Sustainable synthesis of La 0. 8 Sr 0. 2 Co 0. 9 Fe 0. 1 O 3 -δ catalyst using hibiscus flower extract and its performance evaluation for automotive HC and CO exhaust emission control

The increasing environmental concerns associated with vehicular emissions have intensified the need for efficient and cost-effective catalysts for automotive catalytic converters. In this study, a sustainable approach is proposed through the development of a non-noble metal perovskite catalyst combined with catalytic converter design optimization. La 0. 8 Sr 0. 2 Co 0. 9 Fe 0. 1 O 3 -δ (LSCF) was synthesized via a green synthesis method using hibiscus flower powder as a natural chelating agent. The synthesized catalyst was wash-coated onto a cordierite ceramic monolith and integrated into an automotive exhaust catalytic converter. The structural and morphological properties of the catalyst were characterized using X-ray diffraction, scanning electron microscopy and energy dispersive X-ray spectroscopy (EDX), confirming the formation of a crystalline perovskite structure with uniform elemental distribution. Computational fluid dynamics (CFD) simulations were performed to evaluate exhaust gas flow behaviour including velocity distribution and pressure characteristics for different inlet diffuser cone angles (8°, 10° and 14°). Among these configurations the 8° diffuser angle demonstrated the most uniform flow distribution and favourable pressure profile. The performance of the developed catalytic converter was experimentally evaluated on a laboratory scale petrol engine under varying operating conditions. The results indicated a significant reduction in hydrocarbon (HC) and carbon monoxide (CO) emissions compared to baseline conditions without a catalytic converter. The enhanced emission reduction is attributed to the synergistic effect of the green synthesized La 0. 8 Sr 0. 2 Co 0. 9 Fe 0. 1 O 3 -δ catalyst and modified converter geometry. This study demonstrates a sustainable and economically viable alternative to conventional noble metal-based catalyst configuration, highlighting the potential of hibiscus-assisted perovskite green catalysts for effective automotive emission control.

