Shiwei Chen

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.

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.