Synthesis of La0.8Sr0.2Co0.9Fe0.1O3-δ perovskite oxide catalyst and the geometric modification of a catalytic converter for hydrocarbon and carbon monoxide emission reduction

Increasing environmental concerns caused by vehicular emissions have intensified the search for the design and development of non-noble metal catalysts for catalytic converter devices as potential replacements for conventional Pt-, Pd-, and Rh-based noble metal catalysts. This research highlights the development and evaluation of an alternative to conventional catalysts through the synthesis of non-noble metal perovskite-based catalysts and the design modification of a catalytic converter. A non-noble metal catalyst, La₀.₈Sr₀.₂Co₀.₈Fe₀.₂O₃ (LSCF), was synthesized by co-precipitation, coated onto a ceramic monolith of a catalytic converter, and examined for effectiveness under petrol fuel laboratory test setup. The synthesized catalyst was also analyzed using SEM, XRD, and EDX to study surface morphology and confirm the crystal structure. The catalytic converter housing assembly was modified by integrating design modifications and analyzed through computational simulations to investigate velocity profile, pressure distribution, and reaction behavior. Among the three catalytic converter design configurations with diffuser cone angles of 8°, 10°, and 14°, the first was selected as it showed a favorable gas flow pattern, pressure distribution, and velocity profile. The entire module was then experimentally evaluated on a petrol fuel laboratory test setup to assess emission performance under varying loads and speeds. Experimental emission tests revealed a significant reduction in hydrocarbon (HC) and carbon monoxide (CO) emissions compared to engines without a catalytic converter. The results demonstrate that the synthesized La₀.₈Sr₀.₂Co₀.₉Fe₀.₁O₃-δ non-noble metal catalyst, combined with the modified catalytic converter design, effectively reduces vehicular emissions and provides an alternative and practical approach to noble metal catalysts. A noticeable reduction in CO and HC exhaust emissions was achieved using the LSCF catalyst for an automotive catalytic converter.

1 Introduction

Emissions from transportation are a major contributor to air pollution. Millions of cars are produced and are subsequently driven by people worldwide each day. It is anticipated that the number of automobiles will rise rapidly in the years to come. Fossil fuels are necessary for vehicle motion, but as combustion products they release much exhaust pollution. The main source of air pollution, particularly in urban and metropolitan areas, is from vehicle density on the road. Automotive vehicles are one of the main sources for carbon monoxide (CO), unburned hydrocarbons (HC), nitrogen oxides (NOx), and particulate matter (PM) emissions in the atmosphere (Furfori et al., 2010; Prasad and Singh, 2012).

CO and HC emissions from petrol fuel vehicles are poisonous pollutants that draw hemoglobin from the blood more strongly than oxygen. People’s mental acuity may deteriorate if they are exposed to CO levels above 9 ppm (parts per million) for an extended period of time. In addition, unburned fuel vapors, or HC, contribute to smog, respiratory problems, and the risk of cancer. According to current emission standards, the usual allowed levels are 0.10 g/km or less than 200 ppm at idle in vehicle tests (Ministry of Road Transport and Highways, 2025; Ganesan, 2010; Rao and Rao, 2001). Emissions need to be controlled by the strict emission requirements that have been put in place. By burning the fuel in engine and the subsequent combustion process, the harmful chemicals from engine exhaust can be reduced. This can be accomplished with the aid of gasoline additives, engine design modifications, exhaust treatment equipment, and optimized fuel distribution methods. Automobile emissions are classified into three types: exhaust emissions (CO, HC, NOx, and PM), crankcase emissions (blow by gases and HC), and evaporative emissions (fuel vapors) (Acres, 1996; De Nevers, 2000; Rao and Rao, 2001). The major composition of pollutants in typical petrol engine exhausts are CO (0.5 vol.%), HC (350 ppm), and NOx (900 ppm) (Farrauto and Heck, 1999). CO reduces blood-oxygen carrying capacity, especially in individuals with heart problems, while HC and NOx form secondary pollutants (O₃, NO₂, and PAN) that cause respiratory issues, eye irritation, and environmental damage (Wei, 1975; Neeft et al., 1996; Farrauto and Heck, 1999). Particulate matter can penetrate cells and cause lung diseases, asthma, or cancer (Fino et al., 2006). The particles belong to the fine (PM2.5) and ultrafine particle fractions (PM0.1) of PM and can penetrate deep into the respiratory tract; they consist of a complex mixture of elemental carbon, metals, and organic compounds, including polycyclic aromatic HCs which are known carcinogens (Steppuhn et al., 2025). Emissions also contribute to acid rain, the greenhouse effect, ozone depletion, smog, and damage to monuments and heritage sites (Neeft et al., 1996; Rao and Rao, 2001). To comply with stringent global regulations, technologies such as engine improvements, fuel additives, alternative fuels, and exhaust treatment are used (Fino et al., 2006; Prasad and Singh, 2012). Three-way catalytic converters remove CO, HC, and NOx from petrol engines, while DOCs and DPFs treat diesel emissions. Platinum group metals (Pt, Pd, and Rh) are the most effective catalysts due to high activity and thermal stability, though research has focused on alternatives or reduced-PGM catalysts such as oxides, spinels, perovskites, and alloys (Belton and Taylor, 1999; Bera and Hegde, 2010).

