Stability of Y/MCM-48 composite molecular sieve with mesoporous and microporous structures

AbstractY/MCM-48 composite molecular sieve was hydrothermally synthesized at different crystallization temperatures and crystallization times using ethyl orthosilicate as Si source and cetyltrimethyl ammonium bromide as template with the aid of fluoride ions and was characterized by X-ray diffraction, N2 physical adsorption technique, scanning electron microscopy and transmission electron microscopy. The thermal, hydrothermal, acidic, and basic stabilities of the Y/MCM-48 composite were investigated. The results show that Y/MCM-48 composite molecular sieve with meso- and microporous structures was synthesized successfully at 120°C for 36h. The Y/MCM-48 composite has the surface area of 864m2/g and the average pore size is ca. 2.48nm. The bi-porous structure in composite molecular sieve still maintains its stability even after thermal treatment at 800°C for 4h or hydrothermal treatment at 100°C for 48h. After treatment in 1mol/L hydrochloric acid solution or 1mol/L sodium hydroxide solution for 48h, the Y/MCM-48 composite exhibits good acidic stability. The acidic stability is superior to the basic stability at the same treatment time

Photoreductive dechlorination of chlorinated benzene derivatives catalyzed by ZnS nanocrystallites

ZnS nanocrystallites effectively enhanced photo-reduction of chlorinated benzene derivatives in the presence of triethylamine as a sacrificial electron donor under UV irradiation (l > 300 nm), leading to selective and stepwise dechlorination to give benzene at the final stage. Photochemical detoxification of halogenated compounds, such as PCB, dioxin, and DDT, has been attracting much attention because this can be regarded as a promising process to eliminate C-Cl bonds under environmentally relevant and mild conditions. In particular, TiO 2 -catalyzed photoprocesses involving oxidation and reduction in aqueous systems have been extensively investigated. 1 In such systems, however, photooxidation proceeds through the formation of hydroxyl radical (HO•), leading to unavoidable formation of unknown photoproducts especially from polychlorinated compounds. 2,3 Further, the rate of such photodegradation often slows in the case of polychlorinated compounds because they are electron-deficient molecules, i.e. their oxidation potentials are very positive in nature, showing resistance to the electrophilic attack of HO•. A DMF solution of ZnS nanocrystallites was prepared by the reaction of Zn(ClO 4 ) 2 with H 2 S under cooling with ice and water as described elsewhere. 7 Photoreactions were carried out under cooling with water by UV irradiation of a DMF solution (2 ml) containing a substrate (25 mM), ZnS nanocrystallites (2.5 mM in diatomic concentration as ZnS) and triethylamine (TEA, 1 M) in a Pyrex glass tube using a 500 W high pressure mercury lamp. The reaction mixtures were analyzed by gas chromatography with a fused silica capillary column (HiCap-CBP20, 25 m 3 0.2 mm, Shimadzu) using dodecane as an internal standard. The dechlorination proceeded at a relatively high rate even without ZnS nanocrystallites. The absorption spectrum measured for the mixture of 1,4-dichlorobenzene and TEA showed the appearance of a shoulder at the long wavelength edge of the absorption of 1,4-dichlorobenzene, suggesting the formation of the exciplex between the two compounds. The formation of the exciplex should contribute to the photochemical dechlorination without the catalyst. In our earlier report, ZnS nanocrystallites prepared in DMF act as a photocatalyst for the two-electron reduction of CO 2 to HCOOH or CO in the presence of triethylamine

Chlorination of Toluene to <i>o</i>-Chlorotoluene Catalyzed by Ionic Liquids

Ionic liquids with [BMIM], [Et3NH], and [BPy] cations and AlnCl&#8722;3n+1, ZnnCl&#8722;2n+1, and CunCl&#8722;n+1 anions were used as the catalysts for the chlorination of toluene with Cl2. The ZnnCl&#8722;2n+1 containing ionic liquids with high Lewis acid strength had high catalytic activity for the selective chlorination of toluene to o-chlorotoluene via the electrophilic substitution reaction. Dichlorotoluenes were favorably formed when the AlnCl&#8722;3n+1 containing ionic liquids with both Lewis and Br&#246;nsted acid sites were used as the catalysts. When the CunCl&#8722;n+1 containing ionic liquids with weak Lewis acid strength were used as the catalysts, more benzyl chloride was formed via the radical chlorination of methyl group. When the [BMIM]Cl-2ZnCl2 ionic liquid was used as the catalyst, after reacting at 80 &#176;C for 8 h, the conversion of toluene was 99.7% and the selectivities of o-chlorotoluene, p-chlorotoluene, m-chlorotoluene, benzyl chloride, and dichlorotoluenes were 65.4%, 26.0%, 4.0%, 0.4%, and 4.2%, respectively. The [BMIM]Cl-2ZnCl2 ionic liquid catalyst had good recycling performance