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Article

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

1
National Transportation Research Center, Oak Ridge National Laboratory, Knoxville, TN 37932, USA
2
Department of Chemical and Biological Engineering, The State University of New York, Buffalo, NY 14260, USA
*
Author to whom correspondence should be addressed.
Currently at Galbraith Laboratories Inc.
Currently at LG Chem Ltd.
Catalysts 2021, 11(4), 449; https://doi.org/10.3390/catal11040449
Received: 4 March 2021 / Revised: 24 March 2021 / Accepted: 26 March 2021 / Published: 31 March 2021

Abstract

:
An industry-defined evaluation protocol was used to evaluate the hydrocarbon trapping (HCT) and passive NOx adsorption (PNA) potential for BEA, ZSM-5, and SSZ-13 zeolites with ion-exchanged Pd or Ag. All materials underwent 700 °C degreening prior to exposure to an industry-derived protocol gas stream, which included NOx, ethylene, toluene, and decane as measured trapping species as well as common exhaust gasses CO, H2O, O2, CO2, and H2. Evaluation showed that BEA and ZSM-5 zeolites were effective at trapping hydrocarbons (HCs), as saturation was not achieved after 30 min of exposure. SSZ-13 also stored HCs but was only able to adsorb 20–25% compared to BEA and ZSM-5. The presence of Ag or Pd did not impact the overall HC uptake, particularly in the first three minutes. Pd/zeolites had significantly lower THC release temperature, and it aided in the conversion of the released HCs; Ag only had a moderate effect in both areas. With respect to NOx adsorption, the level of uptake was much lower than HCs on all samples, and Ag or Pd was necessary with Pd being notably more effective. Additionally, only Pd/ZSM-5 and Pd/SSZ-13 continue to store a portion of the NOx above 200 °C, which is critical for downstream selective catalytic NOx reduction (SCR). Hydrothermal aging (800 °C for 50 h) of a subset of the samples were performed: BEA, Pd/BEA, ZSM-5, Pd/ZSM-5, and Pd/SSZ-13. There was a minimal effect on the HC storage, ~10% reduction in capacity with no effect on release temperature; however, only Pd/SSZ-13 showed significant NOx storage after aging.

1. Introduction

Since the 1970s automotive emissions control has been a continual challenge due to increasing understanding of the hazards of pollutants and subsequently increasing regulatory efforts to lower harmful emissions. Initially, much of the lean-burn automotive emissions reduction was handled through emissions-conscious engine design and the use of a diesel oxidation catalyst (DOC) [1,2,3,4,5,6,7]. However, modern lean-burn emissions control requires a complex approach involving a series of specialized materials [8,9,10,11,12,13,14] to manage the wide variety of pollutants and exhaust conditions due to the increasingly strict emissions standards. These include diesel particulate filters (DPF) and selective catalytic NOx reduction catalysts (SCR), in addition to the DOC.
This emissions control system requires a minimum exhaust temperature to become fully effective, and thus, a significant percentage of the overall emissions occur in the first 1–2 min after starting the engine [15,16,17]. Additionally, improved engine efficiency results in cooler exhaust [18,19,20,21], such that under low load operation the exhaust and catalyst temperatures could temporarily decrease to the point the catalysts are not active in the emissions control system [20]. In most cases temperatures less than 200 °C would be considered a significant challenge for emissions control catalysts [20]. This temperature is typical for DOCs to be able to convert greater than 90% of the exhaust CO and total hydrocarbons (THCs), and above this temperature urea can be injected, which will hydrolyze to NH3 and is used to reduce NOx over the SCR. Development of a solution to these low temperature emissions control challenges is crucial to meeting future emissions requirements [21,22].
One frequently proposed approach to reducing low temperature emissions is the introduction of trapping materials within the emissions control system that would be capable of adsorbing HC and NOx until the catalysts have warmed up enough to become reactive [16,23,24,25,26,27]. Development of effective trapping materials often focuses on three primary factors: (i) a significant adsorption capacity at low temperatures (<200 °C), (ii) a desorption temperature compatible with emissions control active windows (greater than 200 °C), and (iii) suitable durability against hydrothermal aging. With these factors in mind, a variety of zeolites have shown great promise in studies for the adsorption of common exhaust components such as CO, light and heavy HCs [26,27,28,29,30], and NOx species [31,32,33,34]. Unfortunately, many fundamental studies are often conducted in simplified gas streams which result in many questions as to their applicability to automotive systems which can include high concentrations of water and CO2, multiple types of HC species, NOx, CO, and high space velocity. On the other end of the research spectrum, industrially relevant studies are performed with full exhaust gas from engines [35,36,37]. These realistic evaluations show how the materials would work in the application, but the hundreds of different HCs in the exhaust make it difficult to track the individual components. Thus, evaluation of potential trapping materials under complex, yet manageable flow constituents, is necessary to prove feasibility, highlight challenges, and identify which family of exhaust components are most challenging.
With that in mind, we present an evaluation of nine zeolite-based trapping materials utilizing a flow reactor protocol developed by a collaboration of industry, national laboratories, and academic researchers [38,39] to mimic realistic lean-burn automotive exhaust. As described in detail below, this protocol includes the opportunity to simultaneously trap CO, NOx, and three HCs representative of those found in automotive exhaust: ethylene (short-chain alkenes), toluene (aromatics), and decane (long-chain alkanes). ZSM-5, BEA, and SSZ-13 zeolites and two ion-exchange metals, Pd or Ag, were chosen for this study based on previous reports of high storage efficiency and suitable release temperatures [40,41,42,43,44,45,46]. The representative structure of each of these zeolites are shown in Figure 1. Evaluation of both the storage and release characteristics of these materials was performed to elucidate the attributes of each material.