Many strategies have been proposed to reduce exhaust gas emissions as a mitigation measure. Exhaust reduction is one of the primary areas where such non-noble metals could be utilized to achieve the intended output results. Because of their high activity at various temperatures, redox nature, stability at high temperatures, and capability to store and release oxygen based on performance, perovskite oxides are appropriate replacements (Doggali et al., 2010). Additionally, the design geometry of catalytic converters has much more relevance to the flow reaction rate in the system as far as the temperature, flow pattern, pressure, and velocity parameters are concerned. Maximum reaction only happens with the flowability of the gas and its retention in the substrate geometry. Figure 1 shows the position of the catalytic converter in a vehicle, located between the engine and the exhaust muffler. After combustion, exhaust gases flow through it, where they react with the catalyst and then exit into the environment through the exhaust muffler.

Figure 1

Figure 1. Exhaust system showing catalytic converter placement.

Reactions in a catalytic converter comprise the following.

• Oxidization of CO to CO₂ and HC to carbon dioxide and water:

$2\text{CO}+{\mathrm{O}}_2\to 2{\text{CO}}_2(1)$

• Reduction of NOx to N₂ and O₂:

$2\text{NOx\hspace{0.17em}}\to {\text{xO}}_2+{\mathrm{N}}_2(2)$

Equations 1, 2 represent the reactions in catalytic converter. The ceramic material in the majority of converters has numerous flow openings and a single honeycomb, square, or circular structure. A few converters use loose ceramic granules, with gas moving between the densely packed spheres (Ganesan, 2010). The catalyst materials most used are platinum (Pt), palladium (Pd), and rhodium (Rh). Pd and Pt (noble metals) promote the oxidation reaction for CO and HC. Reducing carbon emission intensity is a crucial element in advancing sustainable development. In the context of continuous technical progress, the expansion of the digital economy may provide avenues for emissions reduction (Chen and Jiang, 2025). Rh promotes the reaction of NOx (Ganesan, 2010). Platinum group metal catalysts demonstrate high oxidation activity even at temperatures below 350 °C. However, their practical use is limited for several reasons discussed in previous content. Among these, Pd and Rh are particularly noted for their high toxicity and carcinogenic properties (Wei, 1975). Noble metal compounds typically escape from exhaust systems only when extremely fine airborne dust particles are generated through catalyst attrition. In some cases, highly toxic metal carbonyls absent in the original catalyst can form through reactions with exhaust gases and be released into the atmosphere as vapor (Wei, 1975). Additionally, road traffic contributes to the release of metallic and organic pollutants due to the wear of the automotive catalyst wash-coat, leading to environmental contamination (Kalavrouziotis and Koukoulakis, 2009; Wei, 1975). Of these three catalysts, Pt acts as an oxidation agent and Pd and Rh accelerate the reduction process. In exhaust pollutant control, three separate catalysts are typically required to facilitate oxidation and reduction reactions. A literature survey highlighted that catalytic converters with non-noble metal catalysts can offer redox activity. Perovskite is a type of non-noble metal-based catalyst which can perform both oxidation and reduction using a single catalyst due to its inherent oxidation and reduction properties. It also has better stability, reduces the volume of the reactor, and stores and releases oxygen as and when required during the catalytic reaction processes (Li et al., 2025; Jiang et al., 2023).

2 Methods, materials, and methodology

2.1 Catalytic converter design

Previous research has found that research and development efforts should focus on modifying the design of catalytic converters based on gas flow patterns and pressure and velocity distribution. Figure 2 provides the reference for the design modification parameters. There is also a need to explore the use of non-noble metal-based catalysts, as they offer simultaneous redox (oxidation and reduction) capability while being more cost-effective than noble metal catalysts.

Figure 2

Figure 2. Catalytic converter showing inlet, outlet, and cone taper dimensions.

Hence, based on research, the La₀.₈Sr₀.₂Co₀.₈Fe₀.₂O₃ (lanthanum strontium cobalt ferrite: LSCF) non-noble-metal-based catalyst was selected and synthesized in the laboratory using co-precipitation. The prepared catalyst was then coated onto a ceramic monolith (cordierite: 2MgO·2Al₂O₃·5SiO₂) using dip-coating and was subsequently tested for performance evaluation.

