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The effect of Na 2 O and NaCl on CeO 2 –TiO 2 catalyst for the selective catalytic reduction of NO with NH 3 was investigated with BET, XRD, XPS, NH 3 -TPD, H 2 -TPR, in-situ DRIFT and catalytic activity measurements. The results showed that both Na species could deactivate the CeO 2 –TiO 2 catalyst and Na 2 O had a stronger effect than NaCl. The more serious deactivation by Na 2 O could be ascribed to smaller surface area, fewer surface Ce3+ and chemical adsorbed oxygen, lower surface acidity, and worse reducibility. The introduction of NaCl and Na 2 O facilitated the formation of new surface NO x adspecies, but were inactive in NH 3 -SCR reaction. The adsorption of NH 3 were inhibited. The NH 3 -SCR reaction over the CeO 2 –TiO 2 catalyst was governed by both E-R and L-H mechanisms. The introduction of NaCl and Na 2 O didn't change the NH 3 -SCR reaction mechanisms. • The poisoning effect of Na 2 O is more serious than NaCl over CeO 2 –TiO 2 catalyst. • The loss of more acid sites (especially Brønsted acid sites) over Na 2 O0.5-CT catalyst than NaCl0.5-CT. • Na 2 O inhibits NH 3 adsorption on CeO 2 –TiO 2 catalyst more significantly than NaCl. • Na species could supply some active sites to absorb NO x species which were inactive in NH 3 -SCR reaction. • The introduction of NaCl and Na 2 O don't change the NH 3 -SCR reactions mechanisms. [ABSTRACT FROM AUTHOR]

The poisoning effect of PbO and PbCl 2 on CeO 2 -TiO 2 catalyst for selective catalytic reduction of NO with NH 3 was investigated and compared. Both Pb species could deactivate the CeO 2 -TiO 2 catalyst and PbO had a stronger poisoning effect than PbCl 2 . From the characterization results of BET, XRD, XPS, NH 3 -TPD and H 2 -TPR, it was concluded that the more serious deactivation by PbO could be ascribed to smaller BET surface area, fewer surface Ce 3+ and chemisorbed oxygen, stronger interaction between PbO and CeO 2 -TiO 2 catalyst, lower redox properties and surface acidity. The in situ DRIFT study results revealed that the NH 3 -SCR reaction over CeO 2 -TiO 2 catalyst was governed by both E-R and L-H mechanisms, which wasn’t changed over the Pb-poisoned samples. The greater loss of Brønsted acid sites attributed to fewer surface Ce 3+ and more serious inhibition of NO oxidation to NO 2 due to fewer surface chemisorbed oxygen were two key factors responsible for more serious deactivation by PbO. Furthermore, the presence of Pb species inhibited the NH 3 adsorption on the Lewis acid sites, aggravating the deactivation of CeO 2 -TiO 2 catalyst. [ABSTRACT FROM AUTHOR]

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]

[Display omitted] • Sulfate increased the adsorption of NH 3 , but the increased NH 3 was not active. • Mo doping could inhibit the sulfation of the catalyst. • Mo doping could alleviate the competitive adsorption among NO x , H 2 O and SO 2. • Mo doping changed the reaction mechanism of CeO 2 -Nb 2 O 5 /TiO 2 catalyst. MoO 3 -doped CeO 2 -Nb 2 O 5 /TiO 2 catalyst was synthesized by a sol–gel method. It was found that Mo doping observably enhanced the tolerance of CeO 2 -Nb 2 O 5 /TiO 2 catalyst to the combined poisoning of H 2 O, SO 2 and K 2 O. Mo doping could restrain the generation of ammonium sulfate and metal sulfate on the surface of the catalyst. This came down to the large specific surface area, strong acidity and superior redox performance of CeO 2 -MoO 3 -Nb 2 O 5 /TiO 2 catalyst. In situ DRIFTS results indicated that K/S/H-CMNT catalyst still proceeded the SCR reaction according to the L-H and E-R mechanisms together, while K/S/H-CNT catalyst only followed the E-R mechanism. Mo doping could enhance the adsorption of NH 3 and NO x species in the presence of K 2 O, H 2 O, and SO 2. [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]

