Search

The catalytic performance of the isomerization of styrene oxide to phenyl acetaldehyde was investigated over different modified beta catalysts under gas-phase atmosphere free of solvents. The physicochemical properties were characterized by a combination of X-ray diffraction (XRD), N adsorption, Fourier transform infrared spectroscopy (FT-IR), Magic Angle Spinning Nuclear Magnetic Resonance (MAS-NMR), NH-Temperature programmed desorption (NH-TPD) and thermo gravimetric analysis (TGA), etc. Acid sites with stronger strength are responsible for the formation of condensation products and fast deactivation of catalysts. The obtained results also demonstrate that the introduction of boron atoms can create suitable acid strength and acid distribution without significantly destroying its microporous structures. Therefore, BAl-BEA sample is highly active and selective for the rearrangement of styrene oxide as well as very stable to deactivation. Graphical Abstract: [ABSTRACT FROM AUTHOR]

Abstract: Zeolitic imidazolate framework-8 (ZIF-8)/chitosan composites were prepared in the chitosan hydrogels. The concentrations of the chitosan and the alkaline solution were varied to the synthesis of the ZIF-8/chitosan composites. In the chitosan hydrogels with the addition of ammonium hydroxide solution, the resulting ZIF-8 crystals exhibited an unusual XRD structure that the XRD peak at about 18o (222) became the strongest. The XRD peak intensity ratio of (222)/(011) increased from 0.68 to 1.5–5.2 in the presence of chitosan hydrogels. ZIF-8/chitosan composites (FC2) were composed of aggregated nanosized particles, and exhibited a higher CO2 adsorption than normal ZIF-8 crystals. After removing chitosan from FC2, XRD pattern of the resulting ZIF-8 crystals returned to the normal state and the morphology kept the same as the composite. [Copyright &y& Elsevier]

Abstract: This paper presents the synthesis of zeolitic imidazolate framework (ZIF)-8 membranes on the outer surface of alumina hollow fibers using a concentrated synthesis gel. The resulting membranes were characterized by X-ray diffraction, scanning electron microscopy, focused ion beam/scanning electron microscopy and high-resolution transmission electron microscopy. The results showed that the crystalline ZIF-8 membranes were compact and continuous, and contained micro-cavities. Single gas permeances of H2, N2, CH4 and CO2 were determined as a function of permeation time at 25°C. H2, N2 and CH4 permeances almost did not change with the permeation time. However, CO2 permeance decreased from 9.8×10−8 to 1.7×10−8 mol/sm2 Pa within 12h, and CO2 permeation led to an unrecoverable reduction in gas permeation rates in the further permeation experiments. After the first round tests, H2, N2, CH4 and CO2 permeances in the second round permeation tests dropped by 40%, 24%, 11%, and 6%, and remained constant in the further repeated measurements; the equilibrium ideal selectivities of H2/CO2, N2/CO2 and CH4/CO2 were 32.2, 12.9, and 11.9, respectively; the H2/CO2 separation factor was 7.1 for a H2/CO2 binary mixture (45% H2). The small CO2 permeance should arise from the strong CO2 adsorption in ZIF-8 membranes with micro-cavities, and the adsorbed CO2 partially blocked the gas permeation. [Copyright &y& Elsevier]

Abstract: Hollow sodalite spheres with a hole on the shell were synthesized in a first-closed then-open system from the synthesis gels aged under ultrahigh N2 pressures. The effect of the synthesis time and the aging pressure was examined. The formation process was characterized by scanning electronic microscopy and X-ray diffraction. The results indicated that high pressure aging and synthesis in the open system were crucial for forming the hollow structure. By changing the synthesis time in the closed system, the size of the hollow sodalite spheres and the diameter of the hole as well as the fine structure of the sodalites could be adjusted. The formation process of the hollow sodalites was observed to follow a surface-to-core crystallization mechanism, i.e., formation of cubic zeolite A crystals in the closed system, growth of small sodalite spheres on the zeolite A crystal, wrap of the zeolite A by sodalite sphere aggregate and dissolution of zeolite A in the open system. Compared with those methods for synthesis of hollow zeolite crystals, this method is simple, effective and without using any template or additives. [Copyright &y& Elsevier]