In this research, the catalytic converter housing was designed and evaluated to complement the overall system configuration and enhance performance analysis. Based on the predetermined geometrical parameters, three design configurations with inlet cone (diffuser) angles of 8°, 10°, and 14° were developed and fabricated. Computational and experimental assessments were made using design, simulation, and validation software to analyze gas flow behavior, pressure distribution, velocity profiles within the system, and the exhaust pattern and pollution intensity in a laboratory-based test petrol fuel test setup.

The design parameters for the various catalytic converter cases (Table 1) are carefully selected based on performance requirements, geometric constraints, and flow optimization considerations. These parameters are then used to develop multiple design configurations, each varying in specific aspects such as inlet cone (diffuser) angle, overall length, inlet and outlet diameters, and taper geometry (Abreu et ak., 2018). Such variations enable a comparative evaluation of how each configuration influences critical performance metrics, including gas flow distribution, pressure drop, and velocity profiles and design configurations (Zhang et al., 2022).

Table 1

Table 1. Common design consideration for the converter (Yang et al., 2023; Zainal et al., 2018).

The design geometry parameters, along with their respective variables, are presented in Table 2. These parameters define the key dimensional and geometric characteristics of the catalytic converter, including total length, inlet (diffuser) diameter, outlet (convergent) diameter, and cone taper angle. To investigate the influence of geometry on performance, three distinct cases are considered, each with a different combination of these design configurations. This variation enables a comparative analysis of gas flow behavior, pressure distribution, and velocity profiles, thereby identifying the efficient and optimal design for the catalytic converter and its functional performance. The fabricated catalytic converter operates under initial inlet velocities at 45 m/s, which vary according to engine load and speed. The inlet gas temperature is typically 500–800 °C, reflecting differences between cold-start and hot-cycle operation. The pressure drop across the converter is generally within 5–25 kPa, influenced primarily by the monolith design. The monolith geometry, with a cell density of 600 cpsi, directly affects both the available surface area and the pressure drop. The converter housing is typically made from stainless steel to ensure durability and efficient heat transfer.

Table 2

Table 2. Selection of design configuration for the converter.

As shown in Table 2, a thorough comparison was conducted of the three proposed design configurations with cone angles of 8°, 10°, and 14°. The results showed that the 8° configuration (Figure 3) delivered the best performance in terms of gas flow uniformity within the catalytic converter system and its overall performance. Based on these findings, and in line with the design objectives, the 8° cone angle was selected as the optimal configuration. This design has been finalized and fabricated for experimental validation, with the intention of subsequent integration into the catalytic converter assembly.

Figure 3

Figure 3. CAD model of converter housing illustrating dimensional parameters.

The monolithic substrate used in the converter features a cell density of 600 cpsi (cells per square inch) and has physical dimensions of 55 mm in width and 120 mm in diameter. A computational fluid dynamics simulation illustrates gas velocity distribution and flow paths through a divergent area. The entrance, where the flow enters as a concentrated jet, exhibits high-velocity patches, but the expanding segment gradually loses velocity because of the increased cross-sectional area. As the geometry tapers, it directs the flow toward the exit (Figure 4). The general flow path is shown by the particle trajectories, which also reveal possible areas of flow non-uniformity and maximum velocity gradients passing through the monolith surface, meaning that the maximum concentration of the flow passes through the surface to initiate a reaction in the monolith. After examining this design under the simulation tool, the actual catalytic converter component was fabricated and integrated with the monolith; Figure 5 illustrates the fabricated assembly of the converter developed in the laboratory.

Figure 4

Figure 4. Velocity distribution and exhaust flow trajectories inside the catalytic converter.

Figure 5

Figure 5. Fabricated catalytic converter prototype assembly.

