Qiguang Dai

Hierarchical Organization and Catalytic Activity of High-Surface-Area Mesoporous Ceria Microspheres Prepared Via Hydrothermal Routes

Mesoporous Ce(OH)CO(3) microspheres with flowerlike three-dimensional (3D) hierarchical structure were successfully synthesized via different hydrothermal systems, including glucose/acrylic acid, fructose/acrylic acid, glucose/propanoic acid, and glucose/n-butylamine systems. After Ce(OH)CO(3) microspheres were calcined, mesoporous CeO(2) microspheres with the same flowerlike morphology as Ce(OH)CO(3) microspheres were obtained. Especially, flowerlike CeO(2) microspheres prepared via the glucose/acrylic acid system are composed of many interconnected mesoporous petal-like nanosheets with thicknesses of 40-60 nm and have high surface area (211 m(2) g(-1)), large pore volume (0.32 cm(3) g(-1)), and narrow pore size distribution ( approximately 3.8 nm in diameter). A possible formation mechanism of Ce(OH)CO(3) microspheres is proposed: the large N-containing organic compounds in situ produced in the above reaction systems played a crucial role in controlling the assembly of Ce(OH)CO(3) building blocks into the flowerlike Ce(OH)CO(3) microspheres. For trichloroethylene combustion, flowerlike CeO(2) microspheres were found to exhibit much higher catalytic activity than general CeO(2) prepared with the conventional methods and the T(10%) and T(90%) were as low as 100 and 204 degrees C, respectively.

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.

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.

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.

Direct synthesis of cerium-incorporated SBA-15 mesoporous molecular sieves

Ce-SBA-15 mesoporous molecular sieves were synthesized by the two-step synthetic method in acid media. The obtained materials were characterized by small angle X-ray diffraction (SAXRD), transmission electron microscopy (TEM), N 2 adsorption-desorption full isotherm and elemental analysis. Cerium has been incorporated into the framework position and walls of silica network of SBA-15. Additionally, the high catalytic activity of Ce-SBA-15 for trichloroethylene (TCE) combustion was observed.

The effect of Ru on the activity of Co3O4 catalysts for chlorinated aromatics oxidation

Ru/Co3O4 catalysts with a Ru content of 0–2 wt% were prepared by wet impregnation, and used in the catalytic combustion of chlorinated aromatic VOCs. Characterization by XRD, HRTEM, EXAFS, XPS, and H2-TPR showed that Co3O4 existed in the form of a spinel structure. Some Ru species entered the octahedral sites of Co3O4 to form Ru–O–Co, which significantly increased the surface oxygen, while the formation of RuOx clusters or nanoparticles on the surface promoted the reducibility of Co3O4. In the oxidation of chlorinated aromatics, Ru species can retard the negative effect of Cl species on the activity of Co3O4 catalysts through modification in the chemical environments of surface oxygen and Cl species. The Ru/Co3O4 catalysts presented good activity and selectivity, with a rate (RRu) of 9.4–9.8 μmol m−2 min−1 under 1000 ppm 1,2-dichlorobenzene at 30 000 ml g−1 h−1. The RRu in wet feed over 2.0% Ru/Co3O4 was increased by almost 100%, through the increase in availability of active surface oxygen from RuOx. A highly stable activity could be maintained for at least 50 h. In situ FT-IR showed that 1,2-DCB adsorbs on the Co3+/Co2+ sites of Ru/Co3O4 catalysts, and the formation of partial oxidation products involve the surface oxygen. For the Co3O4 catalyst, surface active oxygen is almost not available during 1,2-DCB oxidation.