Combined dip-coating/spin-coating depositions on ceramic honeycomb monoliths for structured catalysts preparation

This work focuses on the investigation of a combined dip-coating/spin-coating technique as novel deposition procedure for structured catalysts production; it consists in the use of a spin-coater device to remove the excess slurry entrapped in structured supports porosity after the dip-coating procedure, by centrifugation. In particular, ceramic monoliths (500 cells per square inch, diameter 1 cm, length 1.5 cm) were chosen as a model support and cerium oxide as a catalyst carrier. The support was selected based on its potential in the syngas production field. A preliminary analysis of the deposition conditions was performed by using water/glycerol solutions of various compositions to investigate a broad range of model liquid viscosities. The influence of coating parameters, such as rotation speed and rotation time, on coating thickness was assessed and optimal conditions for washcoat deposition were identified. Then, a cerium oxide carrier layer was deposited by means of slurry coating route. In particular, an acid-free formulation based on water, glycerol and polyvinyl alcohol was used as liquid medium for the ceramic particles dispersion. Washcoat loads in the 10 wt.% range were obtained after four consecutive depositions. Results were evaluated in terms of coating load and adhesion performance. Moreover, a comparison with similar samples obtained by solely using dip-coating was carried out. Washcoat layers of 11 and 5 μm were found for dip-coated and spin-coated samples, respectively. Additionally, the use of spin coating allowed an improvement in both results reproducibility and washcoat adhesion.