Study on the catalytic treatment process of carbon monoxide

1. The core principle of CO catalytic treatment
The essence of CO catalytic reaction is to reduce the activation energy of oxidation reaction through catalyst, and the reaction formula is:
2CO + O₂ → 2CO₂ (ΔH = -566 kJ/mol)
The active sites on the catalyst surface (such as the d orbital of metal atoms) adsorb CO and O₂ molecules, form CO₃⁻ intermediates through electron transfer, and finally dissociate into CO₂. Precious metals (Pt, Pd) can catalyze reactions at room temperature due to their high electron density, while non-precious metals (CuO, MnO₂) need to rely on oxygen vacancy mechanisms to complete oxidation at high temperatures.
2. Detailed explanation of typical process flow
1. Exhaust gas pretreatment system
Pretreatment is the key to ensuring the life of the catalyst, which mainly includes the following links:
Particulate matter removal:
A cyclone separator (removes particles > 10 μm) is connected in series with a bag filter (accuracy up to 1 μm) to reduce the dust concentration to below 5 mg/m³ to prevent the catalyst pores from being blocked.
Sulfide removal:
For sulfur-containing exhaust gases (such as coke oven gas), the H₂S concentration is controlled within 0.1 ppm through wet desulfurization (NaOH spray tower, pH 10~12) or dry adsorption (activated carbon loaded with Fe₂O₃) to avoid catalyst sulfur poisoning.
Humidity regulation:
Use a condenser to reduce the exhaust gas temperature to below the dew point (usually 40~50℃), and use a silica gel adsorption tower to adjust the humidity to 30%~50% relative humidity to prevent water vapor from covering the active sites of the catalyst.
CO concentration homogenization:
Through the gas mixing chamber and dynamic flowmeter (such as mass flow controller), the CO concentration fluctuation range is controlled within ±5% to ensure stable operation of the reactor.
2. Catalytic reactor design and operation
Reactor type selection:
Fixed bed reactor: using honeycomb ceramic or metal corrugated plate carrier, catalyst coating thickness 50~200 μm, suitable for low concentration (<1000 ppm) and large flow exhaust gas (space velocity 10,000~30,000 h⁻¹).
Fluidized bed reactor: using catalyst powder with a particle size of 20~100 μm, the gas-solid contact efficiency is increased by 3~5 times, suitable for high concentration CO (>1%), but a cyclone separator is required to recover the catalyst.
Moving bed reactor: Catalyst particles (1~3 mm) move slowly from top to bottom, which can achieve continuous regeneration and is suitable for complex waste gas containing tar or easy to coke.
Structural parameter optimization:
Length-to-diameter ratio (L/D): Fixed bed is usually 3:1~5:1 to balance pressure drop and conversion rate;
Bed pressure drop: Calculated by Ergun equation, generally controlled at 5~15 kPa/m;
Catalyst loading: Layered loading technology is adopted, high mechanical strength carrier (such as cordierite) is used in the inlet section, high active components (such as Pt/Al₂O₃) are loaded in the middle, and a protective layer (such as zeolite molecular sieve) is set in the outlet section.
3. Dynamic regulation of reaction conditions
Temperature control:
Precious metal catalysts use multi-stage temperature control: preheating section (80~120℃), main reaction section (120~180℃), insulation section (150~200℃), temperature deviation ≤±2℃. Non-precious metals require electric heating or gas combustion to raise the temperature to 250~400℃.
Oxygen concentration adjustment:
Real-time monitoring through online oxygen sensors (such as ZrO₂ solid electrolyte probes). When the O₂/CO molar ratio is lower than 0.5, the oxygen supplement system (air or pure oxygen injection) is started to maintain the excess oxygen coefficient α=1.1~1.3.
Space velocity optimization:
The space velocity (GHSV)-conversion rate model is established based on the Arrhenius equation, and the space velocity is controlled in the optimal range by adjusting the fan frequency (precious metals: 20,000~50,000 h⁻¹; non-precious metals: 5,000~15,000 h⁻¹).
4. Post-treatment and energy efficiency management
Waste heat recovery:
The post-reaction gas (usually 200~350℃) enters the shell and tube heat exchanger, preheating the inlet temperature to above 150℃, and the heat recovery efficiency can reach 60%~80%.
Exhaust gas detection:
Use non-dispersive infrared analyzer (NDIR) to monitor CO concentration online to ensure that the outlet value is ≤50 ppm (national standard GB 16297-1996).
Catalyst regeneration:
Regularly (usually 3000~5000 hours) introduce 5% H₂/N₂ mixed gas at 300℃ for 2 hours to restore the catalyst activity to more than 90% of the initial value.
III. Key technologies for process optimization
1. Catalyst performance improvement
Nanostructure design:
The Pt/TiO₂ core-shell structure (particle size 2~5 nm) is prepared by sol-gel method, the specific surface area is increased to 200~300 m²/g, and the CO ignition temperature is reduced to -30℃.
Anti-poisoning modification:
Add 5% La₂O₃ to the Cu-Mn-Ce catalyst, and the sulfur tolerance is increased from 0.01% to 0.1% through the electronic auxiliary effect.
2. Reactor fluid mechanics optimization
CFD simulation:
Use ANSYS Fluent software to build a three-dimensional model and optimize the gas distributor opening rate (usually 30%~40%) to make the bed velocity distribution uniformity reach more than 95%.
Pressure fluctuation suppression:
Set internal baffles in the fluidized bed to reduce the pressure fluctuation range from ±15% to ±5%.
3. Intelligent control strategy
Model predictive control (MPC):
Build a dynamic model based on CO concentration, temperature, and flow data to adjust the heating power and oxygen supplement in real time to narrow the conversion rate fluctuation range from ±5% to ±1%.
Catalyst life prediction:
Analyze historical deactivation data through machine learning (such as LSTM neural network) to warn of catalyst replacement needs 30 days in advance.
IV. Technical challenges and development trends
At present, it is still necessary to break through bottlenecks such as insufficient low-temperature activity and poor tolerance to complex exhaust gases. Future directions include: large-scale preparation of single-atom catalysts, microwave-assisted heating technology, and integrated process development for the directional conversion of CO into high-value chemicals such as formic acid.
Core of industrial waste gas purification: Toxic CO is efficiently converted into CO through precious metal/non-precious metal catalysts. Key technologies include pre-treatment dust removal and desulfurization, intelligent control of reactors (precise matching of temperature/oxygen concentration/space velocity) and nanocatalyst design, achieving a conversion rate of >99% and reducing energy consumption by 30%.

author: Hazel
date:2025-05-14