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The evaluation of an integrated SCR coated particulate filter Oana Mihai, Stefanie Tamm, Marie Stenfeldt, Carolin Wang-Hansen, and Louise Olsson Ind. Eng. Chem. Res., Just Accepted Manuscript • DOI: 10.1021/acs.iecr.5b02392 • Publication Date (Web): 06 Nov 2015 Downloaded from http://pubs.acs.org on November 18, 2015

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Industrial & Engineering Chemistry Research

The Evaluation of an Integrated SCR-Coated Particulate Filter Oana Mihai1,3, Stefanie Tamm1, Marie Stenfeldt2, Carolin Wang Hansen2, Louise Olsson1,* 1

Chemical Engineering and Competence Centre for Catalysis, Chalmers University of Technology, SE-412 96 Göteborg, Sweden 2 Volvo Cars Corporation, SE-405 31 Göteborg, Sweden 3 Department of Petroleum Processing Engineering and Environmental Protection, Petroleum-Gas University of Ploiesti, 39 Bucuresti Blvd., 100680 Ploiesti, Romania *

Corresponding author:

E-mail address: [email protected], Tel. +46 31-772 4390; fax: +46 31 772 3035.

Abstract In this study, an SCR-coated particulate filter with soot loaded from engine bench experiments was evaluated. Prior to soot loading, the sample was hydro-thermally aged at 850 o C. Flow reactor measurements were performed under various reaction conditions in order to examine the impact of soot in an SCR-coated diesel particulate filter (DPF) on standard SCR, fast SCR, NH3 oxidation and NO oxidation. In the presence of soot, NOx conversion was slightly lower at 200-300 °C due to the blocking of active sites. However, at higher temperatures, the NOx conversion was somewhat higher with soot, indicating that soot more strongly inhibited the oxidation of NH3 than the SCR reaction. When feeding equal amounts of NO and NO2 together with NH3, ammonium nitrates on the sample were formed. The presence of soot significantly decreased the formation or the stability of ammonium nitrate, resulting in higher conversion with soot. In order to further understand this interesting aspect, ammonium nitrate formation and decomposition experiments using model Cu/BEA catalyst with and without soot were performed. It was observed that less N2O was formed in the presence of soot, and this in combination with COx formation during ammonium nitrate formation step, suggested that soot reacted with the ammonium nitrates and we propose that this occurs on CuO species on the outside of the zeolite particles. Keywords: Diesel particulate filter (DPF), Selective catalytic reduction (SCR), SCR-coated filter, fast SCR, NO oxidation, NH3 oxidation 1

Introduction

Nowadays, there are worldwide rigorous emission regulations to reduce NOx emissions, as well as the emissions of particulate matter and, more recently, regulations that even limit the fuel consumption. An integrated exhaust aftertreatment system for diesel engines can decrease 1 ACS Paragon Plus Environment


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pollutant emissions.1 It is well-known that diesel engines are more fuel-efficient than gasoline engines with their lower emissions of hydrocarbons and CO, as well as reduced exhaust temperatures as a result of a higher air-fuel ratio.2-4 Modern diesel exhaust aftertreatment systems typically consist of a diesel oxidation catalyst (DOC), a porous wall-flow diesel particulate filter (DPF), and NOx aftertreatment devices, such as selective catalytic reduction (SCR) catalysts. Within this context, the DPF was developed in the past few years as a way of removing particulate matter (PM) and today possesses an excellent capability to efficiency trap PM. In recent years, different coatings for DPFs have been studied, whereby catalytic material could be added to improve the low temperature soot oxidation, thereby reducing the fuel penalty during filter regeneration. Various noble metals (e.g. Pt or Pd) have been added to the coating material inside the DPF to facilitate the soot oxidation. Song et al.5 examined the performance of the Pt/CeO2 catalyst in a flow reactor system for soot oxidation with NO and O2 and their results indicate that mixing soot and catalyst enhances the NOx conversion. Moreover, silver-based materials (e.g. Ag2O and Ag/Ce catalysts) were found to possess high stability and PM oxidation performance in engine bench testing compared to conventional Ptcatalysts.6 Nowadays, there is a large interest in NH3-SCR catalyst coated particulate filters.7-10 By integrating the SCR and DPF functions into one single unit, packaging volume and costs are optimized.9, 11 In addition, since the SCR-coated filter will be closer to the engine than an SCR catalyst with proceeding DPF, it will heat up faster; thereby reduce the NOx emission during cold start. Thus, SCR-coated filters exhibit high NOx reduction efficiency7, 12, 13 and, in addition, significantly reduce CO and hydrocarbon emissions.7, 12, 13 Furthermore, Yamamoto and Sakai found that the soot oxidation rate is high when the SCR-coated filter is used and the deposited soot inside the filter is oxidized in the presence of the catalyst, which indicates that continuous regeneration is occurring.14 Due to the exotherm during soot oxidation and the high temperatures needed for soot regeneration, it is important that they also are capable of tolerating high temperatures.6, 15 In recent decades, many studies have been focused on NOx reduction in aftertreatment technologies, such as the selective catalytic reduction (SCR) in the presence of ammonia.16, 17 Initially, titanium dioxide (TiO2) supported vanadium oxide (V2O5) catalysts were used for SCR applications.18 The decrease in activity and the release of toxic vanadia compounds19, 20 have encouraged the development of new materials for mobile SCR applications20, such as metal-exchanged zeolite catalysts. Numerous studies have been conducted on zeolite catalysts (BEA, ZSM-5) using copper21-23 or iron24-26 for the active metallic phase. The ion-exchange of Cu and Nb into ZSM-5 zeolite with further incorporation onto the DPF substrate was studied 2 ACS Paragon Plus Environment

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by Kang et al. 27 who found that the material exhibited superior De-NOx performance. Recently, zeolites/silicoaluminophosphates with chabazite (CHA) structures with small pore radii have gained large attention to NH3-SCR due to their high thermal stability and resistance to hydrocarbons.28, 29 The most extensively used catalysts in the CHA-group are the zeolite SSZ-13 and the silicoaluminaphosphate SAPO-34.30 The NOx reduction performance of a Cuzeolite SCR/DPF during different vehicle operating conditions, when using a prototype lightduty diesel engine, has been evaluated by Lee et al.9 and above 80 % NOx conversion was obtained. The thermal durability of Cu-zeolite SCR catalysts and their activity after repeated soot regeneration have been reported in many studies allowing them to be used in the SCRDPF systems.9, 31 Furthermore, Tronconi et al.32 studied the interactions between soot and Cu/Zeolite powder. Despite the growing importance of the SCR-coated DPF systems in the automotive field, mainly studies on the performance of metal-based catalysts for soot oxidation have been conducted, albeit very few studies on the impact of soot on SCR reactions. Therefore, the scope of this paper is to evaluate a soot-loaded SCR-coated filter during NH3-SCR reactions. The effect of soot on the catalytic performances of the SCR-coated filter during standard NH3-SCR, fast SCR, NH3 oxidation and NO oxidation was studied. Mechanistic studies were also performed using a model Cu/BEA catalyst. 2

Experimental

2.1 Activity tests of Cu-zeolite SCR-coated particulate filter A supplier Copper-zeolite SCR-coated particulate filter was loaded with soot using an engine bench at Volvo Cars. The filter contained a copper zeolite as active SCR material and is a state of the art SCR coated filter by a major supplier of automotive catalysts. Prior to soot loading, the catalyst was hydrothermally aged at 850 °C for 12 h. The reason for aging the material was that fresh SCR materials are usually very active and if the conversion in a wide temperature window is 100 %, it would make deactivation difficult to study. After soot loading, this filter was cut into eight slices, whereby Slice no. 1 (outlet of the filter) contained less soot and Slice no. 8 (inlet of the filter) contained the most soot. In this study, filter Slice no. 6 was employed for the flow reactor experiments. From this slice, cylindrical open monolith samples (120 channels, 20 mm length) were cut out. Activity evaluation tests of SCR-coated filter monolith samples were carried out in a laboratory-scale flow reactor consisting of an 800 mm long horizontally placed quartz tube with an inner diameter of 22 mm. Note that the small monolith samples did not contain plugs; thus, the flow went through the channels. LabView software and National Instrument data acquisition hardware were utilized for controlling the experimental protocol and for recording 3 ACS Paragon Plus Environment


