Low-temperature Pd/FER NOx adsorbers: Operando FT-IR spectroscopy and performance analysis

Pd/FER vs Pd/SSZ-13 Passive NOx Adsorbers: Adsorbate-controlled Location of Atomically Dispersed Pd(II) in FER Determines High Activity and Stability

“…Furthermore, ammonia cannot be delivered successfully to the catalyst at temperatures <180ºC when urea is used as the source of ammonia. In order to address the low-temperature cold start problem, Pd/zeolite materials were introduced as passive NOx adsorbers (PNA) [6][7][8][9][10][11][12][13][14][15][16][17][18][19][20][21][22]. Conceptually, NOx is adsorbed at low temperature and released at temperatures when Cu/SSZ-13 is active for SCR (200ºC and higher).…”

“…As it was recently shown, the active sites in these Pd-containing materials are isolated Pd ions located in the micropores of various zeolites [6][7][8][9][10][11][12][13][14][15][16][17][18][19][20]. Various structure-adsorption property relationships have been revealed for a range of Pd/zeolite materials (SSZ-13, BEA, MFI, MWW, SSZ-39) and guidelines for the preparation of highloadings of atomically dispersed materials have been disclosed [6][7][8][9][10][11][12][13][14][15][16][17][18][19][20][21][22][24][25][26][27]. More recently, FER materials were used to support Pd and their PNA performance has been evaluated [21,22].…”

“…Various structure-adsorption property relationships have been revealed for a range of Pd/zeolite materials (SSZ-13, BEA, MFI, MWW, SSZ-39) and guidelines for the preparation of highloadings of atomically dispersed materials have been disclosed [6][7][8][9][10][11][12][13][14][15][16][17][18][19][20][21][22][24][25][26][27]. More recently, FER materials were used to support Pd and their PNA performance has been evaluated [21,22]. Despite this success, there remains a formidable challenge to produce materials that 1) retain hydrothermal stability up to 800⁰C; 800 ⁰C hydrothermal aging is an expedited aging protocol to simulate end of useful life for a material (such a benchmark would circumvent potential degradation stimulated by diesel particulate filter (DPF) regeneration since maximum exhaust gas temperatures reach up to ~700⁰C during this process) 2) perform well in the presence of elevated levels of CO during cold start from a few hundred to a few thousand ppm, and 3) exhibit excellent performance during consecutive PNA cycles and be regenerable.…”

Identification of Ru/Ceria Among Single Atom Ceria Catalysts as a Stable and Superior Material for Abatement of Diesel and Gasoline Engine Pollutants

“…However, during vehicle cold-start and idle operation the temperatures of exhaust are lower (~100-120 ºC) and no known catalyst can catalyse NOx removal at this temperature. In order to circumvent this important issue and trap significant NOx emissions during cold start, low-temperature passive NOx adsorber (PNA) formulations have been disclosed in the last few years [7][8][9][10][11][12][13][14][15][16][17][18][19][20][21][22][23][24][25][26]. These formulations can store NOx at low temperatures (~100 ºC) and release them continuously at higher temperatures > 180 ºC when Cu/zeolite SCR catalysts become active.…”

“…Unfortunately, those materials store only relatively low amounts of NOx and not always hydrothermally stable. The Jonson-Matthey team, first, and then others reported Pd/zeolite formulations [7][8][9][10][11][12][13][14][15][16][17][18][19][20][21][22][23][24][25][26] on SSZ-13, BEA and ZSM-5 zeolites, with considerable NOx storage at 100 °C and release above 200 °C. We recently optimized those formulations and produced high loadings of atomically dispersed Pd(II) species in zeolites SSZ-13, SSZ-39 BEA and FER which as we showed turned out to be the truly active NOx storage sites [8-11, 13, 15, 19].…”