2. Results and Discussion

2.1. Hydrocarbon Trapping

An ideal hydrocarbon trap (HCT) would have high storage below 200 °C and release HCs above 200 °C where a DOC could oxidize them to CO2 and H2O. To understand how the evaluated samples meet these HCT criteria, a systematic analysis routine was employed. Figure 2 shows a characteristic storage and release profile for each of the three trials on Pd/ZSM-5. The difference between the reactor effluent and the bypass gas concentration indicates a large amount of storage on this sample, and we have analyzed this storage in 2 parts. The first portion is 3 min and is related to how much storage would be expected under a typical startup condition [47,48]. It is represented by the blue shading with white dots ( Catalysts 11 00449 i001) in Figure 2a and is quantified in Figure 2b. The second portion up to 30 min is related to total storage capacity (white with blue dots, Catalysts 11 00449 i002, in Figure 2a,b), but as can be seen here, the sample was not fully saturated as the bypass concentration was not reached. After the 30-min storage, the reactant gases are turned off, and the sample is quickly heated to 600 °C. During this portion of the experiment the HCs desorb from the sample, and some of them react to form CO and CO2. As suggested by the protocol [38,39], the release profile is described by three characteristic temperatures. The first is the temperature of 10% release (T10), i.e., the temperature where 10% of the observed desorbed HCs were released. This is also shown in Figure 2a with a dark blue shading () beginning at 30 min (0% release) and continuing to ~33 min (10% release); the temperature is also indicated with a dark blue arrow. Figure 2c indicates this value with the dark blue () portion of the bar. The next segment indicates the temperature of 50% release (T50). In Figure 2a this is represented with the medium blue shading () that reaches from 10% to 50% and the temperature is indicated with medium blue arrow and by the second section of the bar in Figure 2c (). The next segment of interest is for 90% release of the HCs, which is represented by a light blue shading () for the 50–90% release in Figure 2a. The T90 is represented by a light blue arrow in Figure 2a and the top segment of the bar in Figure 2c ().
This approach is used for each of the samples evaluated, and the full bar charts for both HC storage values (mmols C1/gcat) and release temperatures for the degreened samples are shown in Figure 3 with the values listed in Table 1. All the BEA and ZSM-5 samples have similar uptake during the first 3 min with an uptake of 0.9–1.0 mmols C1/gcat. The SSZ-13 samples have notably less uptake with only 0.6–0.7 mmols C1/gcat occurring in the first 3 min. After 30 min the BEA samples store between 4.8 and 5.1 mmols C1/gcat while the ZSM-5 samples have slightly less uptake of 4.3–5.0 mmols C1/gcat. The SSZ-13 samples reach saturation well before 30 min and only uptake a total of 0.9–1.0 mmols C1/gcat after 30 min. These results clearly indicate that the larger pore structures associated with BEA (0.7–0.8 nm) and ZSM-5 (0.5–0.6 nm) allow more uptake of the HCs studied here compared to SSZ-13 (~0.4 nm), which has smaller pores [49,50]. An additional observation is that the presence of Ag or Pd does not generally result in higher uptake of the HCs in any of these samples. The one exception to this observation is that Ag/ZSM-5 uptakes 5.0 mmols C1/gcat 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].
