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A series of 3DOM Cu-Ce catalysts for CO-SCR were prepared by a colloidal template method. Among these catalysts, 3DOM Cu 1 Ce 1 catalyst exhibited the best CO-SCR performance (about 100 %) in the widest temperature window (450–700 ℃). Notably, this catalyst still showed excellent stability in the presence of H 2 O and SO 2. It was found that the appropriate molar ratio of Cu and Ce could optimize the pores of Cu-Ce catalysts, and increase their specific surface area. This could contribute to the contact between reaction gas and active sites. The stronger synergistic effect between Cu and Ce could be conducive to the increase of chemisorbed oxygen, and then enhance the redox properties. These might be the key factors for the improvement of 3DOM Cu 1 Ce 1 catalytic activity. In addition, the molar ratio of Cu to Ce had a significant influence on the adsorption of CO, which might cause the difference in the consumption of active oxygen and the formation of oxygen vacancies, thus affecting the CO-SCR performance of 3DOM Cu-Ce catalysts. • 3DOM Cu-Ce catalysts with ordered macro- and mesoporous were prepared. • The appropriate molar ratio of Cu to Ce could optimize the pores of catalysts. • The molar ratio of Cu to Ce significantly affected the adsorption of CO. • H 2 O could weaken the toxic effect of SO 2 on 3DOM Cu 1 Ce 1 catalyst. [ABSTRACT FROM AUTHOR]

A series of Ce–Nb–Ti oxide catalysts synthesized by a single step sol-gel (SG) method were evaluated and characterized for selective catalytic reduction (SCR) of NO with ammonia. The experimental results showed that the doping of Nb could enhance the catalytic activity of CeO 2 /TiO 2 significantly. Ce 20 Nb 20 Ti exhibited the best NH 3 –SCR activity and great resistance to high gas hourly space velocity (GHSV), H 2 O, and SO 2. Its superior SCR performance could be ascribed to the better dispersion of Ce, more chemisorbed oxygen species and Ce3+/Ce4+ redox pairs on the catalyst surface, increased redox ability and surface acidity, and strong interaction among Ce, Nb, and Ti species after the introduction of Nb 2 O 5. In situ DRIFT results revealed that the doping of Nb was conducive to the adsorption of NO x and NH 3 species, and enhanced the reaction of pre-adsorbed NH 3 species with NO x species and that of adsorbed NO x species with NH 3 species. Image 1 • A series of Ce–Nb–Ti oxides are synthesized by a sol-gel method for NH 3 –SCR • Ce 20 Nb 20 Ti exhibits superior SCR activity and resistance to H 2 O, SO 2 and high GHSV. • Better dispersion of Ce species, more chemisorbed oxygen, and Ce3+ due to Nb doping. • Enhanced surface acidity and redox ability improve NO x and NH 3 species adsorption. [ABSTRACT FROM AUTHOR]

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]

Chlorine-containing volatile organic compounds (CVOCs) present in industrial exhaust gas can cause great harm to the human body and the environment. In order to further study the catalytic oxidation of CVOCs, an active site regulated RuOx/Sn0.2Ti0.8O2 catalyst with different Ru precursors was developed. With Dichloromethane as the model molecule, the activity test results showed that the optimization of Ru precursor using Ru colloid significantly increased the activity of the catalyst (T90 was reduced by about 90 °C when the Ru loading was 1 wt%). The analysis of characterization results showed that the improvement of the catalytic performance was mainly due to the improvement of the active species dispersion (the size of Ru cluster was reduced from 3–4 nm to about 1.3 nm) and the enhancement of the interaction between the active species and the support. The utilization efficiency of the active components was improved by nearly doubling TOF value, and the overall oxidation performance of the catalyst was also enhanced. The relationship between the Ru loading and the catalytic activity of the catalyst was also studied to better determine the optimal Ru loading. It could be found that with the increase in Ru loading, the dispersibility of RuOx species on the catalyst surface gradually decreased, despite the increase in their total amount. The combined influence of these two effects led to little change in the catalytic activity of the catalyst at first, and then a significant increase. Therefore, this research is meaningful for the efficient treatment of CVOCs and further reducing the content of active components in the catalysts. [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]

