Xingyi Wang

Highly Active and Selective Hydrogenation of CO2 to Ethanol by Ordered Pd–Cu Nanoparticles

Carbon dioxide (CO2) hydrogenation to ethanol (C2H5OH) is considered a promising way for CO2 conversion and utilization, whereas desirable conversion efficiency remains a challenge. Herein, highly active, selective and stable CO2 hydrogenation to C2H5OH was enabled by highly ordered Pd-Cu nanoparticles (NPs). By tuning the composition of the Pd-Cu NPs and catalyst supports, the efficiency of CO2 hydrogenation to C2H5OH was well optimized with Pd2Cu NPs/P25 exhibiting high selectivity to C2H5OH of up to 92.0% and the highest turnover frequency of 359.0 h-1. Diffuse reflectance infrared Fourier transform spectroscopy results revealed the high C2H5OH production and selectivity of Pd2Cu NPs/P25 can be ascribed to boosting *CO (adsorption CO) hydrogenation to *HCO, the rate-determining step for the CO2 hydrogenation to C2H5OH.

Template-free and non-hydrothermal synthesis of CeO2 nanosheets via a facile aqueous-phase precipitation route with catalytic oxidation properties

Two types of CeO2 nanosheet, petal-like and belt-like, were synthesized using a facile aqueous phase precipitation method with NH4HCO3 as the precipitant at 0 °C and 25 °C, without hydrothermal or solvothermal treatment, without template or surfactant and without organic solvent. The reaction temperature and the supersaturation played key roles in the formation of the ceria nanosheets, namely, a lower temperature and higher supersaturation were favorable for the synthesis of sheet-like CeO2 by the oriented aggregation of the as-synthesized nanocrystalline precursors, whereas elevated temperatures could cause the dissolution–recrystallization of the precursors and promote the Ostwald ripening process, and finally polyhedral CeO2 could be obtained via thermal decomposition of the precursors. The catalytic oxidation properties were investigated using the catalytic oxidation of CO over CeO2 and the catalytic combustion of 1,2-dichloroethane over VOx/CeO2. Compared with traditional CeO2 nanoparticles, the ceria nanosheets showed excellent catalytic oxidation activities.

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.

Removal of Cl adsorbed on Mn-Ce-La solid solution catalysts during CVOC combustion.

Mn-Ce-La oxide-mixed catalysts prepared by the method of complexation followed by calcination at 750°C were tested in the catalytic combustion of chlorobenzene (CB) taken as a model of chlorinated aromatics. XRD analyses show that Mn and La enter CeO2 matrix with a fluorite-like structure to form solid solution. The catalysts with high ratio of Mn/Mn+Ce+La exhibit high activity for CB combustion, due to high oxygen mobility. For all Mn-Ce-La catalysts, deactivation due to Cl adsorption is observed at different temperatures, depending on composition. At 330°C or higher temperature, the removal of Cl species from the surface in the forms of Cl2 (produced through Deacon reaction) and HCl (produced through hydrolysis of Cl) occurs and the activity of catalysts for CB combustion becomes thus stable. Either the addition of water or the increase in gaseous oxygen concentration can promote the removal of Cl species, and thus to increase the activity for CB combustion. High stable activity of Mn-Ce-La catalysts can be related to the combination of good oxidation and Deacon reaction performances.

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.

Dehydrochlorination of 1,2-dichloroethane over Ba-modified Al2O3 catalysts

Bimodal mesoporous alumina (Al2O3) was prepared using polyethyleneglycol (PEG 20 000) and cetyl trimethyl ammonium bromide as a template. The incorporation of Ba with various loadings was carried out by incipient wetness. Characterization was performed by XRD, N2 sorption isotherms, and pyridine FTIR. Ba can be highly dispersed on Al2O3 covering the strong acid sites of Al2O3. In the catalytic dehydrochlorination of 1,2-dichloroethane (1,2-DCE), the Ba/Al2O3 catalysts present a high activity, of which Al2O3 is most active with 95% conversion at 325 °C, related to the more Lewis acidic Al3+ sites in a tetrahedral environment. 1,2-DCE adsorbs dissociatively on Lewis acid–base pair sites, forming chlorinated ethoxy species, which are supposed to be intermediate species for vinyl chloride (VC) production. At a temperature higher than 400 °C, the dehydrochlorination of VC occurs on the strong acid sites of Al2O3. Ba can promote greatly the selectivity for VC through a decrease in the strong acid sites. A high stable activity for dehydrochlorination and high selectivity for VC can be obtained over Ba/Al2O3 in the presence of oxygen.

Highly dispersive PdCoB catalysts for dechlorination of chlorophenols

Highly dispersive PdCoB nano-particles were prepared by precipitation-reduction with NaBH4 at 273 K. Characterization showed that the dispersion of amorphous alloy PdCoB nano-particles increased with decrease in both Pd/Co ratio and preparation temperature. The size of PdCoB-L(273) (Pd/Co ratio of 0.0005) nano-particles prepared at 273 K was 5 nm and BET specific surface area was estimated to be 177 m(2)/g, much higher than those of bimetallic catalysts reported in literature. During the hydrodechlorination of 4-chlorophenol, PdCoB catalysts were effective within pH range from 2.5 to 11. The activity of PdCoB can be promoted by the increase in B/Co ratio on the surface. PdCoB-L(273) sample presented the highest efficiency, and the reaction constants described in different terms for 4-chlorophenol, 2,4-dichlorophenol and 2,4,6-trichlorophenol were much higher than those obtained over PdFe in literature, probably ascribed to smaller particle sizes, less agglomerations and strong synergistic effect between Pd, Co and B species.

Catalytic oxidation of 1,2-dichloroethane over Al2O3–CeO2 catalysts: combined effects of acid and redox properties

The lower temperature catalytic combustion of 1,2-dichloroethane (DCE) over Al2O3, CeO2 and Al2O3–CeO2 catalysts were studied. An apparent deactivation for pure Al2O3 and CeO2 catalyst was observed at 300 °C, which was ascribed to the formation of coke for pure Al2O3 while the strong adsorption of Cl species at active sites for pure CeO2. However, Al2O3–CeO2 mixed oxides exhibited a high stable activity compared with the pure Al2O3 and CeO2, which indicated that suitable acidity and excellent redox performance was equally important for total oxidation of DCE. TPSR experiments indicated that ClCH2CHO was the intermediate product and vinyl chloride (VC) was the main by-product for DCE catalytic oxidation over Al2O3–CeO2 catalyst, ClCH2CHO and VC were the competitive products of the C–H-scission ethoxides, which generated by α- and β-CH-scission respectively. Based on in situ DRIFTS study, a simple reaction pathway was proposed: Firstly, DCE adsorbed on surface hydroxyl groups or Lewis acid sites via the C–Cl bond and was attacked by the basic site (O2−), and then the intermediates such as aldehyde species and by-product VC formed. Sequentially, the aldehyde species were converted into H2O, COx and HCl via further Cl abstraction and oxidation process, by contrast, VC was not easy to be further decomposed because of its stable structure, the weak adsorption and difficult dissociation on acid sites.