Tizhuang Wang

A fast route for synthesizing nano-sized ZSM-5 aggregates

Nano-sized ZSM-5 aggregates have been rapidly synthesized from leached metakaolin by solid-like state conversion. The influence of synthesis conditions such as TPA(+)/SiO2, NaOH/SiO2 and SiO2/Al2O3 molar ratios on the final products was investigated. The properties of nano-sized ZSM-5 aggregates were characterized by XRD, SEM, HRTEM, Si-29 and Al-27 MAS NMR, NH3-TPD, TG, N-2 adsorption-desorption and particle size analysis. The results clearly showed that nano-sized ZSM-5 aggregates could be obtained within 2 h via solid-like state conversion. SEM revealed that the obtained ZSM-5 aggregates were irregular spheres that consisted of nano-sized crystallites with 30-50 nm. The crystallization process indicated that the size of flaky raw materials gradually decreased and formed nano-sized particles as time prolonged. Therefore, the transformation mechanism followed the solution mediated mechanism, though only a little water was contained in the system. Compared with the conventional hydrothermal route, the solid-like state conversion not only significantly shortened the crystallization time, but also totally avoided the emission of waste liquids. In addition, for the methanol dehydration reaction, the nano-sized ZSM-5 aggregates obtained by this method showed much better catalytic performance, C2-C4 olefin selectivity and longer lifetime to endure coke deposition than the sample obtained by the hydrothermal route.

Direct synthesis of HZSM-5 from natural clay

Highly crystalline HZSM-5 zeolite was directly synthesized through the steam-assisted conversion (SAC) approach using kaolin as the raw material, where NH3·H2O was used as an alkaline vapor source. The catalytic performance of the obtained HZSM-5 with SiO2/Al2O3 ratios from 25.67 to 80 was investigated for converting methanol to light olefins (MTO). The results indicated that NH3·H2O provided alkalinity to dissolve the raw materials and NH4+ cations to balance the charge of the framework. Highly crystalline HZSM-5 with crystal size in the range of 0.8–1 μm was obtained within 1.0 h at 190 °C. The obtained HZSM-5 possessed high SBET (above 440 m2 g−1) and high total pore volume (above 0.3 cm3 g−1). The acidity of the HZSM-5 was affected by the SiO2/Al2O3 molar ratio and residual metallic elements (such as Fe, Ti, Ca, P, etc.) in the leached metakaolin. The existence of the metallic elements similarly affected HZSM-5 modified with metal cations. HZSM-5 with a higher SiO2/Al2O3 molar ratio was favourable for the formation of C2–C4 olefins. The selectivity of C2–C4 olefins reached 68% when the SiO2/Al2O3 molar ratio was 68.79. This productive and facile method is inexpensive because the ammonium and calcination ion exchange processes are unnecessary.

Synthesis of nano/micro scale ZSM-5 from kaolin and its catalytic performance

Nano/micro scale ZSM-5 zeolites were synthesized by using natural kaolin as raw material. The effect of particle size on the catalytic performance of ZSM-5 zeolite for the methanol to olefins conversion was evaluated in a fixed-bed reactor. The results indicated the crystal size had a significant effect on the catalytic stability and the products distribution. ZSM-5 with nanosize showed better tolerance to coke formation, longer catalytic lifetime, and higher selectivity to propylene. The selectivity to propylene on nanosized ZSM-5 was on average 4.5% higher than on the submicron sample and 10% higher than on microsized ZSM-5. After the reaction was conducted for 20 h the ZSM-5 catalyst synthesized from kaolin showed longer lifetime and higher propylene selectivity than the sample synthesized with chemical materials The reason can be explained by the occurence of such elements as Fe, P, and especially Ti.

Effect of reactive nanoclays on performances of PMMA/reactive nanoclay nanocomposites

PMMA/reactive nanoclay nanocomposites were prepared by emulsion polymerization using two different reactive nanoclays. X-ray diffraction (XRD) and thermogravimetric analysis (TGA) results confirmed that the reactive nanoclays, kaolinite and montmorillonite, were obtained by the silylation reaction and the double bonds were grafted onto the edges and surfaces of the nanoclays. The presence of reactive nanoclays could increase the average molecular weights, the glass transition temperatures (Tg) and improve the thermal properties of nanocomposite. The tensile properties, Young’s modulus, and the aging properties of the nanocomposite films were also enhanced while the light transmittance decreased. Furthermore, the nanocomposites with the reactive kaolinite presented better performances than that with the reactive montmorillonite. Finally, the action mechanism of the reactive nanoclays to the performances of PMMA/reactive nanoclay nanocomposites was proposed.

Improved performances of oxygen potentiometric sensor by electrochemical activation

It is shown that the performances of the oxygen potentiometric sensor can be remarkably improved by electrochemical activation. The electrochemical activation were carried out by firstly employing the oxygen potentiometric sensor as a fuel cell (H2 vs. O2), and then running the fuel cell at a low discharge voltage for some time. This activation effect was valid for sensors domestically prepared under different conditions. On the basis of the literature reports and the experimental observations, the possible reasons for the electrochemical activation have been analyzed. The decrease of the concentration of the oxygen ion (oxide) species at the electrode and the decrease of the electrolyte contribution to the total impedance seemed to be the main reasons that have led to the remarkable improvement of the performances of the oxygen potentiometric sensor after the electrochemical activation.