Enhancement of C 5+ Selectivity and Wax Yield in Fischer−Tropsch Synthesis by a Single Cycle of H 2 /CO Feed Ratio Probed by Operando Magnetic Resonance

Enhancing the selectivity to long chain hydrocarbons is important for optimizing industrial Fischer−Tropsch synthesis (FTS). Here, we observe that a single cycle of the H2/CO feed ratio between 2 and 0.5 significantly enhances the steady state C5+ selectivity and wax (C30−C100) yield (>45% increase) for FTS over Ru/TiO2 catalyst pellets occurring in a fixed bed reactor. Operando magnetic resonance measurement reveals that this enhancement arises from changes in olefin mass transfer within the evolving intra-pellet hydrocarbon composition. Time-resolved analysis of intra-pellet hydrocarbon chain length and C5+ selectivity in the exit stream following a feed ratio switch highlights the importance of intra-pellet liquid composition in regulating selectivity.