At the end of the storage phase, a portion of the HCs is released, but most of them stay adsorbed until higher temperatures. The temperature of 10% release (T10) is shown in Figure 3 and listed in Table 1, and there are no distinct trends across the nine samples other than that the Pd/zeolites have the lowest T10. Comparing T50s and T90s, the Pd/zeolites continue to show lower release temperatures for the BEA and ZSM-5 samples. Since a small quantity of HCs are adsorbed on the SSZ-13 samples direct comparisons with BEA and ZSM-5 are difficult, but the trend of T90 being the lowest on the Pd sample is consistent. One of the confounding factors in evaluating the samples as we describe here, is that Pd is an excellent oxidation catalyst and the released HCs are readily oxidized over these zeolites in the presence of excess O2 [40]. Thus, even though 90% of the HCs are released below the previously mentioned goal of 200 °C, the ability to convert the HCs directly on the HCT is a desirable feature. The released HC quantity is listed in Table 1, and in each Pd containing sample the released HC is less than the quantity stored at 30 min. This is most apparent in the Pd/BEA where nearly 60% of the released HC is converted. This feature could possibly allow for a smaller DOC, or at least less PGM content to balance the PGM being used in the HCT; this is the focus of a future study of ours. It should be noted that although Ag is not an excellent oxidation catalyst, it is expected to catalyze a portion of the stored HCs, and there is evidence of this in the Ag/BEA sample with 12% less HCs observed during the release compared to the uptake. Another key observation in the release temperatures is that both BEA and Ag/BEA release 50% of the HC above 200 °C, and thus many DOCs would be able to oxidize the HCs upon their release. ZSM-5 and Ag/ZSM-5 have similar stability, but their T50s are 190 and 185 °C, respectively, and thus not as desirable as the BEA samples. The SSZ-13 zeolites not only store less HCs, but they release nearly all of the HCs by 150 °C, and thus continue to show undesirable HCT properties.

2.2. NO Storage

As discussed above an ideal passive NOx adsorber (PNA) would have high storage below 200 °C and release NOx above 200 °C where a downstream SCR could be used in conjunction with ammonia from hydrolyzed urea. This hydrolysis occurs above 133 °C [53], and the SCR reactivity typically reaches 90% by 180 °C [54,55]. The same systematic analysis procedure described above in the HC section was also used with NOx to understand how the evaluated samples meet the PNA criteria. Figure 4 shows a characteristic NOx storage and desorption profile; Pd/ZSM-5 is shown here, which is the same sample and experiment shown in Figure 2. Notably less NOx is adsorbed than HCs, but the adsorbed NOx is more strongly bound and releases at higher temperatures. Similar to THC, the uptake is divided into two sections, 3 ( Catalysts 11 00449 i003) and 30 ( Catalysts 11 00449 i004) minutes (Figure 4b), and the temperatures of 10%, 50% and 90% NOx release are determined (Figure 4c). The data for all the samples are shown in Figure 5 with the specific values listed in Table 2. From these data two important observations are apparent. First, the Pd-zeolites are the only samples to have significant uptake, and second, only Pd/ZSM-5 and Pd/SSZ-13 maintains 50% of the NOx above 150 °C; in fact, over 50% of the NOx is still on Pd Pd/SSZ-13 at 224 °C. This finding is consistent with other reports of Pd/SSZ-13 being one of the best PNAs [56,57] and that NO storage only occurs on ion-exchanged Pd sites [41]. Neither catalyst closed the NOx balance during release, suggesting there is some direct reduction in the stored NOx from HCs. This typically yields some N2O formation, but this reactor was not equipped with an analyzer that would allow N2O to be measured accurately.

