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Duan Weng - One of the best experts on this subject based on the ideXlab platform.

  • Highly effective La-deficient La1-xCexMnO3 Mixed Oxides for the complete oxidation of methane
    'Elsevier BV', 2021
    Co-Authors: Jiancai Ding, Duan Weng, Rui Ran, Jingbo Jia, Zhigang Yang
    Abstract:

    La-deficient La1-xCexMnO3 Mixed Oxides, obtained by selective dissolution in 1 ​M nitric acid, were employed in methane complete oxidation. The majority of the La cations in these perovskites were removed, resulting in increased specific surface areas, better reducibility and greater activity. Incorporation of a small amount of Ce stabilized the structure and a perovskite phase persisted in La-deficient La1-xCexMnO3 Mixed Oxides after 12 ​h of acid dissolution. La0.95Ce0.05MnO3 after the acid treatment exhibited satisfactory catalytic activity, with T50 and T90 values of 365 and 459 ​°C, respectively, which was even comparable to that previously reported 1% Pd/Al2O3 catalysts. And it showed excellent long-term activity even in the presence of CO2 and H2O

  • mnox ceo2 al2o3 Mixed Oxides for soot oxidation activity and thermal stability
    Journal of Hazardous Materials, 2011
    Co-Authors: Shuang Liu, Duan Weng, Fan Lin, Rui Ran
    Abstract:

    Abstract MnOx–CeO2–Al2O3 Mixed Oxides were prepared by impregnating manganese acetate and cerium nitrate on alumina powders using the sol–gel method. The thermal stabilities of MnOx–CeO2 and Al2O3-modified Mixed Oxides were evaluated by treating at 800 °C in dry air flow for 20 h. The introduction of Al2O3 markedly increases the textural stability of the catalyst with a relatively high dispersion of MnOx and CeO2, remaining a strong synergistic effect between these two Oxides. The NO oxidation activity of the ternary Oxides experiences a smaller loss after high-temperature calcination, and a low soot oxidation temperature is attained in the presence of NO.

  • oxygen activation on cu mn ce Mixed Oxides and the role in diesel soot oxidation
    Catalysis Today, 2008
    Co-Authors: Qing Liang, Duan Weng
    Abstract:

    The Cu- and Mn-doped ceria were prepared using the citric acid sol–gel method. The structural and redox properties of the Mixed Oxides were investigated by means of XRD, BET, O2-TPD, CO-TPR and CO reduction under isothermal conditions. TPO tests were performed to evaluate the catalytic activity for soot oxidation. The results showed that Mnx+ cations entered into the ceria lattice to form solid solutions, which increased the amount of oxygen vacancies and promoted surface oxygen chemisorption. CuxO clusters were more likely to be dispersed on the surface of ceria particles. The interaction between copper and cerium greatly enhanced the rapid release of lattice oxygen of the Oxides in the reducing atmosphere. These two Mixed Oxides showed improved catalytic activities and selectivities to CO2 for soot oxidation compared with pure ceria. The order of activities under different contact conditions was believed to be related to active oxygen species released by the catalysts.

  • thermal ageing of pt on low surface area ceo2 zro2 la2o3 Mixed Oxides effect on the osc performance
    Applied Catalysis B-environmental, 2008
    Co-Authors: Jun Fan, Qing Liang, Rui Ran, Duan Weng
    Abstract:

