Regarding the cost of catalytic converters, Ehteram mentioned that prices range from 600,000 to several million Tomans. Catalytic converters resilient to fuel fluctuations and compatible with various conditions are more expensive. Utilizing these costly catalytic converters for vehicles valued at less than 50 million Tomans is not economically viable.

He emphasized that consistent availability of Euro 4 standard fuel at all gasoline stations would facilitate a reduction in air pollution. However, if the supply of standard fuel fluctuates, and some refineries face challenges in providing standard fuel during specific periods, the disappearance of the catalytic converter would impose costs on citizens and amplify air pollution.

In conclusion, the academic member highlighted the lack of clarity in the law regarding assigning responsibility for catalytic converter damage, ultimately resulting in citizens bearing the financial burden.

The Crucial Role of Catalysts in Emission Reduction

Discussing the pivotal role of catalysts in reducing emissions, Ehteram underlined, “A catalytic converter’s primary function is to eliminate carbon monoxide, unburned hydrocarbons, and nitrogen oxides. Within vehicles, it acts as a converter, transforming carbon monoxide into carbon dioxide and nitrogen oxides into nitrogen.”

He elaborated on the specifics, stating, “Carbon monoxide, a byproduct of incomplete combustion, is a toxic, odorless, and colorless gas that can enter the body through respiration, affecting hemoglobin in the blood. This gas elevates the risk of heart attacks. Fortunately, carbon monoxide isn’t a significant issue in Tehran presently. However, nitrogen oxides, known to irritate the lungs, pose a substantial problem in Tehran and are regarded as the third major contributor to air pollution after particulate matter and ozone.”

The professor further outlined the problem, “Nitrogen oxides can exacerbate the production of particulate matter through a secondary process when exposed to sunlight. Currently, particulate matter stands as the most critical air pollutant in Tehran. Additionally, the catalytic converter can incinerate and eliminate unburned hydrocarbons.”

Emphasizing the Need for Enhanced Focus by the Ministry of Oil on Standardized Fuel Production

Addressing a query regarding the pollution control parts warranty law outlined in the Clean Air Bill, Ehteram emphasized that “while vehicle manufacturers are obliged to provide a warranty for catalytic converters, they are not held responsible for issues caused by fuel quality. Thus, the Ministry of Oil must intensify efforts towards producing standardized fuel. This focus becomes pivotal as we progress towards Euro 5 and 6 standards in the automotive industry; it’s nonsensical to have fuel supplied at distribution stations that do not meet the required standards.”

The Function of Catalytic Converters in Vehicles

A catalytic converter is a vital device placed in the exhaust system of a vehicle. Through a series of chemical reactions, it transforms toxic gases resulting from the vehicle’s combustion into harmless gases, effectively mitigating air pollution. These converters come in various types, with the chemical reactions within them differing based on the type of engine and fuel being used. For example, in diesel vehicles, catalytic converters facilitate oxidation reactions, converting carbon monoxide, nitrogen oxide derivatives, and hydrocarbons from incomplete fuel combustion into carbon dioxide, nitrogen, and water.

While catalytic converters find extensive use in automobiles, they are also essential components in generators, locomotives, trucks, and airplanes. Notably, this device was invented to comply with government regulations and environmental policies aimed at limiting vehicle emissions.

In 1970, the United States government, prompted by a review of the California Air Pollution Control Agency’s report, enacted the Clean Air Act amendments. These amendments compelled American manufacturers to take robust actions to rectify their deficiencies in line with anti-pollution laws. By 1975, laws were put in place mandating most automobile companies to integrate catalytic converter systems into their vehicles. This system is operated by chemically converting toxic gases into carbon dioxide and water. The mandatory installation of catalytic converters commenced in the United States that year and became operational in Europe in 1993.

In Iran, the utilization of catalytic converters in domestically manufactured vehicles became mandatory in the second half of 2002, enforced by the Department of Environment. Following the Comprehensive Plan for Air Pollution Reduction, the validity testing of catalytic converters in technical vehicle inspections for the issuance of a technical inspection certificate and sticker became compulsory at the beginning of 2012. Iranian automobile manufacturers began incorporating catalytic converters into their domestic vehicles in 2003. Vehicles before this period failed to meet the required standards, resulting in pollution levels more than 30 times higher than other vehicles. Consequently, the Department of Environment approved the sale of vehicles from the 2003 model and onwards. It’s important to note that in some vehicles produced in the last quarter of 2007, the catalytic component might not have been installed. However, according to the Comprehensive Plan for Air Pollution Reduction, “Validity testing of the catalytic converter and carbon canister in technical inspections of vehicles for the issuance of a technical inspection certificate and sticker is mandatory from the beginning of 2012.”

