Zeolite Beta Doped with La, Fe, and Pd as a Hydrocarbon Trap

Abstract

Hydrocarbon trapping is a technique of great relevance, since a substantial part of hydrocarbon emissions from engines are released from engines before the catalyst has reached the temperature for efficient conversion of the hydrocarbons. In this work, the influence of doping zeolite beta (BEA) with Fe, Pd, and La on the storage and release of propene and toluene is studied. Five monolith samples were prepared; Fe/BEA, La/BEA, Pd/BEA, Pd/Fe/BEA, and Pd/La/BEA using incipient wetness impregnation, and the corresponding powder samples were used for catalyst characterization by Inductively coupled plasma sector field mass spectrometry (ICP-SFMS), Temperature-programmed oxidation (TPO), X-ray photoelectron spectroscopy (XPS) and Scanning transmission electron microscopy with Energy dispersive X-ray analysis (STEM-EDX). The hydrocarbon trapping ability of the samples was quantified using Temperature-programmed desorption (TPD) of propene and toluene, and in situ Diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS). The results from the TPD experiments show that the addition of Pd and La to the zeolite affected the release patterns of the stored hydrocarbons on the trapping material in a positive way. The in situ DRIFTS results indicate that these elements provide H-BEA with additional sites for the storage of hydrocarbons. Furthermore, EDX-mapping showed that the La and Pd are located in close connection.

Analysis of Ion-Exchanged ZSM-5, BEA, and SSZ-13 Zeolite Trapping Materials under Realistic Exhaust Conditions

“…The one exception to this observation is that Ag/ZSM-5 uptakes 5.0 mmols C 1 /g cat compared to 4.3-4.4 for the other ZSM-5 samples. Enhanced uptake capacity in the presence of Ag has been reported elsewhere [27,40,51], so it is interesting that we do not observe it in this study. A likely explanation is the large size and concentration of the decane molecule used here overwhelming the adsorption sites and zeolite pores; most prior work reporting these benefits of metals focused on shorter hydrocarbon lengths [27,40,51,52] ) minutes for each of the materials studied.…”

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

“…S1,2). In the previous studies [6][7][8][9][10][11][12][13][14][15][16][17][18][19], CO levels around ~200-250 ppm were used during NOx adsorption tests. However, there is continuous interest to test the performance in the presence of higher CO levels that are most relevant during cold start.…”

“…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].…”

“…We show the excellent performance of these materials under practically relevant conditions. Moreover, due to the presence of a specific Pd site in the FER micropores not accessible to water during hydrothermal aging at 800ºC (and even 850 ⁰C) in 10% H2O/O2/N2 mix for 16 hours, no changes in the adsorption of NOx occur, a feature that has not been previously achieved with any PNA material [6][7][8][9][10][11][12][13][14][15][16][17][18][19]. Although previously Pd/SSZ-39 [14]showed stability of NOx uptake after aging at 800ºC, the NOx release profile broadened and shifted to higher temperatures which was not desirable (at CO levels ~250 ppm in [14]).…”