New insights into the deactivation mechanism of VO-WO/TiO catalyst during selective catalytic reduction of NO with NH: synergies between arsenic and potassium species.

Synergies between arsenic (As) and potassium (K) species in the deactivation of VO-WO/TiO catalyst were investigated. Both arsenic oxide and potassium species presented a serious poisoning impact on catalyst activities, and the extent of poisoning of (As + K) was much stronger than their single superposition. The intrinsic reasons were explored and analyzed by N physisorption, XPS, H-TPR, NH-TPD, NH-DRIFTS and FTIR. Results indicated that BET surface area decreased due to the formation of a dense arsenic coating on the catalyst surface. V-OH active sites were destroyed by arsenic and As-OH acid sites were newly generated. After potassium species were added to arsenic-poisoned catalyst, K further neutralized the As-OH acid sites, and the amount and stability of both Lewis and BrØnsted acid sites decreased more greatly. Potassium also reacted with intermediate NH when the temperature was elevated to higher than 250 °C, which resulted in more NH consumption and NH-SCR reaction inhibition. The extent of deactivation was related to the potassium species when both poisons reacted on the catalyst, and the influence sequence followed AsKS < AsKN < AsKC. AsO + KSO presented the weakest impact among these three poisoned catalysts due to the resistance of SO to arsenic.