Automobile exhaust CO emission reduction technology: principles, methods and catalyst applications

The harm of CO and the necessity of emission reduction
Carbon monoxide (CO) in automobile exhaust is a product of incomplete combustion of fuel, and its concentration ranks first among exhaust pollutants. CO is colorless and odorless, but highly toxic. It can bind to hemoglobin, hinder oxygen transport, and cause hypoxia in the human body. In severe cases, it can cause dizziness, suffocation, and even death. 25 In addition, CO, nitrogen oxides (NOx), and hydrocarbons (HC) can form photochemical smog under light, exacerbating air pollution. Therefore, controlling CO emissions from automobile exhaust is a key link in improving air quality and protecting public health.
Core methods and principles of CO emission reduction
1. Engine combustion optimization
Improve fuel combustion efficiency and reduce CO generation by improving combustion conditions.
Air-fuel ratio control: Use oxygen sensors to monitor oxygen content in real time, adjust fuel injection volume, and make the mixture concentration close to the theoretical air-fuel ratio (14.7:1), avoiding incomplete combustion caused by too rich or too lean mixture .
Ignition system upgrade: Use high-energy ignition coils and high-temperature resistant spark plugs to enhance ignition energy, ensure full combustion of the mixture, and reduce CO residue .
Exhaust gas recirculation (EGR): Introducing part of the exhaust gas into the intake system, reducing the combustion temperature, inhibiting the generation of NOx and reducing CO emissions caused by local hypoxia8.
2. Improvement of fuel quality
The physical and chemical properties of the fuel directly affect the combustion efficiency.
Addition of oxygenated fuel: such as ethanol gasoline (E10), which has a high oxygen content, can promote complete combustion of the fuel and reduce CO generation4.
Promotion of low-sulfur fuel: Reduce the poisoning effect of sulfides on catalysts and extend the life of the aftertreatment system.
3. Catalytic purification of tail gas
The oxidation of CO into harmless carbon dioxide (CO₂) through catalytic technology is currently the most mainstream means of emission reduction.
Three-way catalytic converter: The core is a honeycomb ceramic carrier coated with precious metals (platinum, rhodium, palladium), which uses redox reactions to simultaneously convert CO, HC and NOx.
This technology needs to be started at a high temperature above 300°C, but the efficiency is low during the low-temperature cold start stage.
Low-temperature catalyst development: For example, composite catalysts of nitrogen-doped manganese dioxide loaded with precious metals can achieve efficient CO oxidation in a wide temperature range of -40°C to 50°C, which is particularly suitable for the frequent start-stop conditions of hybrid vehicles.
Anti-sulfur and anti-humidity design: Protect active sites through hydrophobic coatings or core-shell structures to prevent water molecules and sulfides from deactivating catalysts and extend service life.
4. New energy technology substitution
Fundamentally eliminate CO emissions.
Pure electric vehicles (BEV): Driven by electricity, zero tail gas emissions.
Hydrogen fuel cell vehicles (FCEV): Generate water through electrochemical reactions, no polluting byproducts.
The key role of carbon monoxide catalysts
The catalyst is the core of the tail gas purification system, and its performance directly affects the emission reduction effect:
Precious metal-based catalysts: Platinum, palladium, etc. are used as active components to achieve CO conversion through surface adsorption-oxidation mechanism, with an efficiency of more than 95%. However, its high cost and scarce resources promote research on non-precious metal substitution.
Metal oxide catalysts: such as cobalt manganese composite oxide (CoMnOₓ), which promotes CO adsorption and oxidation through oxygen vacancies, are low-cost and high-temperature resistant, and are suitable for diesel vehicle exhaust treatment.
Honeycomb structure carrier: stainless steel or ceramic honeycomb matrix, high porosity (≥400 mesh) design reduces airflow resistance, adapts to high air velocity (600,000 mL·g⁻¹·h⁻¹) environment, and improves treatment efficiency.
Future technology trends
Intelligent control: integrated sensors and electronic control units, real-time monitoring of exhaust composition and optimization of catalyst working conditions.
Material innovation: development of new materials such as perovskite oxides and single-atom catalysts to improve low-temperature activity and stability.
System integration: combining catalytic purification with particulate matter filtration (such as DPF) and nitrogen oxide reduction (such as SCR) modules to achieve multi-pollutant coordinated treatment.
Summary
Automobile exhaust CO emission reduction requires comprehensive combustion optimization, catalytic purification and new energy technologies, among which catalysts play a core role in oxidation reactions. With the advancement of materials science and intelligent control technology, low-cost, highly adaptable carbon monoxide catalysts will drive the transformation of the automotive industry towards a cleaner and lower-carbon future, helping to achieve the “dual carbon” goals.