Slurry formulations of low surface area oxides for washcoating applications

Deposition of coating of oxides has a high interest in many innovative activities. Many methods have been proposed to deposit catalytic layers on very different structured support. Usually a two-phase process is performed: first, the support is pretreated in order to improve surface interactions with the washcoat; then, coating is deposited by a specific chosen technique. Among coatings method, dip-coating from a sol or a slurry liquid phase is usually the best compromise between cost, complexity and final product effectiveness. The purpose of thesis work is to develop a new formulation and procedure to produce thin ceramic layers, that could easily be applied, for instance, in the production of ceria catalysts for methane steam reforming process. The ceria based catalyst is the product to be coated on the structured support and consists of an active metal phase (Ni) and a substrate, Cerium oxide powder (CeO2), that supports nickel. Commonly, powders are dispersed by surface charging method, that bases itself on colloids theory and consists in the dispersion of the powder in an acidic water solution, to charge surface and inducing particle repulsion. Unfortunately, this method isn’t exploitable for Ni-CeO2 catalyst, due to its low surface area, and a different dispersion method needs to be managed. Dispersion by steric like mechanism is investigated and, particularly, the evaluation of organic compounds to be used as powder dispersant. In the first part of this work, sedimentation tests carried out with hydroxyl-based organic compounds allowed to point out an increase in stability with the increase of hydroxyl groups content. Glycerol was find out to confer good stability to the dispersion, but a plasticizer (polyvinyl alcohol) was added to the dispersion to improve coating properties. Depositions were performed by using Percolation Blowing and Dip-Coating techniques on YZA open cell foams. Following, the wet washcoated supports were flash-dried to obtain the final coated samples. Influence of different parameter on the deposition process was investigated: flash drying temperature, PVA content and multiple dippings influence on coating loading are evaluated.