# Effect of Low-Cost Perovskite Based Lean NOx Trap to Reduce the NOx Emission for CRDI Engine

Authors: Chinnadurai Kombiah; Senthil Kumar Pachamuthu; Bharathan Rajappa
Journal: Advances in Materials Science and Engineering
 (2022)

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## Abstract

Lean NOx trap (LNT) is an after-treatment technology that targets NOx emissions from an IC Engine and reduces it by using fuel as the reductant. The main mechanisms involved in this process are (i) oxidation of NO into NO2, (ii) Entrapment of NO2 over an alkali Earth metal in the form of nitrates, and (iii) Regeneration and reduction of NO2. The oxidation and reduction reactions are usually performed over rare Platinum Group Metals (PGM). The alternate cycling of operation modes helps in the regeneration and reduction stage due to the presence of unburnt hydrocarbons and carbon monoxides. These HC and CO generated during profitable operation can reduce agents similar to ammonia in SCR (Selective Catalytic Reduction). In the case of LNT, the fuel-injected for reduction imposes a penalty on the system. Cobalt-based perovskites with the chemical formula “ACoO3” (where “A” denotes Ba, Sr, etc.) show excellent absorption and reduction tendencies towards NOx and are highly suited for LNT as they have higher NO oxidation capacity. This research experimented with two different coating procedures (with and without binder) with three other perovskite catalysts–BaCoO3, SrCoO3, and Ba0.5Sr0.5CoO3. Both the coatings were tested for their adherence, and it revealed that the binder-less layer had only 4% coating loss after 2 hrs of sonication. BaCoO3 showed higher NOx absorption due to the higher electropositive nature of barium. The peak conversion efficiency attained in this experiment was 84% at a catalyst temperature of 350°C and 40% load condition.