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the data. The gas composition levels were controlled by using a number of mass flow controllers (MFC, Bronkhorst Hi-Tech), and the water flow was controlled by a Controlled Evaporation and Mixing (CEM) System, from Bronkhorst. All tubing lines were heated and the temperatures were controlled by Eurotherm temperature-controllers and to prevent water and by-product condensation, they were maintained at 200 °C. The catalyst temperature was measured by a thin K-type thermocouple located inside a central monolith channel; whereas another thermocouple measured the gas temperature positioned 10 mm before the catalyst. The monolith samples were wrapped with quartz wool to prevent gas slip between the monolith and the wool. The concentrations of the resulting species were monitored using an FTIR instrument (MultiGas™ 2030 HS). A space velocity equal to about 34500 h-1 and argon as inert balance were used in this study. Prior to each activity test, the samples were pretreated with argon at 500 °C for 20 min in order to remove residual hydrocarbon species. The experimental procedure consisted of the following set of tests: a) Standard SCR from 150 °C: One of the soot-loaded SCR samples was exposed to SCR conditions: 400 ppm NH3, 400 ppm NO, 8% O2 and 5% H2O, balanced with argon. The experiment started at 150 °C and the temperature was stepwise increased (150, 175, 200, 225, 250, 300, 400, 450, 500), with 5 °C/min ramp between each step. This sequence was referred to as Cycle 1 in this study. Thereafter, the temperature was cooled down to 150 °C while exposing the sample to 5 % water in Ar, and Cycle 2 was directly started. For Cycle 2, the catalyst was tested in the same atmosphere as in the first cycle, but the temperature was stepwise increased from 150 to 600 °C. Following the same logic, the successive stepwise temperature increase from 150 to 700 °C was referred to as Cycle 3, and the final temperature increase from 150 to 750 °C was named Cycle 4. It should be noted that the first cycle was followed by the second, third and fourth cycles and a single sample was used for all four cycles; thus, soot was gradually being removed during the course of the cycles. The experimental details are listed in Table 1 and a schematic picture of the experiment is shown in Figure 1. b) Fast SCR from 150 °C and 180 °C: A gas mixture of 400 ppm NH3, 200 ppm NO, 200 ppm NO2, 8 % O2 and 5 % H2O was flushed through the sample. Following the same experimental procedure as for standard SCR experiments, the starting temperature was 150 °C or 180 °C and was stepwise increased to 500 °C for the first cycle. Thereafter, the samples were cooled and the experiment redone from 150 or 180 °C to 600 °C (Cycle 2), then from 150 or 180 °C to 700 °C (Cycle 3) and 150 or 180 °C to 750 °C (Cycle 4) with a cooling step in-between these steps. The experimental details are listed in Table 1. For this set of experiments, one

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sample was used for the experiments starting at 150 °C and another sample for the experiments starting at 180 oC. c) NH3 oxidation from 150 °C: The NH3 oxidation experiment followed the same experimental procedure as described for standard SCR but instead using 400 ppm NH3, 8% O2 and 5% H2O. d) NO oxidation from 150 °C: One sample was subjected to 400 ppm NO, 8% O2 and 5% H2O and the experiment consisted of the same temperature profile as described for standard SCR. Characterization of the soot In order to characterize the soot from the samples, soot was scrapped off the filter and was analysed by a Leo Ultra 55 FEG SEM instrument equipped with a field emission gun and operated in low vacuum mode. 2.2 Impact of soot on ammonium nitrate formation and decomposition over model Cu/BEA For this study, a model Cu/BEA catalyst was used for further experiments. Details regarding catalyst preparation and characterization of Cu/BEA is reported by Mihai et al. 21 Beta zeolite (BEA, silica to alumina ratio of 38, Zeolyst International) was first ion-exchanged with sodium nitrate in two steps and, thereafter, with copper acetate in three steps. The calcined Cu/BEA powder (450 oC, 3 h) was used in the next step for the washcoating of the cordierite monoliths (400 cpsi, 20 mm length and 20 mm diameter). An amount of about 500 mg CuBEA was washcoated on the monoliths. The Cu-BEA and boehmite ratio in the solid phase was 95:5 (based on weight) and the monoliths were immersed into a mixture with liquid/solid ratio = 80/20. The Cu-BEA coated monoliths were calcined at 500 oC for 2 h and the BET analysis resulted in a surface area of 461 m2/g. The copper content was analyzed using ICPAES, giving 4 wt.% Cu, which corresponds to an ion exchange level of 0.87 (Cu/Al). Furthermore, 4 % Cu/BEA catalyst was characterized by UV-vis by Mihai et al.21 and copper hydroxyls were predominately found. The fresh calcined Cu-BEA samples were subjected to degreening and aging. The samples were first degreened at 500 oC with Standard SCR conditions (400 ppm NH3, 400 ppm NO, 8 % O2 and 5 % H2O) for 1 h. After degreening, one Cu/BEA sample was aged at 650 oC, the second sample was aged at 800 oC in the same mixture of 8 % O2, 5 % H2O and 5 % CO2 for 3 h in order to study the aging effect. The total flow was kept at 3000 mL/min during all tests. After cooling at room temperature in Argon, the samples were taken out from the reactor. An amount of 10 g/L soot powder (based on monolith volume, corresponding to 70 mg soot) was 5 ACS Paragon Plus Environment


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deposited on each monolith. The real soot was collected from an uncoated DPF (provided by Volvo Cars). A mixture of soot powder and ethanol (Merck, 99.9 %) was prepared and the obtained mixture was impregnated to the monoliths at room temperature. The soot-Cu-based monoliths were dried at 35 oC for 30 min. The soot-Cu/BEA monoliths (not calcined) were further loaded in the flow reactor system (described above). Prior to the target experiments, the sootloaded aged Cu/BEA monoliths were pre-treated in inert atmosphere (Argon) at 500 °C for 20 min to remove residual species adsorbed on the surface. Ethanol was removed during the pretreatment when the temperature was raised to 500 oC and FTIR results showed an ethanol peak during the first 30 minutes of the pretreatment within the 120-130 oC temperature range with a maximum of 230 ppm. Temperature-programmed desorption (TPD) experiments were performed and the feed concentrations of NH3 and NO2 were 400 ppm each, in the presence of 8 % O2 and 5 % H2O. Since ammonium nitrate species are mainly formed/ decomposed at lower temperatures33, 34, the tests were performed at 200 °C for 1 h. After exposure to (NH3 + NO2 + O2 + H2O) mixture, the catalysts were exposed to 5 % H2O in Ar for 30 min at 200 oC. The temperature was then increased to 400 °C, with a ramp rate of 10 °C min−1 in the presence of 5 % H2O and Ar. This TPD test was denoted as ,,w soot’’ in this study. In order to study the interactions between the soot and the NH3-SCR chemistry, the same aged Cu-BEA monoliths were tested again for TPD after soot was removed. For the removal of soot, the temperature was raised from 200 oC to 650 oC, with a ramp rate of 2 °C· min−1 in the presence of 8 % O2 and 5 % H2O. Thereafter, the sample was kept at 650 oC in the same conditions for 20 min, the temperature was cooled down to 200 oC and a new TPD experiment (denoted as ,,w/o soot’’) was performed.

