Washcoating of microchannel reactors with PdZnO catalyst for methanol steam reforming

Abstract

PdZn catalyst was deposited on the micro-channels reactor wall by the washcoating method. To optimize the coating procedure, preliminary studies were carried out using Fecralloy® micro-monoliths varying different parameters and properties of the catalyst slurry. Initially, the 2.5% Pd/ZnO was prepared by incipient wetness impregnation of pre-synthesized ZnO. The catalyst obtained by drying and calcining the aqueous slurry prepared for washcoating, showed lower activity than the parent catalyst. The difference could be related to the amphoteric nature of the ZnO (dissolution-re-precipitation process). To avoid this phenomenon and optimize the coating procedure, several strategies have been developed to deposit the catalyst on the micromonoliths walls: other solvents, use of primers, and pH control of the slurry. The coating procedure result was evaluated by means of the specific load (mg/cm2), homogeneity (SEM), adherence (ultrasound test) and textural properties. On the other hand, the different slurries were dried, calcined and reduced and then evaluated in the steam reforming of methanol to detect changes produced by the slurry preparation. Water slurries of the parent catalyst produced loss of surface area and palladium dispersion and, consequently, lower activity and stability. When alcohols were used to disperse the catalyst, it was necessary to use a preliminary ZnO primer to obtain good adherence, but loss of activity with respect to the parent catalyst was also observed. A new strategy was developed preparing the washcoating suspension in water with the catalyst precursors: ZnO support and palladium salt. In this way, the catalyst preparation and the substrate coating was carried out in a single step producing a much more active and stable structured catalyst showing excellent adherence.