The present disclosure provides for methods for preparing ruthenium nanoparticles characterized by face centered cubic crystallographic structure characterized by small particle size, substantially homogeneous particle size distribution, substantially uniform spherical shape, and substantial high temperature stability. The present disclosure further provides for methods for preparing ruthenium nanoparticles characterized by face hexagonal close packed crystallographic structure characterized by small particle size, substantially homogeneous particle size distribution, substantially uniform spherical shape, and substantial high temperature stability.