Stringent vehicular emission regulations have driven the extensive use of catalytic converters as the primary exhaust after-treatment technology for controlling carbon monoxide (CO), hydrocarbons (HC) and nitrogen oxides (NO x) (Patel et al., 2022). Conventional automotive catalytic converters rely heavily on platinum-group metals because of their high catalytic activity; however, their high cost, limited availability, and environmental footprint have motivated the search for sustainable non-noble alternatives (Koltsakis and Stamatelos, 1997). As a result, research efforts have increasingly focused on the development of earth-abundant transition-metal catalysts for automotive emission control. Among the various non-noble metal catalysts investigated, perovskite-type oxides with the general formula ABO 3 have emerged as promising candidates due to their high thermal stability, oxygen storage capacity, and redox flexibility. Automotive catalyst studies indicate that transition-metal oxides, particularly perovskites, offer competitive catalytic activity together with superior structural stability and compositional tunability compared to conventional noble-metal systems (Automotive Catalysts, n. d.). Lanthanum cobaltite (LaCoO 3) is widely regarded as a benchmark non-noble perovskite catalyst owing to its high oxygen mobility and favourable redox characteristics. Furthermore, B-site substitution has been shown to significantly enhance catalytic performance; for instance, Fe-substituted LaCoO 3 exhibited improved activity during SO 2 reduction with CO due to increased oxygen vacancy formation and synergistic redox cycling between Co. and Fe species (Yao et al., 2025). The catalytic performance of perovskite oxides is mostly influenced by oxygen vacancies, which enhance oxygen agility, electronic structure and promote redox nature. Oxygen vacancies are generated through cation substitution (ABO 3 -δ), facilitating oxygen adsorption, activation and enhanced catalytic activity (Guan et al., 2026; Wang et al., 2026). These findings confirm that compositional engineering is an effective strategy for improving the activity and durability of non-noble metal perovskites. Perovskite-type transition metal oxides have been extensively reported as effective oxidation catalysts for carbon monoxide and unburned hydrocarbons in automotive exhaust streams due to their high oxygen mobility and redox activity. In parallel with catalyst composition, sustainability considerations have increasingly emphasized the importance of environmentally benign synthesis routes. Green and eco-friendly preparation methods aim to reduce hazardous waste, lower energy consumption, and improve industrial scalability. Wang et al. (2023) reported an eco-friendly in-situ synthesis of monolithic NiFe layered double hydroxide catalysts, demonstrating strong catalyst-support adhesion, high catalytic activity, and long-term stability without the use of fluorine-containing reagents. Broader assessments of sustainable catalysis further indicate that replacing noble metals with earth-abundant transition metals substantially reduces the environmental burden associated with mining and refining processes while enabling scalable catalyst production (Ganesan et al., 2023). Supported non-noble metal catalysts have emerged as cost-effective alternatives to noble metals or Pd base metals. Their catalytic performance activity depends on the fundamental properties of the active metal, metal-support interactions and synthesis methods such as precipitation, sol-gel and ion exchange (Ren et al., 2023). Such green synthesis strategies are therefore increasingly integrated into catalyst development for automotive and environmental applications. Beyond catalyst material and synthesis, the effective performance of catalytic converters is strongly influenced by reactor-level factors, particularly exhaust flow distribution and hydrodynamic behavior. Non-uniform flow within catalytic converters can result in localized catalyst underutilization, increased pressure drop, and reduced overall conversion efficiency. Early foundational studies emphasized that catalytic performance depends not only on intrinsic activity but also on operating conditions, exhaust composition, and reactor design (Koltsakis and Stamatelos, 1997). Subsequent investigations demonstrated that inlet and diffuser geometry plays a critical role in controlling flow uniformity and thermal response in monolithic catalytic converters (Tsinoglou et al., 2004), while complementary analyses confirmed that optimized inlet design is essential for effective catalyst utilization (Flow distribution, n. d.). Accordingly, catalytic converters are increasingly treated as structured chemical reactors in which reaction kinetics, transport phenomena, and geometry are strongly coupled. Flow maldistribution has been shown to significantly reduce the effective utilisation of monolithic catalysts and increase pressure losses (Groppi and Tronconi, 2000) highlighting the need for rational reactor design. Structured catalytic reactors must therefore be analysed as coupled reaction–transport systems rather than purely material-driven components (Hayes and Kolaczkowski, 1997). Computational fluid dynamics (CFD) has consequently become a widely employed design and analysis tool for predicting velocity distribution, pressure drop, and flow uniformity in monolithic catalytic reactors (Kolaczkowski et al., 1999). Advanced CFD frameworks further demonstrate that realistic prediction of catalytic reactor performance requires the integration of chemical reaction kinetics with flow and heat-transfer models across different reactor configurations, including monoliths and porous catalysts (Hettel et al., 2018). Recent reviews confirm a growing shift toward non-noble metal catalysts and alternative wash-coat materials for automotive catalytic converters, while simultaneously emphasizing the importance of converter geometry and reactor-level optimisation to enhance performance under realistic operating conditions (Robles-Lorite et al., 2023; Akhtar and Zaman, 2025). Consequently, the integration of sustainable non-noble metal catalysts with optimised catalytic converter geometries represents a holistic and effective approach for next-generation automotive emission control systems. While significant research has been reported on non-noble perovskite catalysts and catalytic converter exhaust gas flow pattern, their combined development and experimental validation under research engine experimental output remain limited. The novelty of this study lies in combining the green synthesis of La 0. 8 Sr 0. 2 Co 0. 9 Fe 0. 1 O 3 -δ (LSCF) using hibiscus flower extract as a natural chelating agent with geometrically modified catalytic converter and its effect of exhaust pollution mitigation. The inlet diffuser cone angles (8°, 10° and 14°) were comparatively examined to identify the optimum flow characteristics before experimental validation. The synthesised catalyst-coated ceramic monolith along with the catalytic converter was subsequently experimented on a petrol engine test setup, demonstrating the combined influence of sustainable catalyst development and modified converter’s effect on exhaust flow distribution and unburnt hydrocarbon (HC) and carbon monoxide (CO) emission reduction. Figure 1 shows the automotive exhaust system in a vehicle along with the catalytic converter. Equations 1 and 2 shows the chemical reaction taking place during the exhaust gas flow passing through the catalytic converter.

