ИСТИНА

The selective catalytic reduction of NOx by urea (NH3-SCR) is one of the most effective methods for NOx removal from stationary (power plants, chemical factories, etc.) and mobile (gasoline and diesel engines) sources. However, optimal urea dosing control is quite challenging, since overdosing causes release of harmful NH3 to atmosphere (NH3-slip). In order to remove NOx and at the same time to minimize NH3-slip exhaust gas aftertreatment systems are equipped by ammonia slip catalyst (ASC) installed downstream of the NH3-SCR catalyst [1]. An alternative solution is to use combined systems comprising SCR catalyst and a component responsible for NH3 oxidation in one catalytic block [2]. Thus, mechanical mixture [Mn Ce/CeO2-ZrO2+FeBeta] demonstrates favorable performance in NOx reduction and NH3 oxidation at 180–300 °C [3]. However, at reaction temperatures above 300 °C both NH3-SCR and NH3-slip oxidation are significantly deteriorated, due to overoxidation of ammonia to N2O and NOx on Mn-Ce/CeO2-ZrO2 component. In order to extend the temperature range of the effective catalytic performance we designed a dual-bed system consisting FeBeta zeolite (upstream bed) and mechanical mixture [Mn-Ce/CeO2-ZrO2+FeBeta] (downstream bed). The performance of resulted FeBeta||[Mn-Ce/CeO2-ZrO2+FeBeta] catalyst was studied in NH3-SCR at different NH3/NO ratio (0.8–1.4). Data obtained allow us to conclude that the dual-bed FeBeta||[Mn-Ce/CeO2-ZrO2+FeBeta] catalyst can be considered as a promising system for NOx and residual NH3 simultaneous removal, providing high selectivity to N2 within wide temperature range and upon significant variation of NH3/NO ratio.