Supported Iron Nanoparticles as Catalysts for Sustainable Production of Lower Olefins

Abstract

Lower olefins are key building blocks for the manufacture of plastics, cosmetics, and drugs. Traditionally, olefins with two to four carbons are produced by steam cracking of crude oil-derived naphtha, but there is a pressing need for alternative feedstocks and processes in view of supply limitations and of environmental issues. Although the Fischer-Tropsch synthesis has long offered a means to convert coal, biomass, and natural gas into hydrocarbon derivatives through the intermediacy of synthesis gas (a mixture of molecular hydrogen and carbon monoxide), selectivity toward lower olefins tends to be low. We report on the conversion of synthesis gas to C(2) through C(4) olefins with selectivity up to 60 weight percent, using catalysts that constitute iron nanoparticles (promoted by sulfur plus sodium) homogeneously dispersed on weakly interactive α-alumina or carbon nanofiber supports.

Metal organic framework-mediated synthesis of highly active and stable Fischer-Tropsch catalysts

“…The spatial restriction created by encapsulation seems to minimize sintering and oxidation of the active Hägg carbide phase. The high catalytic activity of the solids here presented is further highlighted when comparing their productivity with that of available data on commercial benchmark catalysts, namely the well-known Ruhrchemie 38 and Sasol 39 catalysts for high-temperature FTS (Table 5). The comparison demonstrates that the MOF-derived solids display productivities, on a total catalyst weight basis, one order of magnitude higher than these benchmarks, even when the MOF-based catalysts contain a lower amount of iron.…”

Iron Particle Size Effects for Direct Production of Lower Olefins from Synthesis Gas

“…This iron precursor contained traces of sodium and sulfur which are suitable promoters for FTO. 1,29,30 The preparation procedure was as described for the unpromoted catalysts synthesized with the impregnation technique. The sample code is similar as previously explained for unpromoted samples prepared by impregnation.…”

“…1−3 A catalyst for the selective production of C 2 − C 4 olefins from synthesis gas that has been previously reported consists of iron nanoparticles dispersed on an inert support material. 1,2 The Fischer−Tropsch reaction is recognized as a structuresensitive reaction 4,5 which means that the catalytic performance is strongly related to the particle size of the metal or active phase. The effect of metal particle size has been extensively studied for cobalt 6−10 and ruthenium.…”

“…To study the intrinsic particle size effect and to limit support effects, it is necessary to use a carrier material with limited interaction toward iron such as carbon nanofibers. 1,2,6,7 During the eighties, studies concerning the effect of Fe crystallite size were performed on unpromoted carbonsupported 17,18 and γ-Al 2 O 3 -supported catalysts. 19 Jung et al 17 reported that, under the conditions used (1 bar, 275°C, and H 2 /CO = 3), smaller Fe particle sizes (<1.6 nm) lead to lower turnover frequencies for CO hydrogenation, lower methane selectivities, and higher olefin to paraffin (O/P) ratios.…”

Kinetics of CO2 Hydrogenation to Hydrocarbons over Iron–Silica Catalysts

“…While the size of metal catalyst particles can have as trong effect on reaction performance, the literature shows that this effect becomes significant only for particles sizes below 4nm. [32] As such, it is acceptable to compare catalysts with comparable particle size (entries 1, 2a nd 3) ando bserve that as the pore diameter of the silica increases the CO 2 conversion and selectivity to heavier HCs rises,F igure 2a,b. When the CO 2 conversion is compared, the SiO 2 -150 b (entry 5) does not follow the same trend and is lower than that observed for the smaller particle sizes suggesting possible mass transfer influences.…”