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

Selective catalytic reduction of NO with NH3 was studied on a Cu-beta zeolite catalyst, with specific focus on the distributed NH3 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 NH3 oxidation. We show that the full NH3 capacity (100% coverage) is used within the SCR zone for a range of temperatures. By corollary, unused NH3 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 NH3 inhibition distributions, which create local transient conversion inflections, are measured. Dynamic inhibition is observed where the gas phase NH3 and NO concentrations are high, driving rapid NH3 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 NH3 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.

[1]  I. Moon,et al.  Kinetic studies of reduction of nitric oxide with ammonia on Cu2+-exchanged zeolites , 1994 .

[2]  P. Smirniotis,et al.  Selective Reduction of NO with CO Over Titania Supported Transition Metal Oxide Catalysts , 2008 .

[3]  Ashok Gopinath,et al.  A Kinetic Model for the Selective Catalytic Reduction of NOx with NH3 over an Fe-zeolite Catalyst , 2010 .

[4]  E. Tronconi,et al.  NH3–NO/NO2 chemistry over V-based catalysts and its role in the mechanism of the Fast SCR reaction , 2006 .

[5]  G. Deo,et al.  Reactivity of V2O5Catalysts for the Selective Catalytic Reduction of NO by NH3: Influence of Vanadia Loading, H2O, and SO2 , 1996 .

[6]  James W. Girard,et al.  Combined Fe-Cu SCR Systems with Optimized Ammonia to NOx Ratio for Diesel NOx Control , 2008 .

[7]  Christine Kay Lambert,et al.  Enhanced Durability of a Cu/Zeolite Based SCR Catalyst , 2008 .

[8]  R. T. Yang,et al.  Activity, stability and hydrocarbon deactivation of Fe/Beta catalyst for SCR of NO with ammonia , 2009 .

[9]  Lothar Mussmann,et al.  Investigation of the selective catalytic reduction of NO by NH3 on Fe-ZSM5 monolith catalysts , 2006 .

[10]  Junhui Li,et al.  Heat of adsorption for NH3, NO2 and NO on Cu-Beta zeolite using microcalorimeter for NH3 SCR applications , 2010 .

[11]  G. Centi,et al.  Adsorption and reactivity of NO on copper-on-alumina catalysts. I: Formation of nitrate species and their influence on reactivity in NO and NH3 conversion , 1995 .

[12]  Jae-Soon Choi,et al.  NH3 formation and utilization in regeneration of Pt/Ba/Al2O3 NOx storage-reduction catalyst with H2 , 2009 .

[13]  Jae-Soon Choi,et al.  Sulfur impact on NOx storage, oxygen storage, and ammonia breakthrough during cyclic lean/rich operation of a commercial lean NOx trap , 2007 .

[14]  Wei Li,et al.  Spatially resolving SCR reactions over a Fe/zeolite catalyst , 2011 .

[15]  E. Tronconi,et al.  The chemistry of the NO/NO2–NH3 “fast” SCR reaction over Fe-ZSM5 investigated by transient reaction analysis , 2008 .

[16]  N. Topsoe.  Characterization of the nature of surface sites on vanadia-titania catalysts by FTIR , 1991 .

[17]  Koji Yokota,et al.  The new concept 3-way catalyst for automotive lean-burn engine: NOx storage and reduction catalyst , 1996 .

[18]  Jae-Soon Choi,et al.  Intra-channel evolution of carbon monoxide and its implication on the regeneration of a monolithic Pt/K/Al2O3 NOx storage-reduction catalyst , 2006 .

[19]  John W. Geus,et al.  Preparation and performance of a silica-supported V2O5 on TiO2 catalyst for the selective reduction of NO with NH3 , 1988 .

[20]  E. Fridell,et al.  Identification of adsorbed species on Cu-ZSM-5 under NH3 SCR conditions , 2007 .

[21]  Todd J. Toops,et al.  Intra-fuel cell stack measurements of transient concentration distributions , 2006 .

[22]  Jyh-Ping Chen,et al.  Role of WO3 in mixed V2O5-WO3/TiO2catalysts for selective catalytic reduction of nitric oxide with ammonia , 1992 .

[23]  Enrico Tronconi,et al.  Study of a Fe–zeolite-based system as NH3-SCR catalyst for diesel exhaust aftertreatment , 2008 .

[24]  B. Coq,et al.  The origin of N2O formation in the selective catalytic reduction of NOx by NH3 in O2 rich atmosphere on Cu-faujasite catalysts , 1999 .

[25]  E. Fridell,et al.  The mechanism for NOx storage , 2000 .

[26]  Jae-Soon Choi,et al.  Spatially resolved in situ measurements of transient species breakthrough during cyclic, low-temperature regeneration of a monolithic Pt/K/Al2O3 NOx storage-reduction catalyst , 2005 .

[27]  Yisun Cheng,et al.  Laboratory Testing of Urea-SCR Formulations to Meet Tier 2 Bin 5 Emissions , 2007 .

[28]  Enrico Tronconi,et al.  NH3‐SCR of NO over a V‐based catalyst: Low‐T redox kinetics with NH3 inhibition , 2006 .

[29]  E. Fridell,et al.  NOx storage in barium-containing catalysts , 1999 .

[30]  E. Tronconi,et al.  Modelling of an SCR catalytic converter for diesel exhaust after treatment: Dynamic effects at low temperature , 2005 .

[31]  Neal W. Currier,et al.  Overview of the practically important behaviors of zeolite-based urea-SCR catalysts, using compact experimental protocol , 2010 .

[32]  S. Bhargava,et al.  Adsorption of NO on Cu exchanged zeolites, an FTIR study: Effects of Cu levels, NO pressure, and catalyst pretreatment , 1996 .

[33]  M. Elsener,et al.  Selective catalytic reduction of NO and NO2 at low temperatures , 2002 .

[34]  E. Tronconi,et al.  A comparative study of the NH3-SCR reactions over a Cu-zeolite and a Fe-zeolite catalyst , 2010 .

[35]  M. Elsener,et al.  Urea-SCR: a promising technique to reduce NOx emissions from automotive diesel engines , 2000 .

[36]  V. Balakotaiah,et al.  Experimental and kinetic modeling study of NO oxidation: Comparison of Fe and Cu-zeolite catalysts , 2012 .

[37]  E. Tronconi,et al.  The NH 3 Inhibition Effect in the Standard SCR Reaction over a Commercial Fe-zeolite Catalyst for Diesel Exhaust Aftertreatment: An Experimental and Modeling Study , 2011 .

[38]  J. Ross,et al.  Mechanistic Aspects of the Selective Reduction of NO by Propene over Alumina and Silver–Alumina Catalysts , 1999 .

[39]  Lothar Mussmann,et al.  Influence of NO2 on the selective catalytic reduction of NO with ammonia over Fe-ZSM5 , 2006 .

[40]  E. Fridell,et al.  Selective catalytic reduction of NOx with NH3 over Cu-ZSM-5—The effect of changing the gas composition , 2006 .

[41]  Louise Olsson,et al.  A kinetic model for ammonia selective catalytic reduction over Cu-ZSM-5 , 2008 .

[42]  R. Heck.  Catalytic abatement of nitrogen oxides–stationary applications , 1999 .