3 Results and discussion 3.1 Characterization of the soot material The SEM results of the soot are shown in Figure 2. The soot consists of uniform agglomerated spheres with diameters of about 0.2 – 0.4 µm. 3.2 NH3-SCR The SCR-coated filter sample was exposed to a stream containing 400 ppm NH3, 400 ppm NO, 8 % O2 and 5 % H2O and stepwise increasing the temperature for Cycle 1 (150-500 °C), Cycle 2 (150-600 °C), Cycle 3 (150-700 °C) and Cycle 4 (150-750 °C); see Figure 1 and 6 ACS Paragon Plus Environment

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Table 1 for experimental details. The results from the steady-state concentrations in Cycle 2 are depicted in Figure 3. Close to full conversion of NOx was reached between 225 and 450 °C (Figure 3a). Under SCR conditions, up to 10 ppm N2O at 600 °C and negligible amounts of NO2 up to 500 °C were formed during Cycle 2, as shown in Figure 3b). At higher temperatures, the NO2 increased and reached around 14 ppm at 600 °C. Figure 3c) shows that significant amounts of CO and CO2 were generated during the SCR experiments for the temperature range from 350 °C to 600 °C due to soot oxidation. Cavataio et al.10 proposed two paths for soot oxidation with subsequent formation of CO and CO2 in the presence of SCR-coated filter materials: (1) the catalytically assisted oxidation of soot within the SCRF wall at low temperatures up to around 350 °C; and (2) the oxidation of the bulk soot within the monolith channel, unassisted by the catalyst. Steady-state NOx and NH3 conversions under SCR conditions as a function of temperature for all cycles are presented in Figure 4a) and b). The SCR-coated filter sample achieved an NH3 and NOx conversion at 200 °C of 82 % and the conversion reached 99 % at 300 °C. These results showed a stoichiometry of one between NO and NH3 which is characteristic of the standard SCR reaction over copper zeolites21. At higher temperatures, a significant decrease in NOx reduction activity with temperature increase was observed for all cycles due to the oxidation of NH3, as also observed by Cavataio et al.10 A NOx conversion of 36 % was achieved at 650 °C, while a negative NOx conversion at 750 °C was observed due to ammonia oxidation to produce NO (Figure 4a). Furthermore, in order to understand how soot affects the De-NOx activity, a comparison between all four cycles is shown in Figure 4a). A slight increase in NOx conversion was observed at temperatures of 225, 250 and 300 °C for the final two cycles (Cycles 3 and 4) compared to the first two cycles. For example, at 225 °C, the NOx reduction activity increased from 91 % (for the first two cycles) to 96 % (for the final two cycles). The difference between the first and last two cycles was the gradual removal of soot, which was evident by the CO and CO2 release shown in Figure 5a). An overview of CO and CO2 formation on the soot-loaded SCR-coated filter for all cycles with different temperature domains is depicted in Figure 5a). It should be noted that one sample was subjected to a full SCR test and the catalyst was cooled down to the target temperature at the end of each cycle, while exposing the catalyst to 5 % H2O + Ar. Maximum amounts of 326 ppm CO2 and 59 ppm CO at 500 °C for the first cycle and 408 ppm CO2 and 83 ppm CO at 550 °C for the second cycle were produced during the SCR tests. These results are consistent with the study by Cavataio et al.10 showing that the maximum CO formation occurred at roughly 540 °C, when the oxidation of the bulk soot layer by oxygen in the gas phase occurred without any catalytic assistance. Thus, when comparing our results to those of Cavataio et al.10, it indicates that the SCR-coating did not significantly influence the light-off for the soot combustion. For the final two cycles (with a final temperature of 700 and 750 °C, 7 ACS Paragon Plus Environment


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respectively), negligible amounts of CO2 (roughly 16 ppm) and no CO were produced for the likely reason that most of the soot had been removed in earlier cycles, as shown in Figure 5a). Thus, most of the soot was removed up to 600 oC during Cycle 2. Based on the CO and CO2 released during the SCR experiments, the amount of soot released for each cycle could be determined. The resulting soot amount released for each cycle is shown as a bar chart plot in Figure 5b). The first bar chart in Figure 5b) consists of the integrated CO2 and CO data from the first cycle; the second column contains the integrated results from Cycle 2, etc. Based on these measurements, the total soot loading in this sample, calculated from the total integrated CO and CO2 amount, was roughly 20 g/L. Based on these results, the experimental findings observed from the results in Figure 4a) can be further interpreted. The NOx conversions for Cycles 3 and 4 were slightly higher than for Cycles 1 and 2 at 225, 250 and 300 °C because most of the soot had been removed after Cycle 2 and due to that soot was blocking part of the catalyst, hindering the SCR reaction. Interestingly, at higher temperatures, the opposite trend was observed whereby the NOx conversion was actually lower after soot removal ( similar to Cycles 3 and 4). An increased selectivity for SCR at higher temperatures was also observed after phosphorous poisoning over Cu/BEA.35 The conclusion of this study was that phosphorous more selectively poisoned the ammonia oxidation function of the catalyst than the SCR functionality, thereby resulting in an increased NOx conversion at high temperature. However, the soot particles were quite large, about 0.2-0.4 µm according to SEM (see Figure 2); thus, the soot particles were too large to enter into the small channels of the copper zeolite. Another possibility was that hydrocarbon species, not the soot, were blocking some of the copper sites. However, before our experiments, the filter had been heated to 500 oC in Ar to desorb any possibly adsorbed hydrocarbons. Kim et al.36 studied propene adsorption and desorption from Cu/SSZ-13 and found that the propene had desorbed by 500 oC, which implied that our pre-treatment at 500 o C was sufficient to remove hydrocarbons. Another aspect to consider is that ammonia oxidation occurred at a higher rate on overexchanged copper sites, as had been observed by Mihai et al. in an earlier study 21. Results from combining UV-vis spectroscopy 37, flow reactor experiments38 and kinetic modelling39 of hydrothermal aging of Cu/BEA indicated high activity for NH3 oxidation over copper oxide species. Furthermore, using UV-vis spectroscopy, Wilken et al.38 observed that hydrothermal treatment at 800 and 900 oC resulted in a larger amount of copper oxides formed using Cu/BEA. The SCR-coated particulate filter used in the current study was initially hydrothermally aged at 850 oC for 12 h; thus, some CuxOy species were likely formed. A possible mechanism for the selectivity difference observed at high temperatures after soot had been removed might be the fact that some CuxOy species were present on the surface of the copper zeolite crystallites and that those had been blocked by the soot, thereby reducing the 8 ACS Paragon Plus Environment

