Promoted Iron Nanocrystals Obtained via Ligand Exchange as Active and Selective Catalysts for Synthesis Gas Conversion

Abstract

Colloidal synthesis routes have been recently used to fabricate heterogeneous catalysts with more controllable and homogeneous properties. Herein a method was developed to modify the surface composition of colloidal nanocrystal catalysts and to purposely introduce specific atoms via ligands and change the catalyst reactivity. Organic ligands adsorbed on the surface of iron oxide catalysts were exchanged with inorganic species such as Na2S, not only to provide an active surface but also to introduce controlled amounts of Na and S acting as promoters for the catalytic process. The catalyst composition was optimized for the Fischer–Tropsch direct conversion of synthesis gas into lower olefins. At industrially relevant conditions, these nanocrystal-based catalysts with controlled composition were more active, selective, and stable than catalysts with similar composition but synthesized using conventional methods, possibly due to their homogeneity of properties and synergic interaction of iron and promoters.

Attachment of Iron Oxide Nanoparticles to Carbon Nanotubes and the Consequences for Catalysis

“…[14,15,27] Synthesis methods and characterization can be found in the Supporting Information. [14,15,27] Synthesis methods and characterization can be found in the Supporting Information.…”

“…[4][5][6] For example, Fischer-Tropsch to olefins (FTO) is one of the catalytic reactions particularly sensitive to particles ize, for which colloidal model systems can be beneficial. [14,15] To increase the activity and selectivity of an FTO catalyst, the addition of promoters is of vital importance,a su npromoted iron catalysts usually show high selectivity towards methane. [9][10][11][12][13] In addition, colloidal particles have been shown to be relatively stable and to have catalytic properties that are comparable to those of conventional catalysts, making them interesting model systemsf or fundamentals tudies on FTO.…”

“…[14,15] To increase the activity and selectivity of an FTO catalyst, the addition of promoters is of vital importance,a su npromoted iron catalysts usually show high selectivity towards methane. [15,20] In FTO catalysis, choosing the support material is of importance as well, as strongly interacting supports, such as silica and alumina, can incorporate iron, making reduction and carbidization to the active iron carbidep hase difficult. [16,18] Moreover,c olloidal particles can be promoted by using organic ligand exchange, which specifically targets the promoters on the catalytically active particles.…”

“…[9][10][11][12][13] In addition, colloidal particles have been shown to be relatively stable and to have catalytic properties that are comparable to those of conventional catalysts, making them interesting model systemsf or fundamentals tudies on FTO. [14,15] To increase the activity and selectivity of an FTO catalyst, the addition of promoters is of vital importance,a su npromoted iron catalysts usually show high selectivity towards methane. [16][17][18][19] By promoting ironp articles with Na and Sp romoters, low selectivity to methane and high selectivity to olefins can be obtained.…”

“…[16,18] Moreover,c olloidal particles can be promoted by using organic ligand exchange, which specifically targets the promoters on the catalytically active particles. [15,20] In FTO catalysis, choosing the support material is of importance as well, as strongly interacting supports, such as silica and alumina, can incorporate iron, making reduction and carbidization to the active iron carbidep hase difficult. [21][22][23] Nevertheless, there are many porous carbon materials that can be used as catalysts upports such as activated carbon and graphitic and templated carbon.…”