2.2 Synthesis of catalyst (La₀.₈Sr₀.₂Co₀.₉Fe₀.₁O₃-δ) by co-precipitation

Based on an extensive review of the existing literature, La₀.₈Sr₀.₂Co₀.₉Fe₀.₁O₃-δ (lanthanum strontium cobalt ferrite perovskite, LSCF) was selected as the preferred perovskite-type oxide for this study and prepared by co-precipitation in the laboratory. This composition has attracted significant attention due to its excellent mixed ionic thermal stability, and catalytic performance, particularly in high-temperature applications. Similarly, Doggali et al. (2015), Lokhande et al. (2015) showed that Ba and Ce improve CO oxidation at light-off temperatures, whereas K promotes particulate matter (PM) oxidation but reduces CO performance due to changes in Mn oxidation states. For cobaltate perovskites, La₀.₉Ba₀.₁CoO₃ exhibited a significantly lower CO light-off temperature (120 °C) and enhanced PM oxidation compared to LaCoO₃ owing to improved low-temperature redox and oxygen desorption properties from Ba incorporation (Labhsetwar et al., 2009). Lokhande et al. (2013) prepared thermally stable La₃.₅Ru₄O₁₃ via a biopolymer template, achieving CO oxidation above 150 °C and propene oxidation above 170 °C with minimal SO₂ poisoning, indicating strong potential for emission control applications. In addition, Lokhande et al. (2013) developed a low-cost Cu–Mn mixed oxide catalyst supported on industrial waste fly ash via co-precipitation. The catalyst achieved complete CO oxidation at 175 °C, exhibited good thermal stability, and offered a sustainable option for emission control. Pt-Pd-containing H-USY zeolite catalysts were synthesized by Joshi et al. (2013). Doggali et al. (2011) prepared mesoporous ZrO₂ via a chitosan template and impregnated it with Co, Mn, Fe, Cu, or Ni, identifying Co–ZrO₂ as the most active catalyst for CO and PM oxidation.

To synthesize the perovskite catalyst, a mixed solution of all metal nitrates (La, Sr, Co, and Fe) was prepared in deionized water according to the required stoichiometry. Separately, a 1 M NaOH solution was prepared as the precipitating agent. Under vigorous stirring, the metal nitrate solution was added dropwise into the alkaline solution while maintaining a pH of 9–10. This resulted in the formation of a colored precipitate consisting of metal hydroxides. The suspension was stirred for 1–2 h to complete precipitation and was then allowed to settle and age for 12 h at room temperature. The precipitate was subsequently filtered and washed with deionized water and ethanol to remove residual nitrates. The filtered solid was dried at 110 °C for 12 h in a hot air oven, followed by calcination at 900 °C for 5 h to obtain the desired perovskite structure.

2.3 (A) LaCoO₃ perovskite catalyst requirement calculations

Atomic weight of lanthanum (La): 138.91 ∼ 139 g/mol

Atomic weight of cobalt (Co): 58.93 ∼ 59 g/mol

Molecular weight of LaCoO₃ = 139 + 59 + 3 × 16) = 246 g/mol

Molecular weight of lanthanum nitrate [La(NO₃)₃·6H₂O]

              = 139 + (3 × 14) + (9 × 16)+ (6 × 2) + (6 × 16)

              = 433 g/mol

Molecular weight of cobalt nitrate [Co(NO₃)₂·6H₂O]:

              = 58.93 + (2 × 14) + (6 × 16)+ (6 × 2) + (6 × 16)

              = 290.93 g/mol ∼ 291 g/mol

2.3.1 Preparation of La (NO₃)₃·6H₂O perovskite catalyst: 20 g

2.3.1.1 Calculation of lanthanum (La) and lanthanum nitrate [La(NO₃)₃·6H₂O]

246 g LaCoO₃ = 139 g lanthanum (La)

20 g LaCoO₃ = ?

       = $\frac{20\times 139}{246}$

      = 11.30 g lanthanum (La)

139 g lanthanum (La) = 433 g lanthanum nitrate[La(NO₃)₃·6H₂O]

11.30 g lanthanum (La) = ?

           = $\frac{11.30\times 4.33}{139}$

           = 10.81 g lanthanum nitrate[La(NO₃)₃·6H₂O]

2.3.1.2 Calculation of cobalt (Co) and cobalt nitrate [Co(NO₃)₂·6H₂O]

246 g LaCoO₃ = 59 g cobalt (Co)

20 g LaCoO₃   = ?

      = $\frac{20\times 59}{246}$

      = 4.796 g cobalt (Co)

59 g cobalt (Co)   = 291 g cobalt nitrate [Co(NO₃)₂·6H₂O]

4.796 g cobalt (Co) = ?

        = $\frac{4.796\times 291}{59}$

        = 23.65 cobalt nitrate [Co(NO₃)₂·6H₂O]

2.4 (B) Synthesis of La₀.₈Sr₀.₂Co₀.₉Fe₀.₁O₃-δ perovskite catalyst using the citrate complexation method

• Atomic weight of lanthanum (La): 138.91 ∼ 139 g/mol

• Atomic weight of cobalt (Co): 58.93 ∼ 59 g/mol

• Atomic weight of strontium (Sr): 87.62 g/mol

• Atomic weight of ferrite (Fe): 55.85 g/mol• Molecular weight of La0.8Sr0.2Co0.9Fe0.1O3:= [0.8 × 139] + [0.2 × 87.62] + [0.9 × 59]+ [0.1 × 55.85] + [3 × 16]= 235.40 g/mol