Reactions in a catalytic converter: Oxidization of CO to CO 2 and HC to carbon dioxide and water

Reduction of NOx to N 2 and O 2

Catalytic converter design

A review of earlier research indicates that future research should place greater emphasis on improving catalytic converter designs by considering exhaust gas flow characteristics, along with the flow pressure and velocity distributions within the system and non-noble metal sustainable catalyst. The catalytic converter housing is illustrated in Figure 2, which provides the sectional representation of housing. Also, increasing attention has been directed toward non-noble metal catalysts, as they are capable of enabling both oxidation and reduction reactions while offering a more economical and sustainable alternative to traditional noble-metal based catalyst. Furthermore, non-noble metal perovskite catalyst, La 0. 8 Sr 0. 2 Co 0. 9 Fe 0. 1 O 3 (lanthanum strontium cobalt ferrite, LSCF), was chosen along with the hibiscus flower as shown in Figure 3, extracts as a chelating agent for this research and synthesised using a sol-gel technique. Hibiscus extracts having organic acids such as citric acid, malic acid and hibiscus acid. Polyphenols, flavonoids and anthocyanins are also present in the hibiscus flower extract. These biomolecules carboxyl and hydroxyl functional groups aid in the chelation of metal ions during catalyst production and polyphenols and flavonoids serves as stabilizing and capping agents. Prepared catalyst then after was deposited onto a ceramic cordierite monolith (2MgO·2Al 2 O 3 ·5SiO 2) using a dip-coating process to obtain a uniformly coated catalytic substrate, which was subsequently evaluated for its performance characteristics.

The geometric parameters of the catalytic converter and their functional variables are summarised in Table 1. These parameters describe the key geometrical features of the catalytic converter housing, such as the total length, inlet diffuser diameter, outlet convergent diameter and cone angle. To assess the effect of geometric variation of converter performance, three distinct design configurations were analysed. This approach enabled a comparative study of exhaust gas flow patterns, pressure distribution and velocity profiles. The fabricated converter was evaluated under an inlet gas velocity of approximately 45 m/s, which varies with engine operation load and speed. Inlet gas temperatures usually ranged from 500 °C to 800 °C. The pressure variation within the converter was generally within 5–25 kPa and was influenced by the internal monolithic structure. A ceramic monolith with 600 cpsi (cells per square inch) as cell density was used to provide sufficient catalytic surface area while maintaining acceptable pressure losses. The converter housing was manufactured from stainless steel 409 grade as to ensure durability and effective heat removal. Among the three configurations with inlet diffuser cone angles of 8°,10° and 14°. The 8° design demonstrated the most uniform flow distribution and overall performance under the computational fluid dynamics software.

Hence, this configuration was selected as the optimal design and was finalised for fabrication and experimental validation prior to integration into the catalytic converter appliance.

Figure 4 shows the CAD model of the exhaust catalytic converter geometry with dimensional specifications. The geometry consists of a converging inlet section followed by a gradual diverging cone toward the outlet. The indicated lengths and diameters define the gradual area change, which is essential for achieving uniform flow distribution and reducing pressure losses in exhaust applications.

Figure 5, represents a computational fluid dynamics simulation showing the velocity distribution of gas flow inside a converging-diverging of exhaust component of a catalytic converter. The velocity distribution (m/s) within the geometry at iteration 72, indicating a converged CFD solution. The contours represent velocity magnitude with lower velocities shown in blue and higher velocities in red. The flow enters with relatively higher velocity at the inlet and decelerates in the expanded middle section due to an increase in cross-sectional area, resulting in a more uniform velocity distribution. As the geometry converges toward the outlet, the velocity increases because of area reduction. The smooth variation in velocity indicates stable flow behaviour with minimal separation, demonstrating the effectiveness of the geometry in controlling flow distribution for exhaust-related applications. Here only 8° diffuser cone angle converter’s image is added and explained as it has showed the desirable parametric support for the flow behaviour.

