nbo Yu

Novel Pd promoted Ag/Al2O3 catalyst for the selective reduction of NOx

A novel palladium promoted Ag/Al2O3 catalyst (denoted Ag-Pd/Al2O3) has been developed for the selective catalytic reduction of NO by C3H6. The Ag-Pd/Al2O3 shows a higher NOx conversion than Ag/Al2O3, especially at the temperatures ranging from 300 to 450degreesC. The addition of a small amount of Pd (0.01 wt.%) to Ag/Al2O3 is considered to be favorable for the partial oxidation of C3H6. In situ diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS) suggest that the presence of Pd catalyzes the formation of enolic species which is converted from C3H6. The enolic species is very active towards NO2 and NO3-, resulting in the formation of -NCO species which is the key reaction intermediate in the selective catalytic reduction of NO

The use of ceria for the selective catalytic reduction of NOx with NH3

The selective catalytic reduction of NOx with NH3 (NH3-SCR) is one of the widely used NOx control strategies for stationary sources (particularly for power plants) and mobile sources (particularly for diesel vehicles). The application is aimed at meeting the increasingly stringent standards for NOx emissions. Recently, ceria has attracted much attention for its applications in NH3-SCR catalysts owing to its unique redox, oxygen storage, and acid-base properties. In this article, we comprehensively review recent studies on ceria for NH3-SCR catalysts when used as support, promoter, or the main active component. In addition, the general development of ceria for NH3-SCR catalysts is discussed

Experimental and theoretical studies of surface nitrate species on Ag/Al2O3 using DRIFTS and DFT.

Surface nitrate (NO3(-)) species on the Ag/Al2O3 play an important role in the selective catalytic reduction (SCR) of NOx. In this study, the formation and configuration of surface nitrate NO3(-)(ads) species on Ag/Al2O3 and Al2O3 in the oxidation of NO have been studied using in situ diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS) and density functional theory (DFT) calculations. Different nitrates species (bridging, bidentate and monodentate) were observed by in situ DRIFTS and validated by DFT calculations results. Attention was especially focused on the proposal of two different bidentate nitrates species (a normal bidentate and an isolated bidentate). In addition, the thermal stability of different surface nitrate species was discussed based on the adsorption energies calculations, DRIFTS, and temperature-programmed desorption (TPD) results. It was suggested that the decomposition and desorption of the surface nitrate species could be controlled by kinetics.

Catalytic sterilization of Escherichia coli K 12 on Ag/Al2O3 surface.

Abstract Bactericidal action of Al2O3, Ag/Al2O3 and AgCl/Al2O3 on pure culture of Escherichia coli K 12 was studied. Ag/Al2O3 and AgCl/Al2O3 demonstrated a stronger bactericidal activity than Al2O3. The colony-forming ability of E. coli was completely lost in 0.5min on both of Ag/Al2O3 and AgCl/Al2O3 at room temperature in air. The configuration of the bacteria on the catalyst surface was observed using scanning electron microscopy (SEM). Reactive oxygen species (ROS) play an important role in the expression of the bactericidal activity on the surface of catalysts by assay with O2/N2 bubbling and scavenger for ROS. Furthermore, the formation of CO2 as an oxidation product could be detected by diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS) and be deduced by total carbon analysis. These results strongly support that the bactericidal process on the surface of Ag/Al2O3 and AgCl/Al2O3 was caused by the catalytic oxidation.

Complete catalytic oxidation of o-xylene over CeO2 nanocubes

The activities of CeO2 nanocubes calcined at different temperatures were tested for catalytic oxidation of o-xylene. Using CeO2 nanocubes as catalysts, complete catalytic oxidation of o-xylene was achieved below 210 degrees C. The CeO2 nanomaterials were characterized by means of BET, X-ray diffraction (XRD), transmission electron microscopy (TEM), and high-resolution transmission electron microscopy (HRTEM). From the TEM images, all CeO2 nanocubes displayed cubic morphology irrespective of calcination temperature. The HRTEM images revealed that these nanocubes were enclosed by reactive {001} planes, which may contribute to the intrinsically catalytic property of o-xylene oxidation. The higher activity of CeO2 nanocubes calcined at 550 degrees C than those calcined at above 550 degrees C was attributed to their smaller crystallite size and larger surface area. The influences of reaction conditions were also studied, which found that a higher reaction temperature was necessary for complete catalytic oxidation of o-xylene at higher weight hourly space velocity (WHSV) and o-xylene concentration.