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ammonia oxidation. The reduced ammonia oxidation would then result in a larger selectivity for ammonia SCR, which was also observed. The resulting N2O concentrations are shown in Figure 4c) and about 8 ppm was formed at 225 °C and 11 ppm 550 °C, respectively. At low temperature, the maximum N2O was observed, and this has been suggested to be associated with NH3-NO species on the copper, for both Cu/BEA39 as well as Cu/SSZ-13.40 At higher temperature, the N2O formation started to increase again, which has been observed over Cu/BEA41, Cu/FAU42, Cu/SSZ-1343 and Cu/SAPO-3444. This high temperature N2O formation was suggested to occur on copper in the sodalite cages, according to Delahay et al.42 These results are consisted with the kinetic model developed by Olsson et al.40 The results presented in Figure 4c) showed that when the soot started to be removed from the catalyst, the N2O concentration increased, albeit only slightly. These results are consistent with the hypothesis above, in which we proposed that soot blocked CuxOy species because the N2O formation had been occurring at a higher rate on over-exchanged copper zeolites.23 3.3 Fast SCR at 150 and 180 °C The effect of soot on the fast SCR reaction was investigated by exposing the SCR-coated DPF catalyst to 400 ppm NH3, 200 ppm NO, 200 ppm NO2, 8 % O2 and 5 % H2O. In the same way as for the standard SCR reaction, the sample was exposed to four cycles starting at 150 °C. In addition, a second experiment was performed on another sample starting instead at 180 °C with details regarding the experiments found in Figure 1 and Table 1. The results for Cycle 4 (150 to 750 °C) are shown in Figure 6, where the NO, NO2 and NH3 concentrations are depicted in Figure 6a), the N2O concentration shown in Figure 6b) and, finally, the NOx conversion in Figure 6c). Similarly, as for the standard SCR, very low amounts of CO and CO2 were formed during fast SCR conditions for Cycles 3 and 4, indicating that most of the soot had already been removed in Cycle 1 and Cycle 2. Thus, the results in Figure 6 represent reactions occurring without any soot (or with only minor amount of soot) present. Significant amounts of NOx and NH3 were observed at low temperatures (150, 175 °C) under fast SCR conditions (Figure 6a), which was also clearly seen by the low NOx conversion in Figure 6c). Initially, the NOx conversion had increased because SCR reaction rates are dependent on the ammonia coverage on the surface45 and since ammonia coverage initially had increased due to ammonia storage, this was also the case with the fast SCR reaction. However, shortly thereafter, the NOx conversion significantly dropped (see Figure 6c) because of the build-up of ammonium nitrate species on the surface. Several studies33, 46-48 have shown that the formation of ammonium nitrate species occurred at low temperatures over zeolite catalysts, thereby lowering the N2 selectivity. The simultaneous presence of NO2 and NH3 was critical for the ammonium nitrate formation.21 Further, the state-of-the-art small pore zeolites with CHA structure, like Cu-SAPO-34 and Cu/SSZ-13, exhibited significantly more stable 9 ACS Paragon Plus Environment


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ammonium nitrate species than large pore zeolites such as Cu/BEA.49 Ammonium nitrates are often suggested to decompose to form N2O21 and simultaneously as the N2O production increased (at 200 °C), the NOx conversion was rapidly increasing due to the removal of the ammonium nitrates. As is shown in Figure 6c), the material achieved its maximum NOx conversion of 97-99 % between 225 and 400 °C. At temperatures higher than 400 oC, the NOx conversion declined due to the ammonia oxidation occurring at high temperature, which resulted in lowering the NOx selectivity. Comparing the NOx results for standard SCR and fast SCR tests at the same temperature range (Figures 4a and 6c), it was observed that the NOx conversion improved for fast SCR at 400-550 °C (for example at 450 °C: 93 % NOx conversion for fast SCR versus 89 % for standard SCR). At 650 °C, the NOx conversion was higher during standard SCR showing a conversion of 36 % compared to 29 % for fast SCR, respectively. This is likely because at this high temperature, the NO2 can react with NH3 to produce NO and since this reaction consumes ammonia23, it thereby results in decreasing the NOx reduction selectivity. In addition, more N2O was formed under fast SCR conditions (Figure 6b) compared to standard SCR experiments which was in line with previous studies 23. A possible reason for increased N2O at higher temperatures (e.g. 600 oC, as seen in Figure 6b) could be due to NH3 oxidation, as a side reaction under Fast SCR. However, we found below 6 ppm N2O during NH3 oxidation experiment over the SCR coated filter between 150-750 °C. Thus, the main reason for the high temperature N2O is a reaction involving also NOx. The impact of soot on the fast SCR reaction can be observed by studying the results in Figures 7 and 8. In these figures, the NO, NO2, NOx (Figure 7) and NH3 and N2O concentrations (Figure 8) are shown for Cycles 1-4, at a starting temperature of 150 °C. Surprisingly, at low temperature, the NOx and NH3 concentrations were lower in the presence of large amounts of soot (Cycles 1 and 2) compared to the results when soot had been removed (Cycles 3 and 4). In order to further analyse the reason for this behaviour, a new sample was used and since a higher temperature would result in less ammonium nitrate formation, a fast SCR experiment was instead conducted from 180 °C. The NOx and NH3 concentration profiles for all four cycles, with a starting temperature of 180 °C, are shown in Figure 9. The experimental details are described in Table 1 and a schematic picture of the temperature profile during the experiment is shown in Figure 1. Starting the fast SCR test at 180 °C (Figure 9), the catalyst produced low amounts of NOx and NH3 for all four cycles, suggesting that a higher starting temperature would result in a significantly lower ammonium nitrate formation on the samples. In addition, there were relatively small changes for Cycles 3 and 4 compared to Cycles 1 and 2. In fact, the catalyst was even more active in Cycles 3 and 4 compared to Cycles 1 and 2, showing that the removal of soot increased the fast SCR reaction. These results are in line with the study by Tronconi et al.32 10 ACS Paragon Plus Environment

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Thus, the results from the fast SCR experiments starting at 150 and 180 °C revealed that the interesting effect observed for the 150 °C experiment, during which the activity at low temperature was higher in the presence of soot, was likely related to ammonium nitrate formation. Considering these results, we suggest that soot inhibited the formation of ammonium nitrate species or more easily decompose them at low temperatures which caused the higher activity in the case when soot was present. The corresponding CO2 concentration for temperatures ranging from 150 to 250 °C for Cycle 1 in the fast SCR experiment is shown in Figure 10a). CO is not depicted because during these conditions, the resulting CO concentration was below 1.5 ppm, which was also the case for the standard SCR experiment. It is evident from the results in Figure 10a) that there was a maximum of CO2 produced at lower temperatures and that this CO2 formation coincided with the temperature where ammonium nitrates were likely available on the surface, as shown by the NOx conversion profile (see Figure 6c). A comparison between the average CO2 concentration at each temperature for the standard SCR experiment and the fast SCR experiment from 150 °C and 180 °C, respectively, are shown in Figure 10b). The results presented in Figure 10 clearly show that there was larger CO2 production occurring at low temperature for the 150 °C fast SCR experiment, which indicated that there was a reaction occurring between the ammonium nitrate species and the soot. Indeed, the N2O formation (see Figure 8b) was higher at 175 °C for the case with soot present, which indicated that the ammonium nitrates were decomposing since it had been suggested in the literature that the decomposition of ammonium nitrates would result in N2O formation.21 In addition, the average CO2 concentration at low temperature for all four cycles during the fast SCR experiment from 150 °C is shown in Figure 10c). The first two cycles exhibit similar behaviour, although CO2 from Cycle 2 was slightly lower probably due to the removal of some soot in Cycle 1. The CO2 concentration in Cycle 3 and Cycle 4 showed a completely different behaviour with only slight CO2 production. During these cycles, most of the soot had already been removed. Furthermore, ammonium nitrate formation was occurring more rapidly for over-exchanged copper zeolites and consistent with the previous discussion in Section 3.2, it is possible that our sample contained CuxOy species on the outside of the zeolite particles due to the hydrothermal aging at 850 °C. The soot could then interact with these CuxOy particles and it was not necessary for soot to enter the narrow channels (which is not possible, due to the size of soot particles). At higher temperatures (between 450 to 600 °C), the NOx conversion was decreasing after soot removal similarly to the standard SCR case and this is likely due to increased ammonia oxidation in the absence of soot. In order to study the effect of soot and hydrothermal aging on ammonium nitrate formation and decomposition, model Cu-BEA catalysts were subjected to additional experiments, which will be discussed in Section 3.6.



