Ordered Mesoporous Materials as Supports for Stable Iron Catalysts in the Fischer–Tropsch Synthesis of Lower Olefins

Abstract

The Fe‐catalyzed Fischer–Tropsch to olefins (FTO) synthesis is a non‐oil‐based route for the production of C2–C4 olefins. The understanding of the interplay between the catalytically active species, promoters, and support materials has improved over the last years, but the nanostructures of the various supports used are often not comparable. Several ordered mesoporous materials with a comparable pore size and pore symmetry are used as model supports for Fe‐based FTO catalysts. Ammonium iron citrate is used as the Fe source for all supports, and Na and S are added as promoters. The formation of catalytically active iron carbide species is suppressed within the strongly interacting mesoporous silica support, but the weakly interacting carbon and silicon carbide supports yield highly active FTO catalysts. Carbon‐supported catalysts show a high selectivity towards lower olefins, low methane production, and stable operation for up to 140 h under industrially relevant FTO conditions.

Effects of the Functionalization of the Ordered Mesoporous Carbon Support Surface on Iron Catalysts for the Fischer–Tropsch Synthesis of Lower Olefins

“…Although Co and Fe are the commonly used Fischer–Tropsch metals, nanostructured iron (carbide) catalysts are applied in the high‐temperature FTO process because of their low methane selectivity, high abundance, high water gas shift activity, and low cost . Although numerous species (iron oxides, metallic iron, iron carbides, and their combinations) can play a role in the FTO process, it has been shown that iron carbides are the catalytically active phase . Recently, it was foundthat especially the addition of a combination of Na and S promoters can suppress methane formation and increase the activity of FTO catalysts at the same time …”

Monodisperse Nano‐Fe3O4 on α‐Al2O3 Catalysts for Fischer–Tropsch Synthesis to Lower Olefins: Promoter and Size Effects

“…Despite novel catalysts including OX‐ZEO and cobalt carbide have been reported to obtain a high lower olefins selectivity with a relative lower CO conversion, iron‐based catalysts still arouse much more attention because of their low cost, tolerance for CO/H 2 ratio, resistance to contaminants, and feasibility in industry. Generally, particle size of Fe species, promoter, Fe precursor and support should be taken into account to design iron‐based FTO catalyst.…”

Influence of precursor porosity on sodium and sulfur promoted iron/carbon Fischer–Tropsch catalysts derived from metal–organic frameworks

“…S5, ESI †). All catalysts show the typical multi-step reduction profile 9 for carbonsupported iron catalysts in presence of Na/S promoters and the overall hydrogen consumption is comparable for all samples. However, the hydrogen consumption peaks are shifted to higher temperatures for the Fe/Na/S-C-Micro related to the larger iron particle size and their restricted accessibility caused by the narrow pore system of this catalyst.…”

“…[13][14][15] The most widely applied method for the preparation of carbon-supported FTO catalysts is deposition of the iron precursor (most often by solution impregnation) on the surface of a pre-formed carbon material (e.g., carbon nanotubes, porous carbons, or carbon nanofibers) followed by drying and calcination. 7,9,12,14 However, this process can suffer from its non-continuous character and potentially inhomogeneous distribution of the active phase after drying and calcination. One-pot synthesis of iron/carbon catalysts by pyrolyzing mixtures of precursors of support and metal is one option to overcome this drawback.…”