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Abstract: A series of Ca doped Ce-Ti oxides prepared by a single step sol-gel method were investigated for the selective catalytic reduction of NO with NH3. The results show that Ca doping had both positive and negative effects on the activities of Ce-Ti oxide. Ca0.1CT possessed the best catalytic activity and widest temperature window. Further investigations on BET, XRD, XPS, H2-TPR and NH3-TPD demonstrated that the good SCR performance of Ca0.1CT could be attributed to the increase in the amount of Ce3+ and surface adsorbed oxygen as well as the enhancement of Brønsted acidity and redox ability. In addition, the good dispersion of active Ce species, the alleviation of support sintering, and the interaction among Ce, Ti and Ca species were also responsible for its enhanced activity.Graphical Abstract: [ABSTRACT FROM AUTHOR]

A novel CeO 2 -MoO 3 -WO 3 /TiO 2 (CMWT) catalyst was prepared by a single step sol-gel (SG) method. It exhibited 93.8%–98.9% of NO conversion at 275–450 °C and high tolerance to 10% H 2 O and 1000 ppm SO 2 at a gas hourly space velocity (GHSV) of 90,000 h − 1 . Superior SCR activity of CMWT catalyst could be attributed to the presence of more Ce 3 + and chemisorbed oxygen, higher redox ability, stronger adsorption capacity of NH 3 species and the strong interaction among ceria, molybdenum, tungsten and titania. [ABSTRACT FROM AUTHOR]

The effect of CaO on CeO/TiO catalysts prepared by a single step sol-gel method for selective catalytic reduction of NO with NH was investigated. The results showed that CaO could severely deactivate the CeO/TiO catalysts. Based on the characterization results obtained by BET, XRD, XPS, H-TPR and NH-TPD, the deactivation by CaO of CeO/TiO catalysts should be attributed to pore blockage, lower concentration of Ce on catalyst surface, reduction of Ce and surface adsorbed oxygen, degradation of redox ability and decrease in NH adsorption capacity. The theoretical DFT results demonstrated that Ca atom could strongly interact with cerium oxygen, which inhibits the formation and hydrogenation of oxygen vacancies on catalyst surface. [ABSTRACT FROM AUTHOR]

A Ce–W–Ti mixed oxide catalyst prepared by a single step sol–gel method exhibited excellent SCR activity and high resistance to H 2 O and SO 2 . The excellent catalytic performance might be attributed to the improved dispersion of Ce species on TiO 2 , the increase in the amount of Ce 3+ and chemisorbed oxygen and the strong interaction among ceria, tungsten and titania owing to the addition of WO 3 . [ABSTRACT FROM AUTHOR]

Based on a model for the shell progressive poisoning of a single catalyst pellet in a catalytic reactor, PbCl2-poisoning kinetics of V2O5/TiO2 catalysts for the selective catalytic reduction of NO with NH3 was studied. The PbCl2-poisoning kinetic equation for the catalysts was established. Combining the activity retention fraction from the model simulation with that from the activity experiments, the relation between PbCl2 loadings over the catalysts with reaction time was established. The combined effect of PbCl2 concentration and PbCl2-poisoning reaction rate constant on activity retention fraction was simulated based on the established model. The results indicated that with increasing PbCl2 concentration and PbCl2-poisoning reaction rate constant, activity retention fraction decreased obviously with the increase of reaction time. © 2015 American Institute of Chemical Engineers Environ Prog, 34: 1085-1091, 2015 [ABSTRACT FROM AUTHOR]

[Display omitted] • Ce-W catalyst is optimized by combining Nb-modification and structural manipulation. • 3DOM structure provides abundant diffusion channels for catalytic reactions. • 3DOM structure ensures the high dispersion of active components. • Synergistic effect among the species of Ce, Nb and W promotes the increase of O α. • Active NH 3 and NO x species are increased over 3DOM Ce-W-Nb catalysts. A string of 3DOM Ce-W-Nb ternary catalysts for NH 3 -SCR were prepared by a colloidal template method. The 3DOM Ce-W-Nb 0.15 catalyst had the best SCR activity and yielded more than 90% NO conversion at 275 ∼ 450 °C in the high GHSV of 120,000 h−1. In addition, it exhibited good tolerance to H 2 O and SO 2. The addition of Nb increased the number of active sites and made them dispersed more evenly, optimized the pore structure to a certain extent, and increased the specific surface area. The interaction among Ce, W, and Nb species promoted the increase of chemisorbed oxygen and enhanced the redox properties, thus contributing to the satisfactory SCR activity at low temperatures. In addition, the synergistic effect between Nb and W provided sufficient Lewis acid sites for the 3DOM Ce-W-Nb x catalyst, which was conducive to the good SCR performance at high temperatures. The NH 3 -SCR reaction on 3DOM Ce-W-Nb x catalysts followed both Eley-Rideal and Langmuir-Hinshelwood mechanisms. The doping of Nb was beneficial to boost the adsorption of NH 3 and improved the reactivities of NH 3 adsorbed species while facilitating the generation of active NO x species. These accelerated the reaction rate and optimized the reaction path. [ABSTRACT FROM AUTHOR]