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## Body

## 1. Introduction

Motorization has led to a significant increase in exhaust emissions worldwide in recent years. As a result, developed countries that abide by pollution standards, including such Tier 3 (US), LEV III (California), as well as Euro 6 (EU), are trying to design testing methods that determine emission levels more accurately in real-world conditions rather than in the research group. The Euro 6d emission standard contains both an RDE (Real Driving Emission) test and a WLTC (Worldwide Harmonized Light Vehicle Test Cycle) dynamometer [1]. Developing countries like China, India, and Pakistan have officially fulfilled Euro 6 standards. However, the Indian government has opted to relocate from Bharat Stage IV to Bharat Stage VI standards, commencing in 2020, to meet the global emission standards [2]. Because of their hazardous impact, nitrogen oxides (NOx) and particulate matter (PM) are the two significant pollutants targeted in the present scenario. Impactful NOx emission control is only possible if the formation processes are better understood. The oxidation of atmospheric Nitrogen is indeed the primary source of NO. The diatomic nitrogen molecule (N2), which accounts for approximately 78 percent of atmospheric air, has a partially static nature due to the presence of a triple bond between the two atoms (N=N). On the other hand, Nitrogen-based compounds are formed if enough energy is supplied to break this bond. A high-energy environment like this exists inside the cylinder of a vehicle's internal combustion engine. Peak combustion temperature changes (2500K to 3000K) result in a variation of nitrogen oxides. Exposure to NOx emissions leads to respiratory illness and asthma in human beings [3]. Furthermore, NOx tends to react with unburned hydrocarbons to form smog, which also causes emphysema and eye irritation. It also contributes to particulate matter formation [4]. Particulate matter with a diameter of fewer than 10 microns has been linked to lung illnesses like bronchitis. [5]. The seven nitrogen-based oxides formed depending on the valence states of atomic nitrogen (N2O5) are nitrous oxide (N2O), nitric oxide (NO), di-nitrogen dioxide (N2O2), dinitrogen trioxide (N2O3), nitrogen dioxide (NO2), dinitrogen tetroxide (N2O4), and dinitrogen pentoxide. The NOX family is composed of these seven compounds. Due to their dominance in the exhaust, the primary two forms of nitrogen oxides concentrated on automotive emission control are NO and NO2. Pollutant emissions are caused by the fuel constituent elements, combustion characteristics, and combustion chemistry. For example, nitric oxide appears throughout the burned gases, both in the flame and behind the flame front, as a direct consequence of chemical reactions involving nitrogen and oxygen atoms that do not reach chemical equilibrium. The fuel/air equivalence ratio is significant in determining emissions in spark-ignition engines. In the case of diesel engines, the primary determinant is fuel distribution and how that distribution varies with time due to mixing [6]. Due to nonuniform mixing in diesel engine combustion, NOx is formed in regions where the mixture is close to stoichiometric. These various NOx control techniques have developed into three categories:(1)
Fuel precombustion treatment(2)
Exhaust after-treatment postcombustion. (a) SCR (using ammonia, urea, or HC as a reducing agent). (b) LNT changes to the combustion process(3)
(a) Oxygen reduction (absorption of less air); (b) temperature reduction (water injection and exhaust gas recirculation); (c) reducing residence time (burner configuration and chamber duration)Each method has distinct advantages and disadvantages. However, EGR, water injection (or electronic steam injection (ESI), retarding injection timing (or spark timing for petrol engines), engine downsizing, and divided injection [7] are simple and widely used NOx reduction techniques. On the other hand, EGR has a limited impact on engine efficiency [8, 9], water injection poses corrosion risks [10], and split injection necessitates expensive and time-consuming electronic control systems. Furthermore, the presence of any after-treatment device in the tailpipe diminishes engine efficiency, which can be reduced by optimizing the backpressure [10].The Pt/Ba/Al2O3 catalyst used in this history became the first generation Lean NOx Trap. LNT functionality is divided into five stages:(1)
NOx (NO & NO2) oxidation to NO2—lean(2)
NO2 Adsorption as nitrates or nitrites on alkali site surfaces—lean(3)
Fuel-rich exhaust gas reducing agents (HC, CO, or H2)—lean(4)
Regeneration of NO2 from nitrate sites—rich(5)
NO2 breaks down into Nitrogen and oxygen—richBecause of the stability of the nitrates formed during the reaction of NO2 with barium, the storage mechanisms indicated that the NOx storage capacity increased with the basicity of the storage component used [11]. The NOx is generally stored as nitrates during lean air/fuel conditions. However, experiments have shown the presence of nitrites during this oxidation process [12]. Figure 1 shows the LNT in acts [11].Figure 1
Working of a lean NOx trap.The succeeding components are found in the 1st Generation LNT: the roles of each element in an LNT have been compiled [13], with both the following features having played significant roles:Platinum (as a catalyser): In general, the NOx composition consists mainly of NO (around 95 percent) and NO2 (5 percent). The ability of an LNT to trap NO2 has been affected by the concentration of NO2, as NO2 has a significantly larger tendency to form nitrates or nitrites on the trapping component. As just a result, the catalyst's oxidation is a vital step. It also gives atomic oxygen to the nitrite species, making the production of nitrite layers more likely [14]. Besides that, NOx reduction always occurs over the platinum catalyst.Barium Oxide (Trapping Component): the major component of an LNT participates actively in the trapping process. According to the literature, barium oxide tends to trap NO2 than NO [13]. In Figure 2, they demonstrate two different types of reactions.Figure 2
Nitrate & Nitrite formation in LNT.Alumina (support): alumina's primary role in an LNT is to support the catalyst and trap component. A larger surface area leads to more significant catalytic activity in some instances. Some studies [15] show that alumina forms aluminum nitrate and, in a manner, traps NOx by doing so. However, due to Al (NO3)'s low thermal stability, the percentage of NOx trapped by alumina is usually ignored. Several mechanisms constrain the chemistry of the NOx trap. The widely accepted NOx trap mechanisms, on either hand, follow the nitrate or nitrite route description of the research work [16]. In the early days, NOx chemistry and NO2 disproportionation reactions were common. However, two parallel pathways have recently been found to occur in a lean NOx trap. First, before proceeding to a reduction stage, the NO2 trapped in the alkali component must regenerate. The nitrate decomposition from the trapping component could've been caused by the temperature rise during rich fuel induction and the decrease in oxygen concentration in the decadent phase, minimizing nitrate equilibrium stability [17].Regeneration:BaNO32⟶ΔBaO+2NO2+1/2O2NO2⟶NO+1/2O2.A part of NO2 also reduces into NO.Reduction:2NO (or NO2) + 2 CO ↔ 2 CO2 + N2.NO (or NO2) + HC ↔ CO2 + H2O + N2.x+y/2NOorNO2+CxHy⟶y+x/2N2+yCO2+n/2H2O (x + y).2H2 + 2NO (or NO2) ⟶ 2H2O + N2.H2O+H2⟶NOx−⟶NH3+N2.NH3 + NOx ⟶ N2 + H2O.Ammonia formed during the intermediate reaction have been further used to reduce NOx into N2 and H2O.H2O+CO⟶NOx−⟶H2+CO2N2, CO2, and H2O were the most significant byproducts generated. The reduction and regeneration procedures can differ depending on the reductant used. The reductant is the fuel because the fuel type determines the reduction and regeneration in most cases. Studies would install a secondary injector on the tailpipe to spray a secondary fuel to reduce the NOx stored. This setup would be a less expensive and more effective reductant. This method is similar to SCR because it uses secondary fuel tanks and secondary injection control systems.


