Properties of Potassium-Added Nickel Catalysts Supported on γ-Alumina

Abstract

Nickel catalysts supported on alumina have been studied about their adsorption properties and kinetic behavior of CO hydrogenation as potassium is added up to 2 wt%. Potassium changes not only the structural properties of the nickel catalyst such as the extent of reduction, dispersion and particle size, but also its adsorption strength to hydrogen and carbon monoxide. With potassium addition, nickel adsorbs hydrogen more weakly and carbon monoxide more strongly. Adsorbed carbon monoxide dissociates easily on the potassium-promoted catalyst to accumulate surface carbon.

Supported nickel catalysts lose their initial CO hydrogenation activity and show enhanced selectivity for higher hydrocarbons and olefins as potassium is added to them. When the reaction rate is expressed by a power law for the reactant partial pressures, its pressure dependency on carbon monoxide decreases, that on hydrogen increases, and the activation energy of methanation increases with potassium addition to nickel. The above results may be explained from the adsorption properties of potassium-added nickel catalysts for hydrogen and carbon monoxide.