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.