    Abstract This work aims at exploring the thermal ageing mechanism of Pt on ceria-based Mixed Oxides and the corresponding effect on the oxygen storage capacity (OSC) performance of the support material. Pt was supported on low-surface-area CeO2–ZrO2–La2O3 Mixed Oxides (CK) by impregnation method and subsequently calcined in static air at 500, 700 and 900 °C, respectively. The evolutions of textural, microstructural and redox properties of catalysts after the thermal treatments were identified by means of X-ray diffraction (XRD), Raman, X-ray photoelectron spectroscopy (XPS), temperature programmed reduction (TPR) and high-resolution transmission electron microscope (HRTEM). The results reveal that, besides the sintering of Pt, encapsulation of metal by the Mixed Oxides occurs at the calcination temperature of 700 °C and above. The burial of Pt crystallites by support particles is proposed as a potential mechanism for the encapsulation. Further, the HRTEM images show that the distortion of the Mixed Oxides lattice and other crystal defects are distributed at the metal/Oxides interface, probably indicating the interdiffusion/interaction between the metal and Mixed oxide. In this way, encapsulation of Pt is capable to promote the formation of Ce3+ or oxygen vacancy on the surface and in the bulk of support. The OSC results show that the reducibility and oxygen release behavior of catalysts are related to both the metal dispersion and metal/Oxides interface, and the latter seems to be more crucial for those supported on low-surface-area Mixed Oxides. Judging by the dynamic oxygen storage capacity (DOSC), oxygen storage capacity complete (OSCC) and oxygen releasing rate, the catalyst calcined at 700 °C shows the best OSC performance. This evident promotion of OSC performance is believed to benefit from the partial encapsulation of Pt species, which leads to the increment of Ce3+ or oxygen vacancies both on the surface and in the bulk of Oxides despite a loss of chemisorption sites on the surface of metal particles.

  • structure and oxygen storage capacity of pr nd doped ceo2 zro2 Mixed Oxides
    Solid State Sciences, 2007
    Co-Authors: Xiaodi Wu, Xiaodong Wu, Qing Liang, Duan Weng
    Abstract:

    Abstract Binary Ce–Zr (CZ), trinary Ce–Zr–Pr (CZP), Ce–Zr–Nd (CZN) Mixed Oxides were prepared by coprecipitation. The structural and textural properties were characterized by the X-ray diffraction (XRD) analysis, Brunauer–Emmett–Teller (BET) method, Raman and X-ray absorption near-edge spectra (XANES) techniques, while the oxygen storage capacity (OSC) was evaluated under both dynamic and static conditions at 500 °C. The doping of Pr or Nd cations causes the lattice deformation of the tetragonal Zr-rich Mixed Oxides to form a pseudocubic structure and prevents the phase demixing after calcination in flowing steam/air at 1050 °C for 5 h. After the hydrothermal ageing treatment, the doped samples show higher BET surface areas and better oxygen mobility. Pr exists mainly in the form of trivalent cations in the aged CZP and functions primarily as the doping element with large ionic radius instead of redox couple Pr 3+ /Pr 4+ , which may introduce more Ce 3+ species and hereby more lattice defects. Among the aged samples, CZP shows the best oxygen storage capacity and the fastest oxygen release rate.

Robert J Davis - One of the best experts on this subject based on the ideXlab platform.

  • catalytic reactions of coke with dioxygen and steam over alkaline earth metal doped cerium zirconium Mixed Oxides
    Applied Catalysis A-general, 2017
    Co-Authors: Kehua Yin, Shilpa Mahamulkar, Christopher W Jones, Pradeep K Agrawal, Hirokazu Shibata, Andrzej Malek, Jiahan Xie, Robert J Davis
    Abstract:

    Abstract A series of cerium-zirconium Mixed Oxides doped with alkaline earth metals was prepared by calcining a mixture of Ce 0.8 Zr 0.2 O 2 and the nitrate salt of alkaline earth metals at 1173 K. The results from X-ray diffraction, Raman spectroscopy and analytical electron microscopy indicated the alkaline earth compounds were dispersed on the surface of Ce 0.8 Zr 0.2 O 2 . The doped Mixed Oxides were evaluated in the catalytic reaction of solid coke under tight contact conditions with 10 vol.% O 2 in He at 693 K and with 100 vol.% H 2 O at 993 K using thermogravimetric analysis. For coke oxidation with O 2 , the weight loss was first order in coke, and the measured first order rate constant was proportional to the total surface area of catalyst at low catalyst loadings. For coke gasification with H 2 O, the weight loss was nearly zero order in coke, and the measured areal reaction rate was independent of the total surface area of catalyst at low catalyst loadings. The addition of alkaline earth metals inhibited coke oxidation with dioxygen but promoted coke gasification with steam.

