Effects of SO₂ on the low temperature selective catalytic reduction of NO by NH₃ over CeO₂-V₂O₅-WO₃/TiO₂ catalysts

Abstract

CeO₂ improved the De-NO_x activity and sulfur resistance of catalysts.

The De-NO_x activity of 3% CeO₂ -VWT catalyst reached 89.9 % at 140°C.

CeO₂ promoted the oxidation of NO to NO₂ and inspired the fast SCR reaction.

Active components content and BET decreased slightly after entering SO₂.

The largest loss rate was 0.024%/°C at 380°C–390°C in poisoned catalyst.

The CeO₂-V₂O₅-WO₃/TiO₂ (CeO₂-VWT) catalysts were prepared by one-step and two-step impregnation methods. The effects of different loading of CeO₂ and different preparation methods on De-NO_x activity of catalysts had been investigated. CeO₂ helped to improve the De-NO_x activity and sulfur resistance. The optimal loading of CeO₂ was 3% with the De-NO_x efficiency reached 89.9% at 140°C. The results showed that the De-NO_x activity of 3% CeO₂-VWT catalysts by one-step method was the same as two-step method basically and reached the level of industrial applications, the N₂ selectivity of catalysts was more than 99.2% between 110°C and 320°C. In addition, CeO₂ promoted the oxidation of NO to NO₂, which adsorbed on the Lewis acid site (V⁵⁺═O) to form V⁵⁺═NO₃ and inspired the fast SCR reaction. Not only the thermal stability but also the De-NO_x activity of catalysts decreased with excess CeO₂ competed with V₂O₅. Characterizations of catalysts were carried out by XRF, BET, XRD, TG and FT-IR. BET showed that the specific surface area of catalysts decreased with the loading of CeO₂ increased, the active components content and specific surface area of catalysts decreased slightly after entering SO₂. Ammonium sulfate species were formed in poisoned catalyst which had been investigated by XRF, BET, TG and FT-IR. The largest loss rate of weight fraction was 0.024%·°C⁻¹ at 380°C–390°C, which was in accordance with the decomposition temperature of NH₄HSO₄ and (NH₄)₂SO₄.

Graphical abstract

Keywords

Low temperature SCR / De-NO _x activity / Sulfur resistance / Ammonium sulfate

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