Evaluation of Nanosized Iron in Slurry-Phase Fischer−Tropsch Synthesis

Abstract

The Fischer−Tropsch (F−T) activity of three α-Fe2O3-based materials, two unsupported nanosized, NANOCAT (3 nm) and BASF (20−80 nm), and a supported micrometer-sized (32.5 μm) UCI, were measured with respect to total hydrocarbon production from synthesis gas (H2/CO ∼ 2/1). All three oxides were initially reduced under CO at 553 K in ethylflopolyolefin-164 solvent, and the extent of their reduction was established by monitoring CO2 evolution. The ease of reduction of α-Fe2O3 followed the order: UCI > NANOCAT > BASF. The Fischer−Tropsch (F−T) synthesis activities of the three reduced materials were measured at 513 K. Mössbauer and X-ray absorption fine structure (XAFS) measurements established that the initial oxides were in the α-Fe2O3 phase. Room-temperature XAFS together with low-temperature Mössbauer data of the quenched catalyst samples after 120 h F−T reaction suggest that all three catalysts were essentially a mixture of oxides and carbides with magnetite being the dominant phase. The observed high activity with NANOCAT and the presence of mainly (88%) magnetite phase indicate that either the oxide phase contributes as a catalyst or the minor (12%) carbide phase is extremely active for F−T synthesis. TEM images of the quenched samples remarkably showed that both unsupported nano materials, NANOCAT and BASF, avoided expected agglomeration and the micrometer-sized UCI converted into a nano material of <10 nm under F−T reaction conditions. The narrow particle size distribution of the quenched catalysts in the nano range (∼10−50 nm) explains the very similar activities observed with the three different-sized starting materials in the order: BASF > NANOCAT ∼ UCI. The data suggest a crucial role of nanosized Fe during F−T synthesis.

Fischer‐Tropsch Catalysts for the Biomass‐to‐Liquid (BTL)‐Process

“…2), is to be expected, but has not been shown unequivocally. It has been shown that catalysts containing very small iron crystallites are not as active for the Fischer-Tropsch synthesis as catalysts containing larger crystallites [32,101]. It is presently not clear whether this is caused by a decrease in the intrinsic activity with crystal size or whether the size dependence is introduced due to a size-dependent phase transformation (vide supra).…”

Mechanism of C2+ oxygenate synthesis on Rh catalysts

“…The difference in product selectivity among these catalysts has been attributed to differences in their capabilities to catalyze CO dissociation, hydrogenation, CO insertion, and chain growth [8,[20][21][22]. Fe [23], Co [24], and Ru exhibit excellent CO dissociation and hydrogenation activities; hence serve as typical CO hydrogenation catalysts that produce linear hydrocarbons as major products and C 2+ oxygenates as minor products. Ni is an excellent methanation catalyst due to its CO dissociation and hydrogenation activity [22,[25][26][27].…”

Nanocatalysis: Academic Discipline and Industrial Realities

“…In a desire to reduce costs of large-scale catalytic systems, for example, in the refinery industry, researchers in the 1950s began to produce smaller catalytic particles in order to profit from the resulting advantageous characteristics described above [26]. Thereby, the size was lowered from 100 nm in the beginning to less than 1 nm today [101]. Both, top-down and bottom-up approaches are conceivable for the synthesis of nanoparticle catalysts.…”