The Function of Exhaust and Catalytic Converter Systems in Vehicles

A catalytic converter can neutralize up to 90% of harmful gases by converting unburned hydrocarbons from the engine into water and carbon dioxide. Additionally, it transforms nitrogen oxides into nitrogen gas, making it highly effective in reducing air pollution. Typically, a catalytic converter lasts around 50,000 to 60,000 kilometers. However, in vehicles manufactured in Iran, the catalytic converters installed to mitigate pollution become less effective and notably increase pollution levels after about 80,000 kilometers. On average, a catalytic converter’s lifespan is about 4 years, after which it requires replacement.

The effectiveness of this component diminishes when its porous pathways become blocked or its effective surface is covered. Elevated temperatures, exposure to engine exhaust toxins, and external mechanical impacts can lead to clogging and blockage of the catalysts’ pathways and surfaces, reducing their efficiency. Moreover, engine misfires resulting from faulty spark plugs, wires, and injectors can introduce unburned fuel into this component, further decreasing its lifespan. The operational life of catalytic converter reactors in vehicles is approximately 80,000 kilometers. The decline in efficiency and blockage of the catalyst’s pathways or its non-utilization in the vehicle can result in incomplete combustion in the engine, causing an increase in pollutant concentrations in the exhaust and wear of engine components.

Removing this component, whether to reduce the vehicle’s pollution or due to delayed replacement after its useful life, can cause significant harm to the air we breathe and contribute to increased air pollution.

Isaco’s Warning Regarding Catalytic Converter Removal:

Considering market limitations and sensitivities concerning this vital component, Isaco has implemented necessary measures to ensure its availability through authorized representatives. Presently, the catalytic converter component can be obtained from most authorized representatives of Iran Khodro Aftersales Services Company (Isaco). Regrettably, due to incorrect advice from certain vehicle repair personnel, this component is sometimes removed from vehicles, resulting in long-term disadvantages for the vehicle and significant adverse effects on the environment. Given the current air quality situation in Tehran, this issue is of utmost importance.

However, it is conceivable that targeted subsidy policies could amplify the significance of this matter, as having this component in the exhaust can lead to reduced fuel consumption. Customers should be informed that the average lifespan of this component is approximately four years, and replacement is advisable after this period.

The Role of Exhaust, Muffler, and Catalytic Converter Systems in Vehicles:

As you may be aware, all vehicles equipped with internal combustion engines feature a component known as the exhaust. The exhaust serves the primary function of expelling smoke resulting from chemical processes within the cylinders into the external environment. However, the definition of exhaust has evolved to encompass additional functionalities. The three main functions of the exhaust are pollution reduction, noise reduction, and temperature moderation. The exhaust system comprises three essential parts: the connection to the engine, the middle section, and the end. In this system, the catalyst is integrated into the initial part due to the need for a temperature of 800 degrees Celsius. The second and third parts play a crucial role in decreasing temperature and noise. This device can significantly reduce the emission of hazardous gases resulting from fuel combustion.

Catalytic converter reactors are high-temperature resistant ceramic or metallic components placed in the path of exhaust gases within the exhaust system. They perform the conversion of three toxic and polluting gases, namely carbon monoxide, hydrocarbons from incomplete combustion, and nitrogen oxides, into non-toxic gases: water vapor, nitrogen, and carbon dioxide. The vehicle’s catalytic converter contains an oxygen sensor that regulates the air-to-fuel ratio to achieve complete combustion in the engine.

Engine Exhaust Emissions:

Essentially, exhaust gases typically contain paraffins, olefins, aromatic compounds (all recognized as hydrocarbons resulting from incomplete combustion), water vapor, carbon monoxide, nitrogen oxides, sulfur oxides, nitrogen, oxygen, and carbon dioxide. Among these, three primary hazardous pollutants are carbon monoxide, nitrogen oxides, and unburned hydrocarbons.

For instance, carbon monoxide, a colorless and odorless gas, is primarily generated from the incomplete combustion of fossil fuels. It can bind with hemoglobin in the blood up to 250 times faster than oxygen, leading to various effects ranging from headaches to fatalities. Other detriments of exhaust gases include the risk of premature births and different lung cancers.

Considering the pollutants present in exhaust gases, the objective is to convert these gases into less harmful or predominantly benign substances for the environment and living organisms through oxidation and reduction reactions in catalytic converters.

