Study of potassium promoter effect for Ru/AC catalysts for ammonia synthesis†
Ru/AC catalysts with K promoter were prepared by impregnation of the samples with different amounts of KOH. The catalysts were characterized using a variety of techniques, including X-ray diffraction, X-ray photoelectron spectroscopy, transmission electron microscopy, CO chemisorption and temperature-programmed desorption. The presence of K promoter had a limited effect on the size of Ru particles, but significantly enhanced the amount of adsorbed hydrogen, nitrogen and ammonia. A new desorption peak of nitrogen and ammonia at low temperature can be observed in their TPD profiles for Ru catalysts with K promoter. We propose that the presence of K promoter not only improved the adsorption properties of hydrogen, nitrogen and ammonia for Ru catalyst supported on activated carbon, but also weakened the adsorption strength of nitrogen and ammonia. The change in the chemisorptive properties of reactant gases including hydrogen, nitrogen and ammonia may be responsible for K promoter enhanced ammonia synthesis activity of Ru/AC catalyst, more than just the electronic properties of K promoter.