Structure-Sensitive and Insensitive Reactions in Alcohol Amination over Nonsupported Ru Nanoparticles

The reaction rates and selectivity of many metal-catalyzed reactions depend on the size of the metal particles in the nanoscale range. Primary amines are important platform molecules in the chemical industry. In this work, the catalytic performance of nonsupported Ru nanoparticles with sizes from 2 to 9 nm was investigated in direct amination of octanol and other alcohols into primary amines in the presence of ammonia. The 90% selectivity to octylamine was obtained over small Ru nanoparticles (d = 2 nm) even at 92% conversion, whereas for larger Ru nonsupported and supported nanoparticles, the octylamine selectivity dropped as the octanol conversion approached 70–80%. The primary reaction of alcohol amination into octylamine was found to be nearly a structure-insensitive reaction. The selectivity to primary amine drops over large Ru particles at higher conversions, because of the secondary highly structure-sensitive reaction of amine self-coupling. Over small metal nanoparticles, amine self-coupling is hindered, because of suppression of secondary imine hydrogenation. Similar structure sensitivities of the reactions involved in alcohol amination were observed for different substrates.