Disclosing the synergistic mechanism in the catalytic activity of different-sized Ru nanoparticles for ammonia synthesis at mild reaction conditions

Insights in the mechanism of deposition and growth of RuO2 colloidal nanoparticles over alumina. Implications on the activity for ammonia synthesis

“…Larger nanoparticles meanwhile promote the activation and mobility of hydrogen. A catalytic cooperation mechanism was proposed based on H/D isotopic exchange, 'operando' DRIFTS and reaction order studies [12]. This mechanism involves migration of H atoms from large to small nanoparticles, promoting the hydrogenation of adsorbed NH x species on small metal particles and the release of blocked active sites.…”

“…However, hydrogen is slowly activated and strongly attached to these particles at low temperatures, which affects the hydrogenation of NH x intermediate species and the release of active sites for N 2 adsorption. Indeed, according to the kinetic study previously reported [12], the release of active sites becomes the limiting step for the reaction over small Ru particles. On the contrary, larger Ru nanoparticles decrease the energetic barrier for H 2 activation and allow a higher mobility of hydrogen atoms.…”

“…We have shown [11,12] that the surface configuration (average particle size and distribution of sizes) of Ru-supported nanoparticles has a significant effect on the catalytic activity for ammonia synthesis. The process is better conducted on surfaces having a broad size distribution (2-12 nm) of Ru nanoparticles, where small and larger particles give rise to a catalytic cooperation process.…”

“…On the contrary, larger Ru nanoparticles decrease the energetic barrier for H 2 activation and allow a higher mobility of hydrogen atoms. It was suggested that the catalytic cooperation mechanism involves the migration of H atoms from large to small Ru nanoparticles, promoting the hydrogenation of adsorbed NH x species on small metal particles and the release of blocked active sites [12].…”

H2/D2 isotopic exchange: A tool to characterize complex hydrogen interaction with carbon-supported ruthenium catalysts

“…Two general reaction types are usually investigated: (i) the homomolecular exchange (or "equilibration") in which an equimolar mixture of H 2 and D 2 molecules is scrambled over a surface; (ii) the heterolytic exchange in which a D 2 molecule is scrambled with the "surface" hydrogen species of the catalyst (generally OH species). It has already been applied to carbon materials [41] or to Ru catalysts [42,43] but not directly to Ru/C catalysts at low temperature. In this work we show how the kinetics of the H 2 /D 2 isotopic homomolecular exchange reaction can be related to the surface electron density of the catalyst, which allows us to better understand the effect that both promoters and support have on the metal particles.…”