Shuxing Bai

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.

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.

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.