H-BEA and Fe-BEA were experimentally studied for selective catalytic reduction of NOx using ammonia (NH3-SCR) with a focus on the chemical deactivation caused by potassium exposure where cordierite-supported H-BEA and Fe-BEA samples were exposed to 10 or 50 ppm KNO3 for 14, 24 and 48h in a continuous gas flow reactor at 350 degrees C. The samples were catalytically evaluated and characterized using a flow-reactor system and X-ray photoelectron spectroscopy. The results show that new NOx storage sites are formed on the expense of Bronsted acid sites for ammonia storage for all potassium-exposed samples. The formation of new NOx storage sites results in increased NH3-SCR activity for the potassium-exposed H-BEA samples. However, for the potassium-exposed Fe-BEA samples, the results show a significant decrease in SCR activity. Deconvolution of the Fe 2p(3/2) XPS peak shows a clear increase in the relative amount of Fe3+ for the potassium-exposed Fe-BEA samples, indicating that isolated iron species active for NH3-SCR are exchanged with potassium, forming smaller trivalent iron clusters inside the zeolite pores. Transient experiments during NH3-SCR show that the decrease in ammonia storage capacity due to potassium exposure results in a decreased period with improved NO reduction after NH3 cut-off. (C) 2014 Elsevier B.V. All rights reserved.