Influence of Promotion on the Growth of Anchored Colloidal Iron Oxide Nanoparticles during Synthesis Gas Conversion

Abstract

Using colloidal iron oxide nanoparticles with organic ligands, anchored in a separate step from the supports, has been shown to be beneficial to obtain homogeneously distributed metal particles with a narrow size distribution. Literature indicates that promoting these particles with sodium and sulfur creates an active Fischer−Tropsch catalyst to produce olefins, while further adding an H-ZSM-5 zeolite is an effective way to obtain aromatics. This research focused on the promotion of iron oxide colloids with sodium and sulfur using an inorganic ligand exchange followed by the attachment to H-ZSM-5 zeolite crystals. The catalyst referred to as FeP/Z, which consists of iron particles with inorganic ligands attached to a H-ZSM-5 catalyst, was compared to an unpromoted Fe/Z catalyst and an Fe/Z-P catalyst, containing the colloidal nanoparticles with organic ligands, promoted after attachment. A low CO conversion was observed on both FeP/Z and Fe/Z-P, originating from an overpromotion effect for both catalysts. However, when both promoted catalysts were washed (FeP/Z-W and Fe/Z−P-W) to remove the excess of promoters, the activity was much higher. Fe/Z-P-W simultaneously achieved low selectivity toward methane as part of the promoters were still present after washing, whereas for FeP/Z-W the majority of promoters was removed upon washing, which increased the methane selectivity. Moreover, due to the addition of Na+S promoters, the iron nanoparticles in the FeP/Z(-W) catalysts had grown considerably during catalysis, while those in Fe/Z-P(-W) and Fe/Z(-W) remained relatively stable. Lastly, as a large broadening of particle sizes for the used FeP/Z-W was found, where particle sizes had both increased and decreased, Ostwald ripening is suggested for particle growth accelerated by the presence of the promoters.

Functionalized Carbon Materials in Syngas Conversion

“…[88] Many groups attempted to gain information on the optimized iron particle size with high activity and product selectivity. [89][90][91] During FT reaction, the iron species usually undergo reconstruction, making it difficult to obtain precise correlation between the particle sizes and the intrinsic activity of Fe catalysts. Torres Galvis et al fabricated a series of CNFs-supported iron catalysts by incipient wetness impregnation to study the effect of iron carbide sizes on syngas conversions.…”

Designing Nanoparticles and Nanoalloys for Gas-Phase Catalysis with Controlled Surface Reactivity Using Colloidal Synthesis and Atomic Layer Deposition

“…In the development of FTS catalysts with high selectivity towards olefins, i.e., FT to olefins (FTO), and their further conversion into aromatics, Krans et al [97] prepared Na 2 S-promoted Fe NPs anchored onto H-ZSM-5, denoted as "FeP/Z". For comparison, unpromoted Fe NPs were also deposited onto H-ZSM-5 ("Fe/Z").…”

“…The authors ascribed this to the fact that TTAB and PVP blocked Adapted with permission from Ref. [97], https://pubs.acs.org/doi/abs/10.1021/acscatal.9b04380. Further permissions related to the material excerpted should be directed to the ACS.…”

“…Adapted with permission from Ref. [ 97 ], . Further permissions related to the material excerpted should be directed to the ACS.…”

“…(e) Product selectivities of FeP/Z-W and Fe/Z-P-W in FTO conditions (T = 340 °C, P = 1 bar, H2/CO = 1 (V/V), GHSV: 4 200 h −1 , TOS = 15 h). Adapted with permission from Ref [97],. https://pubs.acs.org/doi/abs/10.1021/acscatal.9b04380.…”