2.3. Hydrothermal Aging

After fully evaluating all the samples, five of the most promising zeolites were hydrothermally aged to investigate their durability. BEA, Pd/BEA, ZSM-5, Pd/ZSM-5, and Pd/SSZ-13 were heated to 800 °C for 50 h and re-evaluated following the same protocols as before. Figure 6 shows the HC metrics for both storage and release with the values listed in Table 3. The amount of deactivation is minimal on storage, as the change is less than 10%. The release temperatures for HCs are also similarly unchanged, as the T10s, T50s, and T90s are generally within a couple degrees of each other. The Pd/ZSM-5 sample did result in a higher release temperature, as the T90 increased from 195 to 216 °C, suggesting its oxidation capability diminished after aging. This is supported by the closer match of storage and release quantities, 4.7 and 4.5 (mmols C1/gcat). However, Pd/BEA maintained a large discrepancy in storage and release values as greater than 50% of the stored HCs are converted during release. In deciding which one of these samples would offer the best HCT functionality, it is clear that each of these hydrothermally aged samples would offer significant HCT capacity. The release profile of unexchanged BEA is slightly more favorable, since ~50% of the stored HCs are released above 200 °C, compared to 185 °C for ZSM-5. If Pd is going to be used for HCTs, Pd/BEA offers significant durability, and although Pd does not aid in the storage capacity, its oxidation capability is valuable with the ability to oxidize over 50% of the stored HCs even after hydrothermal aging.
The NOx storage behavior was notably different after hydrothermally aging. Figure 7 shows the NOx storage and release metrics for the five aged samples with the values shown in Table 4. From these results it is clear only the Pd/SSZ-13 maintains significant NOx storage capacity; in fact, both the storage capacity and release characteristics improve after aging. The storage increased from 0.028 to 0.036 mmols NOx/gcat, and the T50 increased from 224 to 262 °C. Pd/BEA is the only other sample to show storage, but all of the NOx is released before 150 °C. All these results continue to reinforce that Pd/SSZ-13 is the only viable option for PNA amongst the samples studied here.

3. Experimental

3.1. Synthesis of Ion-Exchanged Zeolites

The traps studied here were synthesized by ion-exchange as reported previously [40]. Briefly, commercial BEA (CP814E)-Si/Al = 12.5 and ZSM-5 (CBV 3024E)-Si/Al = 15 zeolites were ion-exchanged with 75 mL of a 0.2 M AgNO3 and 51 mL of a 9.4 mM Pd(NH3)4(NO3)2 stock solution at 60 °C and 80 °C for 24 h, respectively. Prior to ion-exchange the NH4-form zeolites (as purchased from Zeolyst) were converted to their H-form by calcination at 500 °C for 2 h in static air. Single ionic exchange of Ag and Pd with BEA and ZSM-5 zeolites led to the synthesis of 1 wt.% Ag/BEA, 1 wt.% Ag/ZSM-5, 1 wt.% Pd/BEA and 1 wt.% Pd/ZSM-5 catalysts. The samples were filtered, washed with DI water, dried at 100 °C for 8 h and calcined in air at 500 °C for 2 h before further evaluation. For Pd/SSZ-13, an aqueous solution of Pd(NO3)2·2H2O (0.037 mM, 10 mL) was added dropwise to the NH4-SSZ-13-Si/Al = 15 suspension (3.960 g in 50 mL water; 250 RPM stirring) at 80 °C for 20 h. Filtered powder was calcined in air at 500 °C for 5 h. All samples were pelletized to 250–500 μm prior to evaluation. ICP was performed on several of the metal-exchanged materials in this study, and the metal loadings ranged from 0.97–1.07 wt.%, which is in good agreement with the expected value of 1 wt.%.

