Coating di catalizzatori ceramici strutturati a geometria complessa : ottimizzazione di una sospensione colloidale per dip-coating ed estensione ad altre tecniche di deposizione

An acid-free formulation based on water, glycerol and polyvinyl alcohol was studied to disperse and stabilize, via steric-like interaction, cerium and zirconium oxide-based powders on complex geometry substrates (open-cell foams and monoliths). Nickel, cobalt, copper and iron nitrate were used as active phases, in oreder to produce catalytically active powders. Rheological properties were found to be related to the dispersed powder, thus directly affecting washcoat load. Multiple depositions were performed by means of dip-coating on 20, 30 and 40 PPI yttria-stabilized zirconia open cell foams. The use of multiple dippings was proven to fulfill flexibility requirements for washcoat load management. Multiple depositions were carried out with intermediate flash drying steps at 350 °C. Homogeneous coverage and limited pores clogging were obtained after calcination, with washcoat loads in the 6 to 30 % wt. range. Adhesion was evaluated by means of accelerated stress test in ultrasound bath; in most cases, it pointed out good results in terms of washcot to substrate interaction. Then, work was extended even to other geometrical supports: the same powders were washcoated on cordierite monolith by means of support dip-coating into acid-free catalyst dispersion. Good results were obtained both in terms of washcoat load and adhesion. In addition to that, dip-blowing e spin-coating were studied as alternative deposition techniques. Results showed advantages in the use of spin-coating and dip-blowing for depositions on complex geometrical substrates. Finally, thanks to a collaboration with CNR-ITAE research institute, Ni (7.5wt.%)/CeO2 and Ni (7.5wt.%)-Rh (0.5wt.%)/CeO2 powders were washcoated on cordierite monolith and alumina open-cell foam and their catalytic performances were investigated with catalytic test.