Green synthesis of La 0. 8 Sr 0. 2 Co 0. 9 Fe 0. 1 O 3 -δ by sol-gel method

La 0. 8 Sr 0. 2 Co 0. 9 Fe 0. 1 O 3 -δ (LSCF) was selected for this study due to its strong catalytic potential and was synthesized via the sol–gel method. The material exhibits high thermal stability, mixed ionic–electronic conductivity, and effective performance under elevated temperatures (Patel et al., 2025). Previous studies show that compositional modifications enhance catalytic activity; incorporation of Ba and Ce improves CO oxidation near light-off temperatures (Doggali et al., 2010), while La 0. 9 Ba 0. 1 CoO 3 demonstrates lower light-off temperature and improved particulate oxidation compared to LaCoO 3 due to enhanced redox behavior and oxygen mobility (Labhsetwar et al., 2009). Additionally, La 3. 5 Ru 4 O 13 has shown efficient CO and hydrocarbon oxidation with good resistance to SO 2 poisoning, indicating its suitability for emission control (Lokhande et al., 2013).

Figure 6 shows the preparation of the LSCF perovskite green sustainable catalyst (La 0. 8 Sr 0. 2 Co 0. 9 Fe 0. 1 O 3) using the sol-gel method. Initially, the precursor material is dissolved in a citric acid solution and stirred for about 15 min, during which the solution color changes from pink to dark pink, indicating complex formation. The mixture is then heated in an oil bath at around 80 °C to evaporate water until a gel is formed. This gel is subsequently dried in a hot air oven at 110 °C for 16 h as shown in Figure 6, resulting in a light pink dried precursor. Finally, the dried material is calcined in a muffle furnace at 900 °C for 6 h to achieve crystallization of the perovskite phase. After calcination, a dark brown LSCF catalyst is obtained with a final weight of 34.84 g, confirming successful synthesis via the sol-gel route. Table 2, summarizes the stoichiometric calculation used for preparing the LSCF perovskite catalyst, La 0. 8 Sr 0. 2 Co 0. 9 Fe 0. 1 O 3, by selecting appropriate precursor salts and their required quantities.

The obtained material was continuously stirred and allowed to age for 4 h to ensure homogeneity and to facilitate complete preparation. The material was thoroughly washed with distilled water to eliminate any impurities or residuals. The cleaned catalyst was subsequently dried in a hot-air oven at 120 °C for 12 h to remove moisture. The resulting dried powder was then subjected to calcination in a furnace at 900 °C for 6 h, leading to the formation of the targeted perovskite phase, La 0. 8 Sr 0. 2 Co 0. 9 Fe 0. 1 O 3 -δ, as illustrated in Figure 6. The final catalyst of the synthesized catalyst was approximately 34.84 g.

Figure 7 shows the initial steps of LSCF catalyst preparation and component requirements by the sol-gel method. Image (a) shows the precursor chemicals, including metal nitrate salts and citric acid, used in stoichiometric proportions. Image (b) shows the final available catalyst after the drying and calcination process as 30.00 gms.

As shown in Figure 8, the ceramic monolith (2MgO·2Al 2 O 3 ·5SiO 2) cordierite with dimensions of 55 × 120 mm was initially used in its bare, uncoated state and was subsequently coated with the sol-gel synthesised catalyst through a wash-coating process. To ensure uniform and sufficient deposition of the catalytic layer on the substrate, the coating process was carried out in three successive cycles. Following each coating step, the monolith was dried in a hot-air oven at 110 °C for 2 h to remove excess solvent. After completion of the coating cycles, the catalyst-coated monolith was calcined in a muffle furnace at 600 °C for 5 h to strengthen catalyst adhesion its thermal stability.