3.2. Trapping Characterization

Characterization of HC and NOx trapping was conducted utilizing a storage protocol developed by the U.S. DRIVE Advanced Combustion and Emissions Control Technical Team [38,39]. Quartz wool and 100 mg of trapping material were loaded into an 8 mm diameter quartz reactor U-tube to create a plug-flow bed with one K-type thermocouple placed at the center of the bed and another K-type thermocouple approximately 1 cm above the bed to record bed and inlet temperatures, respectively. A visual description of the storage and release characterization is given in Figure 8. All materials were degreened in [O2] = 12%, [CO2] = 6%, and [H2O] = 6% with Ar balance for 4 h at 700 °C prior to evaluation and the gas flow was normalized to 200 L∙g−1 h−1. Water was introduced into the system via a bubbler set to 50.6 °C with heated lines to maintain vapor phase. Decane and toluene were introduced to the reactor similarly via a bubbler at 5 °C. Instrument response time baselines were determined through the reactor bypass by introduction of reactant gasses for 30 min via a 4-way switching valve. NOx concentrations were determined by NOx chemiluminescence analyzer (CLD 822 CM hr; Ecophysics, Dürnten, Switzerland) and the THC concentrations were determined by FID (flame ionization detector, California Analytical HFID-700, Orange, CA, USA) and reported on a C1 basis. As needed, individual HC species were determined by mass spectrometer (Stanford Research Systems RGA 100, Sunnyvale, CA, USA) using m/z = 26, 57, and 91 for ethylene (C2H4), decane (C10H22), and toluene (C7H8), respectively.
Storage and release were characterized sequentially by 30 min exposure of reactant gasses at 80 °C after which the temperature was ramped at 20 °C/min to a maximum temperature of 600 °C in the presence of the O2, CO2, and H2O (Ar balance). Calculation of total reactant storage values and efficiencies were accomplished by subtraction of measured reactor outlet gas concentrations from the baseline, beginning and ending with the moment of valve switching. It should be noted the baseline is measured in the bypass line of the reactor. Release values were calculated by a similar comparison of baseline and reactor values during the 26 min temperature ramp and efficiencies are reported as a percentage of reactant stored. This storage/release procedure was repeated 3 times for each sample and then averaged.
Following the degreened evaluations of the samples, the most promising materials were hydrothermally aged at 800 °C for 50 h in [O2] = 12%, [CO2] = 6%, and [H2O] = 6% with Ar balance. These samples were then re-evaluated according to the procedure outlined above. According to the low-temperature storage protocol [38,39], this time and temperature is intended to stress the materials to a similar level that would be expected at the end of their full-useful-life.

4. Conclusions

Overall, these samples show significant capability to perform both HCT and PNA functionalities. The presence of Ag or Pd does not universally result in increased HC storage, but Pd and its excellent oxidation reactivity aids in the conversion of the released HCs directly on the HCT. The pores of SSZ-13 are too small to store significant quantities of HCs, and thus BEA and ZSM-5 are preferred for HCTs. Pd is crucial for the adsorption of NOx, and under these gas mixtures, Pd/SSZ-13 provides the best storage and release characteristics. Hydrothermal aging largely supports these results with minimal storage losses observed for BEA, Pd/BEA, ZSM-5, Pd/ZSM-5, and Pd/SSZ-13. Only Pd/BEA maintained its HC oxidation reactivity after aging. Pd/SSZ-13 is clearly the only sample evaluated to illustrate reasonable PNA behavior after aging, and in fact its storage capacity increased while its release temperature showed improved characteristics with greater than 50% of the stored NOx being released above 250 °C.

