Evidences of Two‐Regimes in the Measurement of Ru Particle Size Effect for CO Dissociation during Fischer–Tropsch Synthesis

Abstract This work assesses the effect of the particle size for the Fischer–Tropsch synthesis with catalysts based on Ru particles between 4 and 71 nm. CO dissociation is a structure‐sensitive reaction, that is, the turnover frequency (TOF) is affected by Ru particle size. Herein it is demonstrated that two regimes exist for the effect of Ru particle size. On the one hand, the expected relationship of TOF with particle size, that is, the TOF increases with Ru particles <10 nm, is only observed if measured at steady‐state conditions. On the contrary, the TOF increases constantly with Ru particle size if measured at the initial state. However, the TOF measured for catalysts with Ru particles >10 nm declines during time on stream. These observations suggest that two regimes for the measurement of CO dissociation exist during Fischer–Tropsch synthesis. The reason for this is that two sites for CO dissociation on the Ru particles >10 nm exist at the initial state, terraces and step‐edges, but the latter ones deactivate during time on stream.