## 2. Catalysts of the Perovskite-Type and Their Properties

Gustav Rose discovered perovskites in 1839 and named the others after the Russian mineralogist, Count L. A. Perovski. The first Perovskite realized was Calcium Titanate, CaTiO3, which had the general formula ABO3, where “A” and “B” are cations and “O” is the anion that bonds both, as shown in Figure 3. Perovskite generally has a cubic crystal structure, as do most transition metal oxides.Figure 3
Unit cell of Perovskite.Perovskites have several desirable properties, including electrical, magnetic, optical, and catalytic properties, given that nearly 90 percent of all elements in the periodic table can be stable in the perovskite structure and the possibility of partial substitution of A and B sites [13]. The following two conditions must be satisfied to form a stable perovskite:(1)
Cation “A” must have a larger ionic radius than cation “B” to be accommodated properly in the unit cell. In general, rA> 0.090 nm and rB > 0.051 nm, with a tolerance factor ranging from 0.8 to 1.0 [18].(2)
The perovskite compound must be electrically neutral, which is only possible if the total positive ion charge of “A” and “B” constitutes the oxygen ion charge.


### 2.1. NOx Trapping Ability of Perovskites

The NOx trapping ability of perovskites has received considerable attention. According to [19], chemisorption of NO2 occurs due to the formation of nitrate or nitrite, which is quite similar to that of traditional LNT. Moreover, [20] proposed that the oxygen vacancies of perovskites also serve as NOx storage sites in their research. The research [21] also disclosed a chemical reaction in which NO2 was stored as metal nitrates. Metal nitrates would've been reverted to perovskite form during the rich phase due to calcination caused by higher temperatures in the exhaust. The reaction of NO2 trapped in barium cobalt oxide perovskite is represented below.3 BaCoO3 + 6 NO2(g) + 2 (1 + 3y)O2(g) ⟶ 3Ba(NO3)2(s) + Co3O4(g).


### 2.2. Perovskite Synthesis

Perovskites are mainly synthesised using the four methods mentioned below:1. Acetic the Sol-gel Method, 2. Method of co-precipitation, 3. Synthesis of combustion, 4. Reactive grinding method.Each method has a distinct effect on the Perovskite formed in surface area, structure, and morphological parameters. The sol-gel citric acid method of synthesis to generate the following catalysts: BaCoO3, SrCoO3, and Ba0.5Sr0.5CoO3.This process starts by dissolving the nitrate salts of the desired oxides in the stoichiometric amount and then proceeding as explained elsewhere [22]. For example, to begin producing BaCoO3, stoichiometric concentrations of barium nitrate (Ba (NO3)2) and cobalt nitrate hexahydrate (Co (NO3)2.6H2O) are dissolved in deionized water and stirred continuously. In just this solution, a concentration of citric acid equal to the metal ion concentration has been dissolved. This mixture was stirred for 4-5 hours in a magnetic stirrer until a transparent purple gel formed. The release of gas from the combination illustrates this process. Once the gel has been initiated, the drying and calcination processes are conducted to obtain the catalyst.The drying occurred at 120°C for 24 hours before being calcined at 850°C for 5 hours. The hot air oven's airflow rate had to be kept constant at 100 sccm (standard cubic centimeters), and the calcination was done in a muffle furnace. Figure4 depicts the formation of sol, gel, and Perovskite. For phase identification, XRD of the synthesised samples was used. A Bruker axstometer (30 kV, 12 mA) was used to perform X-ray Diffraction with wavelength radiation = 1.5418 A. Each sample's data was collected for a scan range of 10 to 50 degrees and a step width of 0.02 degrees. The measured XRD data corresponds to the standard data from the Crystallography Open.Figure 4
(a) Sol formation, (b) gel formation, and (c) perovskite.
(a)(b)(c)Database (COD). The contaminants BaCoO3 (COD Id: 1520993), SrCoO3 (COD Id: 1551939), Ba0.5Sr0.5CoO3 (COD Id: 7221487), and Co3O4 (COD Id: 1526734) match the standard data from the COD database. In some cases, the XRD analysis shown in Figure 5 detects the presence of metal carbonates and Co3O4 (spinel). At 850°C, XRD confirms that the sample does have a crystalline perovskite (hexagonal) structure.Figure 5
XRD Peaks of synthesised perovskites.


