Cohesive strength measurement of catalyst layer: Uniform drying and on-line monitoring

The cohesive strength obtained was found to vary with particle size, pH of catalyst suspension, and drying rate of the suspension. In short, a suspension with d90 approximately of 9 μm, pH = 4 and dried under a low drying rate led to a layer with high cohesive strength. Variation in the cohesive strength is explained based on particle mobility and packing behaviour obtained from on-line monitoring of the drying process of a washcoat layer. In addition the cohesive strength is also in close agreement with the DLVO theory except at very low and high pHs where dissolution of the particles may have an influence. A combination of low resistance for particle movement and longer exposure to a drying environment was found to improve the cohesive strength. Particle mobility and packing behaviour which was retrieved on a micrometre length scale from on-line monitoring is one step further to understand the origin of cohesive strength of a coated layer beyond the widely investigated macroscopic preparation conditions such as viscosity and drying rate.