Experimental setup

Laboratory test equipment as shown in Figure 9, A four-stroke, single-cylinder research engine with a variable compression ratio was used in this study. The engine was coupled to an eddy current dynamometer for load application and performance evaluation. The setup was equipped with sensors to measure various operating parameters of the system. In petrol mode, the engine operated with a electronic control module, acceleration sensor, trigger sensor and all other necessary sub-systems.

Table 3, shows the experimental setup of single-cylinder, 4-stroke, variable compression ratio (VCR) petrol engine with its operating specifications. The engine was operated within a speed range of 1100–1800 rpm. Fuel supplied from a 15-L fuel tank located on top of the system, while engine operation was controlled by electronic control unit (ECU) featuring a fully built, potted enclosure for reliable performance and data acquisition.

Characterisation of catalyst

SEM analysis

The SEM micrographs illustrate in Figure 10, the surface morphology of the catalyst sample at high magnification. The image shows an irregular, porous structure composed of agglomerated particles with non-uniform shapes, indicating the formation of a rough surface texture that is favourable for catalytic activity. The presence of interconnected pores suggests enhanced surface area and improved accessibility of active sites. Also, presents the corresponding elemental mapping, confirming a uniform distribution of the catalyst components across the surface. The homogeneous elemental dispersion indicates effective synthesis and coating, which is essential for consistent catalytic performance.

XRD analysis

The XRD pattern of the green-synthesized catalyst as shown in Figure 11, prepared via the sol-gel method using hibiscus powder as a chelating agent confirms the successful formation of a crystalline perovskite structure. The presence of well-defined diffraction peaks at characteristic 2θ positions indicates the development of an ordered crystal lattice, demonstrating that the bio-assisted green synthesis route effectively facilitates perovskite phase formation.

The relatively broad and less intense peaks suggest the presence of small crystallite sizes and microstructural strain, which are commonly associated with sol-gel and biologically assisted synthesis methods. These characteristics are attributed to the influence of organic constituents from hibiscus powder on nucleation and crystal growth during the calcination process. Furthermore, the diffraction peaks were indexed to a rhombohedral structure and show the standard JCPDS card No. 48-0123 corresponding to the catalyst, confirming the formation of a phase-pure LSCF perovskite catalyst with suitable crystallinity for catalytic applications.

EDX analysis

The EDX spectrum as shown Figure 12, confirms the presence of the constituent elements La, Sr, Co., Fe, and O in the green-synthesized LSCF catalyst, indicating successful formation of the desired perovskite composition. Prominent oxygen peaks arise from the oxide lattice, while characteristic signals corresponding to lanthanum (La), strontium (Sr), cobalt (Co.), and iron (Fe) confirm their effective incorporation into the perovskite framework. The absence of extraneous elemental peaks suggests high purity of the synthesized catalyst and indicates that no detectable impurities were introduced during the hibiscus-assisted sol-gel synthesis process. These results further validate the compositional integrity of the green-synthesized LSCF catalyst, supporting its suitability for catalytic applications.

Table 4 shows above is the EDX analysis confirmed the elemental presence of O, Sr, La, Fe and Co. in the synthesized catalyst. The Sr was the predominant metallic element, while La, Fe, and Co. were present in smaller amounts, confirming their successful incorporation into the catalyst structure. Overall, the results verify the formation of the intended mixed-metal oxide catalyst.