### 2.3. Coating Procedure

Substrate activation techniques are the most commonly used methods for coating a substrate. The different kinds of substrate activation are discussed extensively in [23]. Structure at 850°C.COAT 1 (support deposition followed by active phase deposition):(1)
Alumina was chosen as a wash coat because it has a large surface area. Alumina (Qualigen) with a particle size of 67 um was milled for 20 hours in a high-energy planetary ball mill. Following the procedure outlined in the research study [24], an alumina slurry was formed. Formalised paraphrase deionised water was mixed with alumina (30% wt), PEG 1000 (2%), and alumina sol (4% wt), pH = 4. In some cases, glacial acetic acid (20 mol l-1) was added to improve slurry stability [25]. The substrate was dipped for a few seconds in this slurry before being dried and calcined to increase the necessary alumina weight. Perovskites tend to form mullites and aluminates [24]. Hence a layer of Ceria is added over it.(2)
A cerium oxide slurry was formed by dissolving polyvinyl alcohol in water at 85°C, followed by glycerol and cerium oxide. This slurry was then dip-coated onto the alumina layer after being ball milled for 20 hours.(3)
This layer was impregnated with the perovskite catalyst by immersing it in a 1 : 3 slurry of nitric acid and deionized water. The amount of perovskite catalyst powder added was proportional to the acid used. This was dried for 30 minutes at 200°C before calcining for 5 hours at 700°C.COAT 2 (Active phase growth on the substrate in situ):(1)
This type of coating was installed following the patent procedures [18]. As previously described, the first step in this type of coating is preparing a perovskite material using the sol-gel technique.(2)
However, rather than proceeding with the drying stage, this gel is used as a dipping medium. By adding a suitable reagent, the gel viscosity can be varied as desired (deionized water in this case).The substrate sample is dipped into the gel wash coat and held for one minute. This allows the gel material to fill the pores of the cordierite. This gel-coated sample is then dried at 120°C. for one hour before calcining at 700°C. for five hours. The gel enters the pore of the substrate and is calcined, allowing high surface perovskite to grow onto the substrate.SEM images of coated samples are shown in Figure6. Uncoated cordierite is highly porous, with a mean wall thickness of 0.8 mm and pores with a mean diameter of 35 um.Figure 6
SEM images cordierite. (a) Uncoated cordierite. (b) First coating. (c) Second coating.
(a)(b)(c)Only when these pores are filled with the coating material will the adhesion of the applied coat be satisfactory. Because of the multilayered coating, COAT 1 has a smaller channel volume than the other two types of layers. This may result in a more significant pressure drop across the exhaust line. The COAT 2 depicts the perovskite material's in-situ growth. Compared to COAT 1, this has better adhesion and a more prominent channel volume.COAT 1 appears to wither from the substrate in Figure7 due to higher mass deposition (3 layers). Each time the substrate sample was dipped into the slurry, the substrate's mass increased. COAT 2 can be seen in Figure 7 to have a flaky layer formed over the substrate, demonstrating better bonding than that of the three-layered coating. Calcination of Perovskite has occurred within the pores of cordierite and results in a flaky layer visible in the SEM images. Figure 8 depicts the EDAX report for uncoated cordierite, as well as COAT 1 and COAT 2.Figure 7
Structures of (a) COAT 1 and (b) COAT 2.
(a)(b)(c)Figure 8
EDAX details of cordierites. (a) Uncoated. (b) COAT 1. (c) COAT 2.The morphology of each coating is depicted in both SEM images in Figure9. The COAT 2 layer is more refined than the COAT 1 layer. In addition, the addition of Ceria to LNT resulted in the formation of bulk sulphate species [26]. The nanoparticles in COAT 2 are formed as a result of the sol-gel Perovskite being calcined. When this nano size comes into contact with exhaust gases, it can increase catalytic activity. This smaller particle size also contributes to good adhesion to the substrate. An ultra sonicator apparatus was used to test the adherence of both sample coatings. For 30 minutes, both sample coated cordierites were immersed in a sonicator water bath. The morphology of each coating is represented in both SEM images in Figure 9. The COAT 2 layer is more refined than the COAT 1 layer. In addition, the addition of Ceria to LNT leads to the formation of bulk sulphate species [26]. The nanoparticles in COAT 2 are formed due to the sol-gel Perovskite's calcination temperature.Figure 9
Structure of (a) COAT 1 and (b) COAT 2.
(a)(b)When this nano size comes into contact with exhaust gases, it can increase catalytic activity. This smaller particle size also helps with adhesion to the substrate. An Ultra Sonicator apparatus was used to test the adherence of both sample coatings. For 30 minutes, both sample coated cordierites were immersed in a sonicator water bath. On the other hand, a shaker table can be used to vibrate the coated substrate at a specific frequency to measure the weight loss due to vibration. Before and after sonicator use, the weights of both coated samples were measured. Samples were measured.After sonication, COAT 1 lost 22 percent of its weight, while COAT 2 lost only 4 percent. This gravimetric analysis was carried out using a highly accurate analytical balance (accuracy of 0.001 gms). This is due to the numerous microcracks in COAT 1, as shown in Figure10. The main result of the adherence tests revealed that layer COAT 1 had a few disadvantages compared to COAT 2. However, due to its excellent adhesion quality, COAT 2 was chosen for the next stage of emission tests. Three cordierite substrates (cylindrical 400 cpsi) with dimensions of 90 mm dia. and 150 mm length were determined based on the engine to perform emission tests in real-time. These substrates were coated using the COAT 2 procedure. The coated substrates were coated with perovskite materials synthesised and tested, which included BaCoO3, Ba0.5Sr0.5CoO3, and SrCoO3.Figure 10
Microcracks in COAT 1.