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3.4 NO Oxidation There are several perspectives regarding the role of the NO oxidation mechanism. Some authors suggest that the NO oxidation to NO2 is the rate-determining step for standard SCR over zeolite-based catalysts50, whereas Metkar et al.51 and Nedyalkova et al.52 suggested that this was not the case due to the fact that NO oxidation activity was significantly decreased, while this was not the case for the SCR reaction. Nevertheless, it is interesting to examine the effect of soot on the NO oxidation activity and one of our samples was exposed to a gas mixture consisting of 400 ppm NO, 8 % O2 and 5 % H2O under four consecutive cycles (150 500 °C, 150 - 600 °C, 150 - 700 °C, 150 - 750 °C). The NO conversion to NO2 as a function of the temperature (calculated based on NO signal) is depicted in Figure 11, showing that low NO conversion to NO2 was observed during the first two cycles, when soot was present in the sample. This was probably due to the fact that the catalyst was blocked by the soot or possibly by that the formed NO2 reacted with soot. Furthermore, NO oxidation activity was revealed from 300 °C for Cycles 3 and 4 and a decrease in NO conversion to NO2 at temperatures above 550 °C owing to thermodynamic restrictions 53. In our previous study21, we found that the NO oxidation predominantly occurred on materials with high copper loading and in addition, CuxOy species are capable of contributing to the NO oxidation, as discussed in the modelling study by Supriyanto et al.39 Since our material was aged at 850 °C, it is likely that it contained CuxOy species that might be on the outside of the zeolite particles and that these sites might be blocked by the soot. This finding may explain why the decrease in NO oxidation is much more severely blocked by soot than in the standard SCR case. Another possible explanation, as described above, is that NO2 is formed with similar rate in the presence of soot, but that this NO2 reacts with soot to produce NO again. When examining the COx production it is found that larger COx amounts is formed at 400 °C for the NO oxidation case (57 ppm) compared to standard SCR (34 ppm) in Cycle 1. These results indicate that it is possible that some of the formed NO2 reacts with soot. However, it should be noted that, opposite trend was found at 500 °C, with 294 ppm for NO oxidation and 384 ppm COx for standard SCR case. Thus, to conclude both the blocking of sites on the outside of the zeolite particles as well as reaction of NO2 with soot is possible explanations for the decreased NO2 production seen in Figure 11. Interestingly, the NO oxidation is significantly more influenced by soot compared to standard SCR case (see Figure 4).

3.5 NH3 Oxidation In order to understand the decrease in NOx activity at high temperatures under SCR conditions, NH3 oxidation experiments were performed in the absence of NOx in the gas feed. As depicted in Figure 12, the conversion of NH3 was very low at 150 °C; it increased with the temperature and full NH3 conversion was found from 600 °C. Small amounts of NO2 (ca. 10 ppm) and N2O (ca. 6 ppm) were formed as by-products (data not shown here) during the 12 ACS Paragon Plus Environment

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experiment. The formation of NO was observed from 550 °C and increased from 17 ppm at 550 °C to 214 ppm at 750 °C, showing a substantial ammonia oxidation to NO at high temperature. After soot removal, the ammonia oxidation increased (compare Cycle 4 to Cycle 1 in Figure 12). These results are consistent with the results for standard SCR (see Figure 4), where the NOx conversion decreased for Cycle 4 at high temperature likely due to increased ammonia oxidation after soot removal. 3.6 The impact of soot and aging on model Cu/BEA catalysts The impact of both soot and aging on the formation/decomposition of the ammonium nitrate species with subsequent formation of N2O during both adsorption and desorption periods of the (NH3 + NO2) TPD test over aged soot-loaded Cu-BEA samples was investigated. Figure 13a shows the N2O formation when 400 ppm NH3 and 400 ppm NO2 are dosed simultaneously in the presence of O2 and H2O. The results clearly show that the catalyst deactivated at high temperature and the N2O formation is significantly lower for the sample aged at 800 oC compared to 650 oC. These results are in line with the study by Wilken et al.41, where large deactivation for ammonia SCR was observed after aging a 4 % Cu/BEA at 800 C. It should be noted, that the integrated amount of COx (CO+CO2) is a factor of 2 larger for the sample aged at 650 oC compared to 800 oC sample. These values are retrieved by integrating the COx amount in the temperature ramp up to 650 oC, where the largest amount of soot is removed, although some soot is also oxidized during the NO2 + NH3 TPD experiment. The reason for the difference in soot loading between the samples is likely the procedure for soot sampling and depositing. It is possible that some ash or cordierite material have been included when scraping off the soot from the filter and thereby giving different soot amounts. o

Interestingly, more N2O is formed when the sample contained soot after aging for both samples (aged at 650 and 800 oC). These results indicate that the ammonium nitrates are more easily being decomposed in the presence of soot, thereby forming more N2O. Indeed, COx (CO + CO2) formation are observed, e.g. for the 650 oC aged sample about 50 ppm COx is formed in the initial part of the storage phase which thereafter decreased. The resulting N2O formation during the temperature ramp is displayed in Figure 13b) and it can be seen that less N2O is formed in the presence of soot. With other words, less ammonium nitrates species are present on the catalyst when soot is available, suggesting that the ammonium nitrates formation with subsequent N2O formation is suppressed by soot or these species are more easily decomposed in the presence of soot. Indeed, COx formation is observed during the storage phase, thus reaction between ammonium nitrates and soot is likely present. Furthermore, the integrated amount of N2O desorbed is shown in Figure 13c), clearly pointing out the impact of the soot and aging treatment on the N2O formation. Based on these results, N2O ratio ,,w soot’’ compared to ,,w/o soot’’ for aged samples were calculated. The N2O ratio of 0.47 (for sample aged at 650 oC ,,w soot’’ compared to ,,w/o 13 ACS Paragon Plus Environment


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soot’’) and 0.52 (for sample aged at 800 oC ,,w soot’’ compared to ,,w/o soot’’) are quite similar. However, as described above the sample aged 800 oC contains about 2 times less soot compared to the sample aged at 650 oC. These results therefore indicate that the impact of soot is larger on the sample aged at 800 oC. Wilken et al.37, 38 investigated the impact of hydrothermal aging on copper species in BEA zeolite and found that copper oxides species were formed during hydro thermal aging at 800 and 900 oC. These copper oxide particles are likely formed on the outside of the zeolite particles and as discussed in the previous sections the soot can interact with these CuO particles on the outside of the particles. Furthermore, the soot particles are quite large (0.2 – 0.4 µm, according to SEM) and they can therefore not enter the pores of the zeolites. For the case when more of the copper is on the outside of the zeolite particles, as is the case for the sample aged at 800 oC, there is more interaction between soot and the ammonium nitrates on the copper oxide particles.

Conclusions The effect of soot, on a DPF-coated filter with Cu-zeolite SCR material on the standard SCR, fast SCR, NH3 oxidation and NO oxidation reactions was the subject of investigation in this study. The soot-loaded sample was exposed to four consecutive cycles, during which the temperature was stepwise increased according to: Cycle 1: 150 (or 180) to 500 °C, Cycle 2: 150 (or 180) to 600 °C, Cycle 3: 150 (or 180) to 700 °C and Cycle 4: 150 (or 180) to 750 °C. Soot combustion resulted in the formation of CO and CO2, and the highest amount of CO and CO2 was released at around 540 °C under SCR conditions during Cycle 2. The resulting CO and CO2 profiles clearly showed that most of the soot was removed after Cycle 2, which goes up to 600 oC. Thus, the results from Cycle 4 predominantly showed the activity of the SCR material, without (or only minor) influence of soot. For the standard SCR experiment, the NOx conversion slightly increased between 200-300 oC when soot was removed because of better access to the catalytically active sites after soot removal. On the other hand, at high temperature the NOx conversion slightly decreased and we suggest that the reason for this is that the ammonia oxidation reaction was more greatly inhibited by the presence of soot compared to the standard SCR reaction and therefore, the soot changed selectivity between these two reactions. Indeed, from the ammonia oxidation experiments, we observed an increase in ammonia oxidation after the removal of soot. Since our SCR-coated filter was hydrothermally aged at 850 oC, prior to soot loading, it is possible that we had CuxOy species or other copper species on the outside of the zeolite particles and that those sites were being blocked by the soot. Since the soot particles (as seen by SEM images) are much larger than the zeolite pores, this is a plausible explanation. Furthermore, copper oxide particles are considered to be more susceptible to NO oxidation reaction compared to SCR and we have indeed witnessed a large decrease in NO oxidation in the presence of soot, which further supports this theory. 14 ACS Paragon Plus Environment

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Interestingly, for fast SCR experiment starting at 150 oC the activity was significantly higher in the presence of soot than in the absence and we suggest that soot inhibits the ammonium nitrate formation or more easily decomposes the soot. Indeed, we observed larger CO2 production at low temperature for the fast SCR experiment starting at 150 oC compared to the fast SCR starting at 180 oC, where only a limited ammonium nitrate formation occurred. Thus, these results indicate that there is an interaction between soot and ammonium nitrates. Furthermore, for the fast SCR starting at 180 oC, the NOx conversion increased at low temperature after soot removal in the same way as for the standard SCR most likely because ammonium nitrates were not dominating the reactions for these cases. In order to further study the effect of copper species on the ammonium nitrate formation and decomposition, experiments using model Cu/BEA catalysts were conducted and we found that soot indeed supress ammonium nitrate build up on the surface. In addition, Cu/BEA aged at higher temperature, which results in CuO particle formation, is more influenced by soot, when also considering the soot loading of the sample. These results show that it is likely the CuO particles on the outside of the zeolite particles that interact with the soot.

