Rui Ran

MnOx–CeO2–Al2O3 mixed oxides for soot oxidation: Activity and thermal stability

MnO(x)-CeO(2)-Al(2)O(3) mixed oxides were prepared by impregnating manganese acetate and cerium nitrate on alumina powders using the sol-gel method. The thermal stabilities of MnO(x)-CeO(2) and Al(2)O(3)-modified mixed oxides were evaluated by treating at 800 °C in dry air flow for 20h. The introduction of Al(2)O(3) markedly increases the textural stability of the catalyst with a relatively high dispersion of MnO(x) and CeO(2), 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.

Ceria-based catalysts for soot oxidation: a review

Abstract Developments in ceria-based soot oxidation catalysts, especially during the last decade, are reviewed. Based on the comparisons of the activity, durability and cost-efficiency of different soot oxidation catalysts, four kinds of applicable ceria-based catalysts have been screened out, which are: (1) CexZr1–xO2 catalyst with high cerium content (x

Rare earth containing catalysts for selective catalytic reduction of NOx with ammonia: A Review

Abstract Increasingly stringent regulations in many countries require effective reduction and control of NOx emissions. To meet these limits, various methods have been exploited, among which the selective catalytic reduction of NOx using ammonia as the reductant (NH3-SCR) is the most favored technology. High catalytic activity, N2 selectivity and resistance to deactivation by sulfur, alkaline metals and hydrothermal conditions are the optimal properties of a successful SCR catalyst. Rare earth oxides, particularly CeO2, have been increasingly used to improve the catalytic activity and resistance to deactivation of deNOx catalysts, both modifying traditional vanadium catalysts, and also developing novel catalysts, especially for low temperature applications. This review summarized the open literature concerning recent research and development progresses in the application of rare earths for NH3-SCR of NOx. Additionally, the roles of rare earths in enhancing the performance of NH3-SCR catalyst were reviewed.

Structure and oxygen storage capacity of Pr-doped Ce0.26Zr0.74O2 mixed oxides

Abstract Binary Ce-Zr (CZ), Pr-Zr (PZ) and ternary Ce-Zr-Pr (CZP) mixed oxides were prepared by an ammonia-aided co-precipitation method, and were aged in a steam/air flow at 1050 °C. X-ray diffraction (XRD), Raman spectra, X-photon spectra (XPS) and CO temperature programmed reduction (TPR) were carried out to characterize the micro-structure and reducibility of catalysts. The oxygen storage capacity (OSC) was evaluated with CO serving as probe gas. The results showed that a pseudo cubic structure was formed for the Zr-rich ceria-zirconia mixed oxides with Pr doping. The insertion of Pr prevented the phase segregation of the mixed oxides during the hydrothermal ageing. The Pr doped samples showed better redox performances in comparison with CZ, and the sample doped with 5 wt.% Pr showed the most remarkably promoted dynamic oxygen storage capacity. This phenomenon was closely related to both the reducibility and oxygen mobility of the mixed oxides. The introduction of praseodymium into ceria-zirconia could accelerate the oxygen migration by increasing the amount of oxygen vacancies, although it was difficult for Pr 3+ ions themselves to participate in the oxygen exchange process.

NO reduction by CO over Rh/Al2O3 and Rh/AlPO4 catalysts: Metal–support interaction and thermal aging

Rhodium was impregnated on γ-Al2O3 and AlPO4 followed by treating in a wet air at 1050°C for 5h. The catalytic activities of the catalysts were evaluated by temperature-programmed reactions in a stoichiometric mixture of NO and CO. The fresh Rh/Al2O3 and Rh/AlPO4 catalysts exhibit similar catalytic activities. After the hydrothermal aging, Rh/Al2O3 experiences a significant deactivation, whereas Rh/AlPO4 shows even higher activity than the fresh sample. A series of structural and surface characterizations were performed to explore different aging mechanisms of these two catalysts. The fresh Rh/AlPO4 catalyst shows superior low-temperature redox property, but its NOx adsorption is weakened due to the acidic nature of the support. Thus, two fresh catalysts present similar catalytic activities. The hydrothermal aging at high temperature leads to the formation of inert Al5Rh2 alloy. Contrarily, no such strong interaction occurs between rhodium and AlPO4. Furthermore, large Rh particles, which facilitate the dissociation of NO, are formed on the aged Rh/AlPO4 catalyst. Thus, a superior high activity for NO-CO is achieved over the aged Rh/AlPO4.

