Isotopic tracing study of K promotion of NH3 synthesis on Ru

There has been much discussion based on indirect evidence about the site heterogeneity of catalysts for ammonia as well as the effect of alkali promotion. This paper presents the results from direct measurements using steady-state isotopic transient kinetic analysis (SSITKA) of surface site heterogeneity on Ru/SiO₂ induced by K promotion. This heterogeneity is caused by the creation of a set of super active sites. It is the high activity of these sites, more than just the increase in number of surface intermediates, which produces the high activity of K promoted Ru for ammonia synthesis.