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Enhancing the resistance of SCR (Selective Catalytic Reduction) catalyst to K poisoning can be effectively achieved through modification. This study investigated the impact of transition metal modification on improving the ability of Ce/TiO 2 (CT) catalysts to resist K poisoning by DFT (Density functional theory) calculations. Mo-, Nb-, and W-doping could effectively suppress the adsorption of K. O v (oxygen vacancy) formation and hydrogenation reactions were both facilitated due to the modification of Cu, Co and Sb. The Cu-doping had a significant contribution to the adsorption of NH 3 and NO, and showed the best resistance to K poisoning in the adsorption of reactive species. Additionally, Cu-doping decreased the energy barriers for NH 3 dehydrogenation, NH 2 NO generation and decomposition, and NO 2 formation on CT catalyst, and weakened the inhibition effect of K on the above elementary reactions. Consequently, this provided an effective improvement in the k-poisoning tolerance of the CT catalysts. [Display omitted] • A method for screening modified elements based on DFT calculation was reported. • M-doping benefits hydrogenation, oxygen vacancy formation, and adsorption of NH 3 /NO. • M-doping mitigated the toxic effect of K in adsorption energy and energy barrier. • The modification effect of Cu was better than that of Co, Sb, Mo, Zr, Nb, W. • CCuT extremely weakened the inhibition of E-R and L-H mechanisms by K. [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]

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]

• 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]

[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]

• 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]

[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]

• Major SO 2 deactivation mechanisms of Ce-based catalysts are summarized. • The positive and negative effects of metal sulfates on Ce-based catalysts are discussed. • Regulatory measures against SO 2 poisoning are proposed. Selective catalytic reduction with ammonia (NH 3 -SCR) technology is an effective process for industrial flue gas denitrification. Ce-based catalysts are widely studied due to their excellent redox properties and superior oxygen storage and release capacity (OSC). However, the unavoidable presence of SO 2 and H 2 O in the coal-fired flue gas leads to their limitations in the application of denitrification technology. SO 2 poisoning not only causes the formation of metal sulfates, but its synergistic interaction with H 2 O also results in the deposition of ammonium sulfate species. All this leads to severe deactivation of Ce-based catalysts in NH 3 -SCR. The development of Ce-based catalysts with excellent sulfur and water resistance is an urgent requirement for SCR technology. This review elucidates the poisoning mechanism of SO 2 , and analyzes the effects of metals/non-metals modification and structural optimization on the anti-SO 2 performance of Ce-based catalysts. This provides the reference and guidance for the subsequent development of Ce-based catalysts resistance to SO 2. [Display omitted] [ABSTRACT FROM AUTHOR]