Low temperature NOx storage on zeolite supported Pd for low temperature diesel engine emission control

2018 Spring Symposium

L. Mantaroşie1, H.Y. Chen2, J. Collier1, D. Liu2, D. Duran-Martin1, V. Novak1, R. R. Rajaram1 and D. Thompsett1
1Johnson Matthey Technology Centre, Sonning Common, Reading, RG4 9NH, UK
2Johnson Matthey Inc., Emission Control Technology, Wayne, PA 19087, USA

Abstract – Recent legislation requirements have turned controlling NOx emissions into one of the biggest technical challenges facing car manufacturers [1]. At present, the main technologies available for this application are NO x storage and reduction (NSR) or urea based selective catalytic reduction (SCR) [2,3]. Both technologies can achieve high NO x reduction efficiencies once they reach their operating temperature (typically 200°C or higher). During cold start, when the exhaust temperature is below 200°C, both systems are less efficient at NOx removal.

To meet the NOx emission standards during the cold start (<200°C) a new concept has been introduced: passive NOx adsorbers (PNA) [4]. These are materials which store NOx (mainly as NO) at low temperatures and then thermally release the stored NOx once the downstream NOx reduction catalyst (NSR or SCR) reaches its operating temperature.

This contribution will report the remarkable ability of zeolite supported Pd to store NO with very high trapping efficiency at temperatures below 200°C and conditions that simulate real exhaust from diesel engines. The study will focus on the characterization of the Pd storage sites on zeolites compared to oxide supports and understanding unique nature of the active species in these materials. The properties of palladium supported on three different zeolites of various pore sizes (CHA, MFI and BETA) will be compared to classical oxidic supports (Al2O3 and CeO2).

Also, with the aim of providing insight into the behaviour of these materials during engine operation, the evolution of the NO storage sites under various gas feed compositions has been probed through combined “operando” IR and XAS experiments. The findings of these study will be discussed in relation to the realistic operation of the novel PNA technology.

References:
[1] L. Yang, V. Franco, A. Campestrini, J. German, P. Mock, ICCT report on NOX control technologies for Euro 6 Diesel passenger cars, 2015
[2] W.S. Epling, L.E. Campbell, A. Yezerets, N.W. Currier, J. E. Parks II, Catalysis Reviews, 163 (2004) 46.
[3] I. Nova, E. Tronconi (Eds.) Urea-SCR Technology for deNOx After Treatment of Diesel Exhausts, Springer New York, 2014.
[4] E. Melville, R.J. Brisley, O. Keane, P.R. Phillips, and E.H. Mountstevens, US patent 8, 105, 559, 2007