Yaning Xie

NO reduction with NH3 over an activated carbon-supported copper oxide catalysts at low temperatures

NO reduction with NH3 over activated carbon-supported copper oxide (CuO/AC) catalyst was studied at low temperatures (30-250 degrees C). The attention was focused on the effects of preparation parameters, reaction temperature and SO2 on the structure and activity of the catalyst. The catalysts show high activities for NO reduction with NH3 in the presence of O-2 at temperatures above 180 degrees C and are gradually deactivated at temperatures below 180 degrees C. Cu2O exists in the catalyst and results in low initial activity but it is easily oxidized into active CuO by O-2 during the NO-NH3-O-2 reaction. Calcination temperature and Cu loading of the catalyst strongly influence the activity and structure of the catalyst. The catalyst with 5 wt% Cu loading and calcined at 250 degrees C shows the highest activity. The activities of the catalysts with higher Cu loadings and/or calcined at higher temperatures are relatively low, mainly derived from aggregation of copper species. The CuO/AC catalyst is greatly deactivated by SO2 due to the formation of CuSO4 which is inactive at low temperatures

Preparation of carbon-encapsulated iron carbide nanoparticles by an explosion method

Abstract Fe7C3 nanocrystals encapsulated in carbon nanoparticles, with sizes ranging from 10 to 40 nm, were synthesized via the explosion of a hybrid xerogel containing oxidized pitch and iron nitrate. Explosion of the hybrid xerogel was induced by heat treatment. Transmission electron microscopy (TEM), energy dispersive X-ray spectroscopy (EDX), X-ray diffraction (XRD) and extended X-ray absorption fine structure (EXAFS) were employed to determine the structure of the nanoparticles in the explosion product. The results show that the Fe7C3 nanocrystals are nested inside amorphous carbon shells that protect them from oxidation by air.

Interaction Between Nano-Anatase TiO2 and Liver DNA from Mice In Vivo

Nano-TiO2 was shown to cause various toxic effects in both rats and mice; however, the molecular mechanism by which TiO2 exerts its toxicity is poorly understood. In this report, an interaction of nano-anatase TiO2 with liver DNA from ICR mice was systematically studied in vivo using ICP-MS, various spectral methods and gel electrophoresis. We found that the liver weights of the mice treated with higher amounts of nano-anatase TiO2 were significantly increased. Nano-anatase TiO2 could be accumulated in liver DNA by inserting itself into DNA base pairs or binding to DNA nucleotide that bound with three oxygen or nitrogen atoms and two phosphorous atoms of DNA with the Ti–O(N) and Ti–P bond lengths of 1.87 and 2.38 Å, respectively, and alter the conformation of DNA. And gel electrophoresis showed that higher dose of nano-anatase TiO2 could cause liver DNA cleavage in mice.

A Study on the Properties and Mechanisms for NOx Storage Over Pt/BaAl2O4-Al2O3 Catalyst

The NOx storage catalyst Pt/BaAl2O4-Al2O3 was prepared by a coprecipitation--impregnation method. For fresh sample, the barium mainly exists as the BaAl2O4 phase except for some BaCO3 phase. The BaAl2O4 phase is the primary NOx storage phase of the sample. EXAFS and TPD were used for investigating the mechanism of NOx storage. It is found that two kinds of Pt sites are likely to operate. Site 1 is responsible for NO chemisorption and site 2 for oxidizing NO to nitrates and nitrites. When NO adsorbs on the sample below 200 °C, it mainly chemisorbs in the form of molecular states. Such adsorption results in an increase of the coordination magnitude of Pt-O, and a decrease of that of Pt-Pt and Pt-Cl. The coordination distance of Pt-Pt, Pt-Cl and Pt-O also increases. When the adsorption occurs above 200 °C, NO can be easily oxidized by O2, and stored as nitrites or nitrates at the basic BaAl2O4. Site 2 is regenerated quickly. A high adsorption temperature is favorable for nitrate formation.

Hydrotalcite-Derived MnxMg3−xAlO Catalysts Used for Soot Combustion, NOx Storage and Simultaneous Soot-NOx Removal

The hydrotalcite-based Mn(x)Mg(3-x)AlO catalysts with different Mn:Mg atomic ratios were synthesized by coprecipitation, and employed for soot combustion, NOx storage and simultaneous soot-NO(x) removal. It is shown that with the increase of Mn content in the hydrotalcite-based Mn(x)Mg(3-x)AlO catalysts the major Mn-related species vary from MnAl(2)O(4) and Mg(2)MnO(4) to Mn(3)O(4) and Mn(2)O(3). The catalyst Mn(1.5)Mg(1.5)AlO displays the highest soot combustion activity with the temperature for maximal soot combustion rate decreased by 210 degrees C, as compared with the Mn-free catalyst. The highly reducible Mn(4+) ions in Mg(2)MnO(4) are identified as the most active species for soot combustion. For NO(x) storage, introduction of Mn greatly influences bulk NO(x) storage, with the adsorbed NO(x) species varying from linear nitrites to ionic and chelating bidentate nitrates gradually. The coexistence of highly oxidative Mn(4+) and highly reductive Mn(2+) in Mn(1.0)Mg(2.0)AlO is favorable to the simultaneous soot-NO(x) removal, giving a NO(x) reduction percentage of 24%. In situ DRIFTS reveals that the ionic nitrate species are more reactive with soot than nitrites and chelating bidentate nitrates, showing higher NO(x) reduction efficiency.

