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Graphical abstract Highlights • The SCR activity and alkali resistance was tested over a series of vanadia-titania catalysts. • V 4 /Ti catalyst displayed the best performance after doping with potassium. • V4+ species were sensitive to be affected by alkali metals. • Acidity played a critical role in the poisoned catalysts. • Competition of NH 3 oxidation mainly caused the deactivation with V > 4%. Abstract A series of vanadia-titania catalysts with different vanadia loadings for the selective catalytic reduction (SCR) of NO by ammonia was prepared via incipient impregnation method. The alkali resistance and SCR activity at low temperature has been investigated on the prepared catalysts. Increasing the vanadia loading from 1% to 10%, the NO removal efficiency of the catalysts gained a 70% growth at 200 °C. With the increase of the vanadia loading, the high loading vanadia-titania catalysts exhibited higher ratio of V5+/(V4++V5+), which enhanced the oxidation of NH 3 at high temperatures and also improved the standard SCR performance at low temperature. After doping with potassium, V 4 /Ti catalyst (V 2 O 5 = 4 wt%) displayed the best performance over which 80% initial activity was retained from 300 °C to 400 °C. More acid sites and active vanadium species were retained in the high loading vanadia-titania catalysts, which made them exhibit better low temperature alkali resistance. However, when vanadia content was higher than 4%, the competition of NH 3 oxidation severely deactivated the catalytic activity above 250 °C. Additionally, in the presence of SO 2 and H 2 O the SCR performance of the high loading vanadia-titania catalysts were also studied in order to investigate the influence of the actual working conditions. [ABSTRACT FROM AUTHOR]

[Display omitted] • Catalyst high-temperature activity was greatly enhanced through adding HSiW. • Doping HSiW led to the formation of abundant acid sites on the catalyst surfaces. • Adding HSiW lowered the amount and reactivity of catalyst surface oxygen species. • The balance of the acidity and oxidability played a key role in the SCR activity. A series of H 4 SiW 12 O 40 -modified Fe 2 O 3 catalysts were synthesized using the precipitation method. Over 80% NO x conversion was obtained in the temperature region of 250–450 °C for the catalysts with the H 4 SiW 12 O 40 content of 5% and 10%. The relationship between the physicochemical properties and performances of the series catalysts was established. Abundant acid sites were introduced with doping H 4 SiW 12 O 40 , which promoted the adsorption of reductant NH 3 on the catalysts at high-temperature regions. Moreover, adding H 4 SiW 12 O 40 lowered the amount and reducibility of catalyst surface reactive oxygen species, which inhibited the oxidation of NH 3 to NO x at higher temperatures to some extent. Thus, most ammonia species were prone to participating in the reaction with NO x instead of being directly oxidized to NO x in the higher temperature region over the H 4 SiW 12 O 40 -decorated catalysts. And it could be concluded that the balance of the acid and redox properties constituted the main reason for the superior activity of the high H 4 SiW 12 O 40 content catalysts. Additionally, SO 2 exerted a slight and reversible inhibition effect on the catalyst activity at 300 °C, suggesting that HSiW-modified Fe 2 O 3 oxide might be a promising catalyst in practical applications. [ABSTRACT FROM AUTHOR]

A series of V-Ce(SO 4 ) 2 /Ti catalysts for selective catalytic reduction (SCR) of NO with ammonia are prepared by impregnation method. Low temperature SCR activity and alkali resistance of the optimal V-0.5Ce(SO 4 ) 2 /Ti sample are found to be better than on the commercial V-W/Ti catalyst. Also, V-0.5Ce(SO 4 ) 2 /Ti shows an excellent durability in the presence of SO 2 and H 2 O, indicating to have prospects for the industrial application. Based on catalysts characterization and in-situ DRIFTS studies, a higher proportion of surface active oxygen generated by the introduction of Ce and a much faster H 2 reduction point out the improved redox properties of V-0.5Ce(SO 4 ) 2 /Ti, which results in a stronger NO oxidative activation and is confirmed by a more abundant formation of surface NO + and NO 3 − species. When exposed to SCR conditions where both NH 3 and NO are present, this enhanced NO activation can produce more reactive nitrite and/or NO + intermediates which then readily react with adsorbed NH 3 and decompose to N 2 and H 2 O, accounting for the improved SCR activity of V-0.5Ce(SO 4 ) 2 /Ti at low temperatures. The addition of Ce(SO 4 ) 2 also provides abundant reactive acid sites and adsorbed NH 3 species thus increase. Even after Na poisoning, adequate surface acidity and redox properties still remain. Furthermore, relatively higher contents of V-OH are preserved owing to the interaction between Na and O S O, acting as a protection for the active sites. These promotional effects contribute to the better alkali resistance of V-0.5Ce(SO 4 ) 2 /Ti. Therefore, all the results suggest that V-0.5Ce(SO 4 ) 2 /Ti is a promising candidate as a catalyst for NH 3 -SCR in coal-fired power plants, especially under high Na-content conditions. [ABSTRACT FROM AUTHOR]

Arsenic (As) is found to be poisonous to the commercial V 2 O 5 WO 3 /TiO 2 catalysts for selective catalytic reduction of NO x with NH 3 . The NO x conversion of catalysts declines and N 2 O formation dominates at high temperature (above 300 °C) after As poisoning. A series of activity and characterization experiments are applied to reveal the deactivation mechanism caused by As. Results indicate that doping of As on the catalysts, which exists as H 2 AsO 4 − and HAsO 4 2− , doesn’t seriously change surface area of catalysts or TiO 2 phase, but greatly decreases both the Lewis and Brønsted acid sites. It is found that V OH is destroyed and less reactive As OH is newly formed. V OH site is crucial to the NH 3 adsorption and its destruction by As contributes to catalyst deactivation. Besides, stronger oxidizability of catalysts that resulted from more surface-active oxygen aroused by As leads to substantial non-selective catalytic reduction reaction and NH 3 oxidation at high temperature. Both of these two aspects result in lower NO x conversion and higher N 2 O formation. However, SO 4 2− can provide remarkable surface acidities and the sites that destroyed by As can thus be supplied. Benefited from these new reactive acid sites, catalysts with prominent SO 4 2− loading show superior arsenic resistance even with a high As content, which indicate to be a promising anti-poisoning formula. Finally, mechanism of arsenic poisoning and resistance effect of SO 4 2− is proposed based on the above analysis. [ABSTRACT FROM AUTHOR]