.43Sb_0.57O_x/Al₂O₃ system.     

Photocatalytic Properties of Silica-supported TiO2

TiO₂ supported on SiO₂ surface is effective on the recovery of photocatalyst, morphological control, and coating on the substrate. Furthermore, it shows much higher photocatalytic activity than pure TiO₂. The silica support is quite influential on the surface properties of TiO₂ supported on SiO₂. The enhanced photocatalytic activity of TiO₂–SiO₂ could be explained by the effects of surface area, adsorption, band-gap energy and local structure. However, it is difficult to say which one is the most important factor responsible for the photocatalytic property of TiO₂–SiO₂. For example, the reduction of particle size could effect on both of the surface area and band-gap energy. And, Ti–O–Si bonds could modify the band-gap energy and local structure. Therefore, the photocatalytic properties of TiO₂–SiO₂ should be expressed by sum of many factors such as surface area, adsorption, band-gap energy and local structure.     

Physical degradation of MEA in PEM fuel cell by on/off operation under nitrogen atmosphere

The durability of PEMFCs is one of the most important issues for application in automotive vehicles with a repeated start-up and shut-down system. The understanding of degradation phenomena such as causes, mechanisms and influence of working condition is essential to improving the performance and lifetime of PEMFC. We conducted on/off cyclic operation in a single cell configuration with ultra purity nitrogen gas to investigate the physical degradation of membrane electrode assembly (MEA). After on/off cycle operation for 100,000 cycles under different humid condition, the characteristics of the MEAs were examined by in situ and ex situ analyses techniques. The physical degradation of MEA by on/off cycling led to a change in the membrane-electrode interfacial structure, which is mainly attributed to the loss of cell performance.     

Preparation of nano-zeolite tubular membrane for ethylbenzene separation from ternary mixed xylene by microwave functional coating method

The ethylbenzene separation from mixed xylene is one of the critical issues in the chemical industry. In this study, separation of ethylbenzene from ternary xylene mixtures system [ethylbenzene (EB), para-xylene (PX) and meta-xylene (MX)] was performed using a nano-zeolite coated tubular membrane system. Nano-zeolite membranes with different Si/Al ratios (Si/Al = 30, 100 and ∞) were prepared by a microwave hydrothermal method and the separation performance was compared. MFI-type nano-zeolite membranes were synthesized on alumina tubes from the randomly oriented seed layers by dip coating and functional coating using 3-chloropropyltrimethoxysilane, respectively. After the microwave-assisted secondary growth, it was observed that thinner layers of nano-zeolites were prepared by functional coating (3–4 μm) compared to the typical dip coating (6–8 μm). Ethylbenzene separation tests were performed using a comparatively high EB-containing ternary mixture feed (EB/PX/MX = 80/5/15 molar ratio). The silicalite-1 (Si/Al ratio = ∞) membrane with a functional layer shows the best ethylbenzene separation factor of 3.11 from the high EB-containing ternary mixture feed (ethylbenzene flux: 1,010.6 mol/m² s Pa ×10^?10).     

Preparation of PAN-zeolite 4A composite ion exchanger and its uptake behavior for Sr and Cs ions in acid solution

A PAN-4A composite ion exchanger containing about 80% 4A powder was prepared to remove strontium and cesium ions from acidic solution. The SEM image of the fracture of composite bead showed that zeolite 4A powder was dispersed homogenously and the pores were well formed. The mean pore size of composite bead was 0.14 μm and its porosity was about 74%, which is much higher in comparison with the existing inorganic adsorbent beads. The acid and radiation stability tests showed that PAN-4A was stable against acid solution higher than pH 2 and radiation dose less than 1.89×10⁸ rad, respectively. Ion exchange tests showed that the PAN-4A was selective for Sr ion. The distribution coefficients of PAN-4A for Sr and Cs ions at pH 2 were 2×10⁴ mL/g and 280 mL/g, respectively. The ion exchange capacities (q_s) of PAN-4A for Sr and Cs ions at pH 2, which are modeled by Dubinin-Polanyi equation, were 3.92 meq/g and 2.47 meq/g, respectively.     

