Impact of the support material on the phosphorus poisoning on Co-based catalysts for Fischer-Tropsch synthesis

Abstract

The role of the support on the poisoning by phosphorus of cobalt-based catalysts for the Fischer-Tropsch synthesis was investigated. Four different supports were used in this study, γ-alumina, titania and two silica gels with different pore sizes and surface areas. The deactivation varies in intensity depending on the type of support. The trend follows the strength of the metal-support interactions, γ-alumina being the least affected, while SiO2 (2 samples with different pore structures) was most affected. These results suggest that in the first case, P interacts mainly with the support while with less interacting supports, P will interact more with the cobalt particles. The addition of different loadings of P was done after the preparation of the catalysts simulating the possible behaviour of a Biomass to Liquids process. The P loading resulted in a decrease in site-time yield and a higher hydrogenation activity leading to a reduced production of value products. Conventional characterization of the catalysts showed two different deactivation mechanisms, including site blocking and electronic effects. The addition of phosphorus decreased the metallic dispersion and reducibility of the catalysts, inhibited the hydrogen desorption and reduced the CO adsorption. Phosphorus species might be altering the catalyst surface, yielding a higher H2/CO ratio adsorbed on the catalyst through the modification of the bonding strength between the cobalt and CO, and preventing the desorption of H2.