Pedro A. Montano

Mössbauer study of transformations of pyrite under conditions of coal liquefaction

Abstract The Mossbauer effect is used to study in-situ transformations of pyrite under conditions of coal liquefaction based on Illinois No. 6 coal from St. Clair County. A marked reduction is observed at high temperatures in the isomer shift of the iron sulphides during coal liquefactions. By contrast the pure sulphides do not show such a strong effect in the presence of solvent and hydrogen. This reduction in the isomer shift may result from covalent bonding between the iron on the pyrrhotite surfaces and the coalderived liquid and gases. Marked broadening of the linewidth of Fe 1 − x S occurs above 300 °C in the presence of solvent and hydrogen. The stoichiometries of the pyrrhotites formed in the different runs were determined and a correlation was observed between the total amount of sulphur in the coal and the iron deficiency in Fe 1 − x S . Coal-derived liquids are more active in enhancing pyrite decomposition than tetralin. Both H 2 S and Fe 1 − x S seem to be actively involved in the liquefaction process.

Mössbauer study of the thermal decomposition of FeS2 in coal

The Mossbauer effect has been used to study the transformations of FeS2 in four different coals: IL No. 6, Ky 914, Blacksville No. 2, and Powhatan No. 5. The transformations of FeS2 in the coals were studied in an inert atmosphere. It was observed that the pyrrhotites formed from FeS2 have a considerable reduction in the isomer shift at 440 °C as compared to the values obtained in the absence of coal. This effect is associated with the interaction of the pyrrhotites with the coal constituents at high temperatures. There is also a significant line-broadening at 440 °C. This broadening is due either to vacancy motion in the iron sulphides and/or to motional broadening due to particle motion in the coal-derived liquids. The percentage conversion of pyrite to pyrrhotite depends markedly on time as well as type of coal. The weathering of the coal has a detrimental effect on the rate of conversion of pyrite to pyrrhotite. The ferrous sulphate layers covering the pyrite particles hinder the removal of sulphur from that surface. The major factor affecting the FeS ratio is the total amount of sulphur available for H2S formation. Partial H2S pressure is the crucial quantity controlling the stoichiometry of the pyrrhotites. Hence, a high percentage of H2S in the reactor at high temperature will assure the formation of pyrrhotites with a high number of metal vacancies.

Mössbauer spectroscopy of iron compounds found in West Virginia coals

Abstract Mossbauer measurements were carried out in several coal samples from various seams in West Virginia. The presence of iron pyrite and iron (II) sulphate was observed in all the samples studied. The two different mineral compounds were clearly identified from their isomer shift and quadrupole splitting, and the Mossbauer spectral area was used to determine their amounts. This method is recommended as a complementary technique for the measurement of the amount of sulphur bonded to iron in coals. No evidence of organically bound iron in coal was found for more than forty different samples analysed. Using the Mossbauer effect, unequivocal evidence of the formation of a new mineral species during the low-temperature ashing process was found.

Hydrocracking of diphenylmethane

Abstract This study presents the role of H 2 S other than H-transfer catalyst in the hydrocracking of diphenylmethane with H 2 –H 2 S-pyrrhotite. The results indicate that the partial pressure of H 2 S controls the conversion of pyrrhotite to FeS and FeS 2 , which in turn is closely related to the promotional activity of pyrrhotite on the diphenylmethane conversion. Under higher H 2 S overpressures, pyrite bands appear in the Mossbauer spectra providing proof of the reversibility of pyrite decomposition under liquefaction conditions. With lower H 2 S pressures, low activity troilite forms from the pyrrhotite. An enhanced activity was observed for a partial pressure of H 2 S, sufficient for the maintenance of a high iron deficient surface on the pyrrhotite particles. When the partial pressure was increased too much, the formation of FeS 2 was observed with a slight decrease in activity. FeS did not show as great an activity as the non-stoichiometric pyrrhotite.

