Overview of the practically important behaviors of zeolite-based urea-SCR catalysts, using compact experimental protocol

Selective catalytic reduction with NH3 (NH3-SCR technology), based on V2O5/WO3/TiO2 catalysts, has been previously commercialized for abating NOx emissions from various stationary and mobile lean-burn or diesel engines. However, meeting the uniquely stringent US EPA 2010 regulations for diesel engines required introduction of a new class of SCR catalysts, based on Cu- or Fe-exchanged zeolites. While remarkably active and stable, these new materials proved substantially more difficult than vanadia-based catalysts to operate transiently on the road, due to their much higher NH3 storage. The objective of this work was to develop a concise experimental protocol, elucidating multiple catalytic functions, steady-state and transient, of practical relevance to the mobile SCR applications. This paper provides a comprehensive overview of such functions, using select data from various representative Cu- and Fe-zeolite catalysts. While the bulk of the reported results originated directly from the developed protocol, additional experiments, validating the assumptions or clarifying unexpected experimental observations, are included. (C) 2010 Elsevier B.V. All rights reserved.