Chemical deactivation of H-BEA and Fe-BEA as NH3-SCR catalysts - Effect of potassium

Journal article, 2015

H-BEA and Fe-BEA were experimentally studied for selective catalytic reduction of NOx using ammonia (NH3-SCR) with 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 48 h in a continuous gas flow reactor at 3500C. The samples where 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 Brønsted 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 2p3/2 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.