  • catalytic oxidation of solid carbon and carbon monoxide over cerium zirconium Mixed Oxides
    Aiche Journal, 2017
    Co-Authors: Kehua Yin, Robert J Davis, Shilpa Mahamulkar, Christopher W Jones, Pradeep K Agrawal, Hirokazu Shibata, Andrzej Malek
    Abstract:

    A series of cerium-zirconium Mixed Oxides was prepared and evaluated in the catalytic oxidation of solid coke with 10 vol % O2 in He at 673 K using a thermogravimetric analyzer. The measured first order rate constant for coke oxidation was proportional to the catalyst loading when the mass ratio of catalyst to coke was low, which enabled the calculation of a surface area specific reaction rate. The validity of the normalization method was confirmed by performing CO oxidation over the cerium-zirconium Mixed Oxides in a fixed bed reactor at 573 K. Although there was no correlation between the coke oxidation rate and the oxygen storage capacity or the reducibility of the catalysts, there was an excellent correlation to the CO oxidation rate. Kinetic studies of both coke and CO oxidation suggested an important role of surface lattice oxygen from the catalyst in the two reactions. © 2016 American Institute of Chemical Engineers AIChE J, 63: 725–738, 2017

Jan Kaspar - One of the best experts on this subject based on the ideXlab platform.

  • nanostructured ceo2 zro2 Mixed Oxides
    ChemInform, 2005
    Co-Authors: Roberta Di Monte, Jan Kaspar
    Abstract:

    Nanostructured CeO2–ZrO2 Mixed Oxides have attracted great interest in the past 10 years, in particular as redox or oxygen storage promoters in the three-way catalysts. However, it has now became clear that both the chemistry of the simple Oxides and the complex metal–CeO2-based oxide interactions can play a critical role in developing novel and highly active materials for a number of processes, ranging from catalysts for H2 production from fuels up to ceramic materials and solid state conductors for fuel cells. Despite the apparent simplicity of these systems, extreme variability of their chemical and textural properties has been observed. An attempt is made here to rationalise the various factors and the inter-connections to the structure, the texture, and the effects of the nanometre scale, which all contribute to the properties of these materials.

  • heterogeneous environmental catalysis a gentle art ceo2 zro2 Mixed Oxides as a case history
    Catalysis Today, 2005
    Co-Authors: Roberta Di Monte, Jan Kaspar
    Abstract:

    More than 20 years ago, Christopher Master used the term gentle – skill-full – art to define homogeneous catalysis. In the present paper, we show that with the advances of knowledge of heterogeneous catalysis (CeO2–ZrO2 Mixed Oxides being taken as an example), this term can nowadays appropriately apply to heterogeneous catalysis as well. Thus, comprehension of the reaction mechanism and the appropriate choice of textural properties appear to allow true design of the properties of these catalytic nanomaterials, in a similar fashion to the way in which ligands gently modify the activity of a metal centre in a homogeneous catalyst.

  • modification of the oxygen storage capacity of ceo2 zro2 Mixed Oxides after redox cycling aging
    Catalysis Today, 2000
    Co-Authors: F Fally, G Colon, Hilario Vidal, Jan Kaspar, Marco Daturi, V Perrichon, Ginesa Blanco, J M Pintado, S Bernal, Jeanclaude Lavalley
    Abstract:

