Honeycomb Ceramic Coating Technology

The catalytic performance of honeycomb ceramic supports is determined by the composition, structure, and process of their surface coating. The coating is a key step in endowing the support with catalytic function.

Functional Composition and Material System of the Coating

High Specific Surface Area Oxide Layer

Main material: γ-alumina (γ-Al₂O₃). Increases the specific surface area of the ceramic support itself (typically <1 m²/g) to 100-300 m²/g. Provides dispersion anchoring sites for active metal components.

Key Additives:

Cerium oxide, Zirconia: Enhance oxygen storage capacity and thermal stability.

Lanium oxide, Barium oxide: Inhibit alumina phase transformation and prevent high-temperature sintering deactivation.

Active Catalytic Components

Noble Metal System:

Platinum, Palladium: Dominate oxidation reactions (CO, HC → CO₂, H₂O).

Rhodium: Dominate reduction reactions (NOx → N₂).

Transition Metal Oxide Systems:

Vanadium-Tungsten-Titanium System: Traditional SCR catalyst (V₂O₅-WO₃/TiO₂).

Copper-Based/Iron-Based Zeolites: Novel wide-temperature SCR catalysts.

Special Functional Additives

Sulfur Resistants: Barium oxide, etc., used to fix SOx and prevent poisoning.

Accelerators: Alkali metals or rare earth elements, optimizing the electron transfer process.

Coating Process Technology Key Points

Carrier Pretreatment: Surface cleaning and activation to ensure coating adhesion strength. Adjusting the isoelectric point through acid treatment or surface modification to optimize wettability.

Coating Methods

Immersion Method: Most commonly used, achieving uniform loading by controlling slurry viscosity and pull-out speed.

Vacuum Coating: Used for high-porosity carriers to ensure uniform coverage deep within the pores.

Spraying Method: Suitable for localized coating or gradient coating designs.

Drying and Firing

Step Drying: Prevents coating cracking and migration.

Temperature-controlled calcination: The coating structure is cured at 400-600°C to avoid sintering of active components.

Application Scenarios and Requirements

Automotive Exhaust Treatment

TWC Coating: Precious metal content 0.5-3%, cerium-zirconium oxygen storage material proportion 20-40%.

SCR Coating: Molecular sieve loading 2-4 g/in³, copper content 1-3%.

DPF Coating: Catalytic coating used to reduce regeneration temperature (CSF technology).

Industrial Waste Gas Treatment

VOCs Oxidation Coating: Platinum/Palladium loading 0.1-0.5%, with added manganese/cobalt oxides to promote complete oxidation.

Ozone Decomposition Coating: Manganese oxide as the main active component, loading 8-15%.

Chemical Process Catalysis

Methane Reforming Coating: Nickel-based catalyst, loading 10-20%, with added magnesium aluminum spinel as a stabilizer.

Summary

The honeycomb ceramic coating is the core of its catalytic function, consisting of three parts: a high surface area oxide layer providing the reaction site, an active metal component performing the catalytic reaction, and a stabilizing agent ensuring durability. Application is done through processes such as impregnation and spraying, requiring precise control of the drying and sintering process. For different applications such as automotive, industrial, and chemical, the coating formulation needs to achieve a balance between activity, anti-toxicity, and stability. The ultimate goal is to ensure that the coating maintains long-term high-efficiency catalytic capability under various harsh conditions through precise formulation and processes.