Acknowledgments This study has been collaboration between Chemical Engineering at the Chalmers University of Technology and Volvo Cars. The funding from the Swedish Energy Agency (FFI 37190-1) is gratefully acknowledged.



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Tables Table 1. Experimental cycles performed in this study under flow reaction conditions. Note that a new sample is used for each experimental set and that each experimental set contain cycles 1,2,3 and 4 done after each other. The experiments either starts at 150 °C (“Exp. set from 150 °C”) or from 180 °C (“Exp. set from 180 °C”). SCR coated Acronym of the Temperature profile (°C) filter cycle

Exp. set from 150 °C

Exp. set from 180 °C

Reaction conditions*

Cycle 1 (150-500 °C)

150, 175, 200, 225, 250, 300, 350, 400, Standard SCR, 450, 500 oC; heating rate 5 °C/min Fast SCR, between each temperature NO oxidation, NH3 oxidation

Cycle 2 (150-600 °C)

150, 175, 200, 225, 250, 300, 350, 400, Standard SCR, 450, 500, 550, 600 oC; heating rate 5 Fast SCR, °C/min between each temperature NO oxidation, NH3 oxidation

Cycle 3 (150-700 °C)

150, 175, 200, 225, 250, 300, 350, 400, Standard SCR, 450, 500, 550, 600, 650, 700 oC between Fast SCR, each temperature; heating rate 5 °C/min NO oxidation, NH3 oxidation

Cycle 4 (150-750 °C)

150, 175, 200, 225, 250, 300, 350, 400, 450, 500, 550, 600, 650, 700, 750 oC; heating rate 5 °C/min between each temperature

Cycle 1 (180-500 °C)

180, 200, 225, 250, 300, 350, 400, 450, Fast SCR 500 oC; heating rate 5 °C/min between each temperature

Cycle 2 (180-600 °C)

180, 200, 225, 250, 300, 350, 400, 450, Fast SCR 500, 550, 600 oC; heating rate 5 °C/min between each temperature

Cycle 3 (180-700 °C)

150, 175, 200, 225, 250, 300, 350, 400, Fast SCR 450, 500, 550, 600, 650, 700 oC; heating rate 5 °C/min between each temperature

Cycle 4 (180-750 °C)

180, 200, 225, 250, 300, 350, 400, 450, Fast SCR 500, 550, 600, 650, 700, 750 oC; heating rate 5 °C/min between each temperature

*

Standard SCR, Fast SCR, NO oxidation, NH3 oxidation

The experimental sequence was repeated, using new monoliths for different gas compositions.


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Figures Figure 1. (a). Temperature profile during all performed experiments from 150 or 180 oC. Note that same procedure was done for the temperatures 300, 350 and 400 oC, but is not shown due to size limitation; (b) Schematic picture of the experiments including all four cycles. The figure inserted in the right-hand corner represents the expansion of the temperature profile (ramp + steady-state) to target temperature for Cycle 1 (chosen as example). The experimental details are listed in Table 1. Figure 2. SEM images of the soot particles. The scale is 200 nm (A, C) and at 100 nm (B), respectively. Figure 3. The resulting NH3, NO (a), NO2, N2O (b), and CO, CO2 (c) during standard SCR experiments conducted on SCR coated particulate filter for cycle 2 (from 150 to 600 °C). The sample was exposed to 400 ppm NH3, 400 ppm NO, 8 % O2 and 5 % H2O, balanced with Ar. The experimental details are listed in Table 1 and the schematic picture of the temperature profile during experiments is shown in Figure 1. Figure 4. Standard SCR experiments conducted on SCR coated particulate filter for Cycle 1 (150-500°C), Cycle 2 (150-600 °C), Cycle 3 (150-700 °C) and Cycle 4 (150-750 °C). NOx conversion (a), NH3 conversion (b) and the resulting N2O concentration (c) as function of the temperature. The sample was exposed to 400 ppm NH3, 400 ppm NO, 8 % O2 and 5 % H2O, balanced with Ar. Figure 5. CO and CO2 concentration profiles as a function of the time (a), the amount of soot released in each cycle (b). During this experiment the sample was exposed to 400 ppm NH3, 400 ppm NO, 8 % O2 and 5 % H2O. The experimental details are listed in Table 1 and the schematic picture of the temperature profile during experiments is shown in Figure 1. Figure 6. The resulting NO, NH3, NO2 (a), N2O concentrations (b), and NOx conversion (c) versus time during fast SCR experiments for Cycle 4 (150-750 °C). The sample was exposed to 400 ppm NH3, 200 ppm NO, 200 ppm NO2, 8 % O2 and 5 % H2O, balanced with Ar. The experimental details are listed in Table 1 and the schematic picture of the temperature profile during experiments is shown in Figure 1. Figure 7. The resulting NOx (a), NO (b), and NO2 concentrations (c), as function of the time under fast SCR for Cycle 1 (150-500 °C), Cycle 2 (150- 600 °C), Cycle 3 (150 -700 °C) and Cycle 4 (150- 750 °C). The samples were exposed to 400 ppm NH3, 200 ppm NO, 200 ppm 17 ACS Paragon Plus Environment


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NO2, 8 % O2 and 5 % H2O, balanced with Ar. The experimental details are listed in Table 1 and the schematic picture of the temperature profile during experiments is shown in Figure 1. Figure 8. The resulting NH3 (a), and N2O concentrations (b) versus time during fast SCR from 150 °C conducted on SCR coated filter (slice no. 6) for Cycle 1 (150- 500 °C), Cycle 2 (150600 °C), Cycle 3 (150-700 °C) and Cycle 4 (150- 750 °C). The samples were exposed to 400 ppm NH3, 200 ppm NO, 200 ppm NO2, 8 % O2 and 5 % H2O, balanced with Ar. The total gas flow was 3000 ml ⋅ min−1. Figure 9. The resulting NOx (a), and NH3 concentrations (b) versus time for fast SCR from 180 °C for Cycle 1 (180- 500 °C), Cycle 2 (180- 600 °C), Cycle 3 (180 -700 °C) and Cycle 4 (180- 750 °C). The sample was exposed to 400 ppm NH3, 200 ppm NO, 200 ppm NO2, 8 % O2 and 5 % H2O, balanced with Ar. Figure 10. a). CO2 concentration at low temperatures (150-250 oC) during Fast SCR from 150 o

C, Cycle 1; b). The averaged CO2 concentrations at lower temperatures (150-350 oC) for