    Abstract High surface area CeO2–ZrO2 Mixed Oxides were treated at 900–950°C either under wet air or under successive reducing and oxidizing atmospheres in order to study the evolution of the oxygen storage capacity (OSC) of these solids after different aging treatments. Several complementary methods were used to characterize the redox behavior: temperature programmed reduction (TPR) by H2, TPO, magnetic susceptibility measurements to obtain the Ce3+ content, FT-IR spectroscopy of adsorbed methanol and a method to compare the oxygen buffering capacity (OBC) of the Oxides. All the results confirm that the Mixed Oxides exhibit better redox properties than pure ceria, particularly after aging. The enhancement in the OSC at moderate temperature has to be related to a deeper penetration of the reduction process from the surface into the under-layers. Redox cycling aging promotes the reduction at low temperature of all the Mixed Oxides, the improvement being much more important for low surface area aged samples. The magnitude of this effect does not depend on the BET surface areas which have similar values after cycling. This underlines the critical influence that the preparation and activation procedure have on the final OSC behaviors of the ceria–zirconia Mixed Oxides.

  • surface and structural characterization of cexzr1 xo2 cezirencat Mixed Oxides as potential three way catalyst promoters
    Journal of the Chemical Society Faraday Transactions, 1998
    Co-Authors: G Colon, Michele Pijolat, Francoise Valdivieso, Hilario Vidal, Jan Kaspar, Elisabetta Finocchio, Marco Daturi, Claude Binet, Jeanclaude Lavalley, Richard T Baker
    Abstract:

    The textural and structural properties of high specific surface area (HS) CexZr1-xO2 Mixed Oxides (CeZrMO) and their modification upon thermal aging have been investigated. Results from BET area determination and complete porosity analysis, as well as high-resolution electron microscopy, XRD, Raman and FTIR spectroscopies are presented. Some relationships between the molar composition of the binary systems and their textural and structural properties are presented. In addition, it has been possible to propose an explanation for structural features of the Mixed Oxides (solid-solution structures and possible phase segregation) as a function of Ce content, a point of great interest for the knowledge of phase composition and stability of CeZrMO.

Lucia G Appel - One of the best experts on this subject based on the ideXlab platform.

  • mg and al Mixed Oxides and the synthesis of n butanol from ethanol
    Applied Catalysis A-general, 2012
    Co-Authors: Debora L Carvalho, Roberto R De Avillez, Michelly T Rodrigues, Luiz E P Borges, Lucia G Appel
    Abstract:

    Abstract n -Butanol is used in a wide range of applications, especially for the production of paint, solvents and plasticizers. Recently, some companies have proposed the use of n -butanol as a fuel, which can be employed pure or blended with gasoline or diesel. At present, there is great interest in developing a one-step process that generates n -butanol from ethanol. Some works showed that Mg–Al Mixed Oxides are very promising catalysts for this matter. Analyzing the physical–chemical properties of these catalysts, this work aims at further studying this reaction. The Mg–Al Mixed Oxides were obtained by thermal decomposition of hydrotalcites employing two Mg/Al different ratios. Magnesium oxide (MgO) and alumina (Al 2 O 3 ) were also prepared following the same synthetic route used for the Mg–Al Mixed Oxides. The synthesized samples were characterized by the following techniques: XRD, NMR, BET and XRF. The acid and basic properties of the samples were also analyzed employing probe molecules. The catalytic tests were performed using a fixed bed reactor at atmospheric pressure. It was verified that the Mg and Al Mixed Oxides are able to promote the synthesis of C4 compounds from ethanol. Adjacent acid and medium basic sites are needed in order to generate the intermediate compounds. These pairs of acid and medium basic sites are obtained by the insertion of Al in the MgO lattice or in consequence of the presence of Mg in the γ-Al 2 O 3 lattice. It was observed that the higher the concentration of Mg is, the higher the hydrogenation capacity of the catalyst, since a greater selectivity to n -butanol was observed. Strong basic sites and a specific superficial atomic arrangement seem not to be essential for the synthesis of C4 from ethanol.

