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• 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]

[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]