A First-Principle Study of Chain Propagation Steps in the Fischer-Tropsch Synthesis on Fe(100)

摘要

We presented density functional theory based calculations on the formation and reactivity of C3 species produced from CO and H2 over Fe(100). The results indicated that the conversion of syngas to propylene and propane is overall exothermic, and the most stable C3 surface species are CCCH2 and CCCH3. It was found that the chain propagation on Fe(100) is initiated by the recombination of C and CCCH2/CCCH3 rather than by the coupling reaction of surface vinyl and methylene. The potential energy surface associated with such an alkynyl mechanism has been computed and validated. Furthermore, this alkynyl mechanism has been compared to the conventional alkenyl mechanism in explaining the experimental observations of the ~(13)C2H4-probed polymerization over Fe. It was finally found that the two propylene isotopomers observed experimentally in the product mixture are produced from surface ethylene along different reaction paths rather than the isomerization of surface allyl.