The pollutants emitted from the petrol fuel engine, as hydrocarbons and carbon monoxide, were monitored during test operation under varying speed and load conditions. Emission levels were analysed under the AVL make exhaust emission analyser and the pollutant level measured in a catalytic converter coated with La 0. 8 Sr 0. 2 Co 0. 9 Fe 0. 1 O 3 catalyst were evaluated and compared with those from the non-catalytic system at identical engine operating conditions. Table 5 shows the emission analysis of hydrocarbon (HC) and carbon monoxide (CO) emissions at different engine speed and load from the La 0. 8 Sr 0. 2 Co 0. 9 Fe 0. 1 O 3 catalyst synthesised by a sol-gel green catalytic converter and without catalytic converter. The emission reduction performance observed in the present study is constant with previous results on perovskite catalysts for automotive exhaust emission control. Ba-substituted La 0. 9 Ba 0. 1 CoO 3 shown CO oxidation enhancement activity due to improved redox performance and oxygen agility (Doggali et al., 2010). Similarly, thermally stable La 3. 5 Ru 4 O 13 demonstrated effectiveness on carbon monoxide and hydrocarbon oxidation, highlighting its suitability for automotive exhaust gas treatment (Labhsetwar et al., 2009). Additionally, our previous study presented that La 0. 8 Sr 0. 2 Co 0. 9 Fe 0. 1 O 3 -δ synthesised through co-precipitation method and integrated with catalytic converter effectively reduces hydrocarbon and carbon monoxide exhaust emissions under the experimentation on petrol engine test setup (Patel et al., 2025). The comparable performance achieved by the current sol-gel green synthesized catalyst shows that the hibiscus flower assisted synthesis route continues and improves the catalytic activity and providing a more sustainable catalyst preparation approach.

Above graphical analysis presents the variation of hydrocarbon (HC) emissions with engine load and speeds of 1000, 1200, 1400, and 1600 rpm, Figures 13–16 for both the La 0. 8 Sr 0. 2 Co 0. 9 Fe 0. 1 O 3 (LSCF) catalytic converter and operation without a converter. At all engine speeds, Hydrocarbon emissions are considerably higher when no catalytic converter, particularly at lower speeds and higher loads, due to incomplete combustion and insufficient oxidation of unburned hydrocarbons. The introduction of the LSCF-coated monolith of catalytic converter results in a substantial reduction in hydrocarbon (HC) emissions across the entire load range, demonstrating effective catalytic oxidation even at relatively low loads. As engine speed increases, hydrocarbon emissions generally decrease for both cases owing to higher exhaust gas temperatures and improved combustion efficiency; however, the reduction is significantly more pronounced with the catalytic converter prepared by La 0. 8 Sr 0. 2 Co 0. 9 Fe 0. 1 O 3 sol-gel synthesised method. Overall, the results confirm that the green LSCF perovskite catalyst provides stable and effective hydrocarbon emission control over a variable range of operating conditions. Hence, hydrocarbon emissions decreased from 641 to 64 ppm at low engine speed and 409 to 94 ppm at medium speed, corresponding to a maximum emission conversion efficiency of about 89%. At higher engine speeds, hydrocarbon pollutant reduces from 237 to 112 ppm and 182 to 98 ppm, achieving conversion efficiencies of approximately 74% and 46%, respectively.

Figures 17–20, shows the variation of carbon monoxide (CO) emissions with engine load and speeds of 1000, 1200, 1400, and 1600 rpm, comparing the La 0. 8 Sr 0. 2 Co 0. 9 Fe 0. 1 O 3 (LSCF) coated monolith for catalytic converter with operation without a catalytic converter. At all engine speeds, Carbon monxide emissions are substantially higher in the absence of a catalytic converter, particularly at increased loads, due to incomplete oxidation of Carbon monxide (CO) under fuel-rich conditions. The incorporation of the La 0. 8 Sr 0. 2 Co 0. 9 Fe 0. 1 O 3 based catalytic converter results in a noticeable reduction in Carbon monoxide (CO) emissions across all engine operating variables, indicating effective oxidation of Carbon monoxide (CO) to Carbon dioxide (CO 2) and the emission rate decreases from 5.59% to 1.27% vol. As engine speed increases, the exhaust gas temperature rises, which enhances catalytic activity and improves conversion efficiency, leading to lower Carbon monoxide levels with the catalyst. The carbon moxide (CO) emissions were reduced from approximately 4.5% to 0.6% vol, 4.2% to 1.4% vol, and 3.0% to 0.1% vol, at the different engine operating conditions. Demonstrating consistently high catalytic activity. Although Carbon monoxide emissions without the converter show some reduction at higher speeds due to improved combustion, they remain significantly higher than those obtained with the catalytic converter. Overall, the results demonstrate that the sustainable green catalyst synthesised by the sol-gel method reliable and efficient for improving CO emission under varying engine speeds and load conditions.

