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Xian H.,Tianjin University of Technology | Xian H.,Pei Yang Distillation Engineering Ltd Company | Ma A.-J.,Tianjin University of Technology | Meng M.,Tianjin University of Technology | Li X.-G.,Tianjin University of Technology
Wuli Huaxue Xuebao/ Acta Physico - Chimica Sinica | Year: 2013

A La0.7Sr0.3Co0.8Fe0.2O3 perovskite-type catalyst was synthesized by a sol-gel method. The influence of different reductants (CO, C3H6, and H2) on the NOx storage capacity and NO-to-NO2 conversion of the perovskite was evaluated before and after the NOx storage-reduction (NSR) tests. Our O2 temperature programmed desorption findings showed that a large number of oxygen vacancies were generated in the CO reduced perovskite. These oxygen vacancies are effective sites for NOx storage. The catalytic tests and Fourier transform infrared (FTIR) spectroscopy results showed that during the NSR tests of catalysts that used CO as the reductant, the catalysts demonstrated excellent NOx storage performance. Further investigations revealed the generation of a new Sr3Fe2O7 phase in the catalyst. This new phase may possess better NOx storage ability than the La0.7Sr0.3Co0.8Fe0.2O3 perovskite. In conclusion, the NOx storage ability of the catalyst was greatly improved after reduction by CO due to an increase in oxygen vacancies and the generation of a Sr3Fe2O7 phase during NSR cycling. © Editorial office of Acta Physico-Chimica Sinica.


Ding Q.,Tianjin University | Ding Q.,Tianjin Key Laboratory of Applied Catalysis Science and Technology | Xian H.,Tianjin University | Xian H.,Pei Yang Distillation Engineering Ltd Company | And 4 more authors.
Catalysis Science and Technology | Year: 2013

Herein, we successfully synthesized well crystallized La 0.7Sr0.3CoO3 perovskite nanoparticles confined in the mesopores of a SiO2 support. This perovskite exhibited extremely high NOx adsorbability for lean-burn exhausts, as well as improved stability in reducing atmospheres. © 2013 The Royal Society of Chemistry.


Ma A.-J.,Tianjin University of Technology | Wang S.-Z.,Tianjin University of Technology | Liu C.,Tianjin University of Technology | Xian H.,Tianjin University of Technology | And 9 more authors.
Applied Catalysis B: Environmental | Year: 2014

Herein, we reported the NOx storage capacity, NO oxidation ability and sulfur resistance of the La0.7Sr0.3CoO3-based perovskite-type catalysts. NO could be readily oxidized to NO2 with around 83% of NO-to-NO2 conversion at 300°C over the perovskite. After sulfation, the NSC of the La0.7Sr0.3CoO3 catalyst calcined in static air decreased 58.0%. Nevertheless, a significant improvement of the sulfur tolerance could be achieved through partial substitution of Co with Fe cations, as well as calcination in flowing air. The NSC of the pre-sulfated La0.7Sr0.3Co0.8Fe0.2O3 catalyst maintained 360.7μmol/g and dropped only 6.4% as compared with the fresh one. The XPS results confirmed the presence of Fe2(SO4)3 in the sulfated La0.7Sr0.3Co0.8Fe0.2O3 catalyst. The EXAFS results further revealed that the formation of Fe2(SO4)3 in the perovskite inhibited the sulfation of neighboring strontium from the viewpoint of the local atomic level. These findings strongly suggest that the La0.7Sr0.3Co0.8Fe0.2O3 perovskite is a possible NOx absorber used for aftertreatment systems upon lean-burn engines with the advantages of the excellent NO oxidation ability, NOx storage capacity and the high sulfur tolerance. © 2013 Elsevier B.V.


Guo L.,Tianjin University | Guo L.,Tianjin Key Laboratory of Applied Catalysis Science and Technology | Xian H.,Tianjin University | Xian H.,Pei Yang Distillation Engineering Ltd Company | And 7 more authors.
Journal of Hazardous Materials | Year: 2013

NOx emission control of lean-burn engines is one of the great challenges in the world. Herein, the MnOx model catalysts with the different calcination temperatures were synthesized to investigate their NO adsorbability for lean-burn exhausts. The transformation from (β-)MnO2 to (α-)Mn2O3 following the increased calcination temperatures was evidenced from the viewpoint of the local atomic level. Among these samples, the one calcined at 550°C containing the single α-Mn2O3 phase displayed the best NO adsorbability: NO was mainly adsorbed in the forms of NO/nitrites and NO2/nitrates at the low and high temperatures, respectively; the NO oxidation ability displayed the volcano-shape following the increased operating temperatures, and reached the maximum, i.e. 92.4% of the NO-to-NO2 conversion, at 250°C. Moreover, this sample presented the efficiently reversible NO adsorption/desorption performance in alternative lean-burn/fuel-rich atmospheres, due to the weakly bonded NOx on it. The superficial oxygen species plays a critical role for the NO oxidation over α-Mn2O3. The consumed superficial oxygen could be further compensated by the gaseous and lattice oxygen therein. Our findings show that the α-Mn2O3 material is a promising NOx adsorber for lean-burn exhausts even at low operating temperatures. © 2013 Elsevier B.V.


Dong Y.-H.,Tianjin University of Technology | Xian H.,Tianjin University of Technology | Xian H.,Pei Yang Distillation Engineering Ltd Company | Lv J.-L.,Tianjin University of Technology | And 6 more authors.
Materials Chemistry and Physics | Year: 2014

Synthesis conditions of catalysts can significantly affect catalytic activities for a certain reaction. Here, a series of the La0.7Sr 0.3MnO3 perovskite-type catalysts was prepared by the sol-gel method under the different synthesis conditions. The faster calefactive velocities during calcination of the xerogel precursors would produce a lot of the impurities and cause the dropped amount of the excessive oxygen in perovskite, as well as the aggregated particles and the decreased surface areas; the higher calcination temperature would sinter the perovskite phases seriously; and the initial pH value of the precursor solution would greatly affect the morphology of the catalysts including the shape and the size, which directly linked to their NOx storage capacity. Moreover, our findings revealed that the NO oxidation ability was determined by the amount of the excessive oxygen species in the perovskite. Here, the optimum synthesis conditions were achieved with the calcination temperature of 700 C, the calefactive velocity of 2 C min-1, and the precursor solution of pH = 8. This catalyst presented the best performances for the NO oxidization and NOx storage, i.e. the NO-to-NO2 conversion of 70.2% and the NOx storage capacity of 170.4 μmol g-1. © 2013 Elsevier B.V. All rights reserved.

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