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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.