1. Core Reaction Overview

VOC catalytic oxidation uses precious metal (Pt/Pd) or non-noble metal oxide catalysts to decompose volatile organic pollutants at low-to-medium temperature (180–400 ℃). Organics fully oxidize into harmless CO₂ and H₂O without open flame.

General chemical reaction:

Oxygen-containing VOCs (alcohols, ketones, esters) follow similar complete oxidation routes with less oxygen consumption.

2. Four-Step Complete Catalytic Mechanism

Step 1: Physical Adsorption

Waste gas flows through honeycomb catalyst carrier. VOC molecules and oxygen in air are physically adsorbed onto the high-specific-surface-area alumina coating layer of the catalyst, gathering around active metal sites.

Step 2: Chemical Adsorption & Activation

Active components (Pt, Pd, Mn-Ce composite oxides) capture electrons from VOC molecular C-H / C-C bonds, lowering molecular activation energy. Weak bonds break, forming active organic free radicals. Lattice oxygen inside metal oxides also migrates to the surface for oxidation.

Step 3: Complete Oxidation Degradation

Activated organic fragments react with lattice oxygen and gaseous oxygen, thoroughly breaking long organic chains, benzene rings and heterocyclic structures. Intermediate aldehydes, alcohols are further oxidized, finally generating carbon dioxide and water vapor.

Step 4: Desorption & Oxygen Regeneration

CO₂ and H₂O desorb from the catalyst surface and are discharged with exhaust airflow. Ambient oxygen supplements consumed lattice oxygen, restoring catalyst activity sites to sustain continuous cyclic reaction.

3. Key Function of Catalyst Structure

1. Cordierite honeycomb substrate: Low air resistance, high thermal stability, supports the whole coating layer.
2. γ-Al₂O₃ washcoat: Provides huge specific surface area to disperse active components evenly, avoid active metal sintering.
3. Active phase (Pt/Pd or metal oxides): The core to reduce VOC ignition temperature (T50) and full conversion temperature (T99).
4. Rare earth additives (Ce, La): Store lattice oxygen, enhance anti-sintering and anti-toxic performance, extend service life.

4. Why Catalytic Oxidation Outperforms Direct Thermal Incineration

1. Catalyst cuts reaction activation energy drastically; full degradation at 280–350 ℃ vs 700–900 ℃ for direct combustion, saving massive fuel.
2. No high-temperature flame, inhibits thermal NOₓ generation, reducing secondary air pollution.
3. Circulating lattice oxygen enables continuous low-energy operation, suitable for long-running industrial waste gas treatment.

5. Catalyst Deactivation Mechanism (Side Note of Working Principle)

Normal cycle relies on unblocked active sites; three conditions block the reaction cycle:

1. Silicone, tar, dust physically cover active sites;
2. Sulfur, halogen compounds form stable metal sulfide/halide, causing chemical poisoning;
3. Long-term ultra-high temperature leads to sintering of active metal particles, reducing available reaction sites.