CeO 2 /TiO 2 catalyst is a promising material for realizing the integration of denitrification and mercury removal to reduce mercury emissions. Oxidation mechanism of Hg0 on CeO 2 /TiO 2 (001) surface in the presence of HCl and O 2 was studied by density functional theory (DFT). The results indicated that Hg0 was physically adsorbed on CeO 2 /TiO 2 (001) surface. As an important intermediate, HgCl was adsorbed on the surface of CeO 2 /TiO 2 (001) utilizing enhanced chemisorption, while the adsorption energy of HgCl 2 was only −57.05 kJ/mol. In the absence of HCl, mercury oxidation followed the Mars-Maessen mechanism with a relatively high energy barrier, and the product (HgO) was difficult to desorb, which hindered the reaction process. When HCl existed, reactive chlorine (Cl*) would be produced by the dissociation of HCl, and the mercury oxidation would follow the Langmuir-Hinshelwood mechanism. The co-existence of HCl and O 2 had no significant effect on the adsorption of Hg0, but reduced the reaction energy barrier and the final product (HgCl 2) was more easily desorbed from the catalyst surface. In addition, two complete cyclic reaction pathways for catalytic oxidation of Hg0 on CeO 2 /TiO 2 (001) surface were constructed to clarify the detailed reaction process. [Display omitted] • Hg0 oxidation mechanism on CeO 2 /TiO 2 (001) surface was studied by DFT calculation. • Difficult formation and desorption of HgO result in low oxidation efficiency. • HCl and O 2 could significantly reduce the reaction energy barrier. • Hg0 oxidation by HCl followed Langmuir-Hinshelwood mechanism. • Two complete catalytic cycles were constructed to understand the reaction pathway. [ABSTRACT FROM AUTHOR]

[Display omitted] • The inhibition of K on the evolution of NH 2 NO is the main cause of CT inactivation. • Impeded formation of NO 2 explains the apparent decrease in low-temperature activity. • K inhibits the adsorption and activation process of NH 3 on the CT catalyst. • K promotes the adsorption and decomposition of O 2 on the CT catalyst. K species can cause severe deactivation of CeO 2 /TiO 2 NH 3 -SCR catalyst. In this work, the effects of K on the adsorption and activation of reactive species, the evolution of intermediates, and the surface reactions on the CT catalyst were systematically studied using DFT calculations. The adsorption of K caused the recombination of surface electrons, resulting in the active sites Ce and O getting electrons from K and becoming less reactive, which inhibited the adsorption and activation of NH 3. The presence of K could promote the adsorption of NO and O 2 , and the decomposition of O 2. But most of the adsorbed NO and O 2 would transform into inactive NO x species, and then cover the active sites on the surface. The continuous dehydrogenation reaction of NH 3 was suppressed, thereby hindering the formation of NH 2. The formation and decomposition of the intermediate NH 2 NO were both inhibited, which seriously affected the reduction of NO. In addition, the formation of NO 2 involved in the fast-SCR reaction was inhibited, which is the main reason for the deactivation of CT catalysts at low temperatures. [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]

• The modification of CeO2/TiO2 catalyst with W could neutralize its deactivation by PbO. • The amount of brønsted acid sites increased significantly ascribed to increased surface Ce3+and the highly dispersed W species. • The oxidation of NO to NO2 was motivated after w doping. • The PbO resistance mechanism of W was proposed. The novel CeO 2 /TiO 2 catalysts were modified by W in this work. It revealed that W modification could significantly facilitate the capacity of CeO 2 /TiO 2 catalyst for resisting Pb poisoning. And various characterizations were applied to explore the underlying resistance mechanism. XPS and H 2 -TPR analysis revealed that the W modification promoted the transformation from surface Ce4+ to Ce3+. Then the increased surface Ce3+ along with highly dispersed W species provided more Brønsted acid sites for NH 3 adsorption on the surface of CeO 2 /TiO 2 catalyst (NH 3 -TPD and DFT). By XPS and NO+O 2 co-adsorption results, the oxidation of NO to NO 2 was motivated due to the increased surface chemisorbed oxygen. Furthermore, both E-R and L-H mechanisms were suitable for the NH 3 -SCR reaction over CWT and CT catalysts according to in situ DRIFT analysis. The deposition of PbO merely inhibited the NH 3 and NO x adsorption, while the NH 3 -SCR mechanism wasn't changed. [ABSTRACT FROM AUTHOR]