## 2.1. NOx Trapping Ability of Perovskites

The NOx trapping ability of perovskites has received considerable attention. According to [19], chemisorption of NO2 occurs due to the formation of nitrate or nitrite, which is quite similar to that of traditional LNT. Moreover, [20] proposed that the oxygen vacancies of perovskites also serve as NOx storage sites in their research. The research [21] also disclosed a chemical reaction in which NO2 was stored as metal nitrates. Metal nitrates would've been reverted to perovskite form during the rich phase due to calcination caused by higher temperatures in the exhaust. The reaction of NO2 trapped in barium cobalt oxide perovskite is represented below.3 BaCoO3 + 6 NO2(g) + 2 (1 + 3y)O2(g) ⟶ 3Ba(NO3)2(s) + Co3O4(g).


## 2.2. Perovskite Synthesis

Perovskites are mainly synthesised using the four methods mentioned below:1. Acetic the Sol-gel Method, 2. Method of co-precipitation, 3. Synthesis of combustion, 4. Reactive grinding method.Each method has a distinct effect on the Perovskite formed in surface area, structure, and morphological parameters. The sol-gel citric acid method of synthesis to generate the following catalysts: BaCoO3, SrCoO3, and Ba0.5Sr0.5CoO3.This process starts by dissolving the nitrate salts of the desired oxides in the stoichiometric amount and then proceeding as explained elsewhere [22]. For example, to begin producing BaCoO3, stoichiometric concentrations of barium nitrate (Ba (NO3)2) and cobalt nitrate hexahydrate (Co (NO3)2.6H2O) are dissolved in deionized water and stirred continuously. In just this solution, a concentration of citric acid equal to the metal ion concentration has been dissolved. This mixture was stirred for 4-5 hours in a magnetic stirrer until a transparent purple gel formed. The release of gas from the combination illustrates this process. Once the gel has been initiated, the drying and calcination processes are conducted to obtain the catalyst.The drying occurred at 120°C for 24 hours before being calcined at 850°C for 5 hours. The hot air oven's airflow rate had to be kept constant at 100 sccm (standard cubic centimeters), and the calcination was done in a muffle furnace. Figure4 depicts the formation of sol, gel, and Perovskite. For phase identification, XRD of the synthesised samples was used. A Bruker axstometer (30 kV, 12 mA) was used to perform X-ray Diffraction with wavelength radiation = 1.5418 A. Each sample's data was collected for a scan range of 10 to 50 degrees and a step width of 0.02 degrees. The measured XRD data corresponds to the standard data from the Crystallography Open.Figure 4
(a) Sol formation, (b) gel formation, and (c) perovskite.
(a)(b)(c)Database (COD). The contaminants BaCoO3 (COD Id: 1520993), SrCoO3 (COD Id: 1551939), Ba0.5Sr0.5CoO3 (COD Id: 7221487), and Co3O4 (COD Id: 1526734) match the standard data from the COD database. In some cases, the XRD analysis shown in Figure 5 detects the presence of metal carbonates and Co3O4 (spinel). At 850°C, XRD confirms that the sample does have a crystalline perovskite (hexagonal) structure.Figure 5
XRD Peaks of synthesised perovskites.


