Fischer-Tropsch synthesis on mono- and bimetallic Co and Fe catalysts in fixed-bed and slurry reactors

Abstract

Mono- and bimetallic cobalt and iron oxide nanoparticles deposited on the surface of a silica substrate were tested in a fixed-bed reactor and stirred-tank slurry reactor under different process conditions, for the Fischer–Tropsch reaction, this comparison is presented for the first time, being presented in this work a comparison of above systems in both reactor types. For the fixed-bed reaction, the monometallic iron-based catalyst presented the highest activity at low reaction temperatures. By contrast, the monometallic cobalt catalyst is the less active for all reaction temperatures. This catalyst records high values for the α parameter, whereas the iron catalyst reveals major selectivity to alcohols. Moreover, the introduction of iron produces a decrease in hydrocarbon chain growth and an increase in alcohol selectivity. This behaviour might be due to the formation of a Co–Fe alloy, observed by several characterization techniques. In the slurry studies, CO conversion is greater for the cobalt-based catalyst and lower for bimetallic systems, whilst the iron catalyst deactivates in a few hours, which is explained by the formation of carbonaceous deposits. The bimetallic catalysts record a decrease in CO conversion and an enhancement in the selectivity of methane and light hydrocarbons with the increase in iron amount. The absence of alcohols in this type of reactor is explained by the greater solubility of hydrogen, as well as by the greater contact time of reactants, which decreases the possibility of non-dissociative CO insertion.