[Display omitted] • Mn 5 Cu 1 possessed a unique three-phase coexisting structure. • The strong synergistic effect between Mn and Cu contributed to the excellent catalytic activity. • Appropriate loading of Cu facilitated the adsorption and activation of toluene. • The reaction pathway of toluene oxidation over Mn 5 Cu 1 was investigated. • The oxidation of maleic anhydride to CO 2 was a crucial step of toluene oxidation. A series of Mn-Cu composite oxides with different Mn/Cu molar ratios were synthesized via a facile ethanol-redox precipitation method and investigated for the oxidation of toluene. Among as-synthesized Mn x Cu y catalysts, Mn 5 Cu 1 showed the most excellent toluene catalytic activity at a weight hourly space velocity (WHSV) of 30000 mL∙g−1∙h−1, with 90 % conversion achieved at 212 °C. Furthermore, the Mn 5 Cu 1 catalyst exhibited exceptional thermal stability over a 12-hour period at 215 °C, along with outstanding resistance to H 2 O in the range of 5 vol% to 40 vol%. As characterized by XRD, BET, XPS, EPR, H 2 -TPR, and O 2 -TPD, it was found that Mn 5 Cu 1 possessed a unique three-phase coexisting structure, large specific surface area (57 m2·g−1), plentiful oxygen vacancies, excellent redox capacity, and strong mobility of oxygen, which were attributable to the synergistic effect between Mn and Cu. This strong synergy between Mn and Cu is the underlying reason for the strong catalytic activity of Mn 5 Cu 1. Moreover, toluene-TPD and TPSR results indicated that appropriate Cu loading was favorable for the adsorption and activation of toluene. The potential reaction pathway for toluene oxidation was presented based on in situ DRIFTS characterization. Maleic anhydride was the critical reaction intermediate species. [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]

[Display omitted] • Nb doping enhances the acidity of Ce-Ti catalysts and anti-poisoning performance. • Zn prefers to adsorb around Nb and the Ce sites are further protected by Nb. • Zn species reduce the specific surface area and occupy acidic sites of CNT. • Anions creates new NH 3 adsorption sites but the activation of adsorbed NH 3 is more difficult. The effect of different Zn species (ZnSO 4 , ZnCl 2 , and ZnO) on Nb-doped Ce-Ti catalyst (CNT) was explored with XRD, N 2 physisorption, NH 3 -TPD, H 2 -TPR, XPS, in situ DRIFTS and DFT calculation. The experimental results show that the deactivation rate of CNT by different Zn species was in the order: CNT-ZC > CNT-ZO > CNT-ZS. Nb doping enhanced the acidity of Ce-Ti catalyst and protected Ce active sites from different Zn species. After different Zn species were loaded on CNT, its specific surface area decreased, and the acid sites were occupied. The results from in situ DRIFTS demonstrated that, after anion poisoning, anions (SO 4 2-, O2–, and Cl-) would create new NH 3 adsorption sites while theoretical calculations also indicated that NH 3 adsorption was enhanced by the poisoning of anions, but the activation of adsorbed NH 3 was more difficult. Finally, in situ DRIFTS reveals that the SCR reaction on CNT is still under both E-R and L-H mechanisms. [ABSTRACT FROM AUTHOR]

• Na poisoning mechanism on Ce/TiO 2 (001) surface was studied by DFT calculations. • Ce/TiO 2 (001) surface was easily poisoned due to the high affinity with Na. • Na doping changed the catalyst structure and reduced the reactivity of the surface. • Na poisoning significantly increased the energy barrier of elementary reactions. • Both Eley-Rideal and Langmuir-Hinshelwood mechanisms were inhibited. The presence of alkali metal Na in flue gas can significantly impair the reactivity of Ce/TiO 2 (CT) SCR (Selective Catalytic Reduction) catalyst. This study investigates the deactivation mechanism of Na on the Ce/TiO 2 catalyst using Density Functional Theory (DFT) calculations, focusing on the adsorption of surface species and the pathway of elementary reaction. Due to the high affinity between Na atom and the catalyst surface, Na poisoning readily occurs on Ce/TiO 2 (001) surface. The presence of Na on the catalyst surface hampers hydrogenation, oxygen vacancy formation, and NH 3 adsorption, while also reducing the catalyst's acidity and reducibility. Additionally, Na impedes the NH 3 dehydrogenation reaction, as well as the formation and decomposition of NH 2 NO and the dissociation of O 2 on the catalyst surface, thereby inhibiting the NH 3 -SCR reaction. The inhibition of NO 2 formation further affects the fast SCR reaction, which may explain the low-temperature deactivation of the catalyst. [Display omitted] [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] • 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]

