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Lan L.,Sichuan University | Chen S.,Sichuan Zhongzi Exhaust Gas Cleaning Co. | Zhao M.,Sichuan University | Gong M.,Sichuan University | Chen Y.,Sichuan University
Journal of Molecular Catalysis A: Chemical | Year: 2014

Three Ce0.5Zr0.5O2-Al2O 3 compounds were prepared using conventional coprecipitation method, mechanical mixing technique and a novel modified coprecipitation route, afterwards the corresponding Pd-only three-way catalysts were obtained by wet-impregnation method. Differences in textural, structural, morphological, reduction properties and catalytic performance, together with the thermal aging behaviors of the catalysts were investigated systematically. The results revealed that different mixing strategies of Ce0.5Zr 0.5O2(CZ) and Al2O3 led to different interaction between CZ and Al2O3, thus modified the textural, structural and reduction properties of the supported catalysts to different extents, and brought about various atom rearrangements during the aging process. The catalyst supported on Ce0.5Zr0.5O 2-Al2O3 obtained by the modified coprecipitation method displayed the least distinction before and after aging treatment, and it presented superior textural, structural and reduction properties after aging, which consequently resulted in enhanced three-way catalytic performance, the light-off temperatures of C3H8, CO and NO were 327 °C, 164 °C and 208 °C, respectively, obviously lower than those of the catalysts originated from the conventional coprecipitation method and mechanical mixing route. © 2014 Elsevier B.V.

Shang H.,University of Sichuan | Wang Y.,Sichuan Zhongzi Exhaust Gas Cleaning Co. | Cui Y.,University of Sichuan | Fang R.,University of Sichuan | And 4 more authors.
Cuihua Xuebao/Chinese Journal of Catalysis | Year: 2015

The composite support CeZrYLa+LaAl was prepared by a co-precipitation method, and Pt-Rh bimetallic catalysts were fabricated on this support using different preparation procedures. The catalytic activities of these materials were tested in a gas mixture simulating the exhaust from a stoichiometric natural gas vehicle. The as-prepared catalysts were also characterized by X-ray photoelectron spectroscopy, X-ray diffraction, N2 adsorption-desorption and H2-temperature-programmed reduction. It was found that the order of activities for CH4, CO and NO conversion was Cat3 ≈ Cat2 > Cat1, where Cat3 had the lowest light-off temperature (T50) for CO (114℃) and NO (149℃), the lowest complete conversion temperature (T90) for CH4 (398℃) and CO (179℃), and the lowest ΔT (T90-T50) for CH4 (34℃) and CO (65℃). Cat2 showed the lowest T50 for CH4 (342℃), the lowest T90 for NO (174℃), and the lowest ΔT for NO (17℃). Cat1 had the highest T50 and T90 and the largest ΔT out of all three catalysts. Indicating that Pt-Rh bimetallic catalysts (Cat2 and Cat3) prepared by physically mixing Pt and Rh powders exhibited much better catalytic activity than those (Cat1) prepared by co-impregnation, since homogeneous Pt and Rh sites made a significant contribution to CH4/CO/NO conversions. In contrast, strong Pt-Rh interactions in the co-impregnation materials affected the oxidation states of Pt, and the Pt-enriched surface blocked active Rh sites. Moreover, Cat3 was prepared by adding additives (La3+, Zr4+ and Ba2+) into the physically mixed Pt-Rh catalysts. XRD results demonstrated that the additive cation (Zr4+) was incorporated into the CeO2-ZrO2 lattice, thus creating a higher concentration of defects and improving the O2-mobility. XPS results showed that the Cat3 had the highest Ce3+/Ce ratio, suggesting the presence of a significant quantity of oxygen vacancies and cerium in the Ce3+ state. All of these further promoted the three-way catalytic activity and widened the air-to-fuel working-window. ©, 2015, Dalian Institute of Chemical Physics, Chinese Academy of Sciences. Published by Elsevier B.V. All rights reserved.