Cycle 1 in the three experiments (Standard SCR, Fast SCR from 150 °C and Fast SCR from 180 °C); c) The averaged CO2 concentrations at lower temperatures (150-350 oC) in Fast SCR from 150 oC during all Cycles. Figure 11. NO conversion to NO2 versus temperature during NO oxidation conducted on SCR coated filter for Cycle 1 (150- 500 °C), Cycle 2 (150- 600 °C), Cycle 3 (150-700 °C) and Cycle 4 (150- 750 °C). The sample was exposed to 400 ppm NO, 8 % O2 and 5 % H2O, balanced with Ar. The experimental details are listed in Table 1 and the schematic picture of the temperature profile during experiments is shown in Figure 1. Figure 12. NH3 conversion as function of the temperature during NH3 oxidation using an SCR coated filter for Cycle 1 (150-500 °C), Cycle 2 (150-600 °C), Cycle 3 (150-700 °C) and Cycle 4 (150-750 °C). The sample was exposed to 400 ppm NH3, 8 % O2 and 5 % H2O, balanced with Ar. The experimental details are listed in Table 1 and the schematic picture of the temperature profile during experiments is shown in Figure 1. Figure 13. Effect of soot and aging treatment on NH3-NO2 reacting system over aged Cu-BEA catalysts during adsorption (a), during desorption (b), total N2O integrated during desorption (c). Feed: adsorption: NH3= 400 ppm, NO2 = 400 ppm, 8 % O2, 5% H2O, balanced with Ar, 200 oC, 1 h; desorption: 5 % H2O, balanced with Ar, 200 oC, for 30 min, followed by the temperature ramp to 400 °C, with a ramp rate of 10 °C min−1 in the presence of 5 % H2O and Ar. 18 ACS Paragon Plus Environment

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Figure 1.



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Figure 2.


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Figure 3.


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Figure 4.



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Figure 5.


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Figure 6.



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Figure 7.


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Figure 8.



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Figure 9.


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Figure 10.



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Figure 11.

Figure 12.


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Figure 13.



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References (1). Johnson, T. V., Review of Diesel Emissions and Control. SAE Int. J. Fuels Lubr. 2010, 3, 16. (2). Katrašnik, T., Hybridization of powertrain and downsizing of IC engine – A way to reduce fuel consumption and pollutant emissions – Part 1. Energy Convers. Manage. 2007, 48, 1411. (3). Xin, Q., Diesel aftertreatment integration and matching. In Diesel Engine System Design, Xin, Q., Woodhead Publishing, 2013. (4). Körfer, T.; Schnorbus, T.; Holderbaum, B.; Wittka, T., Advanced, combined exhaust aftertreatment systems for light-duty diesel engines to meet next emission regulations. In Internal Combustion Engines: Performance, Fuel Economy and Emissions, ImechE, Woodhead Publishing, 2013. (5). Song, C.; Jung, J.; Song, S.; Chun, K. M., Experimental Study on Soot Oxidation Characterization of Pt/CeO2 Catalyst with NO and O2 Using a Flow Reactor System. 2009. (6). Matsumoto, T.; Mori, T.; Hirose, S.; Takeuchi, H., Enhancement of Regeneration Performance by a New Catalyzed DPF. In Proceedings of the FISITA 2012 World Automotive Congress, Springer Berlin Heidelberg, 2013. (7). Jeong, J.-W.; Choi, B.; Lim, M. T., Catalytic oxidation for carbon-black simulating diesel particulate matter over promoted Pt/Al2O3 catalysts. J. Ind. Eng. Chem. 2008, 14, 830. (8). Watling, T. C.; Ravenscroft, M. R.; Avery, G., Development, validation and application of a model for an SCR catalyst coated diesel particulate filter. Catal. Today 2012, 188, 32. (9). Lee, J. H.; Paratore, M. J.; Brown, D. B., Evaluation of Cu-Based SCR/DPF Technology for Diesel Exhaust Emission Control. SAE Int. J. Fuels Lubr. 2008, 1, 96. (10). Cavataio, G.; Warner, J. R.; Girard, J. W.; Ura, J.; Dobson, D.; Lambert, C. K., Laboratory Study of Soot, Propylene, and Diesel Fuel Impact on Zeolite-Based SCR Filter Catalysts. SAE Int. J. Fuels Lubr. 2009, 2, 342. (11). Tang, W.; Youngren, D.; SantaMaria, M.; Kumar, S., On-Engine Investigation of SCR on Filters (SCRoF) for HDD Passive Applications. SAE Int. J. Engines 2013, 6, 862. (12). T. Ballinger; J. Cox; M. Konduru; D. De; W. Manning; Andersen, P., Evaluation of SCR Catalyst Technology on Diesel Particulate Filters. SAE Technical Paper 2009-01-0910 2009. (13). M. Naseri; S. Chatterjee; M. Castagnola; H.-Y. Chen; J. Fedeyko; H. Hess; Li, J., Development of SCR on Diesel Particulate Filter System for Heavy Duty Applications. SAE Technical Paper 2011-01-1312 2011. (14). Yamamoto, K.; Sakai, T., Simulation of continuously regenerating trap with catalyzed DPF. Catal. Today 2015, 242, Part B, 357. (15). Cavataio, G.; Girard, J. W.; Lambert, C. K., Cu/zeolite SCR on high porosity filters: Laboratory and engine performance evaluations. SAE Technical Papers 2009, 2009-01-0897, 1. (16). Guan, B.; Zhan, R.; Lin, H.; Huang, Z., Review of state of the art technologies of selective catalytic reduction of NOx from diesel engine exhaust. Appl. Therm. Eng. 2014, 66, 395. (17). Brandenberger, S.; Kröcher, O.; Tissler, A.; Althoff, R., The State of the Art in Selective Catalytic Reduction of NOx by Ammonia Using Metal-Exchanged Zeolite Catalysts. Catal. Rev. Sci. Eng. 2008, 50, 492. (18). Nova, I.; Ciardelli, C.; Tronconi, E.; Chatterjee, D.; Bandl-Konrad, B., NH3-SCR of NO over a V-based catalyst: Low-T redox kinetics with NH3 inhibition. AIChE J. 2006, 52, 3222. (19). Nicosia, D.; Elsener, M.; Kröcher, O.; Jansohn, P., Basic investigation of the chemical deactivation of V2O5/WO3-TiO2 SCR catalysts by potassium, calcium, and phosphate. Top. Catal. 2007, 42-43, 333. (20). Kröcher, O., Aspects of catalyst development for mobile urea-SCR systems — From Vanadia-Titania catalysts to metal-exchanged zeolites. Stud. Surf. Sci. Catal. 2007, 171, 261.


