Effect Of K Promoter On Carbon Deposition And Carbonization On The Cobalt Catalyst Surfaces

Fischer-Tropsch synthesis?FTS?is the key technology for clean and efficient coal conversion where the core is the selectivity of high efficient catalyst.In this technology,cobalt based catalyst plays an important role in FTS reaction because of its high generation rate of long chain hydrocarbon and low activity of water gas shift reaction.Alkali metal promoters can improve the catalytic activity and selectivity,which is significant for promoting the performance of cobalt-based catalysts.In the dissertation,density functional theory was used to study the carbon deposition and carbonization processes on the surface of fcc Co?111?and Co?311?,as well as hcp Co?0001?and and Co?11-21?under different carbon coverage,and the influence of K promoter on these processes.The hydrogenation of carbon on cobalt surfaces was systematically simulated.The results show that carbon atoms tend to adsorb at the position with more coordination Numbers and form C₂ by coupling.With the increase of carbon coverage,carbon atoms tend to accumulate on the surface,and some carbon atoms may diffuse into the subsurface,and the surface configuration will undergo obvious deformation.Dynamically,the surface carbon atoms have no driving force to migrate to the subsurface.K promoter has little effect on the most stable adsorption configurations of carbon atoms,but increases the adsorption energy of carbon species,which can be explained by the decreasing of the surface work function resulting from the electron effect of potassium promoter.In addition,the CH group is the key species in the hydrocarbon processes on the Co?111?and Co?0001?surfaces.