Insight into the roles of ammonia during direct alcohol amination over supported Ru catalysts

Abstract

The direct amination of alcohols with ammonia is a promising route to make primary amines, but a full understanding of various parameters, especially the effect of co-adsorbed nitrogen-containing species on the catalyst surface during amination, has still been lacking. Here, we report that the presence of dissociated ammonia species on Ru nanoparticles substantially enhances its activity in catalyzing the dehydrogenation step that is kinetically-relevant to amination. Kinetic, spectroscopic, and theoretical methods are combined to highlight how ammonia affects this rate-determining step: in the dissociated form the surface NHx species interact with the alcohol reactant and lower the corresponding barrier of OH scission, thus promoting the activity on Ru. In contrast to Pd-based catalysts, the N atom in the generated R-NH2 product binds moderately strongly with Ru sites, thus inhibiting the formation of undesired secondary amine via further CN coupling. This work unveils the overlooked role of ammonia in the amination reaction over Ru-based catalysts.