• Molecular weight of lanthanum nitrate [La(NO₃)₃·6H₂O]:= 138.91 + (3 × 14) + (9 × 16) + (6 × 2) + (6 × 16)= 432.91 g/mol ∼ 433 g/mol

• Molecular weight of strontium nitrate [Sr(NO₃)₂]:= 87.62 + (2 × 14) + (6 × 16) = 211.62 g/mol

• Molecular weight of cobalt nitrate [Co(NO₃)₂·6H₂O]:= 55.85 + (2 × 14) + (6 × 16) + (6 × 2) + (6 × 16)= 290.93 g/mol ∼ 291 g/mol

• Molecular weight of ferrite nitrate [Fe(NO₃)3·9H₂O]:= 55.85 + (3 × 14) + (9 × 16) + (9 × 18)= 403.85 g/mol ∼ 404 g/mol

2.5 (C) Preparation of La₀.₈Sr₀.₂Co₀.₈Fe₀.₂O₃ = 20 g

235.40 g La₀.₈Sr₀.₂Co₀.₈Fe₀.₂O₃ = (0.8 × 139)

           20 g = ?

      = 20 × (0.8 × 139)/235.40 g = 9.44 g

La (Atomic wt) 139 g/mol  = 433 g La(NO₃)₃

Required (La) 9.44 g  = ?

La(NO₃) ₃ = (433 × 9.44)/139 = 29.44 g La(NO₃)₃·6H₂O

Table 3 above shows the step-by-step calculations for all components’ mass requirements to synthesis the catalyst. The preparation of La₀.₈Sr₀.₂Co₀.₉Fe₀.₁O₃-δ begins by dissolving stoichiometric amounts of La(NO₃)₃, Sr(NO₃)₂, Co(NO₃)₂, and Fe(NO₃)₃ in distilled water to form a homogeneous mixed-metal nitrate solution (Figure 6). This solution is then slowly added, under continuous stirring, into a separate beaker containing a NaOH solution and maintaining a pH of 7–10 to ensure complete co-precipitation of the corresponding metal hydroxides.

Table 3

Table 3. Catalyst calculations for 20 g.

Figure 6

Figure 6. Preparation steps for La₀.₈Sr₀.₂Co₀.₉Fe₀.₁O₃ catalyst.

The resulting precipitate is stirred and aged 4 h to promote uniformity and complete precipitation. After aging, the precipitate is washed with distilled water to remove any residuals. The washed precipitate is then dried at 120 °C for 12 h in a hot air oven. Finally, the dried powder was kept for calcination in a furnace at 900 °C for 6 h, resulting in the formation of the desired perovskite phase of La₀.₈Sr₀.₂Co₀.₉Fe₀.₁O₃-δ (Figure 6) of 45.285 g.

As shown in Figure 7, the ceramic monolith was coated with the prepared catalyst using the wash-coating technique. The coating process was repeated three times to ensure uniform deposition of the catalyst on the substrate surface. After each coating, the monolith was dried in a hot air oven at 110 °C for 1 h. Subsequently, the coated monolith was subjected to calcination at 550 °C for 5 h in order to enhance the adhesion and thermal stability of the catalyst layer.

Figure 7

Figure 7. Monolith substrate (a) before and (b) after catalyst wash-coating.

The substrate used for the catalytic converter was a ceramic monolith composed of cordierite (2MgO·2Al₂O₃·5SiO₂) with dimensions of 55 × 120 mm. Cordierite was chosen due to its low thermal expansion and high thermal stability.

2.6 Experimental setup

With the support of laboratory test equipment (Figure 8), the four-stroke, single cylinder, variable fuel/air compression ratio research engine setup was connected to the eddy current dynamometer. It was provided with combustion pressure, crank angle, airflow, fuel flow, temperature, and load measurement instruments. These signals interfaced with a computer through a high-speed data acquisition system. Rotameters were provided for cooling water and calorimeter water flow measurement. In petrol mode, the engine works with a programmable open ECU, throttle position sensor (TPS), fuel pump, ignition coil, fuel spray nozzle, and trigger sensor. Table 4 illustrates the functional specification of the petrol fuel laboratory test setup: a four-stroke single cylinder engine.

Figure 8

Figure 8. Experimental setup of a petrol fuel single cylinder engine.

Table 4

Table 4. Engine specification.