  • obtaining ceo2 zro2 Mixed Oxides by coprecipitation role of preparation conditions
    Applied Catalysis B-environmental, 2005
    Co-Authors: Sonia Letichevsky, Roberto R De Avillez, Marco A Fraga, Claudio A Tellez, Maria Isabel Pais Da Silva, Lucia G Appel
    Abstract:

    Abstract The preparation of CeO 2 –ZrO 2 Mixed Oxides preparation was studied by evaluating the influence of several conditions. Coprecipitation was taken as the standard method and the effects brought about by the cerium salt precursor ((NH 4 ) 2 Ce(NO 3 ) 6 or Ce(NO 3 ) 3 ), the introduction of drying and aging steps as well as pH controlling upon precipitation were analyzed. The samples were characterized by X-ray diffraction, Raman spectroscopy, temperature-programmed reduction, infrared spectroscopy, oxygen storage capacity and surface area. The use of Ce(NO 3 ) 3 leads to the formation of c -CeO 2 and t -ZrO 2 Mixed oxide whereas a solid solution is achieved by using (NH 4 ) 2 Ce(NO 3 ) 6 . It was observed that the cerium precursor is the most significant parameter of preparation procedure since it defines the crystalline phases and consequently the reducibility behavior of the CeO 2 –ZrO 2 system.

Kehua Yin - One of the best experts on this subject based on the ideXlab platform.

  • catalytic reactions of coke with dioxygen and steam over alkaline earth metal doped cerium zirconium Mixed Oxides
    Applied Catalysis A-general, 2017
    Co-Authors: Kehua Yin, Shilpa Mahamulkar, Christopher W Jones, Pradeep K Agrawal, Hirokazu Shibata, Andrzej Malek, Jiahan Xie, Robert J Davis
    Abstract:

    Abstract A series of cerium-zirconium Mixed Oxides doped with alkaline earth metals was prepared by calcining a mixture of Ce 0.8 Zr 0.2 O 2 and the nitrate salt of alkaline earth metals at 1173 K. The results from X-ray diffraction, Raman spectroscopy and analytical electron microscopy indicated the alkaline earth compounds were dispersed on the surface of Ce 0.8 Zr 0.2 O 2 . The doped Mixed Oxides were evaluated in the catalytic reaction of solid coke under tight contact conditions with 10 vol.% O 2 in He at 693 K and with 100 vol.% H 2 O at 993 K using thermogravimetric analysis. For coke oxidation with O 2 , the weight loss was first order in coke, and the measured first order rate constant was proportional to the total surface area of catalyst at low catalyst loadings. For coke gasification with H 2 O, the weight loss was nearly zero order in coke, and the measured areal reaction rate was independent of the total surface area of catalyst at low catalyst loadings. The addition of alkaline earth metals inhibited coke oxidation with dioxygen but promoted coke gasification with steam.

  • catalytic oxidation of solid carbon and carbon monoxide over cerium zirconium Mixed Oxides
    Aiche Journal, 2017
    Co-Authors: Kehua Yin, Robert J Davis, Shilpa Mahamulkar, Christopher W Jones, Pradeep K Agrawal, Hirokazu Shibata, Andrzej Malek
    Abstract:

    A series of cerium-zirconium Mixed Oxides was prepared and evaluated in the catalytic oxidation of solid coke with 10 vol % O2 in He at 673 K using a thermogravimetric analyzer. The measured first order rate constant for coke oxidation was proportional to the catalyst loading when the mass ratio of catalyst to coke was low, which enabled the calculation of a surface area specific reaction rate. The validity of the normalization method was confirmed by performing CO oxidation over the cerium-zirconium Mixed Oxides in a fixed bed reactor at 573 K. Although there was no correlation between the coke oxidation rate and the oxygen storage capacity or the reducibility of the catalysts, there was an excellent correlation to the CO oxidation rate. Kinetic studies of both coke and CO oxidation suggested an important role of surface lattice oxygen from the catalyst in the two reactions. © 2016 American Institute of Chemical Engineers AIChE J, 63: 725–738, 2017