Applications of isotopic tracers in Fischer–Tropsch synthesis

Abstract

In this review, five different applications of isotopic tracers to the Fischer–Tropsch synthesis reaction on cobalt, iron, and ruthenium catalysts are reviewed. By co-feeding molecules containing a radioactive ¹⁴C-label and monitoring the fate of the species in the product distribution, researchers have identified molecules that are candidates for chain initiation or reincorporation into the growing chain. Kinetic isotope effects resulting from H₂/D₂ switching have provided insights into the rate limiting steps involved in chain initiation and propagation. H₂/D₂ switching has also been employed in order to account for the holdup of heavier products in the reactor, thus allowing one to correct for the product accumulation effect on the ASF plot so that the true impact of olefin reincorporation on the product distribution can be assessed. The competitive adsorption of H₂ and D₂ on the catalyst surface has also been explored in order to identify if H–D partitioning effects could influence the probability for one isotope to be favored for reaction during FTS and thus influence KIE results. Finally, steady state isotopic transient kinetic analysis (SSITKA) has been utilized to obtain a number of important kinetically relevant parameters (e.g., number of active sites, rate constant, TOF, etc.), to quantify the pool of reactive intermediates on the catalyst surface, and explore how co-adsorbed molecules may influence the size or reactivity of the reactive pool.