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Chen J.,Tsinghua University | Shi W.,Tsinghua University | Zhang X.,Tsinghua University | Arandiyan H.,Tsinghua University | And 3 more authors.
Environmental Science and Technology | Year: 2011

Co 1-xM xCr 2O 4 (M = Li, Zr; x = 0-0.2) catalysts were prepared via the citric acid method and investigated for catalytic combustion of methane. Substitution at tetrahedral (A) sites with monovalent (Li) or tetravalent (Zr) metal ions led to a decrease or increase of the catalytic activity, respectively. The Co 0.95Zr 0.05Cr 2O 4 catalyst proved to be the most active and its catalytic activity reached 90% of methane conversion at 448 °C, which dropped by 66 °C compared with that of the undoped CoCr 2O 4 catalyst. XRD and Raman results indicated that lithium or zirconium substitution could modify the spinel structure and electronic properties. For lithium-doped catalysts, oxygen deficiency and a strong surface enrichment in lithium and chromium were detected. Zirconium substitution enhanced the reducibility of zirconium-doped catalysts and decreased the strength constant of both the Co-O band and the Cr-O band, which may contribute to the catalytic activity toward methane combustion. In addition, the prevalent catalytic combustion activity of the zirconium-substituted catalysts could be explained by their higher concentration of suprafacial, weakly chemisorbed oxygen. © 2011 American Chemical Society.


Chen J.,Tsinghua University | Shi W.,Tsinghua University | Yang S.,Tsinghua University | Arandiyan H.,Tsinghua University | And 2 more authors.
Journal of Physical Chemistry C | Year: 2011

A series of vanadium-doped CoCr2-xVxO4 (x = 0-0.20) catalysts were prepared via the citric acid method and investigated for methane combustion. A significant improvement of the catalytic activity was observed over a CoCr1.95V0.05O4 catalyst, and the catalytic activity reached 90% of methane conversion at 438 °C, which was 76 °C lower than that of the undoped catalyst. Vanadium doping caused disorder in the spinel structure and various changes in physicochemical properties. The higher concentration of suprafacial, weakly chemisorbed oxygen and the active cobalt species, especially Co3+, could play a major role in the oxidation reaction. Results of XRD, Raman, and XPS suggested that excess vanadium probably formed separate catalytically inactive VOx species, which would explain the decline of catalytic activity for samples with a higher substitution degree. © 2011 American Chemical Society.


Wang R.,Tsinghua University | Li J.,Tsinghua University | Li J.,State Key Joint Laboratory of Environment Simulation and Pollution Control SKLESPC
Environmental Science and Technology | Year: 2010

Volatile organic compounds (VOCs) emitted from many industrial processes and transportation activities are major organic pollutants in the atmosphere and toxic to human health. Octahedral molecular sieve (OMS-2) catalysts with different precursors and sulfate-acidified OMS-2 catalysts were synthesized using refluxing methods. The catalysts were investigated on complete oxidation of ethanol and acetaldehyde, and both demonstrated good reactivity. However, acidification resulted in a decrease in activity. OMS-2 catalyst using MnSO 4 as precursor exhibited the best catalytic performance and, thus, was selected for catalyst deactivation by sulfur dioxide. The results of this study suggested that the Mn-O bond of OMS-2 catalysts was the main determinant of the catalytic activity toward oxygenated VOC oxidation and weaker acid sites benefited higher acetaldehyde selectivity. Catalyst deactivation resulted from a strong but slow chemical interaction between the Mn-O bond and sulfur dioxide, probably forming manganese sulfate. © 2010 American Chemical Society.


Wang C.,Tsinghua University | Liu S.,Tsinghua University | Wang J.,Tsinghua University | Zhang X.,Tsinghua University | And 2 more authors.
Journal of Environmental Sciences (China) | Year: 2015

A sampling campaign was conducted monthly to investigate the occurrence of N-nitrosamines at a conventional water treatment plant in one city in North China. The yield of N-nitrosamines in the treated water indicated precursors changed greatly after the source water switching. Average concentrations of N-nitrosodimethylamine (NDMA), N-nitrosomorpholine (NMOR), and N-nitrosopyrrolidine (NPYR) in the finished water were 6.9, 3.3, and 3.1 ng/L, respectively, from June to October when the Luan River water was used as source water, while those of NDMA, N-nitrosomethylethylamine (NMEA), and NPYR in the finished water were 10.1, 4.9, and 4.7 ng/L, respectively, from November to next April when the Yellow River was used. NDMA concentration in the finished water was frequently over the 10. ng/L, i.e., the notification level of California, USA, which indicated a considerable threat to public health. Weak correlations were observed between N-nitrosamine yield and typical water quality parameters except for the dissolved organic nitrogen. © 2015.


Chen J.,Tsinghua University | Shi W.,Tsinghua University | Li J.,Tsinghua University | Li J.,State Key Joint Laboratory of Environment Simulation and Pollution Control SKLESPC
Catalysis Today | Year: 2011

Cerium modified cobalt chromite catalysts were prepared via co-precipitation method and investigated for the catalytic combustion of methane. Characterization studies by X-ray diffraction (XRD), Raman spectroscopy, BET, scanning electron microscopy (SEM), X-ray photoelectron spectroscopy (XPS), temperature-programmed reduction mass spectroscopy (CH 4 TPR-MS) and temperature-programmed desorption of oxygen (O 2-TPD) were carried out. An improvement of the catalytic activity was observed over cerium-substituted cobalt chromite catalysts with appropriate cerium substitution degrees. The best result has been attained with 5% cerium modified catalyst, for which 5% chromium in CoCr2O4 was substituted by cerium, and the catalytic activity reached 90% of methane conversion at 465 °C. The characterization results indicated that cerium doping could deform the spinel structure and cause redistribution of metal ions with different oxidation states; consequently, they would increase crystal defects and oxygen vacancy concentration, which facilitate oxygen mobility and thus increase the catalytic performance of cerium modified cobalt chromite catalysts. © 2011 Elsevier B.V. All rights reserved.

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