Search

Abstract: Ce0.8Sm0.2O2− δ electrolytes were prepared by sol–gel methods with different thermal treatment conditions. It was found that the particle size of the powders thermally treated in N2 could be controlled less than 10 nm, due to the fact that carbons that enwrapped the precursors could inhibit their crystallization. At the same time, the nano-sized precursors could form larger nuclei at the initial stage of sintering, resulting in the formation of electrolyte with higher density and larger grain size. At the same consent of oxygen vacancies, the enhancement of electrical properties for the electrolyte was correlated to its microstructure obtained by the N2 thermal treatment. [Copyright &y& Elsevier]

Modulating the active sites in atomic level is very meaningful to optimize catalyst performance but still very challenge. Herein, Pt catalysts loaded on different supports (ZSM-5, Al 2 O 3 , ZrO 2 , CeO 2) were sulfate modified by in situ pyrolysis of (NH 4) 2 SO 4 mixed with Pt catalyst. Sulfate remarkably improves these catalyst activities for propane combustion, particularly for the sulfate modified Pt/ZSM-5 catalyst with the highest activity among them. Through controlling the amount of (NH 4) 2 SO 4 used and the loading of Pt, Pt/S atomic ratio in the sulfate modified Pt/ZSM-5 catalyst was successfully regulated. Pt/S atomic ratio significantly affects the electron transfer from Pt species to sulfate and also their interaction strength, which is decisive to the synergetic catalysis of sulfate and Pt species. The 5S-2Pt/ZSM-5 with Pt/S atomic ratio of 0.5 shows a moderate strength of sulfate and Pt species interaction, which is responsible for its highest reaction rate of 86.5 μmol·g Pt −1·s−1 at 200 °C. [Display omitted] • Pt based catalysts were modified with sulfate species by in situ pyrolysis of (NH 4) 2 SO 4. • Pt/S atomic ratio was successfully regulated to optimize catalytic activity for propane oxidation. • The synergy catalysis of sulfate and Pt species for propane oxidation is affected by their interaction strength. • Moderately strong interaction between sulfate and Pt species achieves the highest activity. [ABSTRACT FROM AUTHOR]

[Display omitted] • The CO oxidation catalyzed by various CuO-CeO 2 interfacial sites involves a typical Mars-van Krevelen mechanism. • The CuO-CeO 2 interfaces in the CeO 2 -CuO/c-Cu 2 O (cubes) nanocomposites are more intrinsically active at CeO 2 loadings no less than 0.75 wt%. • The higher activity is relevant to lower coordinated oxygen ions and thus better CO reactivity for the CeO 2 -CuO/c-Cu 2 O nanocomposites. • The active oxygen species on CuO-CeO 2 interface in catalyzing CO oxidation should come from CuO rather than CeO 2. • A highly active 13.2 %CeO 2 -CuO/c-Cu 2 O(s) (small) catalyst with high density of active sites for CO oxidation is realized on fine Cu 2 O cubes. Several CeO 2 -CuO/Cu 2 O nanocomposites with different CuO structures were used to identify the structure sensitivity of CuO in the CeO 2 -CuO/Cu 2 O catalyzed CO oxidation. The CO oxidation catalyzed by various CuO-CeO 2 interfacial sites involves a typical Mars-van Krevelen mechanism, in which the CuO-CeO 2 interfaces in the CeO 2 -CuO/c-Cu 2 O (cubes) nanocomposites are more intrinsically active, exhibiting ca. 15 kJ mol−1 lower activation energy than those in the CeO 2 -CuO/o-Cu 2 O (octahedra) and CeO 2 -CuO/d-Cu 2 O (rhombic dodecahedra) nanocomposites at CeO 2 loadings no less than 0.75 wt%. The higher activity is relevant to lower coordinated oxygen ions on CuO/c-Cu 2 O surface and thus better CO reactivity for the CeO 2 -CuO/c-Cu 2 O nanocomposites, which therefore indicates that the active oxygen species on CuO-CeO 2 interface should come from CuO rather than CeO 2. Moreover, a highly active 13.2 %CeO 2 -CuO/c-Cu 2 O(s) catalyst for CO oxidation is realized on fine Cu 2 O cubes, which thus has high density of active sites. [ABSTRACT FROM AUTHOR]

