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Here, we investigate competitive adsorption and photocatalytic reaction over TiO 2 @SiO 2 : NO conversion efficiency decreases by 29.1%, and the adsorption capacity decreases from 0.125 to 0.095 mmol/g due to the influence of SO 2 . According to identification and comparative analysis of the IR signal, SO 2 has little effect on the NO conversion route and intermediates (adsorbed NO → nitrite → nitrate), but accelerates the deactivation of catalysts. The electronic interaction scheme from density functional theory (DFT) confirms that surface hydroxyls create an unsaturated coordination of neighboring Ti or O atoms, which is favorable for NO/SO 2 adsorption on anatase (101). In addition, the lone pair electrons of N or S atoms prefer to be delocalized and form covalent bonds with active surface-O on the (101) facet with terminal hydroxyls. However, preadsorbed SO 2 could offset the increase of hydroxyls and strongly inhibit NO adsorption, which is consistent with the result performance evaluation. A possible reaction mechanism characterized by oxygen vacancies and·O 2 - is proposed, while the essential reason of catalyst deactivation and regeneration is theoretically analyzed based on the experimental and DFT calculation.

Catalytic combustion technology is one of the effective methods to remove VOCs such as toluene from industrial emissions. The decomposition of an aromatic ring via catalyst oxygen vacancies is usually the rate-determining step of toluene oxidation into CO 2 . Series of CeO 2 probe models were synthesized with different ratios of surface-to-bulk oxygen vacancies. Besides the devotion of the surface vacancies, a part of the bulk vacancies promotes the redox property of CeO 2 in toluene catalytic combustion: surface vacancies tend to adsorb and activate gaseous O 2 to form adsorbed oxygen species, whereas bulk vacancies improve the mobility and activity of lattice oxygen species via their transmission effect. Adsorbed oxygen mainly participates in the chemical adsorption and partial oxidation of toluene (mostly to phenolate). With the elevated temperatures, lattice oxygen of the catalysts facilitates the decomposition of aromatic rings and further improves the oxidation of toluene to CO 2 .

In this study, the poisoning effects of SO 2 on the V 2 O 5 -WO 3 /TiO 2 (1%VWTi) and CeO 2 -WO 3 /TiO 2 (5%CeWTi) selective catalytic reduction (SCR) catalysts were investigated in the presence of steam, and also the regeneration of deactivated catalysts was studied. After pretreating the catalysts in a flow of NH 3 + SO 2 + H 2 O + O 2 at 200 °C for 24 h, it was observed that the low-temperature SCR (LT-SCR) activity decreased significantly over the 1%VWTi and 5%CeWTi catalysts. For 1%VWTi, NH 4 HSO 4 (ABS) was the main product detected after the poisoning process. Both of NH 4 HSO 4 and cerium sulfate species were formed on the poisoned 5%CeWTi catalyst, indicating that SO 2 reacted with Ce 3+ /Ce 4+ , even in the presence of high concentration of NH 3 . The decrease of BET specific surface area, NO x adsorption capacity, the ratio of chemisorbed oxygen, and reducibility were responsible for the irreversible deactivation of the poisoned 5%CeWTi catalyst. Meanwhile, the LT-SCR activity could be recovered over the poisoned 1%VWTi after regeneration at 400 °C, but not for the 5%CeWTi catalyst. For industrial application, it is suggested that the regeneration process can be utilized for 1%VWTi catalysts after a period of time after NH 4 HSO 4 accumulated on the catalysts.

A CeO 2 -WO 3 /TiO 2 -SiO 2 catalyst was employed to investigate the poisoning mechanisms of Pb and SO 2 during selective catalytic reduction (SCR). The introduction of Pb and SO 2 suppressed the catalytic performance by decreasing the numbers of surface acid and redox sites. Specifically, Pb preferentially bonded with amorphous WO 3 species rather than with CeO 2 , decreasing the numbers of both Lewis and Brønsted acid sites but exerting less influence on the reducibility. SO 2 preferentially bonded with CeO 2 as sulfate species rather than with WO 3 , leading to a significant decrease in reducibility and the loss of surface active oxygen groups. Although SO 2 provided additional Brønsted acid sites via the interaction of SO 4 2- and CeO 2 , it had little positive effect on catalytic activity. A synergistic deactivation effect of Pb and SO 4 2- on CeO 2 was found. Pb covered portions of the weakly bonded catalyst sites poisoned by SO 4 2- , which increased the decomposition temperature of the sulfate species on the catalyst.

Phosphorus compounds from flue gas have a significant deactivation effect on selective catalytic reduction (SCR) DeNOx catalysts. In this work, the effects of phosphorus over three catalysts (CeO2, CeO2-MoO3, and V2O5-MoO3/TiO2) for NH3-SCR were studied, and characterizations were performed aiming at a better understanding of the behavior and poisoning mechanism of phosphorus over SCR catalysts. The CeO2-MoO3 catalyst showed much better catalytic behavior with respect to resistance to phosphorus and N2 selectivity compared with V2O5-MoO3/TiO2 catalyst. With addition of 1.3 wt % P, the SCR activity of V2O5-MoO3/TiO2 decreased dramatically at low temperature due to the impairment of redox property for NO oxidation; meanwhile, the activity over CeO2 and CeO2-MoO3 catalysts was improved. The superior NO oxidation activity contributes to the activity over P-poisoned CeO2 catalyst. The increased surface area and abundant acidity sites contribute to excellent activity over CeO2-MoO3 catalyst. As the content of P increased to 3.9 wt %, the redox cycle over CeO2 catalyst (2CeO2 ↔ Ce2O3 + O*) was destroyed as phosphate accumulated, leading to the decline of SCR activity; whereas, more than 80% NOx conversion and superior N2 selectivity were obtained over CeO2-MoO3 at T > 300 °C. The effect of phosphorus was correlated with the redox properties of SCR catalyst for NH3 and NO oxidation. A spillover effect that phosphate transfers from Ce to Mo in calcination was proposed.

The performances of fresh and sulfated MnOx-CeO₂ catalysts for selective catalytic reduction of NOx by NH₃ (NH₃-SCR) in a low-temperature range (T < 300 °C) were investigated. Characterization of these catalysts aimed at elucidating the role of additive and the effect of sulfation. The catalyst having a Sn:Mn:Ce = 1:4:5 molar ratio showed the widest SCR activity improvement with near 100% NOx conversion at 110-230 °C. Raman and X-ray photoelectron spectroscopy (XPS) indicated that Sn modification significantly increases the concentration of oxygen vacancies that may facilitate NO oxidation to NO₂. NH₃-TPD characterization showed that the low-temperature NH₃-SCR activity is well correlated with surface acidity for NH3 adsorption, which is also enhanced by Sn modification. Furthermore, as compared to MnOx-CeO₂, Sn-modified MnOx-CeO₂ showed remarkably improved tolerance to SO₂ sulfation and to the combined effect of SO₂ and H₂O. In the presence of SO₂ and H₂O, the Sn-modified MnOx-CeO₂ catalyst gave 62% and 94% NOx conversions as compared to 18% and 56% over MnOx-CeO₂ at temperatures of 110 and 220 °C, respectively. Sulfation of SnO₂-modified MnOx-CeO₂ may form Ce(III) sulfate that could enhance the Lewis acidity and improve NO oxidation to NO₂ during NH₃-SCR at T > 200 °C.