Shang H.-Y.,University of Sichuan | Hu W.,University of Sichuan | Wang Y.,Sichuan Zhongzi Exhaust Gas Cleaning Co. | Ren C.-J.,Sichuan University | And 3 more authors.
Wuli Huaxue Xuebao/ Acta Physico - Chimica Sinica | Year: 2015

Composite support CeZrYLa + LaAl was prepared by co-precipitation, and platinum catalyst supported on the composite support was prepared by impregnation. The behavior of the Pt catalyst for the reaction of NO reduction by CH4 from the exhausts of natural gas vehicles (NGVs) was studied under stoichiometric conditions. Additionally, the effects of 10% (volume fraction, φ) H2O and stoichiometric O2 on the reaction in the presence of CO2 were also investigated. Results show that N2 and CO2 were the main products for the different reactions, CO was detected under high temperature, and NOx was detected under low temperature (in the presence of O2, the NOx was NO2, whereas the NOx was N2O when no O2 was present). In the presence of 10% (φ) H 2O, the conversion of CH4 noticeably decreased and NO conversion remained unchanged, possibly because the presence of H2O weakens the reforming reaction of CH4 with CO2, but does not affect the activity of NO reduction by CH4. In the presence of stoichiometric O2, there was an obvious increase of CH4 conversion and a decrease of NO conversion. These could be explained by the competition between NO and O2, where the oxidation of methane by O2 is the main reaction, limiting the reaction of NO reduction by CH4. Moreover, in the presence of 10% (φ) H2O and stoichiometric O2, CO2 reforming of CH4 was negligible. Numerous reactions were detected simultaneously, such as the oxidation of CH4 by NO, steam reforming of CH 4, and the reduction of NO by CH 4, thus improving the conversions of CH4 and NO. © Editorial office of Acta Physico-Chimica Sinica.All rights reserved.

Lan L.,University of Sichuan | Chen S.,Sichuan Zhongzi Exhaust Gas Cleaning Co. | Cao Y.,University of Sichuan | Zhao M.,University of Sichuan | And 2 more authors.
Journal of Colloid and Interface Science | Year: 2015

A CeO2-ZrO2 compound with mixed phase composition (CZ4) was prepared by modified co-precipitation method, and for comparison, single-phase Ce0.2Zr0.8O2, Ce0.5Zr0.5O2 and Ce0.8Zr0.2O2 were synthesized via simultaneous co-precipitation method. The textural, structural and redox properties, together with the catalytic performance of the supported Pd-only three-way catalysts were investigated systematically. The results revealed that the generation of numerous interface sites in Pd/CZ4 due to its mixed phase composition (as confirmed by TEM observation) had a positive influence on modifying its structural, redox properties and thermal stability. The XRD and Raman results revealed that the highest structural stability was obtained by Pd/CZ4 with negligible lattice variation and slightest grain growth after aging treatment. The XPS analysis demonstrated that the compositional heterogeneity of Pd/CZ4 could facilitate the formation of Ce3+, and was beneficial to preserve high dispersion of Pd as well as maintain Pd at a more oxidized state. The H2-TPR and oxygen storage capacity measurements indicated that Pd/CZ4 possessed highest reduction ability as well as largest oxygen storage capacity regardless of thermal aging treatment. And consequently Pd/CZ4 exhibited improved three-way catalytic activity compared with the catalysts supported on single-phase CexZr1-xO2 both before and after thermal aging treatment. © 2015 Elsevier Inc.

Lan L.,Sichuan University | Chen S.,Sichuan Zhongzi Exhaust Gas Cleaning Co. | Cao Y.,Sichuan University | Gong M.,Sichuan University | Chen Y.,Sichuan University
Catalysis Science and Technology | Year: 2015

In this work, a Ce0.5Zr0.5O2-Al2O3 (CZA) mixed oxide prepared by a coprecipitation method was deeply investigated and some new insights into the microstructure were obtained. The XRD, Raman, TEM and XPS results revealed that compositional inhomogeneity existed in fresh CZA; some Zr-rich species were in close contact with Al2O3, leading to the observed CZ nanocrystallites being richer in Ce, which was detrimental to the oxygen mobility, and consequently an undesirable redox property was obtained. During thermal treatment from 600 °C to 900 °C, atomic rearrangement took place, giving rise to the enhanced homogeneity of CZ solid solutions, accompanied by a weakened interaction between CZ and Al2O3, and a homogeneous CZ solid solution with a Ce/Zr ratio approaching the theoretical value of 1 was obtained for CZA treated at 900 °C. The TPR and OSC results indicated that the enhanced homogeneity of the CZ solid solution could facilitate the improvement of the redox property. However, further treatment at 1000 °C brought about the phase segregation of CZ, which led to significantly deteriorated textural and structural properties as well as a worse redox property. As a result, the catalyst Pd/CZA900 (CZA was treated at 900 °C) exhibited the best redox and catalytic performances, as well as excellent thermal stability. © The Royal Society of Chemistry 2015.

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