## 2.3. Coating Procedure

Substrate activation techniques are the most commonly used methods for coating a substrate. The different kinds of substrate activation are discussed extensively in [23]. Structure at 850°C.COAT 1 (support deposition followed by active phase deposition):(1)
Alumina was chosen as a wash coat because it has a large surface area. Alumina (Qualigen) with a particle size of 67 um was milled for 20 hours in a high-energy planetary ball mill. Following the procedure outlined in the research study [24], an alumina slurry was formed. Formalised paraphrase deionised water was mixed with alumina (30% wt), PEG 1000 (2%), and alumina sol (4% wt), pH = 4. In some cases, glacial acetic acid (20 mol l-1) was added to improve slurry stability [25]. The substrate was dipped for a few seconds in this slurry before being dried and calcined to increase the necessary alumina weight. Perovskites tend to form mullites and aluminates [24]. Hence a layer of Ceria is added over it.(2)
A cerium oxide slurry was formed by dissolving polyvinyl alcohol in water at 85°C, followed by glycerol and cerium oxide. This slurry was then dip-coated onto the alumina layer after being ball milled for 20 hours.(3)
This layer was impregnated with the perovskite catalyst by immersing it in a 1 : 3 slurry of nitric acid and deionized water. The amount of perovskite catalyst powder added was proportional to the acid used. This was dried for 30 minutes at 200°C before calcining for 5 hours at 700°C.COAT 2 (Active phase growth on the substrate in situ):(1)
This type of coating was installed following the patent procedures [18]. As previously described, the first step in this type of coating is preparing a perovskite material using the sol-gel technique.(2)
However, rather than proceeding with the drying stage, this gel is used as a dipping medium. By adding a suitable reagent, the gel viscosity can be varied as desired (deionized water in this case).The substrate sample is dipped into the gel wash coat and held for one minute. This allows the gel material to fill the pores of the cordierite. This gel-coated sample is then dried at 120°C. for one hour before calcining at 700°C. for five hours. The gel enters the pore of the substrate and is calcined, allowing high surface perovskite to grow onto the substrate.SEM images of coated samples are shown in Figure6. Uncoated cordierite is highly porous, with a mean wall thickness of 0.8 mm and pores with a mean diameter of 35 um.Figure 6
SEM images cordierite. (a) Uncoated cordierite. (b) First coating. (c) Second coating.
(a)(b)(c)Only when these pores are filled with the coating material will the adhesion of the applied coat be satisfactory. Because of the multilayered coating, COAT 1 has a smaller channel volume than the other two types of layers. This may result in a more significant pressure drop across the exhaust line. The COAT 2 depicts the perovskite material's in-situ growth. Compared to COAT 1, this has better adhesion and a more prominent channel volume.COAT 1 appears to wither from the substrate in Figure7 due to higher mass deposition (3 layers). Each time the substrate sample was dipped into the slurry, the substrate's mass increased. COAT 2 can be seen in Figure 7 to have a flaky layer formed over the substrate, demonstrating better bonding than that of the three-layered coating. Calcination of Perovskite has occurred within the pores of cordierite and results in a flaky layer visible in the SEM images. Figure 8 depicts the EDAX report for uncoated cordierite, as well as COAT 1 and COAT 2.Figure 7
Structures of (a) COAT 1 and (b) COAT 2.
(a)(b)(c)Figure 8
EDAX details of cordierites. (a) Uncoated. (b) COAT 1. (c) COAT 2.The morphology of each coating is depicted in both SEM images in Figure9. The COAT 2 layer is more refined than the COAT 1 layer. In addition, the addition of Ceria to LNT resulted in the formation of bulk sulphate species [26]. The nanoparticles in COAT 2 are formed as a result of the sol-gel Perovskite being calcined. When this nano size comes into contact with exhaust gases, it can increase catalytic activity. This smaller particle size also contributes to good adhesion to the substrate. An ultra sonicator apparatus was used to test the adherence of both sample coatings. For 30 minutes, both sample coated cordierites were immersed in a sonicator water bath. The morphology of each coating is represented in both SEM images in Figure 9. The COAT 2 layer is more refined than the COAT 1 layer. In addition, the addition of Ceria to LNT leads to the formation of bulk sulphate species [26]. The nanoparticles in COAT 2 are formed due to the sol-gel Perovskite's calcination temperature.Figure 9
Structure of (a) COAT 1 and (b) COAT 2.
(a)(b)When this nano size comes into contact with exhaust gases, it can increase catalytic activity. This smaller particle size also helps with adhesion to the substrate. An Ultra Sonicator apparatus was used to test the adherence of both sample coatings. For 30 minutes, both sample coated cordierites were immersed in a sonicator water bath. On the other hand, a shaker table can be used to vibrate the coated substrate at a specific frequency to measure the weight loss due to vibration. Before and after sonicator use, the weights of both coated samples were measured. Samples were measured.After sonication, COAT 1 lost 22 percent of its weight, while COAT 2 lost only 4 percent. This gravimetric analysis was carried out using a highly accurate analytical balance (accuracy of 0.001 gms). This is due to the numerous microcracks in COAT 1, as shown in Figure10. The main result of the adherence tests revealed that layer COAT 1 had a few disadvantages compared to COAT 2. However, due to its excellent adhesion quality, COAT 2 was chosen for the next stage of emission tests. Three cordierite substrates (cylindrical 400 cpsi) with dimensions of 90 mm dia. and 150 mm length were determined based on the engine to perform emission tests in real-time. These substrates were coated using the COAT 2 procedure. The coated substrates were coated with perovskite materials synthesised and tested, which included BaCoO3, Ba0.5Sr0.5CoO3, and SrCoO3.Figure 10
Microcracks in COAT 1.