Back pressure represents the resistance encountered by exhaust gases as they exit the engine and pass through the catalytic converter. Maintaining an optimal level of back pressure is essential to preserve favourable exhaust gas flow, gas pressure and velocity flow profiles required for actual catalytic oxidation of CO and HC. Excessive exhaust back pressure can adversely affect engine performance by restricting exhaust flow, limiting oxygen availability within the converter, promoting incomplete combustion, and causing undesirable temperature rise that may lead to catalyst overheating. In the present study, catalytic converter designs incorporating different diffuser inlet-cone angle as 8°,10° and 14° were assessed in a computational flow dynamics software. Among these configurations, the 8° exhaust inlet diffuser cone angle was identified as the most suitable design, as it showed the minimum pressure drop along with improved velocity distribution and more constant exhaust flow compared to the other design configuration. The balanced exhaust pressure achieved with the 8° configuration ensured stable gas flow patterns and effective interaction between exhaust gases and the monolithic catalytic structure.

Experimental investigations further confirmed the effectiveness of the green LSCF perovskite catalytic converter in reducing hydrocarbon (HC) and Carbon monoxide (CO) emissions over a wide range of engine speeds (1000–1600 rpm) and load conditions. Compared with operation without a catalytic converter, the LSCF-coated monolithic system consistently achieved significant reductions in both HC and CO emissions, which can be attributed to its strong redox properties, high oxygen mobility, and enhanced gas-catalyst interaction. Increasing engine speed further improved emission reduction performance due to higher exhaust gas temperatures and favourable reaction kinetics, while the optimised converter geometry ensured uniform flow distribution and efficient catalyst utilisation. Overall, the combined approach of non-noble metal catalyst development and geometric modification offers an effective, sustainable, and cost-efficient alternative to conventional noble-metal-based catalytic converters for automotive exhaust emission control.

This study demonstrates a sustainable and integrated approach for automotive exhaust emission mitigation by combining green synthesis of a non-noble metal perovskite sustainable catalyst with catalytic converter geometry modification. A La 0. 8 Sr 0. 2 Co 0. 9 Fe 0. 1 O 3 -δ (LSCF) perovskite catalyst was successfully synthesised by sol-gel method using a hibiscus flower extract and effectively coated into a cordierite ceramic substrate of catalytic converter. Structural and compositional characterisation using SEM, XRD, and EDX confirmed the formation of a phase-pure perovskite structure with uniform elemental distribution and favourable surface morphology for catalytic applications. Computational fluid dynamics analysis of the catalytic converter housing revealed that inlet diffuser geometry plays a crucial role in controlling exhaust gas flow pattern. Among the investigated configurations, the 8° diffuser inlet cone angle provided the most uniform velocity distribution and the lowest pressure drop, ensuring balanced exhaust gas flow and improved catalyst utilisation, this modified design was therefore selected for experimental validation on laboratory based petrol engine test setup.

Engine test results clearly showed that the La 0. 8 Sr 0. 2 Co 0. 9 Fe 0. 1 O 3 -δ (LSCF) coated catalytic converter achieved significant reductions in hydrocarbon (HC) and carbon monoxide (CO) emissions across a variable range of engine speeds (1000–1600 rpm) and load conditions when compared to operation without a catalytic converter. Improved emission control at higher engine speeds was attributed to increased exhaust gas temperature, enhanced redox activity of the perovskite catalyst, and favourable gas-catalyst interaction enabled by modifying flow distribution. The results further indicate that maintaining moderate exhaust back pressure is essential for achieving effective oxidation reactions without compromising engine performance.

Overall, the combined implementation of a sustainable green-synthesised non-noble metal based perovskite catalyst and modified catalytic converter geometry offers a cost-effective, environmentally, and technically viable alternative to conventional noble-metal based catalyst for exhaust emission control systems. The findings highlight the potential of integrating catalyst development with reactor and flow design as a promising pathway for next-generation automotive exhaust after-treatment technologies.