hcp-Co nanowires directly grown on various supports as catalysts for Fischer-Tropsch synthesis

J. Harmel, L. Peres, A. Berliet, S. Maury, A. F├ęcant, B. Chaudret, D.P. Minh, P. Serp, K. Soulantica
Toulouse University,
France

Keywords: cobalt, Fischer-Tropsch, nanowires, slurry, fixed-bed

Summary:

Due to the decreasing the oil resources, and because of the the fluctuations of the price as a result of the geopolitical context, the Fischer-Tropsch synthesis (FTS), that enables the production of hydrocarbons form the syngas mixture (CO and H2) in the presence of a catalyst based on cobalt or iron, has recently gained a renewed interest from industrial as well as form the academic communities. Still today, the mechanisms that come into play during this reaction and the crucial properties of the catalyst properties remain uncertain. In this context, the work presented, aims to investigate the impact of parameters such as the crystallographic structure and the shape of cobalt nano-objects, which is the active phase of the catalyst for this reaction. For this purpose, model cobalt nano-objects were synthetized and their catalytic properties were investigated both in slurry and fixed-bed reactors. First, a cobalt based catalyst exhibiting an hcp crystallographic structure and an anisotropic shape (nanowires, hcp-Co NWs) was prepared on an alumina support via a synthetic route involving the decomposition of an organometallic precursor of cobalt on Co germs pre-deposited on the support. Catalytic tests were then conducted in a slurry reactor under conditions very close to actual industrial conditions. These studies revealed an increased stability of these catalysts compared to reference catalysts that deactivate other time. In a second stage, hcp-Co NWs were selectively grown on copper and nickel metallic foams, giving rise to catalyst monoliths, which can be used in a fixed bed reactor for the FTS. The use of the hcp-Co/Cu catalyst allows achieving performances that outer pass that of a Co/Al2O3-SiO2 commercial reference catalyst in terms of catalyst activity, selectivity and stability, while preliminary experiments have shown that the hcp-Co/Ni exhibits an excellent selectivity towards methane.