Abstract
Various wall-type nickel catalysts were prepared on aluminum plates by electroless plating under changing conditions for displacement plating of zinc and chemical reduction plating of nickel, and their physicochemical properties were investigated. Correlation between these physicochemical properties and the decomposition properties of methanol over these plated catalysts was examined. The results show that the decomposition performance of the plated catalysts does not correlate with the surface areas of the plated layer but depends on the ratio of the crystallite size of nickel particles, as determined by XRD, to that of aluminum particles. This finding suggests the involvement in catalytic activity of aluminum that dissolves from the substrate in the plated layer as well as nickel, which is considered as the active site.
Elemental component analysis and elemental state analysis in the plated layer indicate that the use of sodium hypophosphite monohydrate as a reducing agent results in the incorporation of phosphorus in the plated layer, and the plated catalyst with high selectivity of carbon monoxide and hydrogen for methanol decomposition contains large amounts of zinc and phosphorus, and a small amount of aluminum, with nickel in the bulk layer of this catalyst being in a metallic-state. The finding in which granular Ni3P and Ni/ZnO catalysts, with high selectivity for methanol decomposition, had metallic-state nickel suggests that some incorporation of phosphorus and zinc oxide, that increased the metallic-state of nickel, and the small amount of aluminum in the plated layer produce the high selectivity for methanol decomposition.
