Title : Enhancing the stability of Co Fischer-Tropsch catalysts with boron promotion
Fischer-Tropsch synthesis (FTS) converts synthesis gas, a mixture of CO and H2, into various hydrocarbon products. Co catalysts are supported on various inert materials to increase their dispersion. They are preferred for FTS because of their good hydrocarbon selectivity, high CO conversion, and low water gas shift activity. Natural gas and gasification of coal is traditionally the preferred route for FTS to produce high quality hydrocarbons. However, with increasing environmental regulations, feedstocks obtained via gasification of biomass appears to be an excellent alternative for FTS. This shift towards sustainability and more carbon neutral processes is desirable for producing various hydrocarbons deemed essential for human civilisation.
Nevertheless, supported Co catalysts are known to deactivate under realistic FTS conditions, and it is hence desirable to improve the stability of Co catalysts. A number of deactivation mechanisms have been investigated and proposed, including sintering and oxidation of the metallic Co catalyst by product water. Nevertheless, the work of Tan et al in Journal of Catalysis showed that carbidic and graphitic coke can deactivate Co catalyst under realistic conditions. To improve the resiliency of Co catalyst towards carbon deposition, Tan et al used promoted Co catalyst with boron. Their study elucidated how boron doping can enhance Co catalyst against carbon deposition in the Journal of Catalysis, both from molecular modelling and reactor studies.
In this oral presentation, the relative stability of various forms of deposited carbon and the effect of boron on the carbon deposition mechanism will be discussed using periodic Density Functional Theory (DFT-PBE). To confirm the first principles based predictions, a series of Co catalyst promoted with various concentrations of boron were synthesized, characterized and tested in a fixed bed reactor under realistic FTS conditions.
- FTS can be deactivated with carbon deposition under realistic operating conditions of 220 – 2400C with H2/CO syngas ratio of 2. This discovery can help scientists and engineers to plan effective ways to regenerate Co catalysts or enhance its stability against carbon deposition.
- Ab-initio modeling can be extremely useful to design an effective promoter to enhance the stability of Co catalyst used in FTS. Additionally, deploying theoretical modeling not only speeds up the screening of potential promoters, but also reduces experimental risks.
- The effectiveness of boron as a promoter to Co catalyst is elucidated both from ab-initio molecular modeling and reactor studies. The amalgation of both disciplines allows designing catalyst from theory and accruing its tangible benefits in realistic FTS conditions.