Types of Catalytic Converters:

In catalytic converters, a two-stage or three-stage reaction occurs, depending on the type of converter. We will now elucidate each of them:

1. a) Two-Stage Reaction-Based Catalytic Converters:

In this reaction, carbon monoxide and hydrocarbons resulting from incomplete combustion of fuel are converted into carbon dioxide and water.

1. b) Three-Stage Reaction-Based Catalytic Converters:

In this reaction, nitrogen oxides are oxidized into nitrogen gas and oxygen, followed by the conversion of carbon monoxide and hydrocarbons resulting from incomplete combustion of fuel into carbon dioxide and water.

Based on these reactions, there are two main types of catalytic converters:

Dual Catalytic Converter:

Primarily used in diesel engines, this type of catalytic converter reduces pollutants like carbon monoxide and unburned hydrocarbons. Due to their inefficiency in reducing nitrogen oxides, they are not employed in gasoline engines today. The dual catalytic converter simultaneously performs two actions:

• Oxidation of carbon monoxide to carbon dioxide: CO + 0.5O2 → CO2
• Oxidation of unburned hydrocarbons, converting them to carbon dioxide and water: CxH2x+2 + [(3x+1)/2] O2 → xCO2 + (x+1) H2O

Three-Way Catalytic Converter:

This type accomplishes three essential tasks:

• Reduction of nitrogen oxides to oxygen and nitrogen: 2NOx → xO2 + N2
• Oxidation of carbon monoxide to carbon dioxide: CO + 0.5O2 → CO2
• Oxidation of unburned hydrocarbons, converting them to carbon dioxide and water: CxH2x+2 + [(3x+1)/2] O2 → xCO2 + (x+1) H2O

A crucial point regarding these catalysts is their optimal efficiency when the exhaust gases entering the catalyst have a slightly higher composition than the stoichiometric point. This implies that in gasoline engines, the air-to-fuel weight ratio in the mixture entering the catalyst should be approximately 14.6 to 14.8.

It’s important to note that besides the main reactions resulting in the production of non-toxic products, some unintended reactions occur in the catalytic converter, leading to minute amounts of toxic substances such as hydrogen sulfide (H2S) and ammonia (NH3). These unintended reactions typically occur in catalytic converters based on three-stage reactions. While complete elimination of these reactions is not feasible, modifications to the catalyst material and the oxide layer can minimize these undesired reactions. For instance, to prevent the production of hydrogen sulfide, one can introduce metallic oxides like nickel or manganese to the oxide layer. These metals are sensitive to sulfur absorption, preventing its absorption by the oxide layer. In other words, hydrogen sulfide is produced only when sulfur is absorbed by the oxide layer at low temperatures. After absorption at low temperatures, sulfur is released at high temperatures and combines with hydrogen to form hydrogen sulfide gas.

Types of Catalytic Converters Based on Material:

Catalysts can be categorized into three primary types based on their materials:

• Pellet Catalysts
• Ceramic Catalysts
• Metal Catalysts

The initial type of catalytic converters utilized pellets made from perforated alumina (Al2O3) spheres impregnated with precious metals (PM). These pellets, with diameters ranging from 1/8 to 1 inch, were placed beneath vehicles in metal enclosures. Such converters were employed for engines with large volumes, low speeds, and low temperatures, commonly found in trucks.

The second type comprises catalysts made from thin-walled ceramic structures resembling honeycombs, known as ceramic monoliths. In these structures, precious metals are not directly placed on the walls but rather on an outer layer called a washcoat, containing metal oxides (BMO) like alumina (Al2O3) and ceria (CeO2) to increase the contact surface.

The primary structure of ceramic catalysts is typically created through the extrusion of a ceramic material called cordierite (2Al2O3-5SiO2-2MgO).

The third type, less prevalent than the second type, consists of metallic monoliths. These are crafted from high-temperature-resistant metal alloys and resemble ceramic ones in having numerous holes, constructed from shaped metal foils assembled.

Advantages of ceramic catalysts over metallic ones include ease of production, simpler and more cost-effective coating, better temperature maintenance, and easier recycling. Conversely, advantages of metallic catalysts over ceramic ones include higher resistance to impact and heat, the ability to reduce wall thickness (allowing for more holes or higher cpsi), and less pressure drop and quicker warm-up. Presently, the prevalent commercial catalyst is ceramic, constituting approximately 85% of the total catalytic converter production.

Operating Conditions of Catalytic Converters:

Exhaust gases from a gasoline engine typically range in temperature from 300 to 400 degrees Celsius, reaching up to 900 degrees Celsius under full load conditions. For a catalytic converter to function optimally, the temperature indicator for a converter in good condition should ideally fall within the range of 500 to 600 degrees Celsius. Therefore, converters should be designed to endure a spectrum of temperatures from 400 to 800 degrees Celsius.

