Washcoating of Different Zeolites on Cordierite Monoliths

Cordierite monoliths were washcoated with slurries of different zeolites (ZSM5, β zeolite, mordenite, and Zeolite Y) in order to establish the relationship between washcoat characteristics and the powder and slurry properties. To achieve this objective, initially, the zeolite particle size was reduced to 2–3 μm by wet ball milling, and during this process the crystallinity and surface area of the powder were not significantly affected. The rheological behavior of the zeolite slurries is a function of the type of zeolite and solid content. The washcoat properties, such as loading, thickness, uniformity, and reproducibility, depend on the particle size of the powder, number of immersions, slurry concentration, slurry viscosity, and surface tension. The mechanical stability of the zeolite washcoat decreases with an increase in cumulative loading and slurry particle size. Addition of binder (colloidal silica) results in an improvement in zeolite loading and washcoat adherence.