A Pressure Gap in Fischer-Tropsch Synthesis Revealed with Multi-bar Soft X-ray Spectroscopies

Catalytic surfaces can dramatically restructure with reaction conditions, influencing activity and selectivity, as well as making it challenging to identify the active phase. Using graphene windows decorated with mass-selected Co nanoparticles (4 or 8 nm), we probe the chemical state and adsorbate coverage during Fisher-Tropsch synthesis at multi-bar pressures. Operando electron yield X-ray absorption spectroscopy and photoelectron spectroscopy reveal the formation of a Co carbonyl-like species at 4 bar, which is not detected for similar nanoparticles at 1 bar. By comparing with smaller nanoparticle sizes at 1 bar, this species is found to be associated with low coordination sites where CO preferentially binds. A clear pressure gap is identified through the emergence of the carbonyl-like species at the elevated pressures of industrial Fisher-Tropsch synthesis, suggesting an important role for pressure-induced restructuring in increasing activity during reaction.