Preparation of mesoporous silica fiber matrix for VOC removal

A novel method for the preparation of the mesoporous silica fiber matrix was introduced for a removal of volatile organic compounds (VOCs). Paper making technology was applied to make a sheet of mesoporous silica fiber matrix. Reinforcing the mesoporous silica fiber with the ceramic fibers (50 wt.%) increased the mechanical strength of the matrix. Mesoporous silica fibers using TMOS (tetramethoxysilane) as a silica source and CTAC (cetyltrimethyl-ammoniumchloride) as a surfactant were drawn by the spinning method. The spinning process increased both the crystallinity and the fraction of mesopores (1.9 nm) of the fiber. As the spinning rate was increased both the crystallinity and the specific area of the mesoporous silica fiber increased, but the diameter of fiber decreased. We could control the size and morphology of mesoporous silica fiber matrix by changing the shape of substrates. This leads to easy fabrication of honeycomb-structured adsorbent which can be used for the VOC removal.     

Preparation of TiO<Subscript>2</Subscript>/SiO<Subscript>2</Subscript> hollow spheres and their activity in methylene blue photodecomposition

PSA [poly-(styrene-methyl acrylic acid)] latex particle has been taken into account as template material in SiO₂ hollow spheres preparation. TiO₂-doped SiO₂ hollow spheres were obtained by using the appropriate amount of Ti(SO₄)₂ solution on SiO₂ hollow spheres. The photodecomposition of the MB (methylene blue) was evaluated on these TiO₂-doped SiO₂ hollow spheres under UV light irradiation. The catalyst samples were characterized by XRD, UV-DRS, SEM and BET. A TiO₂-doped SiO₂ hollow sphere has shown higher surface area in comparison with pure TiO₂ hollow spheres. The 40 wt% TiO₂-doped SiO₂ hollow sphere has been found as the most active catalyst compared with the others in the process of photodecomposition of MB (methylene blue). The BET surface area of this sample was found to be 377.6 m²g⁻¹. The photodegradation rate of MB using the TiO₂-doped SiO₂ catalyst was much higher than that of pure TiO₂ hollow spheres.     

Catalytic activity and characterization of V2O5/γ-Al2O3 for ammoxidation of m-xylene system

An ammoxidation of m-xylene was evaluated in a fixed-bed reactor using V₂O₅ on various oxides. Catalysts were prepared by wet impregnation method. At first, the loading of V₂O₅ was varied from 5 wt% to 20 wt% on γ-Al₂O₃ support to estimate the most effective amount of V₂O₅. Second, the effect of catalyst supports was examined at 10 wt% loading of V₂O₅. V₂O₅/TiO₂ and V₂O₅/SiO₂ catalysts were employed to compare the ammoxidation reaction with V₂O₅/γ-Al₂O₃. Most catalytic activity was observed when γ-Al₂O₃ was used as a support. Careful characterization was followed by physicochemical techniques, such as BET measurement, X-ray diffraction (XRD), Raman spectroscopy and temperature-programmed reduction (TPR). The results provided the clue that monolayer V₂O₅ was favorably dispersed on the surface of γ-Al₂O₃ up to 10 wt%, which led to the highest yield of isophthalonitrile (IPN).     

Preparation of silica-based proton conductors for intermediate temperature fuel cells

The ternary system SiO₂-P₂O₅-ZrO₂ electrolyte and phosphotungstic acid (PWA) doped SiO₂-P₂O₅-ZrO₂ electrolyte were prepared for intermediate temperature fuel cell by using sol-gel technique. These silica-based proton conductors were confirmed to be non-crystalline structure without phase separation and good thermal stability by XRD and TG/DTA analysis. The doped PWA was found to be stabilized within the silica matrix and to enhance the proton conductivity. The proton conductivities of SiO₂-P₂O₅-ZrO₂ and SiO₂-P₂O₅-ZrO₂-PWA electrolytes showed 3.3×10⁻⁵ and 1.8×10⁻³ S/cm at 90 °C, respectively, and the cell performance of SiO₂-P₂O₅-ZrO₂-PWA electrolyte was obtained as 0.02–0.25 mA/cm² at 300 °C under humid condition.     

Pt nanoparticle-reduced graphene oxide nanohybrid for proton exchange membrane fuel cells

A platinum nanoparticle-reduced graphene oxide (Pt-RGO) nanohybrid for proton exchange membrane fuel cell (PEMFC) application was successfully prepared. The Pt nanoparticles (Pt NPs) were deposited onto chemically converted graphene nanosheets via ethylene glycol (EG) reduction. According to the powder X-ray diffraction (XRD) pattern and transmission electron microscopy (TEM) analysis, the face-centered cubic Pt NPs (3-5 nm in diameter) were homogeneously dispersed on the RGO nanosheets. The electrochemically active surface area and PEMFC power density of the Pt-RGO nanohybrid were determined to be 33.26 m2/g and 480 mW/cm2 (maximum values), respectively, at 75 degrees C and at a relative humidity (RH) of 100% in a single-cell test experiment.