A study on deactivation of V2O5-WO3-TiO2 SCR catalyst by alkali metals during entrained-flow combustion

To study the deactivation mechanism of V2O5-WO3-TiO2 SCR catalyst by alkali metals, an entrained flow combustion system is built, and the deactivation process is accelerated by exposing the catalyst to aerosols which are generated from combustion of the Zhundong coal sample doped with potassium and sodium salts. As the exposure time and load rate of alkali salt increase, the contamination of catalyst becomes more serious and the activity of catalyst decreases. The poisoning effects of different alkali salts on catalyst follow a sequence of Na2CO3 < K2CO3 < Na2SO4 < K2SO4 < NaCl < KCl. The combined poisoning effect of chlorides of potassium and sodium lies between those of the individual effects. Further investigations are performed on catalyst through NH3-chemisorption test and characterizations of BET, SEM and EDX, XRF, FTIR and XPS. The results show that after exposing to aerosols, the surface of catalyst is contaminated by particles of alkali salts with different morphologies. The decrease of the specific surface area and the masking of V2O5 can cause the mechanical deactivation of catalyst. The chemical deactivation also occurs because the deposited particles of alkali salts can coordinate to the hydroxyl groups on the surface and interact with the lattice oxygen in the vanadium species. The chemical deactivation makes the dominant contribution to the activity reduction of the catalyst. (C) 2016 Energy Institute. Published by Elsevier Ltd. All rights reserved.