Abstract: A series of Ce x Gd1−x O2−δ samples were prepared by a citrate method. Phase structure and AC impedance spectroscopy of these electrolytes were studied. It was found that doping of Gd3+ into CeO2 could help to form solid solutions, which is beneficial to the formation of more oxygen vacancies and consequently improves electrical conductivity of the electrolytes. The highest conductivity was obtained on a Ce0.6Gd0.4O2−δ electrolyte. Arrhenius plot of the Ce0.6Gd0.4O2−δ electrolyte shows an inflexion at 600°C, implying that the electrolyte has dual mechanisms of electrical conductivity. It was also found that the phase transition has influence on the electrical conductivity, as the activation energy increases when the electrolytes transit from a mixed CeO2-based and Gd2O3-based solid solution phases to only CeO2-based solid solution phase. [Copyright &y& Elsevier]

Abstract: The catalytic behavior of CeO2-based solid solution catalysts (Ce0.7Zr0.3O2, Ce0.7Pr0.3O2−δ , and Ce0.7Gd0.3O1.85) had been studied for soot combustion. These catalysts were characterized using X-ray diffraction (XRD), UV-visible, Raman, and H2 temperature-programmed reduction (H2-TPR) measurements. The Zr, Pr, and Gd cations replaced Ce cations in the CeO2 lattice to form nanocrystalline CeO2-based solid solutions. The crystallite size of Ce0.7Zr0.3O2, Ce0.7Pr0.3O2−δ , and Ce0.7Gd0.3O1.85 is 7.3, 7.8, and 11.1nm, respectively, which are much smaller than pure CeO2 (36.2nm). The substituting process can promote the formation of oxygen vacancies, which can hasten the diffusion rate of oxygen, then improve the combustion activity. According to the catalytic soot combustion results, the ranking in activity of these catalysts is Ce0.7Zr0.3O2 >Ce0.7Pr0.3O2−δ >Ce0.7Gd0.3O1.85 ∼CeO2, which is well consistent with the reducibility sequence of the samples. The mass of catalyst plus soot mixture have effect on soot combustion: the T ig and T max decrease with the increasing of sample weight. Combustion activity of catalysts decreases slowly with cycled runs, which can be attributed to the activity lost of catalyst. [Copyright &y& Elsevier]

[Display omitted] • The Pd-CeO 2 interaction is related to the oxygen vacancy concentration in the CeO 2. • Higher oxygen vacancy concentration in Pd/r-CeO 2 results in higher content of Pd2+ species. • The highest content of metallic Pd species in Pd/p-CeO 2 accounts for the best activity. • Hydrogenation of bidentate carbonate and bicarbonate species is the rate determining step. Several Pd catalysts supported on CeO 2 with different morphologies (i.e. CeO 2 rods (r-CeO 2), cubes (c-CeO 2) and polyhedra (p-CeO 2)) were tested for the CO 2 hydrogenation into formate. Remarkable morphology - dependent Pd-CeO 2 interaction was observed, which was related to the oxygen vacancies in the CeO 2. The r-CeO 2 with the highest concentration of oxygen vacancy resulted in smaller Pd particles and more positively-charged Pd species in the Pd/r-CeO 2 catalyst. The best performance was obtained over the Pd/p-CeO 2 catalyst, giving a turnover frequency of 746 h−1 at 40 °C. The enhanced activity was due to the highest content of metallic Pd species in the catalyst, which was responsible for the facile activation of H 2. Moreover, in situ spectroscopic results revealed that the hydrogenation of the carbonaceous intermediates was the rate - determining step. This work demonstrates oxide morphology engineering as a powerful strategy in developing efficient Pd - based catalysts for CO 2 hydrogenation. [ABSTRACT FROM AUTHOR]

[Display omitted] • Surface active sites on Co 3 O 4 catalyst for CO and propane oxidation have been clearly differentiated. • CO oxidation activity of Co 3 O 4 catalyst depends on O 2 activation on oxygen vacancies. • Synergistic catalysis of Co 3 O 4 species and acid sites from ZSM-5 accelerates propane oxidation. • Increasing surface Co3+ specie of Co 3 O 4 catalyst is beneficial for both CO and propane oxidation. Identifying active sites is critical for rational catalyst design. We clarified the surface active sites for propane and CO oxidation over Co 3 O 4 -based catalysts using probe reactions of propane and CO oxidation, respectively. In comparison to Co 3 O 4 /ZSM-5, Co 3 O 4 /CeO 2 has superior CO oxidation activity but inferior propane oxidation activity. CeO 2 oxygen vacancies promote O 2 activation, the rate-determined step (RSD) for CO oxidation, and avoid competitive adsorption of O 2 and CO on Co 3 O 4 species, resulting in superior CO oxidation activity on Co 3 O 4 /CeO 2. Whereas the RSD for propane oxidation is synergistic catalysis of Co 3 O 4 species and acid sites, Co 3 O 4 /ZSM-5 exhibits improved propane oxidation activity as a result of the abundant acid sites from ZSM-5. Due to a lack of oxygen vacancies for O 2 activation, competitive adsorption of O 2 with propane or CO on Co 3 O 4 species is observed on Co 3 O 4 /ZSM-5. Furthermore, surface Co3+ species in Co 3 O 4 are discovered to be active sites for both CO and propane activation. As a result of the increased surface Co3+ species, the pre-reduced and post-oxidized Co 3 O 4 catalysts (Co 3 O 4 /ZSM-5-A and Co 3 O 4 /CeO 2 -A) exhibit improved activity for both propane and CO oxidation. [ABSTRACT FROM AUTHOR]

