L.M. Tau

Nature of surface species on supported iron during CO/H2 reaction

Abstract The transient method has been used to study the H 2 CO reaction over 10% Fe Al 2 O 3 and 10% Fe SiO 2 at 1 atm and 285 °C in a differential reactor. Responses to perturbations in the feed composition to the reactor were measured by on-line mass spectrometry. Additional studies were made with the reactants CO He , C 2 H 4 H 2 , and C 2 H 4 He . The effect of water in the feed was also investigated. The nature of the species remaining on the surface or in the bulk of the iron was investigated by hydrogen and by oxygen flushing. The observations are explained by proposing a common surface carbon precursor to the formation of surface CH, surface carbidic carbon, surface graphitic carbon, and bulk iron carbides.

Investigation of supported iron Fischer-Tropsch synthesis catalysts by Mössbauer spectroscopy

The carburization of the iron in a 10% Fe on Al2O3 (Alon-C) catalyst has been followed by Mossbauer spectroscopy. The studies were made mostly at 270–285 °C and the catalyst was exposed to CO/H2 and CO/He gas mixtures. The decarburization by H2 was also studied. The principal carbides found are χ-carbide, Fe2.5C, e′-carbide, Fe2.2C with a tendency for a preponderance of the latter at long reaction times. The carburization by CO is promoted by the presence of H2, even in a small concentration. The promoting action of H2 seems to be related to the ease of carburizing a particle with a well-reduced surface. Adding water to CO/H2 slows the carburization rate without slowing the carbon deposition rate. Similar experiments with 10% Fe/SiO2 (Cab-O-Sil) catalyst give similar results. Rates are somewhat reduced, but there is no qualitative change introduced by the different support.

Kinetic and mössbauer study of the COH2 reaction over FeTiO2 reduced at various temperatures

Abstract The CO H 2 reaction over Fe TiO 2 has been studied by Mossbauer spectroscopy and kinetic measurements after the catalyst was reduced at 558, 723, and 773 K. The particle size estimated from the uptake of H 2 by the desorption method is comparable to that from X-ray line broadening. Mossbauer parameters show that the bulk phase of fresh catalyst is essentially identical to metallic iron. Mossbauer spectroscopy indicates that carbide formation is suppressed during the CO H 2 reaction for the catalyst reduced at 723 and 773 K. The reaction activity for the catalyst reduced at 558 K is an order of magnitude higher than that of the 773 K-reduced catalyst. The nature of the surface species formed during the CO H 2 reaction is quite different from those found for the Fe SiO 2 and Fe Al 2 O 3 systems. The changes in the activation energy and selectivity for the catalysts reduced at various temperatures are appreciable. The experimental results are discussed in terms of a localized charge transfer from the metal to the support during the course of high-temperature reduction. The requirement for this localized charge transfer is the presence of TiO x species on top of the metal surface.

Synthesis, characterization, and Fischer-Tropsch studies of iron-containing zeolites

Iron has been incorporated into several zeolites with adsorption, ion-exchange, and anionic complexation procedures. These samples have been reduced in flowing hydrogen at temperatures between 300 and 500 °C. Particle size measurements using X-ray powder diffraction and electron microscopy techniques reveal that all of the iron phases of the reduced samples are between 50 and 150 A. Changes in the catalysts due to their interactions with 10% COH2 at temperatures ranging from 260 to 400 °C were determined by Mossbauer spectroscopy using an in situ cell. Catalytic activity was monitored by a gas chromatograph and quantitative analysis of the product distribution was done in a separate differential reactor which was interfaced to a mass spectrometer. Alloy formation was not observed.

Reaction intermediates on Fe/TiO2 during CO/H2 reaction

The nature of the surface species present on 10% FeTiO2 in the low-temperature reduced state (558 K) has been studied after short times of reaction in 10% COH2 at 558 K and 1 atm. After various reaction times the surface has been titrated by H2, O2, or D2. The results show that the surface during reaction is covered with about 46 μmol/g of CH and large quantities of surface carbidic carbon. The intermediate for the reaction of 10% C2H4H2 appears to be only CH.