Residual organics, if desired, and chloride ions in the bath are removed from the solution by a chemisorption or physisorption treatment.

The impregnation is carried out at a temperature which substantially reduces chemisorption rates such that reactions between the monolith substrate and catalytically active materials in the catalyst solution are minimized.

The first process usually involves the formation of very weak intermolecular bonds, a process known as physisorption, followed by chemical bonds being formed, a process known as chemisorption.