One of the challenges in Fischer-Tropsch synthesis is to shape the distribution of products in order to minimize the formation of methane and C2-4 hydrocarbons and at the same time maximize the fraction of C5+ hydrocarbons. Our studies have shown that both objectives can be met by the strategic used of metal oxide promoters, such as MnOx, TiOx, and ZrOx added to Co/SiO2. Analysis of high-resolution HAADF-STEM-EDS images visualizes the location of the promoter relative to the metal and enables determination of the extent to which the promoter covers the metal. Data from IR spectroscopy, TPD, and DFT calculations demonstrate that CO adsorbed at the boundary between the promoter oxide and the metal, the CO molecule is bound to the metal through its C atom, and through it O atom to metal cations in the oxide. Such interactions strengthen the binding of adsorbed CO and facilitate cleavage of the C-O bond. This effect reaches a maximum for a metal oxide coverage of 0.5 and results in a lower ratio of adsorbed H to CO than is observed in the absence of the promoter. Because of these effects, the formation of methane decreases and the probability of chain growth increases. The promoter also enhances the readsorption of light alkenes and their insertion into the chain growth process. For a given metal oxide coverage, all of these effects increase with the Lewis acidity of the metal cations in the oxide.

Factors that shape the distribution of products obtained from Fischer–Tropsch synthesis

2019 Fall National Meeting

The official archive and repository for all ACS Meetings & Expositions abstracts and select posters or presentations.