2.7 Characterization of catalyst

2.7.1 SEM analysis

As shown in Figure 10, representation of the scanning electron microscopy (SEM) and X-ray diffraction pattern that studied the surface morphology and coating layer of La₀.₈Sr₀.₂Co₀.₈Fe₀.₂O₃ over the substrate. An SEM image of a La₀.₈Sr₀.₂Co₀.₈Fe₀.₂O₃ perovskite sample was magnified 2500×, with a scale of 10 μm. The pore structure played a crucial role in determining catalytic performance. When the pores become narrower, they restricted access to the active catalytic sites. In contrast, a well-developed porous network enhanced the surface area and offered a notable advantage for oxidation reactions (Bashir et al., 2023; Chen and Jiang, 2025). The micrograph shows that the pores and grain boundaries are quite distinct, and the porous structure is beneficial for catalytic applications as it enhances gas diffusion and increases the active surface area.

2.7.2 XRD analysis

According to the XRD image shown in Figure 9 octahedral crystalline structure is identified. confirming the successful deposition of the perovskite coating over the monolith. The sharp and intense peaks in the 2θ range of 10°–35° indicate the presence of well-crystallized LSCF, which are characteristic of the perovskite crystal structure. The well-defined peaks indicate good crystallinity, and the peak positions correspond well with standard LSCF perovskite structures, confirming the successful formation of the desired phase. Strong peaks at approximately 2θ ≈ 23°, 33°, 40°, 47°, and 58° match the characteristic reflections of rhombohedral LSCF perovskite, especially the 110, 200, 211, 220, and 310 planes. The XRD pattern of the LSCF catalyst coating shows characteristic peaks of a single-phase rhombohedral perovskite structure, which are in agreement with the standard JCPDS card No. 48-0124 for La₀.₆Sr₀.₄Co₀.₂Fe₀.₈O_3-δ. This crystalline structure and phase purity make the LSCF coating suitable for catalytic structural stability and active surface sites, which are an essential part. The average crystallite dimension was estimated using the Scherrer equation.

$\mathrm{D}=\frac{K\lambda }{\beta \mathit{cos}\theta }\frac{0.9*0.15406}{\beta \mathit{cos}\theta },$

where, D is the average thickness in the vertical direction of the crystal face, K is the Scherrer constant, λ is the wavelength of the x-ray, β is the full width at half maximum, and θ is the Bragg diffraction angle.

Figure 9

Figure 9. SEM patterns of coated and powder of La₀.₈Sr₀.₂Co₀.₈Fe₀.₂O₃ catalyst.

2.7.3 EDX analysis

The results of EDX analysis performed to determine the weight percentages of elements and compounds in the catalytic converter are presented in Figure 10. The energy-dispersive X-ray spectroscopy (EDX) spectrum illustrates the elemental composition of the synthesized catalyst. Prominent peaks correspond to oxygen (O), cobalt (Co), lanthanum (La), strontium (Sr), and iron (Fe). O exhibits the highest intensity, suggesting a high oxide content typical of metal oxide catalysts. The distinct signals for Co, La, Sr, and Fe confirm the successful incorporation of metals into the catalyst structure, which is expected to enhance thermal and chemical stability during catalytic reactions. As shown in Figure 11 the analysis of the synthesis confirms the presence of all the constituent elements of the designed perovskite composition. Prominent peaks corresponding to La and Co indicate that these are the dominant cations, while smaller peaks of Sr and Fe reflect their lower concentrations, in line with the stoichiometric ratios. The qualitative elemental distribution shows that La and Co are the major constituents, each accounting for approximately 40% of the metallic elements, whereas Sr and Fe contribute approximately 10% each, confirming that the synthesized material is phase pure. Thus, the EDX results are consistent with the expected composition of La₀.₈Sr₀.₂Co₀.₈Fe₀.₂O₃ and support the successful formation of the catalyst.

Figure 10

Figure 10. XRD pattern of the LSCF coating, confirming perovskite phase formation.

Figure 11

Figure 11. EDX spectrum of catalyst coating, showing the presence of La, Sr, Co, Fe, and O elements.

3 Results and discussion

Major pollutants from petrol vehicles such as HC and CO were observed during engine operation and analyzed for its intensity at various speed and load conditions. The comparisons was examined as rate of pollutants from catalytic converter versus engine without catalytic converter. Figure 12 shows the measurement of exhaust pollution at 1,200 rpm with varying load conditions.

Figure 12

Figure 12. Exhaust gas analyzer display showing measured emissions.

Exhaust emission measurements were recorded using an exhaust gas analyzer. The pollutant intensities obtained with the catalytic converter containing La₀.₈Sr₀.₂Co₀.₈Fe₀.₂O₃-coated monolith were compared against system without the converter at the same engine speed for pollutants.

