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

Abstract

Ordered mesoporous carbon (CMK‐3) with different surface modifications is applied as a support for Fe‐based catalysts in the Fischer–Tropsch to olefins synthesis (FTO) with and without sodium and sulfur promoters. Different concentrations of functional groups do not affect the size (3–5 nm) of Fe particles in the fresh catalysts but iron (carbide) supported on N‐enriched CMK‐3 and a support with a lower concentration of functional groups show higher catalytic activity under industrially relevant FTO conditions (340 °C, 10 bar, H2/CO=2) compared to a support with an O‐enriched surface. The addition of promoters leads to more noticeable enhancements of the catalytic activity (3–5 times higher) and the selectivity to C2–C4 olefins (≈2 times higher) than surface functionalization of the support. Nitrogen surface functionalization and removal of surface groups before impregnation and calcination, however, further increase the activity of the catalysts in the presence of promoters. The confinement of the Fe nanoparticles in the mesopores of CMK‐3 restricts but does not fully prevent particle growth and, consequently, the decrease of activity under FTO conditions.

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

“…Owing to conversion of the Fe-NPs into the active carbidep hase, core-shell particles had formed and were observed in all catalysts, albeit mostly in the promoted ones. [34] Finally,t hese findings indicate that attaching colloidalp articles to an oxidized carbon nanotube support resulted in deactivation during the catalytic reactiono wing to the poor interaction of the Fe-NPs with the surface. This nicely matched the Mçssbauer spectroscopy results (Tables S2 and Figure S3) that the same amount of Fe-NPs was converted into the e-Fe 2.2 Ca nd c-Fe 5 C 2 phases, which are considered activei n FTO.…”

“…[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. [30][31][32][33][34] The attachment of colloidal particles to support materials has so far not been researched abundantly;h owever,i th as been found that the support material can alter the behavior of the particlesd uring catalysis. [27][28][29] More importantly,i tw as found that functionalization of carbon supports suppressed particleg rowth by the anchoring particles, thereby increasing the stability of the impregnated catalysts.…”

Mechanochemical Functionalization of Carbon Black at Room Temperature

“…The requirements carbons have to meet are strongly dependent on their applications. As electrode materials they have to provide high conductivities and high specific surface areas [7], as support materials in catalysis they have to ensure strong interaction between the surface and the active species [8], and in adsorptive applications such as wastewater purification they have to remove chemicals like heavy metal ions [9] or pharmaceuticals [10] rapidly and to a large extent. Therefore, the porosity and the surface polarity of carbons are key and need to be specifically tailored to the corresponding application.…”

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

“…7,11,12 Furthermore, carbonaceous supports stand out due to high chemical stability, high surface area, variable pore structure, and versatile surface chemistry. [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.…”

“…[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.…”