Abstract
In order to examine fundamental processes connected with the use of an unpromoted iron based Fischer–Tropsch synthesis (FTS) catalyst, model studies examining the temporal formation of hydrocarbonaceous species that form over the catalyst are undertaken using a combination of temperature-programmed oxidation, powder X-ray diffraction, Raman scattering, transmission electron microscopy and inelastic neutron scattering (INS). Catalyst samples were exposed to ambient pressure CO hydrogenation at 623 K for defined periods of time-on-stream (3, 6, 12 and 24 h) prior to analysis. INS reveals a progressive retention of hydrogenous species that is associated with the evolution of a hydrocarbonaceous overlayer, as evidenced by the presence of sp2 and sp3 hybridized C–H vibrational modes. Correlations between the formation of aliphatic and olefinic/aromatic moieties with post-reaction characterization leads to the proposal of a number of chemical transformations that, collectively, define the conditioning phase of the catalyst under the specified set of reaction conditions. A comparison between the inelastic neutron scattering spectra of the 24 h sample with that of an iron catalyst extracted from a commercial grade Fischer–Tropsch reactor validates the relevance of the experimental approach adopted.
Highlights
Fischer–Tropsch synthesis (FTS) is a non-selective heterogeneously catalyzed industrial reaction that can produce a variety of hydrocarbon products from the reaction of CO and H2 obtained from coal, natural gas or biomass sources.[1,2,3] These hydrocarbon products may be further processed to produce sulfur-free diesel and high value chemicals utilized by the chemical manufacturing industry.[4]
Previous characterization efforts have established the phase of the iron oxide catalyst sample, investigated for this study, to be a-Fe2O3.19 Those studies discussed the reaction chemistry during the representative FTS reaction.[19]
In situ X-ray diffraction (XRD) identi es the morphological transformations during this period, with the reduction of a-Fe2O3 to Fe3O4 leading to the formation of iron carbides (Fig. 1b)
Summary
Fischer–Tropsch synthesis (FTS) is a non-selective heterogeneously catalyzed industrial reaction that can produce a variety of hydrocarbon products from the reaction of CO and H2 (syngas) obtained from coal, natural gas or biomass sources.[1,2,3] These hydrocarbon products may be further processed to produce sulfur-free diesel and high value chemicals utilized by the chemical manufacturing industry.[4]. Xu and Bartholomew used high pressure in situ Mossbauer absorption spectroscopy to study the phase transformation of an Fe-based catalyst under realistic FTS conditions (10 atm, 538 K).[11] Other in situ studies utilizing X-ray absorption spectroscopy (XAS), X-ray diffraction (XRD), and scanning transmission X-ray microscopy (STXM) have been reported.[12,13,14] An alternative approach to in situ analysis is to investigate the Fe catalyst undergoing ambient pressure hydrogenation of CO at elevated temperatures.[15] no polymerization occurs to form the typical distribution of high molecular weight hydrocarbon products, the surface chemistry involved in CO/H2 dissociation and C–C/C–H bond formation is informative and relevant Previous studies from this group have utilized this test reaction to study how hydrogen is partitioned within the catalyst matrix of reacted Fe FTS catalysts through the application of inelastic neutron scattering (INS).[16,17,18,19] From measuring industrially reacted and laboratory prepared Fe FTS catalysts, the formation of hydrocarbonaceous deposits during the large scale. A qualitative model is proposed to account for the experimental observations
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Free) 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