[Display omitted] • CeO 2 -TiO 2 catalyst followed both E-R and L-H mechanisms. • NH 2 NO was an important intermediate in E-R mechanism. • The reaction of adsorbed NO 2 with adsorbed NH 3 was the only form of L-H mechanism. • NH 2 formation from NH 3 dehydrogenation was the rate-limiting step of N 2 formation. The reaction mechanism over CeO 2 -TiO 2 catalyst was investigated using in-situ DRIFTS spectra and density functional theory (DFT) calculations. DRIFTS results revealed that the SCR reactions on CeO 2 -TiO 2 catalyst followed both E-R and L-H mechanisms. In the E-R mechanism, NH 2 NO species was considered as the reaction intermediate that decomposed into H 2 O and N 2. In the L-H mechanism, only adsorbed NO 2 species reacted with NH 3 to generate H 2 O and N 2. Based on the two mechanisms, the corresponding adsorption energy, activation energy barrier, and reaction heat in the process of NH 3 adsorption and activation, NH 2 NO formation and decomposition, O 2 dissociation, and NO oxidation were calculated by DFT. By combining the DRIFTS and DFT results, the detailed reaction pathways over CeO 2 -TiO 2 catalyst were obtained finally. [ABSTRACT FROM AUTHOR]

• K 2 O deactivated Ce-Ti oxide catalyst more seriously than KCl at the same K loading. • Fewer Ce3+ and chemical adsorbed oxygen on the surface of K 2 O-CT. • Lower surface acidity and worse reducibility over K 2 O-CT. • K species inhibited the adsorption of NH 3 and promoted the formation of NO x. Based on experiments and DFT studies, CeO 2 -TiO 2 catalyst was found to be deactivated by KCl or K 2 O, and the poisoning effect of K 2 O was more serious than that of KCl. The characterization results showed that compared with KCl, K 2 O could lead to a greater decrease in surface acidity, reducibility, the ratio of Ce3+/Ce4+ and the concentration of the chemisorbed oxygen on the surface of CeO 2 -TiO 2 catalyst. The results of in situ DRIFT showed that K 2 O had a stronger inhibition effect on NH 3 adsorption on the catalyst surface than KCl. The introduction of K 2 O or KCl promoted the adsorption of NO on the catalyst surface, but not all NO x adspecies were reactive in the NH 3 -SCR reaction. These results were further demonstrated by DFT calculations. The PDOS of different K species doped CeO 2 -TiO 2 catalysts and the adsorption energies of oxygen vacancy, chemisorption oxygen, NH 3 and NO x were calculated by MS DMol3. It was found that the introduction of K species weakened the reactivity of the catalyst surface, inhibited the formation of oxygen vacancies and chemisorption oxygen, and reduced the adsorption of NH 3 on the catalyst surface, all of which led to the decrease in the catalytic activity. [ABSTRACT FROM AUTHOR]

[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]

[Display omitted] • PbO could deactivate CeO 2 -MoO 3 /TiO 2 catalyst greatly. • The amount of Brønsted acid sites decreased greatly ascribed to reduced surface Ce3+and the interaction between PbO and Mo species. • The oxidation of NO to NO 2 was inhibited due to decreased surface chemisorbed oxygen by PbO. • The PbO poisoning mechanism of CeO 2 -MoO 3 /TiO 2 catalyst was proposed. The impact of PbO on CeO 2 -MoO 3 /TiO 2 catalyst for selective catalytic reduction of NO with NH 3 was studied and analyzed with BET, XRD, XPS, NH 3 -TPD, H 2 -TPR and in situ DRIFTS characterizations. The catalytic activity results showed that PbO could greatly deactivate CeO 2 -MoO 3 /TiO 2 catalyst. PbO could interact with Mo species to form PbMoO 4 while inhibit the transformation from surface Ce4+ to Ce3+, which caused a significant decrease in the surface acidity and reducibility of CeO 2 -MoO 3 /TiO 2 catalyst. The oxidation of NO to NO 2 was suppressed owing to a decline in the amount of surface chemisorbed oxygen. Additionally, the adsorption of NH 3 and NO x on Brønsted and Lewis acid sites was restrained. These factors were responsible for the deactivation of CeO 2 -MoO 3 /TiO 2 catalyst by PbO. The in situ DRIFTS results suggested that the NH 3 -SCR reaction on CeO 2 -MoO 3 /TiO 2 catalyst was governed by E-R and L-H mechanisms, which wasn't changed by PbO. [ABSTRACT FROM AUTHOR]