Effects of silica additive on the NH 3 -SCR activity and thermal stability of a V 2 O 5 /WO 3 -TiO 2 catalyst

V 2 O 5 /WO 3 -TiO 2 and V 2 O 5 /WO 3 -TiO 2 -SiO 2 catalysts were prepared by a wetness impregnation method, and both the catalysts were hydrothermally aged at 750 ℃ in 10 vol% H 2 O/air for 24 h. The catalysts were evaluated for NO x conversion using NH 3 as the reductant. Hydrothermal ageing decreased the NO x conversion of V 2 O 5 /WO 3 -TiO 2 catalyst severely over the entire measured temperature range. Interestingly, the NH 3 -SCR activity of the silica-modified catalyst at 220-480 ℃ is enhanced after ageing. The catalysts were characterized by X-ray diffraction, nitrogen adsorption, X-ray fluorescence, Raman spectroscopy, H 2 temperature-programmed reduction, and NH 3 temperature-programmed desorption. The addition of silica inhibited the phase transition from anatase to rutile titania, growth of TiO 2 crystallite size and shrinkage of catalyst surface area. Consequently, the vanadia species remained highly dispersed and the hydrothermal stability of the V 2 O 5 /WO 3 -TiO 2 catalyst was significantly improved.

Structure and oxygen storage capacity of Pd/Pr/CeO2-ZrO2 catalyst: effects of impregnated praseodymia

Abstract Praseodymium (Pr) was impregnated to CeO 2 -ZrO 2 solid solution by an impregnation method. The as-obtained Pr modified CeO 2 -ZrO 2 was impregnated with 1 wt.% Pd to prepare the catalysts. The structure and reducibility of the fresh and hydrothermally aged catalysts were characterized by X-ray diffraction (XRD), Raman, X-ray photoelectron spectroscopy (XPS), CO chemisorption and H 2 temperature-programmed reduction (H 2 -TPR). The oxygen storage capacity (OSC) was evaluated with CO serving as probe gas. Effects of impregnated Pr on the structure and oxygen storage capacity of catalysts were investigated. The results showed that the aged Pr-impregnated samples had much higher OSC and better reducibility than the unmodified ones. The scheme of structural evolutions of the catalysts with and without Pr was also established. Partial of the impregnated Pr diffused into the bulk of CeO 2 -ZrO 2 during ageing, which inhibited the sintering, and increased the amount of oxygen vacancies in CeO 2 -ZrO 2 support. Furthermore, those impregnated Pr species which covered on the surface of the support obstructed the strong metal-support interaction between Pd and Ce so as to reduce the encapsulation of Pd as well as the back spill-over of the oxygen during the catalytic process.

In situ DRIFTS study of NOx adsorption behavior on Ba/CeO2 catalysts

Abstract A series of Ba/CeO 2 catalysts with different Ba loading amounts were prepared by incipient wetness impregnation. Their NO x adsorption behaviors under NO and NO+O 2 conditions were investigated by in situ DRIFTS. It was found that NO x was adsorbed and stored in the form of nitrites and nitrates on both Ba and Ce sites on the surface of the catalysts. The less thermally stable BaCO 3 was suggested to be the main active phase for NO x trapping. Ceria served primarily as an oxygen supplier in the absence of O 2 , and the reaction from nitrites to nitrates on Ba sites was the key step in this case. In the presence of O 2 , however, gaseous O 2 became the main oxygen source. The NO x adsorption capacity of the catalyst was dominated by the Ba content. Moreover, the stability of nitrites and nitrates formed on Ce sites was found to be lower than those formed on Ba sites which existed in the form of the ionic barium nitrate species.

NO catalytic oxidation over an ultra-large surface area LaMnO3+δ perovskite synthesized by an acid-etching method

The perovskite oxides LaMnO3+δ were prepared by a citrate method and then etched by acid solution with different times. After etching, the perovskite structures of all the catalysts remained, the surface area enlarged apparently, and the NO catalytic oxidation activities were obviously promoted by increasing the etching time. Long-term experiments revealed the acceptable stability of the etched catalysts. The favorable activities of the etched LaMnO3+δ catalysts were mainly due to their high specific surface area, abundant activated oxygen species and vacancies, as well as the higher valence state of Mn ions resulting from the loss of La3+ in the perovskite structure.

A facile ceria–zirconia binary oxide used for degradation of 2-chloroethyl ethyl sulfide

Ceria–zirconia binary oxides (CexZr1−xO2) with different Ce/Zr ratios were prepared through a facile co-precipitation method using ammonia as the precipitating agent, and used for the first time as reactive sorbents for degradation of 2-chloroethyl ethyl sulfide (2-CEES). The synthesized samples were characterized by XRD, Raman spectroscopy, BET, TGA–DSC, XPS, as well as CO2-TPD. The results revealed that Ce0.5Zr0.5O2 exhibited the best degradation performance, hence providing its possible applicability as a new reactive sorbent against CWAs. The 2-CEES was destroyed through the hydrolysis and elimination by surface bound alkoxy species formed on the surface of ceria–zirconia binary oxides. The chemisorbed water and the strong basicity were the key factors to the effective degradation of 2-CEES.