As shown in Table 5, HC emissions are recorded as very high (200–350 ppm) and subsequently rise with load without a catalytic converter. Regardless of load, emissions are always kept low (28–54 ppm) when the emission is recorded with a catalytic converter. As shown in Table 5, the exhaust pollution is considerably lower and more environmentally friendly when a catalytic converter is installed at the engine exhaust tail pipe because it drastically reduces HC and CO emission intensity compared to no catalytic converter at different rpm with varying loads. At higher loads, the fuel–air mixture tends to become richer, and the combustion process becomes less complete, resulting in higher concentrations of unburned HC and partially oxidized MO.

Table 5

Table 5. Exhaust emissions at 1,200 rpm: La₀.₈Sr₀.₂Co₀.₈Fe₀.₂O₃-coated converter vs. without converter.

At higher loads, the emission reduction effect remains consistent and demonstrates that the importance of the catalytic converter and the effect of a La₀.₈Sr₀.₂Co₀.₈Fe₀.₂O non-noble metal catalyst integrated with design parameter modifications enhances catalytic performance and emissions reduction efficiency. Figure 13 shows that in the absence of a catalytic converter, HC and CO emissions exhibit a sudden rise as engine load and speed increase, which indicates inefficient and poor exhaust treatment. However, a catalytic converter with a non-noble metal catalyst incorporated with a modified design parameter as an 8° diffuser cone angle enhances the catalytic performance exhaust gas flow streamline, with an emissions reduction of 28–54 ppm volume and 0.16%–0.33% volume CO (emission regulatory standards), proving its effectiveness in controlling harmful pollutants.

Figure 13

Figure 13. HC and CO emissions at different engine speeds under varying loads.

Furthermore, exhaust emission measurements were recorded at higher rpm to examine the effectiveness of the catalyst at higher speed and subsequently at different load conditions. The pollutant intensities obtained by the La₀.₈Sr₀.₂Co₀.₈Fe₀.₂O₃-coated monolith are also compared against the engine without the converter. At elevated engine loads, the fuel–air mixture tends to become richer, and the combustion process becomes less complete, resulting in higher concentrations of HC and CO. HC and CO emissions significantly reduce when a catalytic converter with La₀.₈Sr₀.₂Co₀.₈Fe₀.₂O₃ non-noble-metal-catalyst-coated catalytic converter is installed in a system. Without a catalytic converter, a higher load leads to increased exhaust pollution. However, when a catalytic converter is used, the recorded emissions are significantly lower than without one. Table 5 presents the pollution recorded at different variable conditions and the result of an examination of the importance of the La₀.₈Sr₀.₂Co₀.₈Fe₀.₂O₃ catalyst in catalytic converter reaction activity and its role in reducing harmful emissions, thereby contributing to environmental protection by lowering pollutant intensity.

As per Figure 14, exhaust emissions data from commercially available catalytic converter are also compared with La₀.₈Sr₀.₂Co₀.₈Fe₀.₂O₃ catalyst performance (where RPM-C indicates the commercial catalytic converter). A La₀.₈Sr₀.₂Co₀.₈Fe₀.₂O₃-catalyst-coated catalytic converter shows a difference in both HC and CO emissions. Engine speeds varied 1,200–1,800 rpm, and for each speed, engine loads of 4 kg, 8 kg, and 12 kg were applied and compared. At lower engine speed (1,200 rpm), the La₀.₈Sr₀.₂Co₀.₈Fe₀.₂O₃ catalytic converter showed a significant reduction in HC emissions compared with the commercial converter, particularly at higher loads (35 ppm vs. 56 ppm at 12 kg). However, the CO emissions for the perovskite converter are slightly higher (0.23%–0.30%) than those from the commercial converter (0.03%–0.04%). With an increase in speed to 1,400–1,600 rpm, HC emissions from both converters reduce overall, showing improved emission efficiency. The La₀.₈Sr₀.₂Co₀.₈Fe₀.₂O₃-coated converter maintains low HC levels (29–33 ppm). At the highest speed at 1,800 rpm, HC emissions from the La₀.₈Sr₀.₂Co₀.₈Fe₀.₂O₃ catalyst increase compared to its lower-speed performance, likely due to incomplete oxidation at elevated exhaust flow rates. Conversely, the commercial converter exhibits very low HC levels (19–22 ppm), suggesting higher oxidation efficiency under these conditions. CO emissions for the perovskite converter remain 0.32%–0.33%, slightly higher than the commercial converter (0.02%–0.04%). However, the resulting emission levels were still maintained within the limits specified by the BS-VI emission regulatory standards, which ranges 10–100 ppm for HC and 0.1%–0.5% vol for CO (Ministry of Road Transport and Highways, 2016).

Figure 14

Figure 14. Exhaust emission analysis: La₀.₈Sr₀.₂Co₀.₈Fe₀.₂O₃ catalyst vs. commercial catalytic converter.

