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.

[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