Effect of KCl on vanadia-based catalysts for selective catalytic reduction of NO with NH3 was investigated by means of BET and pore size distribution measurements, XRD, XPS, FTIR, and NO reduction measurements. The catalytic activity was found to decrease rapidly with increasing the amount of KCl addition at different reaction temperatures. When the molar ratio of K/V exceeded 2.0, most of the activity was lost. The presence of KCl caused the sintering of the catalysts as well as the decrease in the amount of V atoms and the change of V valence state at the catalyst surface. Based on the analysis of physical and chemical properties of the catalysts, the KCl-poisoning mechanism model of the vanadia-based SCR catalysts was proposed. © 2013 American Institute of Chemical Engineers Environ Prog, 33: 390-395, 2014 [ABSTRACT FROM AUTHOR]

Highlights: [•] PbCl2 was a serious poison for vanadia-based SCR catalysts. [•] The decrease in surface acidity and reducibility caused serious catalyst deactivation. [•] The PbCl2-poisoning mechanism model of vanadia-based catalysts was proposed. [ABSTRACT FROM AUTHOR]

Abstract: A series of Ce-Ti mixed-oxide catalysts were prepared by the sol–gel method for selective catalytic reduction (SCR) of NO with ammonia as reductant. These catalysts were characterized by XRD, BET, and XPS techniques. The experimental results show that the best Ce-Ti mixed-oxide catalyst yielded 98.6% NO conversion, and 100% N2 selectivity at typical SCR reaction temperatures (300–400°C) and the high gas hourly space velocity of 50,000h−1. As the Ce loading (the mass ratio of CeO2/TiO2) was increased from 0 to 0.6, NO conversion increased markedly, but decreased at higher Ce loading. The most active catalyst was obtained with a Ce loading of 0.6. The high activity might be attributed to high Ce loading, strong interaction between Ce and Ti, high concentration of amorphous Ce on the catalyst surface, or the increase of chemisorbed oxygen or/and weakly bonded oxygen species, resulting from the presence of Ce3+ after Ce addition. The effect of the calcination temperature was also investigated, and the optimal calcination temperature was 500°C. The presence of oxygen played an essential role in NO reduction, and the activity of the Ce(0.6)Ti catalyst was not depressed when oxygen concentration was higher than 1%. The effect of SO2 and H2O on the activity of the Ce(0.6)Ti catalyst was bound up with the reaction temperature. [Copyright &y& Elsevier]

Abstract: CeO2/TiO2 catalysts were prepared by three methods, and their activities for SCR of NO with NH3 were investigated in the presence of O2. The experimental results indicate that the catalysts prepared by the single step sol–gel method have the best SCR activity and SO2 resistance regardless of the concentration of NO or SO2. High surface area and good redox ability are important to the catalytic activity, while the strong interaction between ceria and titania as well as high concentration of amorphous or highly dispersed nano-crystalline ceria should be the reason for the excellent performance of the catalyst prepared by the single step sol–gel method. [Copyright &y& Elsevier]

[Display omitted] • CeNbTi oxide catalysts were synthesized by impregnation, co-precipitation and solid process methods. • The CeNbTi catalyst prepared by impregnation showed the superior NH 3 -SCR activity and better resistance to K 2 O and SO 2. • The surface acidity and redox ability of the CeNbTi catalyst prepared by impregnation were enhanced. • CeNbTi catalyst prepared by impregnation could accelerate the reaction of pre-adsorbed NH 3 /NO x and pre-adsorbed NO x /NH 3. Ce-Nb-Ti metal oxide catalysts (CeNbTi) were synthesized for NH 3 -SCR by impregnation (IM), co-precipitation (CP) and solid process (SP) methods and characterized by various techniques. The results of NH 3 -SCR activity evaluations showed that CeNbTi-IM possessed the superior NH 3 -SCR performance in different gas hourly space velocity and better resistance to SO 2 and potassium. The characterization results showed that the CeNbTi-IM catalyst had relatively high concentrations of Ce3+ and chemisorbed oxygen, strong synergistic effect among different components and well dispersed active species. More importantly, the catalyst had stronger reduction capacity and a large number of Lewis acid sites, which contributed to its excellent catalytic performance. The in situ DRIFTS results revealed that the impregnation method was beneficial to the adsorption of weakly adsorbed NO 2 , bidentate nitrate and NH 3 species. In addition, it was revealed that the reaction paths over CeNbTi-IM, CeNbTi-CP and CeNbTi-SP obeyed both Langmuir-Hinshel wood and Eley-Rideal mechanisms, but the impregnation method could accelerate the reaction between pre-adsorbed ammonia/NO x species and NO x species/ammonia. [ABSTRACT FROM AUTHOR]

Abstract: DFT calculations were carried out to study the behavior of NO2 in the selective catalytic reduction of nitric oxides with ammonia on the surface of the V2O5 catalyst. The results showed that NO2 could readily reoxidize V4+–OH through two reaction routes: (1) NO2 directly reoxidizing V4+–OH to V5+ NO2 reacting with H2O or NH3 to produce HNO3, which subsequently reoxidizes V4+–OH to V5+ te-determining step of route 1 is the desorption of cis-HNO2 from the reoxidized V5+ endothermic by 9.91kcal/mol. Route 2 possesses an energy barrier of 7.44kcal/mol, less than route 1. This energetic comparison shows that route 2 is the predominant reaction mechanism at low temperature. Reactions of the by-product, HNO2, were also investigated. The results showed that both cis-HNO2 (route 1) and trans-HNO2 (route 2) can either react with NH3, producing H2O and N2, or react with themselves, producing H2O, NO and NO2. A systemic description of the behavior for NO2 in “fast” SCR on V2O5 surface, including the reaction routes and energy profiles, has been proposed in our work. [Copyright &y& Elsevier]