Catalytic Converters: A Crucial Component in Combating Pollution
Air pollution is a leading global health concern, responsible for approximately 2.4 million deaths annually, according to the World Health Organization (WHO) [1]. In urban areas, the transport sector is the primary contributor to air pollution worldwide [1].
Gasoline (petrol) engines release harmful pollutants such as Carbon Monoxide (CO), Hydrocarbons (HC), and Nitrogen Oxides (NOx). Diesel engines, in addition to these, emit Diesel Particulate Matter (DPM). These pollutants are linked to severe health issues, including respiratory and cardiovascular diseases, suffocation, and even cancer [1].
Automobiles have become indispensable to modern life, and catalytic converters, which drastically reduce vehicle emissions, have become equally essential.
The introduction of increasingly stringent automobile emission standards in the 1970s led to the development of catalytic converters. Decades later, these regulations continue to drive the global market for catalytic converters, which is projected by Grand View Research to reach a valuation of $273 billion by 2024 [2].
Initially, two-way catalytic converters were used in petrol and diesel vehicles in the U.S. and Canada until 1981. These converters could neutralize CO and HC emissions but were ineffective against NOx. As a result, petrol vehicles transitioned to three-way catalytic converters capable of reducing all three pollutants. Diesel vehicles, on the other hand, still rely on two-way converters, supplemented by Selective Catalytic Reduction (SCR) systems to reduce NOx emissions and Diesel Particulate Filters (DPF) to trap DPM [3].
One of the primary functions of catalytic converters is oxidizing CO into Carbon Dioxide (CO2), a greenhouse gas that contributes to global warming. However, even without catalytic converters, CO in vehicle emissions would eventually oxidize to CO2 in the atmosphere. The converters expedite this process, reducing the immediate local impact of CO emissions [4].
Automobile Exhaust and the Impact of Catalytic Converters
Carbon monoxide, nitrogen oxides, and hydrocarbons are highly toxic emissions, making their reduction a key focus in automobile engine design [5]. Major pollutants in vehicle exhaust include the following [1]:
- Carbon Monoxide (CO): Produced by incomplete combustion of fuel, CO can cause suffocation, slower reflexes, impaired focus, and confusion.
- Nitrogen Oxides (NOx): High operating temperatures in diesel engines lead to increased NOx emissions, including nitrogen oxide (NO) and nitrogen dioxide (NO2). Road transport accounts for 40-70% of urban NOx emissions. NOx contributes to lung diseases, respiratory problems, smog, acid rain, reduced visibility, and ozone formation.
- Hydrocarbons or Volatile Organic Compounds (VOCs):Unburned fuel releases VOCs. Diesel engines typically emit fewer hydrocarbons, but these pollutants can cause cancer, breathing difficulties, and ground-level ozone formation.
- Particulate Matter (PM): Resulting from the incomplete combustion of hydrocarbons in fuel and lubricating oil, PM emissions from diesel engines are 6-10 times higher than those from gasoline engines. PM is linked to climate change, lung cancer, asthma, reduced visibility, lower agricultural productivity, building soiling, and premature mortality.
Emission Reductions by Catalytic Converters:
Three-way catalytic converters can reduce emissions from gasoline engines by 80-90%, including:
- Carbon Monoxide (CO)
- Hydrocarbons (HC)
- Nitrogen Oxides (NOx)
These converters are most effective when the engine operates within a narrow range of the stoichiometric (ideal) air-to-fuel ratio [6].
Diesel Engine Emission Controls:
Properly designed catalytic converters for diesel engines achieve the following reductions [7]:
- 80-95% reduction in CO emissions
- 85-90% reduction in HC emissions
- 25-35% reduction in Diesel Particulate Matter (DPM)
Additionally, diesel engines employ Selective Catalytic Reduction (SCR) systems to achieve [8]:
- Up to 90% reduction in NOx
- 50-90% reduction in CO and HC
- 30-50% reduction in DPM