Author Contributions

Conceptualization, T.J.T.; Data curation, T.J.T., A.J.B., P.K. and E.A.K.; Formal analysis, T.J.T. and J.-S.C.; Funding acquisition, T.J.T.; Investigation, T.J.T.; Methodology, T.J.T.; Project administration, T.J.T.; Supervision, T.J.T.; Writing—original draft, T.J.T. and A.J.B.; Writing—review and editing, T.J.T., P.K., E.A.K. and J.-S.C. All authors have read and agreed to the published version of the manuscript.

Funding

Funding for this work was provided by the U.S. Department of Energy’s Vehicle Technologies Office (VTO). The authors greatly appreciate support from Ken Howden, Siddiq Khan, and Gurpreet Singh at VTO.

Data Availability Statement

The data presented in this study are available on request from the corresponding author.

Acknowledgments

This manuscript has been authored by UT-Battelle, LLC, under Contract No. DE-AC0500OR22725 with the U.S. Department of Energy. The publisher, by accepting the article for publication, acknowledges that the United States Government retains a non-exclusive, paid-up, irrevocable, worldwide license to publish or reproduce the published form of this manuscript, or allow others to do so, for the United States Government purposes. The Department of Energy will provide public access to these results of federally sponsored research in accordance with the DOE Public Access Plan (http://energy.gov/downloads/doe-public-access-plan, accessed on 29 March 2021).

Conflicts of Interest

The authors declare no conflict of interest.