4 Conclusion

“Back pressure” refers to the resistance of the exhaust gases when exhaust is emitted from the engine and flows through the catalytic converter. Moderate back pressure helps maintain a sufficient flow rate, pressure, and velocity profile for the effective catalytic oxidative reactions of carbon monoxide (CO) and hydrocarbon (HC). Excessive back pressure can reduce engine performance, lower the exhaust flow rate due to incomplete combustion, or restrict oxygen availability in the converter and overheat the catalytic converter. Of the designs we proposed as cone angles from 8°, 10° and 14°, the 8° inlet cone angle (diffuser) is best suited for from design considerations as it has the lowest pressure drop and better velocity and exhaust flow profiles than all other 10° and 14° combinations. In addition, maintaining a balanced exhaust pressure does not affect gas flow patterns, pressure distribution, and velocity as exhaust gases enter and exit the monolithic structure.

The successful synthesis of La₀.₈Sr₀.₂Co₀.₈Fe₀.₂O₃ perovskite catalyst by the co-precipitation method highlights its structural stability, which directly contributes to its reliability in pollution filtering control as an alternate to the noble catalyst. The uniform crystalline phase and wash-coat adhesion ensure a consistent layer of catalyst, which better promotes catalytic activity under varying engine loads and speeds and allows the constant reduction of HC and CO pollutants from the engine exhaust. This demonstrates that the developed non-noble metal (perovskite) catalyst serves not only as an effective alternative but also as a superior alternative to noble metal catalysts for achieving effective exhaust emission mitigation, as found by the comparison of results. It offers a promising and sustainable replacement for conventional noble metal catalysts in engine exhaust pollution mitigation systems.

The overall results clearly demonstrate that the La₀.₈Sr₀.₂Co₀.₈Fe₀.₂O₃ (perovskite)-based non-noble metal catalyst for catalytic converters exhibits acceptable catalytic activity and emission control performance across the different engine speeds and load conditions. The converter effectively lowers HC and CO emissions compared to untreated exhaust and maintains a performance equivalent to commercial catalytic converters, particularly at moderate engine loads. Although CO levels are marginally higher at elevated speeds, the overall emission values remain well within the BS-VI regulatory limits (10–100 ppm for HC and 0.1%–0.5% vol for CO), validating the environmental compatibility of the system developed. These findings confirm that the La₀.₈Sr₀.₂Co₀.₈Fe₀.₂O₃-coated catalytic converter not only serves as a feasible replacement but also as an alternative to noble metal catalysts for achieving efficient exhaust emission mitigation and promoting sustainable pollution-control technologies in automotive exhaust applications.

Data availability statement

The original contributions presented in this study are included in the article and the Supplementary Material. Further inquiries can be directed to the corresponding author.

Author contributions

KP: Methodology, Resources, Software, Supervision, Writing – original draft, Writing – review and editing. DS: Supervision, Writing – review and editing. FP: Supervision, Writing – review and editing. GP: Writing – review and editing.

Funding

The author(s) declared that financial support was not received for this work and/or its publication.

Conflict of interest

Author GP was employed by Engineering Technique.

The remaining author(s) declared that this work was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest.

Generative AI statement

The author(s) declared that generative AI was not used in the creation of this manuscript.

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Nomenclature

LSCF La₀.₈Sr₀.₂Co₀.₉Fe₀.₁O₃-δ, lanthanum strontium cobalt ferrite

La Lanthanum

Sr Strontium

Co Cobalt

Fe Iron

O Oxygen

HC Hydrocarbons

CO Carbon monoxide

CO₂ Carbon dioxide

NOx Oxides of nitrogen

H₂O Water

NaOH Sodium hydroxide

C₆H₈O₇ Citric acid

La(NO₃)₃·6H₂O Lanthanum nitrate hexahydrate

Sr(NO₃)₂ Strontium nitrate

Co(NO₃)₂·6H₂O Cobalt nitrate hexahydrate

Fe(NO₃)₃·9H₂O Ferric nitrate nonahydrate

ECU Electronic control unit

SEM Scanning electron microscopy

XRD X-ray diffraction

EDX Energy-dispersive X-ray spectroscopy

cpsi Cells per square inch (monolith cell density)

ppm Parts per million

g/km Grams per kilometer

mm Millimeter

°C Degrees Celsius

kg Kilogram

rpm Revolutions per minute

2CO + O₂→ 2CO₂ Oxidation reaction of carbon monoxide

HC + O₂→ CO₂+ H₂O Oxidation reaction of hydrocarbons

2NOx → xO₂+ N₂ Reduction reaction of nitrogen oxides