A series of Pt/CeO 2 catalysts with different Pt contents were prepared using an incipient wetness impregnation method and tested for CO oxidation. Kinetic study on the catalysts indicated that the reaction rate was independent of the partial pressures of CO and O 2 ( r = k app [CO] 0 [O 2 ] 0 ). The derived reaction pathways involved chemisorption of CO on surface Pt atoms and reacting with lattice oxygen provided by the CeO 2 support at the Pt–CeO 2 interface, suggesting a Mars van-Krevelen type reaction on these catalysts and the interfacial Pt–O–Ce ensembles being the active sites. Also, turnover frequencies (TOFs) calculated based on Pt dispersion and periphery Pt atoms were found to be proportional to the Pt particle size, with the large Pt particles possessing higher TOF than the small ones. Such a trend was interpreted by the important role of the oxygen vacancies via the formation of Pt–Ce–O solid solution, which could accelerate the mobility of lattice oxygen and consequently the activity. [ABSTRACT FROM AUTHOR]

Abstract: A series of CeO2–Al2O3 catalysts with different CeO2 contents were prepared by a co-precipitation method, and supported Pt/CeO2–Al2O3 catalysts were also prepared by an impregnation method. These catalysts were tested for catalytic oxidation of dichloromethane (CH2Cl2). It was found that these catalysts were active for the reaction, with a 100% conversion of CH2Cl2 obtained at 410°C over a catalyst with 15% of CeO2. Various characterization results such as ammonia temperature programmed desorption, hydrogen temperature programmed reduction suggested that the catalytic behaviors were synergistically influenced by surface acidity and redox property of the catalysts. An optimal combination of surface acidity and redox property in the catalyst resulted in a high activity. Moreover, the addition of Pt could further enhance the activity, due to the promotion of surface acidity by the introduction of chlorine species in the catalyst during the preparation using H2PtCl6 as the precursor and reducibility of the catalyst probably via the formation of Ce–Pt–O solid solution. [Copyright &y& Elsevier]

Abstract: Gold catalysts supported on high surface area CeO2 were synthesized and tested for low temperature formaldehyde oxidation. It was found that the reactivity was greatly enhanced by increasing surface area of the support. Complete conversion of formaldehyde was obtained on a 3.0Au/CeO2-270 catalyst with a surface area of 270m2 g−1 at 50°C, and a conversion of 92.3% was obtained at 37°C over the same catalyst, which made it promising for indoor formaldehyde removal. Detailed characterizations of the catalyst showed that the enhancement could be attributed to two factors. One was that Au species mainly in high oxidation states formed on the high surface area CeO2 resulted in a high degree of HCHO adsorption, as revealed by in situ diffuse reflectance infrared Fourier transform spectroscopy. The other was the high surface area CeO2 provided more oxygen vacancies by the nano effect and the formation of Au x Ce1−x O2−δ solid solution as revealed by Raman spectroscopy, on which oxygen molecules could be transformed to active species for the reaction. [Copyright &y& Elsevier]

Abstract: Using Cerium chloride octahydrate as a precursor and dodecyl sodium sulfate as a template, nano-sized CeO2 with extra-high surface area were synthesized by a surfactant-templated method. The highest surface area of the synthesized CeO2 was 457m2 g− 1. Combined with XRD, TEM and BET results, it was found that when the calcination temperature was lower than 600°C, the particle size of CeO2 hardly changed while the surface area declined due to the co-action of the sintering and agglomeration of the particles. However, with a high calcination temperature (above 600°C), the sintering was the mainly reason to the decline of the BET surface area and the rapid growth of the particles size. Moreover, by the test for CO oxidation, it was found that the reactivity of the CeO2 sample remarkably increased with decreasing particle size, which was due to the fact that smaller particles provided more structural defects. [Copyright &y& Elsevier]