## 3. Materials and Methods

### 3.1. Fabrication of the LNT, Experimental Setup, And Baseline Reading

Following the appropriate procedures, the coated cylindrical substrates were canned. The fabricated shell volume was kept constant at the same level as the displacement volume of the engine used. To prevent cordierite damage due to thermal expansion, an Alumina Fibre mat was used at the contact area between the cordierite and steel, as shown in Figure11. An emission analyser was used to measure engine-out emissions. This experiment modified the Kirloskar AV1, a nonautomotive stationary engine, to control the Lean-Rich injection cycle. The engine-out NOx emission from this modified engine was measured under various load conditions. Figure 12 depicts the experimental schematic diagram of engine setup and Table 1 shows the specification of the engine used for the experiment.Figure 11
Fabrication images with Alumina support mat.Figure 12
Experimental schematic of Lean NOx Trap.Table 1
IC engine specifications.
Type4S diesel (1 Cyl.)Bore80 mmStroke110 mmCompression ratio17.5 : 1Maximum power3.7 kWSpeed1500 rpmLoading deviceEddy current dynoMode of startingManually crankingMechanical injector pressure220 barElectronic injector pressure1000 barInjection timing23° BTDCThe first set of measurements was taken without electronic injection, i.e., with the engine as it was. Various conditions were used to record the emission and performance outcomes. Table2 shows the specifications of the IC engine and the electronic fuel injector used in this experiment.Table 2
Electronic fuel injector specifications.
Injection pressure1000 barNo. of nozzle holes3Nozzle diameter0.518 mmStart of injection23° BTDCInjection duration650–3000μsec


## 3.1. Fabrication of the LNT, Experimental Setup, And Baseline Reading

Following the appropriate procedures, the coated cylindrical substrates were canned. The fabricated shell volume was kept constant at the same level as the displacement volume of the engine used. To prevent cordierite damage due to thermal expansion, an Alumina Fibre mat was used at the contact area between the cordierite and steel, as shown in Figure11. An emission analyser was used to measure engine-out emissions. This experiment modified the Kirloskar AV1, a nonautomotive stationary engine, to control the Lean-Rich injection cycle. The engine-out NOx emission from this modified engine was measured under various load conditions. Figure 12 depicts the experimental schematic diagram of engine setup and Table 1 shows the specification of the engine used for the experiment.Figure 11
Fabrication images with Alumina support mat.Figure 12
Experimental schematic of Lean NOx Trap.Table 1
IC engine specifications.
Type4S diesel (1 Cyl.)Bore80 mmStroke110 mmCompression ratio17.5 : 1Maximum power3.7 kWSpeed1500 rpmLoading deviceEddy current dynoMode of startingManually crankingMechanical injector pressure220 barElectronic injector pressure1000 barInjection timing23° BTDCThe first set of measurements was taken without electronic injection, i.e., with the engine as it was. Various conditions were used to record the emission and performance outcomes. Table2 shows the specifications of the IC engine and the electronic fuel injector used in this experiment.Table 2
Electronic fuel injector specifications.
Injection pressure1000 barNo. of nozzle holes3Nozzle diameter0.518 mmStart of injection23° BTDCInjection duration650–3000μsec


