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  • Author or Editor: Yue Yao x
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Abstract  

β-MCM41 composite molecular sieves were hydrothermally synthesized using NaOH treated β zeolite as precursors, and Pt/β-MCM41 bifunctional catalysts were prepared by impregnation. Hβ, desilicated Hβ by NaOH treatment (Dβ), and the physical mixture of Hβ and MCM41 (β+MCM41) were also used as control supports for bifunctional catalysts. All the catalysts were characterized by ICP, XRD, BET, nitrogen adsorption–desorption isotherm and NH3-TPD, and evaluated in the hydroisomerization of n-heptane using an atmospheric fixed bed flow reactor. Dβ, β+MCM41, or β-MCM41 supported Pt catalysts showed higher selectivity to isoheptanes than the counterpart Pt/Hβ did due to the presence of mesopores in addition to the zeolite micropores. Moreover, Pt/β-MCM41 was demonstrated to be a much more selective catalyst among them because the connection between mesopores and micropores accelerated the diffusion of larger molecules of isoheptanes. Under optimal conditions, Pt/β-MCM41 provided a very high selectivity to isomerization of 96.5%, coupled with a considerable high conversion of n-heptane of 56.0%.

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Abstract  

Alkaline earth metal (Mg, Ca, Sr and Ba) ions were exchanged into Hβ zeolite, which were used as the supports to load the noble metal Pt to prepare bifunctional catalysts for hydroisomerization of n-heptane. The catalysts were characterized by ICP, XRD, BET, NH3-TPD, H2-TPR and H2-chemisorption techniques, and evaluated in an atmospheric fixed bed reactor. The catalysts promoted by the alkaline earth metals are revealed to present much higher selectivity to isomerization than the counterpart Pt/Hβ. Moreover, the Ba-bearing catalyst loaded with 0.4 wt% Pt and 5:1 molar ratio of Ba to Pt gives a very high selectivity to iso-heptanes 95.4% with a considerable high conversion of n-heptane 61.7%. The promotion effect of alkaline earth metals is briefly discussed in relation to characterization data.

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Abstract

The ionic liquid analogue containing MgCl2 based on choline chloride and glycerol was reported. The solubility of MgCl2 in the ionic liquid analogue based on choline chloride and glycerol was measured from T = 293–393 K. The empirical equation about the solubility and temperature was obtained. Thermal analysis showed that the ionic liquid analogue was stable from room temperature to 140 °C. The physical properties such as conductivity σ, density ρ and viscosity η of ionic liquid analogue were measured as function of the content of MgCl2 and temperature. An empirical equation about the density (ρ) and temperature was obtained. The ions transport behaviours are analyzed using hole-theory. It is shown that the conductivity of the ionic liquid analogues is controlled by the ion mobility and the suitable voids.

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Abstract

A bifunctional catalyst Pt/Hβ-n (Pt loading: 0.4 wt%) was prepared by the impregnation of an aqueous solution of chloroplatinic acid with β zeolite, wherein the β zeolite support has an unusual morphology of egg-like microspheres assembled by nanocrystallites. Other two control catalysts were also prepared using a β support with micro-sized crystals and a commercial one with varying crystal sizes. The catalysts were characterized by XRD, SEM, ICP, N2 sorption isotherms and mesopore size distribution, and evaluated in the hydroisomerization of n-heptane in an atmospheric fixed bed flow reactor. Though Pt/Hβ-n has similar acidity and Pt loading (0.4 wt%) to the two control catalysts, it exhibits remarkably higher conversion of n-heptane and selectivity to isomerization. According to the characterization data, the higher activity of Pt/Hβ-n is the result of the faster diffusion of reactants in shorter channels of nanocrystallines and the uniformly distributed mesopores within the microspheres.

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A high-performance thin-layer chromatographic (HPTLC) method for simultaneous analysis of temephos and fenitrothion in green tea has been established and validated. The sample was extracted with ethyl acetate by mechanical vibration at room temperature and the extract was cleaned by use of an SPE tandem column, before elution with dichloromethane. The extract was applied as bands to glassbacked silica gel 60F254 HPTLC plates. The plates were developed with acetone-hexane 3+7 (v/v), in an unsaturated glass twin-trough chamber. The developed HPTLC plates were evaluated densitometrically. The detection limits of temephos (R F 0.55) and fenitrothion (R F 0.69) were 20 and 10 ng, respectively. Recovery from green tea of the two pesticides at levels of 0.2 to 4 mg kg−1 was 80–107% with relative standard deviations of 4.4–20.2%. The precision and accuracy of the method were generally fit for analysis of temephos and fenitrothion residues in green tea.

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