Direct evidence for interaction between nano-anatase and superoxide dismutase from rat erythrocytes

Nano-TiO2 and superoxide dismutase (SOD, EC 1.15.1.1) have been added to cosmetics and used to prevent injury of skin from UV-radiation, which might be related to the decrease of oxidative damage of skin. In previous studies we had proven that nano-anatase could increase the activity of SOD and decrease the oxidative damage in vivo. The mechanisms by which nano-anatase promoted SOD activity, however, are still not clearly understood. In the present work, nano-anatase in various concentrations was added to SOD from rat erythrocytes in vitro to gain insight into the mechanism of molecular interactions between nano-anatase and SOD by various spectral methods, suggesting that the reaction between SOD and nano-anatase was two-order, which meant that the SOD activity was greatly increased by low concentration of nano-anatase and inhibited by high concentration of nano-anatase. The spectroscopic assays suggested that the nano-anatase was determined to directly bind to SOD; the binding site of nano-anatase to SOD was 0.256 and the binding constants were 6.54 x 10(5) and 3.6 x 10(5)Lmol(-1); Ti was bound with three oxygen or nitrogen atoms and a sulfur atoms of amino acid residues at the Ti-O(N) and Ti-S bond lengths of 1.86 and 2.37 A, respectively, the binding nano-anatase entirely altered the secondary structure of SOD. It implied that the nano-anatase coordination created a new metal ion-active site form in SOD, thus leading to an enhancement in SOD activity.

Application of a combined system of polycapillary x-ray lens and toroidal mirror in micro-x-ray-absorption fine-structure facility

A micro-x-ray-absorption fine-structure facility based on a monolithic half focusing polycapillary x-ray lens (MHFPXRL), a toroidal mirror, and synchrotron radiation is proposed. The synchrotron radiation is focused by using a combined system of a MHFPXRL and a toroidal mirror. At 8.0keV, the synchrotron radiation beam with a 2.3×26-mm2 area is first focused into a beam spot with a 0.9×0.3-mm2 area by a toroidal mirror. This focused beam is then focused into a focal spot with a 21.4-μm diameter by using a MHFPXRL. The gain of power flux density in the focal spot of the combined system is 47 473. The focal distance of the MHFPXRL is 13.3mm. The transmitting extended x-ray-absorption fine-structure (EXAFS) spectrum of Ni foil and the fluorescent EXAFS spectrum of zinc in the zinc hyperaccumulator are measured.

EXAFS study of γ-Mo2N and Mo nitrides supported on zeolites

Abstract By analysis of the extended X-ray absorption fine structure (EXAFS) of the Mo K-absorption edge, the structural information of both oxidic and nitrided Mo catalysts supported on zeolites was obtained. The supported MoO 3 samples show three peaks in the radial structure function (RSF). The first two peaks represent the nearest Mo–O coordination shell and the ratio of the first peak to the second one is much larger than that of the MoO 3 crystallites, which suggests that the MoO 3 supported on zeolites has a compact structure than the unsupported one. Three peaks on the RSF of γ-Mo 2 N represent one Mo–N and two Mo–Mo coordination shells, respectively. This is in good agreement with the face-centered cubic model. Calculation from X-ray diffraction data and EXAFS spectra reveals that the N atoms in γ-Mo 2 N lengthen the distance between Mo atoms and weaken the Mo–Mo bond. Supported Mo 2 N samples give out nearly the same RSFs as the γ-Mo 2 N and only the peak corresponding to Mo–N shell is weak. This suggests the supported Mo 2 N has more configurational disorder.

Effect of Steam in CO2 Reforming of CH4over a Ni/CeO2–ZrO2–Al2O3 Catalyst

CO2 reforming of CH4 was carried out with and without steam over a Ni/CeO2–ZrO2–Al2O3 catalyst. The catalytic performance, amount of carbon deposit and the EXAFS of the Ni K-edge of samples were measured. The results show that when the catalyst is used for CO2 reforming of CH4 without the addition of steam, the catalyst gradually deactivates, however, addition of a small amount of steam to the feed gas can significantly inhibits the deactivation, which is due to the great suppression of coke formation on the catalyst during the reaction. The EXAFS result shows that, maybe due to the penetration of more carbon atoms into the Ni lattice, the coordination number of the nearest Ni–Ni of the sample after the reaction without steam reduces more than that of samples after the reaction with a small amount of steam in the feed gas.

The interfacial structure of PPV/TiO2 nanocomposite

The aim of this work is to investigate the interfacial structure of poly(phenylenevinylene)(PPV)/TiO 2 nanocomposite by analyzing X-ray absorption spectroscopy at the Ti K edge. The pre-edge regions of X-ray absorption near-edge structure (XANES) spectra displayed distortions of octahedral geometry (TiO 6 ) in the surface of TiO 2 nanoparticles, while the post-edge regions of XANES showed PPV could modify the surface of nano-TiO 2 . From analyzing extended X-ray absorption fine structure spectra of the nanoparticles and comparing them with bulk TiO 2 , it was found that bond length (Ti-O) and coordination number decrease in nano-TiO 2 , which is attributed to coordinatively unsaturated TiO x surface species (x < 6). In PPV/TiO 2 nanocomposite, PPV molecule can bond to the surface of TiO 2 nanoparticles, leading the interfacial structure reconstructed.