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Figure 1. Representation of zeolite structures deployed in this study.
Figure 1. Representation of zeolite structures deployed in this study.
Catalysts 11 00449 g001
Figure 2. (a) THC concentration for each of the three reactor evaluations throughout the 60 min experiment. The shading represents 3 ( Catalysts 11 00449 i001) and 30 ( Catalysts 11 00449 i002) minutes of adsorption during uptake and the zones/temperatures associated with 10% (T10, ), 50% (T50, ), or 90% (T90, ) of THC released during desorption, which are also indicated with arrows. These characteristics are then represented by bar charts for both (b) adsorption and (c) desorption.
Figure 2. (a) THC concentration for each of the three reactor evaluations throughout the 60 min experiment. The shading represents 3 ( Catalysts 11 00449 i001) and 30 ( Catalysts 11 00449 i002) minutes of adsorption during uptake and the zones/temperatures associated with 10% (T10, ), 50% (T50, ), or 90% (T90, ) of THC released during desorption, which are also indicated with arrows. These characteristics are then represented by bar charts for both (b) adsorption and (c) desorption.
Catalysts 11 00449 g002
Figure 3. (a) THC adsorption after 3 ( Catalysts 11 00449 i001) and 30 ( Catalysts 11 00449 i002) minutes for each of the materials studied. (b) The temperature where 10% (T10, ), 50% (T50, ), or 90% (T90, ) of THC is released.
Figure 3. (a) THC adsorption after 3 ( Catalysts 11 00449 i001) and 30 ( Catalysts 11 00449 i002) minutes for each of the materials studied. (b) The temperature where 10% (T10, ), 50% (T50, ), or 90% (T90, ) of THC is released.
Catalysts 11 00449 g003
Figure 4. (a) NOx concentration for each of the three reactor evaluations throughout the 60 min experiment. (b) NOx adsorption after 3 ( Catalysts 11 00449 i003) and 30 ( Catalysts 11 00449 i004) minutes for Pd ZSM-5, and (c) the temperature where 10% (T10, ), 50% (T50, ), or 90% (T90, ) of the NOx is released for PD/ZSM-5.
Figure 4. (a) NOx concentration for each of the three reactor evaluations throughout the 60 min experiment. (b) NOx adsorption after 3 ( Catalysts 11 00449 i003) and 30 ( Catalysts 11 00449 i004) minutes for Pd ZSM-5, and (c) the temperature where 10% (T10, ), 50% (T50, ), or 90% (T90, ) of the NOx is released for PD/ZSM-5.
Catalysts 11 00449 g004aCatalysts 11 00449 g004b
Figure 5. (a) NOx adsorption after 3 ( Catalysts 11 00449 i003) and 30 ( Catalysts 11 00449 i004) minutes for each of the materials studied. (b) The temperature where 10% (T10, ), 50% (T50, ), or 90% (T90, ) of the NOx is released.
Figure 5. (a) NOx adsorption after 3 ( Catalysts 11 00449 i003) and 30 ( Catalysts 11 00449 i004) minutes for each of the materials studied. (b) The temperature where 10% (T10, ), 50% (T50, ), or 90% (T90, ) of the NOx is released.
Catalysts 11 00449 g005aCatalysts 11 00449 g005b
Figure 6. Following hydrothermal aging at 800 °C for 50 h (a) THC adsorption after 3 ( Catalysts 11 00449 i001) and 30 ( Catalysts 11 00449 i002) minutes for each of the materials studied, and (b) the temperature where 10% (T10, ), 50% (T50, ), or 90% (T90, ) of THC is released.
Figure 6. Following hydrothermal aging at 800 °C for 50 h (a) THC adsorption after 3 ( Catalysts 11 00449 i001) and 30 ( Catalysts 11 00449 i002) minutes for each of the materials studied, and (b) the temperature where 10% (T10, ), 50% (T50, ), or 90% (T90, ) of THC is released.
Catalysts 11 00449 g006aCatalysts 11 00449 g006b
Figure 7. Following hydrothermal aging at 800 °C for 50 h (a) NOx adsorption after 3 ( Catalysts 11 00449 i003) and 30 ( Catalysts 11 00449 i004) minutes for each of the materials studied, and (b) the temperature where 10% (T10, ), 50% (T50, ), or 90% (T90, ) of the NOx is released.
Figure 7. Following hydrothermal aging at 800 °C for 50 h (a) NOx adsorption after 3 ( Catalysts 11 00449 i003) and 30 ( Catalysts 11 00449 i004) minutes for each of the materials studied, and (b) the temperature where 10% (T10, ), 50% (T50, ), or 90% (T90, ) of the NOx is released.
Catalysts 11 00449 g007aCatalysts 11 00449 g007b
Figure 8. Storage and release characterization protocol (left) and gas concentrations (right). *—hydrocarbons are listed on a C1 basis.
Figure 8. Storage and release characterization protocol (left) and gas concentrations (right). *—hydrocarbons are listed on a C1 basis.
