Exploring Ruthenium Nanoparticles Geometric Complexity to Boost Kellogg Advanced Ammonia Process Through Confinement Effect

Abstract

Ammonia consumption is expected to increase in the future due to its use as a zero-carbon fuel and as a material for hydrogen storage and shipping. Among all single metal catalysts, ruthenium has the highest catalytic activity for the synthesis of ammonia. This study investigates the catalytic performance of ruthenium nanocages (CGs) towards ammonia production. Additionally, the effect of spatial constraints on reaction kinetics has been investigated using CGs with large (20 nm) and small (2 nm) confinements. The kinetic parameters for NH3 synthesis were determined using temperature-programmed surface reaction and temperature programmed desorption experiments. The results of the ammonia production by the CGs were compared with those of control materials that would possess little to no confinement effects – nanospheres and nanoplates synthesized in the same conditions. It has been demonstrated that the uptake, activation energy and frequency factor of nitrogen desorption on ruthenium nanoparticles increases in the following order: no confinements < large confinements < large + small confinements. The nanoparticles with “small” confinements were shown to reach optimal temperatures for ammonia production at 310 °C, lower than both controls and CGs with larger confinements. The validity of attributing the potential catalytic improvement to the confinement effect, rather than to differences in morphology, structural defects, and alloying, is discussed.