Operando magnetic resonance imaging of product distributions within the pores of catalyst pellets during Fischer–Tropsch synthesis

The optimization of a heterogeneous catalytic process requires characterization of the catalyst at industrially relevant conditions and length scales. Here we use magnetic resonance imaging to gain insight into the Fischer–Tropsch synthesis occurring in a pilot-scale fixed-bed reactor operating at 220 °C and 37 bar, for three H2/CO feed ratios. The molecular diffusion and carbon number of the hydrocarbon products are spatially resolved within both the reactor and individual 1 wt% Ru/TiO2 catalyst pellets. These data highlight the importance of mass transfer, in addition to the nanoscale catalyst activity, on catalyst performance. In particular, a start-up time of up to three weeks is required for the steady state to be achieved in the catalyst pores. Further, the average carbon number present in the pores can be as much as double that in the product wax. The operando characterization of water and oxygenates present in the pores is also achieved. The presence of a water-rich liquid at the pore surface is confirmed. The practical optimizations of heterogeneous catalytic processes and reactor engineering are intertwined, but often what occurs inside the reactor remains elusive. Now, the molecular diffusion and carbon number of hydrocarbon products during Fischer–Tropsch synthesis on a Ru/TiO2 catalyst are spatially resolved via magnetic resonance imaging in a pilot-scale fixed-bed reactor.