Dao Li

Liquid phase hydrodechlorination of chlorophenols at lower temperature on a novel Pd catalyst.

Pd catalyst supported on mesoporous silica-carbon nano-composite (Pd/MSCN) was prepared by the method of wet impregnation, and its activity for hydrodechlorination (HDC) of 2-chlorophenol, 4-chlorophenol and 2,4-dichlorophenol was evaluated at 258-313 K under ordinary hydrogen pressure by using triethylamine (Et(3)N) as a base additive. XRD analysis indicates that Pd/MSCN catalyst possesses the ordered mesostructure. Meanwhile, the results from TEM and H(2) chemisorption analysis indicate the high dispersion of Pd on MSCN with Pd nanoparticles whose average size is 3.2 nm. For the first time, the high activity of nano-size Pd on MSCN for HDC of chlorophenols was observed at 258 K. In addition, it was found that the inhibition effect of Et(3)N on HDC existed obviously, and can be efficiently reduced by stepwise addition of Et(3)N. The correlations of the dielectric constants of base and the polarity of solvent to the activity of Pd/MSCN for HDC of chlorophenols were obtained.

Effect of CeO2 preparation method and Cu loading on CuO/CeO2 catalysts for methane combustion

Abstract CeO 2 was synthesized by sol-gel, hydrothermal, nitrate thermal decomposition methods, respectively, and used as support to prepare CuO/CeO 2 catalysts. According to characterization and reaction results, preparation method of CeO 2 had a great influence on the physicochemical properties and activities of CuO/CeO 2 catalysts. CuO with high dispersion and strong interaction with CeO 2 was highly active in methane combustion, while CuO particles less associated with CeO 2 showed less activity. The CuO catalyst supported on CeO 2 which was prepared via nitrate thermal decomposition method showed the largest area, the smallest particle size, the highest dispersion of copper species and strong support metal interactions. Therefore, it presented the highest redox ability and activity for methane combustion. Activities of the catalysts with different copper content kept increasing until 5% Cu loading and from then on kept constant. Moreover, methane conversion decreased as methane space velocities increased on CuO/CeO 2 catalyst. Addition of CO 2 to the feed did not produce a significant effect on the catalytic activity, but the presence of H 2 O provoked a remarkable decrease on the activity of CuO/CeO 2 catalyst.

Catalytic Combustion of Methane over High Copper-Loading ZSM-5 Catalysts

Abstract Two series of Cu/ZSM-5 catalysts, loading from 5 to 20 wt% CuO, were prepared by the deposition-precipitation and impregnation methods, respectively. The catalysts prepared by the impregnation method showed better catalytic performances than those prepared by the deposition-precipitation method and the increase of copper loading favored methane conversion. 20Cu(I)/ZSM-5 had the highest activity with T 90% of 746 K, and for 20Cu(D)/ZSM-5, T 90% was as high as 804 K. The characterization of X-ray diffraction (XRD), temperature-programmed reduction (TPR), temperature-programmed desorption (TPD), and X-ray photoelectron spectroscopy (XPS) revealed that the dispersion of copper species could be improved by using the deposition-precipitation method instead of the impregnation method, but the fraction of surface CuO, corresponding to active sites for methane oxidation, was larger on 20Cu(I)/ZSM-5 than 20Cu(D)/ZSM-5. The results of Pyridine-Fourier transform infrared spectrum (Py-FT-IR) showed that a majority of Lewis acidity and a minority of Bronsted acidity were present on Cu/ZSM-5 catalysts. 20Cu(I)/ZSM-5 presented more Lewis acid sites. The number of Lewis acid sites changed significantly with preadsorption of oxygen. Adsorption of methane and oxygen on acid sites was observed. The properties of Cu/ZSM-5 catalysts were correlated with the activity for methane oxidation.

Effect of water on the performance of Pd-ZSM-5 catalysts for the combustion of methane

Palladium-based catalysts were prepared using impregnation (I) and ion-exchange method (E) with ZSM-5 as support. Pd-ZSM-5(I) and Pd-ZSM-5(E) catalysts presented the high activity for the combustion of methane. The order of activity was consistent with Bronsted acidity of the catalysts: Pd-ZSM-5(I)>Pd-ZSM-5(E). It was shown by FT-IR that methane was adsorbed on the acidic bridging hydroxyl groups of ZSM-5-supported Pd catalysts. The effect of water on the activity of Pd-ZSM-5 was investigated. The inhibition effect of water on the conversion of methane was observed. However, water promoted the stability of Pd-ZSM-5 obviously during extended time periods. XPS measurement showed that Pd/Si ratio near the surface of Pd-ZSM-5(E) decreased more pronouncedly with time in dry stream than that of Pd-ZSM-5(I), this is attributed to the dispersion of Pd into the micropores. The addition of water, however, retarded Pd dispersion. And high partial pressure of methane reduced this effect of water vapor. The decrease in activity during the stability test can be explained on the basis of the reduction of Pd/Si ratio.