Catalysts influence – as we know - chemical reactions. And to make sure that all chemical compounds (in our case mainly CO and Hydrocarbons) get the “chance” to get in contact with our catalytic combustor, we’ve to provide as much surface area as possible.
This is firstly and most obviously achieved by using ceramic (cordierite) honeycombs as substrate.
But while it is obvious that honeycombs are increasing surface area (standard dimensions in wood burning vary from 16 and 25cpsi (combs per square inch) while specially designed cats for industrial use go up to 1,000cpsi), the main increase in surface area is achieved by applying a wash coat of “super porous” gamma alumina to carry precious metal particulates.
The gamma alumina is applied as slurry and then reduced to a powdery substance by the application of high heat to fix it. This tremendously increases surface - approaching 2,000 times the surface area of the bare substrate - is now ready for the catalyst.
Cordierite ceramic is characterized by
- High porosity: which makes it easy to coat and enhances the surface area for maximum roughness (surface area)
- Low thermal expansion: cordierite has a near zero thermal expansion which makes it very stable and not prone to sloughing off the coating.