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(21). Mihai, O.; Widyastuti, C. R.; Andonova, S.; Kamasamudram, K.; Li, J.; Joshi, S. Y.; Currier, N. W.; Yezerets, A.; Olsson, L., The effect of Cu-loading on different reactions involved in NH3-SCR over Cu-BEA catalysts. J. Catal. 2014, 311, 170. (22). Olsson, L.; Sjövall, H.; Blint, R. J., A kinetic model for ammonia selective catalytic reduction over Cu-ZSM-5. Appl. Catal. B. 2008, 81, 203. (23). Mihai, O.; Widyastuti, C.; Kumar, A.; Li, J.; Joshi, S.; Kamasamudram, K.; Currier, N.; Yezerets, A.; Olsson, L., The Effect of NO2/NOx Feed Ratio on the NH3-SCR System Over Cu–Zeolites with Varying Copper Loading. Catal. Lett. 2014, 144, 70. (24). Grossale, A.; Nova, I.; Tronconi, E.; Chatterjee, D.; Weibel, M., The chemistry of the NO/NO2–NH3 “fast” SCR reaction over Fe-ZSM5 investigated by transient reaction analysis. J. Catal. 2008, 256, 312. (25). Grossale, A.; Nova, I.; Tronconi, E., Ammonia blocking of the “Fast SCR” reactivity over a commercial Fe-zeolite catalyst for Diesel exhaust aftertreatment. J. Catal. 2009, 265, 141. (26). Colombo, M.; Nova, I.; Tronconi, E., A comparative study of the NH3-SCR reactions over a Cu-zeolite and a Fe-zeolite catalyst. Catal. Today 2010, 151, 223. (27). Kang, W.; Choi, B.; Kim, H., Characteristics of the simultaneous removal of PM and NOx using CuNb-ZSM-5 coated on diesel particulate filter. J. Ind. Eng. Chem. 2013, 19, 1406. (28). Kwak, J. H.; Tonkyn, R. G.; Kim, D. H.; Szanyi, J.; Peden, C. H. F., Excellent activity and selectivity of Cu-SSZ-13 in the selective catalytic reduction of NOx with NH3. J. Catal. 2010, 275, 187. (29). Schmieg, S. J.; Oh, S. H.; Kim, C. H.; Brown, D. B.; Lee, J. H.; Peden, C. H. F.; Kim, D. H., Thermal durability of Cu-CHA NH3-SCR catalysts for diesel NOx reduction. Catal. Today 2012, 184, 252. (30). Wijayanti, K.; Andonova, S.; Kumar, A.; Li, J.; Kamasamudram, K.; Currier, N. W.; Yezerets, A.; Olsson, L., Impact of sulfur oxide on NH3-SCR over Cu-SAPO-34. Appl. Catal. B. 2015, 166–167, 568. (31). Ballinger, T.; Cox, J.; Konduru, M.; De, D.; Manning, W.; Andersen, P., Evaluation of SCR Catalyst Technology on Diesel Particulate Filters. SAE Int. J. Fuels Lubr. 2009, 2, 369. (32). Tronconi, E.; Nova, I.; Marchitti, F.; Koltsakis, G.; Karamitros, D.; Maletic, B.; Markert, N.; Chatterjee, D.; Hehle, M., Interaction of NOx Reduction and Soot Oxidation in a DPF with CuZeolite SCR Coating. Emiss.Control Sci.Technol. 2015, 1, 134. (33). Colombo, M.; Nova, I.; Tronconi, E., Detailed kinetic modeling of the NH3–NO/NO2 SCR reactions over a commercial Cu-zeolite catalyst for Diesel exhausts after treatment. Catal. Today 2012, 197, 243. (34). Oxley, J. C.; Smith, J. L.; Rogers, E.; Yu, M., Ammonium nitrate: thermal stability and explosivity modifiers. Thermochimica Acta 2002, 384, 23. (35). Andonova, S.; Vovk, E.; Sjöblom, J.; Ozensoy, E.; Olsson, L., Chemical deactivation by phosphorous under lean hydrothermal conditions over Cu/BEA NH3-SCR catalysts. Appl. Catal. B. 2014, 147, 251. (36). Kim, D. J.; Wang, J.; Crocker, M., Adsorption and desorption of propene on a commercial Cu-SSZ-13 SCR catalyst. Catal. Today 2014, 231, 83. (37). Wilken, N.; Nedyalkova, R.; Kamasamudram, K.; Li, J.; Currier, N.; Vedaiyan, R.; Yezerets, A.; Olsson, L., Investigation of the Effect of Accelerated Hydrothermal Aging on the Cu Sites in a Cu-BEA Catalyst for NH3-SCR Applications. Top. Catal. 2013, 56, 317. (38). Wilken, N.; Wijayanti, K.; Kamasamudram, K.; Currier, N. W.; Vedaiyan, R.; Yezerets, A.; Olsson, L., Mechanistic investigation of hydrothermal aging of Cu-Beta for ammonia SCR. Appl. Catal. B. 2012, 111–112, 58. (39). Supriyanto; Wijayanti, K.; Kumar, A.; Joshi, S.; Kamasamudram, K.; Currier, N. W.; Yezerets, A.; Olsson, L., Global kinetic modeling of hydrothermal aging of NH3-SCR over Cu-zeolites. Appl. Catal. B. 2015, 163, 382. (40). Olsson, L.; Wijayanti, K.; Leistner, K.; Kumar, A.; Joshi, S. Y.; Kamasamudram, K.; Currier, N. W.; Yezerets, A., A multi-site kinetic model for NH3-SCR over Cu/SSZ-13. Appl. Catal. B. 2015, 174–175, 212. 33 ACS Paragon Plus Environment


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(41). Wilken, N.; Wijayanti, K.; Kamasamudram, K.; Currier, N. W.; Vedaiyan, R.; Yezerets, A.; Olsson, L., Mechanistic investigation of hydrothermal aging of Cu-Beta for ammonia SCR. Appl. Catal. B 2012, 111, 58. (42). Delahay, G.; Coq, B.; Kieger, S.; Neveu, B., The origin of N2O formation in the selective catalytic reduction of NOx by NH3 in O2 rich atmosphere on Cu-faujasite catalysts. Catalysis Today 1999, 54, 431. (43). Olsson, L.; Wijayanti, K.; Leistner, K.; Kumar, A.; Joshi, S.; Kamasamudram, K.; Currier, N. W.; Yezerets, A., A multi-site kinetic model for NH3-SCR over Cu/SSZ-13. Appl. Catal. B: Environmental. 2015, 174-175, 212. (44). Leistner, K.; Brüsewitz, F.; Wijayanti, K.; Kumar, A.; Li, J.; Kamasamudram, K.; Currier, N. W.; Yezerets, A.; Olsson, L., Impact of Copper Loading on NH3-SCR and Related Reactions over Cu/SAPO-34. In manuscript. 2015. (45). Olsson, L.; Sjovall, H.; Blint, R. J., A kinetic model for ammonia selective catalytic reduction over Cu-ZSM-5. Appl. Catal. B 2008, 81, 203. (46). Ciardelli, C.; Nova, I.; Tronconi, E.; Chatterjee, D.; Bandl-Konrad, B.; Weibel, M.; Krutzsch, B., Reactivity of NO/NO2–NH3 SCR system for diesel exhaust aftertreatment: Identification of the reaction network as a function of temperature and NO2 feed content. Appl. Catal. B. 2007, 70, 80. (47). Grossale, A.; Nova, I.; Tronconi, E., Study of a Fe–zeolite-based system as NH3-SCR catalyst for diesel exhaust aftertreatment. Catal. Today 2008, 136, 18. (48). Koebel, M.; Madia, G.; Elsener, M., Selective catalytic reduction of NO and NO2 at low temperatures. Catal. Today 2002, 73, 239. (49). Leistner, K.; Mihai, O.; Wijayanti, K.; Kumar, A.; Kamasamudram, K.; Currier, N. W.; Yezerets, A.; Olsson, L., Comparison of Cu/BEA, Cu/SSZ-13 and Cu/SAPO-34 for ammonia-SCR reactions. Catal. Today http://dx.doi.org/10.1016/j.cattod.2015.04.004. (50). Devadas, M.; Kröcher, O.; Elsener, M.; Wokaun, A.; Söger, N.; Pfeifer, M.; Demel, Y.; Mussmann, L., Influence of NO2 on the selective catalytic reduction of NO with ammonia over FeZSM5. Appl. Catal. B. 2006, 67, 187. (51). Metkar, P. S.; Salazar, N.; Muncrief, R.; Balakotaiah, V.; Harold, M. P., Selective catalytic reduction of NO with NH3 on iron zeolite monolithic catalysts: Steady-state and transient kinetics. Appl. Catal. B. 2011, 104, 110. (52). Nedyalkova, R.; Kamasamudram, K.; Currier, N. W.; Li, J.; Yezerets, A.; Olsson, L., Experimental evidence of the mechanism behind NH3 overconsumption during SCR over Fe-zeolites. J. Catal. 2013, 299, 101. (53). Olsson, L.; Westerberg, B.; Persson, H.; Fridell, E.; Skoglundh, M.; Andersson, B., A Kinetic Study of Oxygen Adsorption/Desorption and NO Oxidation over Pt/Al2O3 Catalysts. J. Phys. Chem. B 1999, 103, 10433.


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