If the converter’s temperature in the exhaust system reaches 800 to 1000 degrees Celsius for a prolonged period, the primary metal and its coating can undergo thermal stress, leading to the degradation of the converter. A catalytic converter, under ideal conditions, has a useful life of approximately 100,000 kilometers.

Excessive force on the engine and subsequent energy loss can occur due to incomplete combustion at unreasonable speeds and excessive loads under abnormal conditions. This can significantly elevate the temperature of the exhaust gases from the converter. If this temperature surpasses 1400 degrees Celsius, it can cause the layers beneath the used materials in the converter to melt, resulting in the malfunction of the converters, particularly in honeycomb passages.

At a consistent temperature exceeding 300 degrees Celsius, a new catalytic converter can effectively handle 68% to 99% of carbon monoxide (CO) and 95% of hydrocarbons (HC). However, catalytic converters experience a loss in efficiency at considerably lower temperatures than 300 degrees Celsius. The term “light-off temperature” or “transition temperature” is used when converters achieve around 50% efficiency.

A catalytic converter’s efficiency diminishes when its active components are exposed to exhaust gas temperatures. Prolonged exposure of active materials to exhaust gas temperatures can cause a decline in efficiency due to excessive heat and specific welding conditions. This occurs due to the extended contact of the active surface with these conditions, resulting in a loss of gas absorption properties that pass through the active passage. Prolonged contact with interfering elements such as the anti-knock element in fuel during combustion (lead) and phosphates added to oils can obstruct the active sites in converters, hindering the function of chemically active substances. This phenomenon is known as poisoning the catalytic converter, which can happen even with lead-free gasoline over an extended duration.

Catalytic converters need to become active quickly in terms of handling monoxides of carbon (CO) and hydrocarbons (HC), ideally within a minute and even around 30 seconds. Achieving this is feasible by placing the converter in the nearest location to the engine manifold.

While proximity to the exhaust manifold may lead to exhaust gases (under specific conditions) and their heat exceeding appropriate levels, potentially damaging the primary metal and active layers of the converter and consequently reducing its lifespan, a catalytic converter should function effectively under relative stoichiometric conditions of the fuel-to-air ratio.

The production of nitrogen oxides is significantly influenced by the engine load, especially the fuel-air mixture, particularly if this ratio is at a low stoichiometric level. Emphasizing the importance of fuel and air composition, especially near the ideal stoichiometric point, in this condition, the emission of harmful gases is minimized.

Due to a vehicle’s Engine Control Unit (ECU) being calibrated with the presence of a catalytic converter in mind, any modifications or removal of the catalytic converter, although initially potentially improving the vehicle’s acceleration, will eventually result in improper engine performance and increased fuel consumption.

Moreover, from the carburetor or injector in the engine, a precise fuel and air mixture is expected to be blended. Any deviation in the carburetor or injector’s performance can directly impact the stoichiometry of the reaction in the cylinders, consequently increasing pollutant levels.

The constituents present in the fuel can also directly influence pollutant levels and the catalytic converter’s performance. For instance, sulfur poisons the catalytic converter by reacting with the catalytic surface, hindering the desired reaction and deactivating the catalyst.

In compliance with European standards (98/69/EC and 8/2002/EC), the sulfur and lead concentrations for gasoline are specified.

Factors leading to damage and deterioration of the catalytic converter’s efficiency encompass:

• High temperatures.
• Poisoning by substances in the engine’s exhaust.
• Mechanical damage to the converter.

Excessively high temperatures cause heavy metals to amalgamate and reduce their effective surface area in catalysts, diminishing their efficiency. Temperatures typically exceeding 800 to 1000 degrees Celsius lead to agglomeration and sticking of heavy metals. The primary factor contributing to temperature elevation is the absence of spark plugs igniting the fuel.

Common poisons found in catalytic converters include lead, phosphorus, and sulfur, often present as additives in gasoline and oil. Lead is commonly used as an anti-knock agent, phosphorus as an oil additive, and sulfur is present in recognized quantities in gasoline and oil. The first two elements have a more detrimental impact on heavy metals, while the third has a more adverse effect on metal oxides.

External mechanical impacts on catalytic converters, especially on aged catalysts that have become brittle, can cause fractures, seizures, and other damage to the catalysts. Each of these mentioned factors contributes to the diminished efficiency of catalytic converters in vehicles.