Little attention has been given to the use of osmium (Os) as a catalyst or promoter for the Fischer Tropsch synthesis (FTS). Reports indicate that Os primarily produces C(1)and C(2)hydrocarbons and no long chain hydrocarbons, and that Os deactivates in the reaction. To investigate osmium based catalysts used in FT reactions, the synthesis and use of osmium nanoparticles supported on SiO2, or encapsulated inside hollow carbon spheres (HCSs), was studied. Os@HCS was prepared by loading Os (as (NH4)(2)OsCl6) onto a sacrificial Stober SiO(2)sphere template and the Os/SiO(2)was then encapsulated by a carbon layer, deposited by CVD, using toluene. Removal of the sacrificial template, shown by EM, PXRD, TGA, BET and TPR studies revealed that the Os@HCS catalyst had been successfully synthesized (d(Os) = 9-23 nm; d(HCS) = 454-560 nm; shell thickness = ca.20 nm). FTS evaluation studies showed that Os@HCS and Os/SiO2(as reference), mainly produced C(1)and C(2)hydrocarbons with a high selectivity towards methane (> similar to 65%). Post analysis of the catalysts by XRD and HRTEM revealed that the Os readily sintered on the supports under syngas, providing a deactivation pathway for the catalyst under FT conditions. [GRAPHICS] .