Catalysts 11 00449 g008
Table 1. THC storage values (mmol/gcat) for ion-exchanged zeolites during lean trapping evaluation after 3 and 30 min; THCs are reported on a C1 basis. The total amount of observed THC released during the first 15 min of the ramp, and the temperature where 10% (T10), 50% (T50), or 90% (T90) of THC is released is also shown.
Table 1. THC storage values (mmol/gcat) for ion-exchanged zeolites during lean trapping evaluation after 3 and 30 min; THCs are reported on a C1 basis. The total amount of observed THC released during the first 15 min of the ramp, and the temperature where 10% (T10), 50% (T50), or 90% (T90) of THC is released is also shown.
LTC-D (Storage)THC StorageTHC ReleaseRelease Temperature
Degreened Zeolite(mmols C1/gcat)(mmols C1/gcat)T10T50T90
3 min30 min15 min(°C)(°C)(°C)
BEA0.95.15.2109205251
Ag/BEA1.05.14.5101203262
Pd/BEA1.04.82.082160170
ZSM-51.04.34.7123190231
Ag/ZSM-51.05.05.0116185224
Pd/ZSM-50.94.43.8105174195
SSZ-130.60.91.091102168
Ag/SSZ-130.71.01.08897164
Pd/SSZ-130.60.90.889100144
Table 2. NOx storage values (mmol/gcat) for ion-exchanged zeolites during lean trapping evaluation after 3 and 30 min. The total amount of observed NOx released during the first 15 min of the ramp, and the temperature where 10% (T10), 50% (T50), or 90% (T90) of NOx is released is also shown.
Table 2. NOx storage values (mmol/gcat) for ion-exchanged zeolites during lean trapping evaluation after 3 and 30 min. The total amount of observed NOx released during the first 15 min of the ramp, and the temperature where 10% (T10), 50% (T50), or 90% (T90) of NOx is released is also shown.
LTC-D (Storage)NOx StorageNOx ReleaseRelease Temperature
Degreened Zeolite(mmols NOx/gcat)(mmols NOx/gcat)T10T50T90
3 min30 min15 min(°C)(°C)(°C)
BEA0.0020.0040.001909090
Ag/BEA0.0020.0070.001909090
Pd/BEA0.0150.0120.00782134178
ZSM-50.0000.0000.000909090
Ag/ZSM-50.0030.0070.000909090
Pd/ZSM-50.0100.0160.00784188294
SSZ-130.0020.0070.0019191198
Ag/SSZ-130.0020.0040.0028888191
Pd/SSZ-130.0280.0280.00889224264
Table 3. THC storage values (mmol/gcat) for hydrothermally aged samples; THCs are reported on a C1 basis. The temperature where 10% (T10), 50% (T50), or 90% (T90) of THC is released is also shown.
Table 3. THC storage values (mmol/gcat) for hydrothermally aged samples; THCs are reported on a C1 basis. The temperature where 10% (T10), 50% (T50), or 90% (T90) of THC is released is also shown.
LTC-D (Storage)NOx StorageNOx ReleaseRelease Temperature
Aged Zeolite(mmols C1/gcat)(mmols C1/gcat)T10T50T90
3 min30 min15 min(°C)(°C)(°C)
BEA0.94.84.9108199248
Pd/BEA0.94.32.185158171
ZSM-50.94.94.8122185226
Pd/ZSM-50.94.74.5121180216
Pd/SSZ-130.50.90.58889154
Table 4. NOx storage values (mmol/gcat) for hydrothermally aged samples. The total amount of observed NOx released during the first 15 min of the ramp, and the temperature where 10% (T10), 50% (T50), or 90% (T90) of NOx is released is also shown.
Table 4. NOx storage values (mmol/gcat) for hydrothermally aged samples. The total amount of observed NOx released during the first 15 min of the ramp, and the temperature where 10% (T10), 50% (T50), or 90% (T90) of NOx is released is also shown.
LTC-D (Storage)StorageReleaseRelease Temperature
Aged Zeolite(mmols NOx/gcat)(mmols NOx/gcat)T10T50T90
3 min30 min15 min(°C)(°C)(°C)
BEA0.0020.0050.002909090
Pd/BEA0.0100.0120.00483103138
ZSM-50.0010.0010.000909090
Pd/ZSM-50.0030.0060.000909090
Pd/SSZ-130.0260.0360.021153262311
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Toops, T.J.; Binder, A.J.; Kunal, P.; Kyriakidou, E.A.; Choi, J.-S. Analysis of Ion-Exchanged ZSM-5, BEA, and SSZ-13 Zeolite Trapping Materials under Realistic Exhaust Conditions. Catalysts 2021, 11, 449. https://doi.org/10.3390/catal11040449

AMA Style

Toops TJ, Binder AJ, Kunal P, Kyriakidou EA, Choi J-S. Analysis of Ion-Exchanged ZSM-5, BEA, and SSZ-13 Zeolite Trapping Materials under Realistic Exhaust Conditions. Catalysts. 2021; 11(4):449. https://doi.org/10.3390/catal11040449

Chicago/Turabian Style

Toops, Todd J., Andrew J. Binder, Pranaw Kunal, Eleni A. Kyriakidou, and Jae-Soon Choi. 2021. "Analysis of Ion-Exchanged ZSM-5, BEA, and SSZ-13 Zeolite Trapping Materials under Realistic Exhaust Conditions" Catalysts 11, no. 4: 449. https://doi.org/10.3390/catal11040449

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