## 4. Results and Discussion

The engine was first run under various load conditions to obtain baseline readings, and then the process was repeated to ensure no errors were present. Finally, the fabricated LNT device was attached to the exhaust end, and the emission reading for neat Diesel without electronic injection was recorded. The following observations were made using the AVL DIGAS 444N Gas Analyser.Only NO is recorded because the equipment detects NO using an electrochemical sensor. The following are the emission results with a BaCoO3 catalyst LNT on a mechanical injection engine. The different loading values and corresponding emission values were plotted. Figure 13 depicts the P-Theta and HRR curves. The experiment was carried out with Neat Diesel and Prosopis-juliflora bio-oil [a blend of 85 percent diesel and 15 percent juliflora oil], denoted as PJ 15, to learn about the impact of LNT on a biofuel. NOx emissions plummet under high load conditions. Because of incomplete combustion, NOx levels in biodiesel PJ15 are even lower [13]. Figure 14 depicts the NOx level at load variations.Figure 13
Curves for different load conditions with mechanical injection. (a) Load and crank angle curve. (b) HRR and crank angle curve.
(a)(b)Figure 14
NOx emission curve for Diesel and PJ15 with LNT.The main engine modification was the electronic injection control, which was used to control the alternating lean-rich cycling required for the lean NOx trap. Various injection cycles were tested, and the best injection strategy was a lean-rich cycle of 120 seconds (lean) to 20 seconds (rich). As shown in Figure15, BaCoO3-LNT significantly reduced HC emission levels (with LNT) at high load conditions while having no effect at low load conditions. The main reason for this could be the lower levels of nitrogen oxides. The rich mixture converts NOx to Nitrogen and Oxygen in high load conditions.Figure 15
HC emission for Diesel and PJ15 with LNT.These released oxygen molecules undergo oxidation with hydrocarbons and carbon monoxide. However, due to the poor atomization of the fuel, PJ 15 biodiesel emits an overall higher level of HC.Nitrogen oxide reduction mechanisms are slower in low load conditions than in high load conditions. This leads to lower oxygen release in the exhaust, which has little or no impact on HC emissions under common load conditions. CO emission levels are depicted in Figure16. CO emissions can be reduced slightly during high load conditions. The oxygen molecules released during NOx decomposition undergo oxidation of carbon monoxides to carbon dioxide, resulting in a slight increase in CO2 emissions proportional to the decrease in CO emissions.Figure 16
CO emission for Diesel and PJ 15 with LNT.Because of the different fuels used (diesel & PJ15), the exhaust gas temperature varies in Figures14–16, and as a result, emissions cannot be measured using temperature as a reference. As a consequence, the load is being used as the X-axis parameter. The impact of LNT causes a rise in CO emissions in the case of PJ15 biofuel, but the levels are not as high as they are in neat diesel. However, when compared to neat diesel, the CO levels are higher due to the poor atomization of the biofuel. Collected on the basis of all of these readings, the engine was modified, and the effect of this modification is depicted in Figure 17.Figure 17
Engine-Out NOx with cyclic injection.This injection cycle was used to collect baseline readings. The engine was run at 40% load (average out NOx of 740 ppm and a catalyst temperature of 240°C), and the NOx reading was recorded as a function of time. As a result of the rich phase, the injection cycle resulted in periodic NOx reduction.Figure18 depicts NOx absorption and regeneration. All three catalysts exhibit comparable absorption and reduction, but BaCoO3 absorbs that much more NOx than SrCoO3. This is due to barium's more electropositive behaviour in the past when compared to strontium. In addition, due to its larger size when compared to strontium, barium (Atm no. 56) quickly loses its outermost electron (Atm no. 38). Finally, as previously stated, the metal nitrate or nitrite species formed during absorption significantly impact trapping capacity.Figure 18
Average NOx reduction with LNT at 240°C.The release of trapped NOx and incoming engine-out nitrogen oxides cause a sudden spike in NOx emission in the exhaust at the start of the regeneration phase. As stated previously, the metal nitrate or nitrite species formed during absorption significantly impact absorption capacity. Figure19 depicts the average NOx reduction achieved in the same engine with and without a lean NOx trap. The LNT reduced engine-out nitrogen oxides with a conversion efficiency of 63.5 percent at 240°C. As shown in Figure 20, at 40% engine load, the engine-out NOx is 740 ppm. On the other hand, the LNT-Out NOx at 240 C is 270 ppm. This NOx reduction accounts for 63.5 percent of the conversion efficiency. If the temperature is raised to 350°C, the LNT-Out NOx drops to 118.4 ppm, resulting in a peak conversion efficiency of 84 percent. LNT's performance in this range is optimal, and it can be considered excellent at low temperatures. However, after 170°C, there is a noticeable change caused by the attainment of the light-off temperature. As a result, the conversion efficiency increases with temperature.Figure 19
NOx conversion efficiency.Figure 20
NOx stored in Lean phase and reduced in the rich phase by three perovskite catalyst.The percentage of conversion is calculated as follows:Stored NOx (ppm) = total NOx in−total NOx out.NOx conversion (percent) = 100 × (total NOx in−total NOx out)/total NOx.Conversion efficiencies of up to 84 percent were achieved at higher temperatures (350°C).Figure19 depicts the variation of LNT efficiency concerning temperature.


## 5. Conclusions

The most important part of this research work is to find a suitable replacement for Pt in a Lean NOx trap. Three catalysts were selected based on a literature survey and synthesised by proper procedures. The final output using the BaCoO3 catalyst in an LNT reactor shows high NOx conversion efficiency but not as high as platinum-based LNT. Therefore, the low-cost catalyst will serve as a suitable replacement but has certain limitations apart from conversion efficiency.The selected catalyst was the cheapest among the three, and the coating, COAT 2, showed higher adherence with a mass loss of only 4% during sonication.Regarding the emission tests, at low load conditions, the NOx decomposition percentage is minimum and erratic. There occurs no gradual rise in NOx decomposition with a stage-wise increase in loads. However, at high load conditions, the increase in the NOx decomposition percentage is very high. NOx conversion obtained was 63.5% at 240°C and increased up to 84% at 350°C in the experiment.The impact of LNT on other emissions was also recorded. HC and CO values dropped due to the oxidation of the oxygen molecule released during nitrogen oxide break up. No considerable change in smoke emission was observed.Long-time usage during the experiment showed a drop in performance of the LNT, which could be due to Sulfur poisoning of the catalyst material. The project has a wide range of future scope. The Coatings studied were selected only based on their adherence. Since COAT 1 is an alumina-perovskite LNT, it showed the formation of aluminates in some instances. This hinders the reduction reactions. This could be researched, and methods to prevent this can be developed. The LNT reactor developed if subjected to the artificial thermal aging test, and the long-term durability can be analysed.



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*Source: 1863296-2022-04-13.xml*