Local ammonia storage and ammonia inhibition in a monolithic copper-beta zeolite SCR catalyst

Selective catalytic reduction of NO with NH ₃ was studied on a Cu-beta zeolite catalyst, with specific focus on the distributed NH ₃ capacity utilization and inhibition. In addition, several other relevant catalyst parameter distributions were quantified including the SCR zone, or catalyst region where SCR occurs, and NO and NH ₃ oxidation. We show that the full NH ₃ capacity (100% coverage) is used within the SCR zone for a range of temperatures. By corollary, unused NH ₃ capacity exists downstream of the SCR zone. Consequently, the unused capacity relative to the total capacity is indicative of the portion of the catalyst unused for SCR. Dynamic NH ₃ inhibition distributions, which create local transient conversion inflections, are measured. Dynamic inhibition is observed where the gas phase NH ₃ and NO concentrations are high, driving rapid NH ₃ coverage buildup and SCR. Accordingly, we observe dynamic inhibition at low temperatures and in hydrothermally aged states, but predict its existence very near the catalyst front in higher conversion conditions where we did not specifically monitor its impact. While this paper addresses some general distributed SCR performance parameters including Oxidation and SCR zone, our major new contributions are associated with the NH ₃ capacity saturation within the SCR zone and dynamic inhibition distributions and the associated observations. These new insights are relevant to developing accurate models, designs and control strategies for automotive SCR catalyst applications.