Shape dependence of nanoceria on complete catalytic oxidation of o-xylene

BTX (benzene, toluene, and xylene) in atmosphere, mainly emitted from various industrial processes and transportation activities, are of particular concern due to their potentially highly toxic effects on human health. Catalytic oxidation of o-xylene was investigated on nanosized CeO2 particles, cubes, and rods, among which rods show the highest activity, which is comparable with those of traditional noble-metal catalysts. CeO2 nanorods also exhibit long durability for o-xylene oxidation, without deactivation during a 50 h time-on stream test. Over the CeO2 rods and particles, the presence of water vapor slightly decreased o-xylene conversion, while water vapor enhanced o-xylene oxidation on the CeO2 cubes. High-resolution transmission electron microscopy, X-ray photoelectron spectroscopy, positron annihilation spectroscopy, and O2 temperature-programmed desorption measurements revealed that ceria rods enclosed by (111) and (100) facets exhibit the highest concentration of oxygen vacancy clusters (VCs), the presence of which promoted the adsorption of molecular oxygen. The lower the temperature for desorption of chemisorbed O2 species is, the higher is the activity for o-xylene oxidation, identifying the key role of VCs in this reaction via the activation of molecular oxygen over nanoceria. The finding may also be fundamental for designing ceria-based catalysts with better performance for catalytic oxidation of volatile organic compounds.

Flower-like tungsten oxide particles: Synthesis, characterization and dimethyl methylphosphonate sensing properties

Flower-like WO(3) particles with high specific surface area were synthesized via a template/surfactant-free way. Scanning and transmission microscopies and X-ray diffraction were applied to investigate the formation mechanism of the morphology. Gas sensing characterization showed an enhanced sensitivity (70 Hz/ppm) to dimethyl methylphosphonate (DMMP) as compared with previously reported WO(3) nanoflakes (38 Hz/ppm) at a DMMP concentration of 4ppm. Cross-sensitivity results revealed that flower-like WO(3) still showed sound sensitivity in presence of interfering agents, which benefited from its intrinsic high sensitivity. The mechanism of DMMP adsorption on the flower-like WO(3) particle was studied by in situ diffuse reflectance infrared Fourier transform spectroscopy.

Catalytic inactivation of SARS coronavirus, Escherichia coli and yeast on solid surface

Abstract Catalytic oxidation is a potential way to disinfect air through a air-condition system. We find that the SARS coronavirus, bacteria and yeast are completely inactivated in 5 min on Ag catalyst surface and in 20 min on Cu catalyst surface at room temperature in air. Scanning electron microscopy (SEM) images show that the yeast cells are dramatically destructed on the Ag/Al2O3 and Cu/Al2O3 surfaces, which indicates that the inactivation is caused by catalytic oxidation rather than by toxicity of heavy metals.

Morphology-dependent bactericidal activities of Ag/CeO2 catalysts against Escherichia coli

Silver-loaded CeO2 nanomaterials (Ag/CeO2) including Ag/CeO2 nanorods, nanocubes, nanoparticles were prepared with hydrothermal and impregnation methods. Catalytic inactivation of Escherichia coli with Ag/CeO2 catalysts through the formation of reactive oxygen species (ROS) was investigated. For comparison purposes, the bactericidal activities of CeO2 nanorods, nanocubes and nanoparticles were also studied. There was a 3-4 log order improvement in the inactivation of E. coli with Ag/CeO2 catalysts compared with CeO2 catalysts. Temperature-programmed reduction of H2 showed that Ag/CeO2 catalysts had higher catalytic oxidation ability than CeO2 catalysts, which was the reason for that Ag/CeO2 catalysts exhibited stronger bactericidal activities than CeO2 catalysts. Further, the bactericidal activities of CeO2 and Ag/CeO2 depend on their shapes. Results of 5,5-dimethyl-1-pyrroline-N-oxide spin-trapping measurements by electron spin resonance and addition of catalase as a scavenger indicated the formation of OH, O2(-), and H2O2, which caused the obvious bactericidal activity of catalysts. The stronger chemical bond between Ag and CeO2 nanorods led to lower Ag(+) elution concentrations. The toxicity of Ag(+) eluted from the catalysts did not play an important role during the bactericidal process. Experimental results also indicated that Ag/CeO2 induced the production of intracellular ROS and disruption of the cell wall and cell membrane. A possible production mechanism of ROS and bactericidal mechanism of catalytic oxidation were proposed.

Low CO content hydrogen production from oxidative steam reforming of ethanol over CuO-CeO2 catalysts at low-temperature

Abstract CuO-CeO 2 catalysts were prepared by a urea precipitation method for the oxidative steam reforming of ethanol at low-temperature. The catalytic performance was evaluated and the catalysts were characterized by inductively coupled plasma atomic emission spectroscopy, X-ray diffraction, temperature-programmed reduction, field emission scanning electron microscopy and thermo-gravimetric analysis. Over CuO-CeO 2 catalysts, H 2 with low CO content was produced in the whole tested temperature range of 250–450 °C. The non-noble metal catalyst 20CuCe showed higher H 2 production rate than 1%/oRh/CeO 2 catalyst at 300–400 °C and the advantage was more obvious after 20 h testing at 400 °C. These results further confirmed that CuO-CeO 2 catalysts may be suitable candidates for low temperature hydrogen production from ethanol.