CO dissociation over cobalt-based catalysts with different crystal facets

The way of CO dissociation, as a crucial step in the Fischer-Tropsch (F-T) synthesis process, has been a subject of intense debate in literature. In order to understand the F-T synthesis reaction behavior of cobalt catalysts with different crystal planes, the CO dissociation behavior over three cobalt catalysts with different crystal facets during F-T reaction was investigated by excluding the influence of support, promoter and particle size. The catalysts were characterized by temperature programmed desorption (TPD), diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS), in-situ Raman and Chemical Transient Kinetics (CTK). The results show that CO on the Co(10-11) is activated by direct dissociation, among which small amount of carbonaceous species generated by CO dissociation forms carbon depositing on the catalyst surface under F-T reaction condition, and a large amount of carbonaceous species are hydrogenated to CH_x species. The CO on the Co(0001) crystal surface is activated predominantly by hydrogen-assisted dissociation, a large fraction of CO is dissociated into carbon deposition and a tiny fraction of CO is hydrogenated into CH_x. CO is directly dissociated on the Co(11-20) plane. The weak dissociation of CO on this catalyst results in a trace amount of carbon deposition, and a trace amount of CH_x intermediate in the presence of hydrogen.