Deposition of iron on MgO (100): reaction of CO and H2

Abstract Ultraviolet photoelectron spectroscopy (UPS), electron energy loss spectroscopy (EELS) and surface extended energy loss fine structure (SEELFS) were used to study the deposition of Fe on MgO(100) and to identify the surface compounds formed after reaction of CO/H2 (1:1). The clean MgO(100) surface was characterized using the above techniques and the effect of argon ion bombardment damage to the surface was investigated. With the deposition of iron, metallic characteristics appear in the photoemission spectrum; the electron energy loss peaks of the MgO(100) substrate diminish in intensity with no significant shifts in loss energies. Fine structure analysis of the oxygen K-edge of the MgO(100) surface with less than 2 monolayers (ML) of iron suggests that the iron atoms bond with the oxygen at the surface of the MgO(100) lattice. For less than 4 ML of iron, the EEL spectra show that the deposited iron is oxidized after reaction of CO/H2. Higher iron coverages result in carburization of the surface. Carbon deposition was observed with CO for all Fe coverages. Measurement of the fine structure above the carbon K-edge suggests that the types of carbide formed depend on the iron coverage; one carbide has a short CFe distance of 1.78 A and the other a distance of 2.06 A (high metal coverage).

Mössbäuer study of decomposition of pyrite in hydrogen

Abstract A well-characterized Illinois No. 6 coal and mineral pyrite of different particle sizes have been studied by 57 Fe Mossbauer spectroscopy at various temperatures between 25 and 400 °C in a hydrogen atmosphere. Particle sizes of the pyrites were measured by SEM. The transformation of pyrite to pyrrhotites commences at 300 °C in all the samples and is almost complete at ≈400 °C for the Illinois No. 6 coal. The decomposition of coal and mineral pyrite in a hydrogen atmosphere is dependent on particle size. Breakage of larger particles occurs during the decomposition. A significant reduction in the activation energy as a function of the particle size was also observed.

In situ Mössbauer spectroscopic characterization of FeAI2O3 and FeThO2 Fischer-Tropsch catalysts

Mossbauer spectroscopy has been used to study in situ the transformation of FeAl2O3 and FeThO2 catalysts under different stages of calcination, reduction, carburization, and Fischer-Tropsch synthesis reactions. At room temperature the calcined FeAl2O3 catalyst is composed of Fe3+ ions strongly interacting with the alumina support, and about 10% of bulk α-Fe2O3. The calcined FeThO2 sample consists of a bulk phase of α-Fe2O3. After reduction in flowing hydrogen at 400 °C, the FeAl2O3 catalyst contains about 70% of α-Fe and 30% of FeAl2O4 (a spinel phase). The calcined sample of FeThO2 is completely reduced to α-Fe in flowing H2 at 400 °C in 9 h. When the reduced FeAl2O3, catalyst is carburized at 250 °C in synthesis gas (2H2CO), all the α-Fe is converted to an interstitial alloy of a composition resembling Haggs carbide and e′-Fe2.2C. Carburization of the reduced FeThO2 catalyst at 250°C in 2H2CO converted about 50% of the α-Fe to χ-Fe5C2. However, after the Fischer-Tropsch synthesis reaction, the remaining amount of α-Fe in the catalyst is also changed to χ-Fe5C2. The product distribution in the case of FeAI2O3 reveals a high selectivity for unsaturated and saturated C3 hydrocarbons. For the FeThO2 catalyst, calcined for 24 h, a high selectivity for C5C10 hydrocarbons is shown. For the sample FeThO2 calcined for 48 h, a high selectivity for C5 hydrocarbon and oxygenated products is obtained.

In-situ study of the decomposition of pyrite in an oxygen atmosphere

Abstract In-situ 57 Fe Mossbauer spectroscopy has been used to study the decomposition of mineral pyrite of various sizes and pyrite in coal in an oxygen atmosphere at different temperatures between 25 and 400 °C. The study has shown that the oxidation of pyrite in Illinois No. 6 (IL6) coal occurs in three steps: 1. (1) to iron sulphates between 25 and 310 °C; 2. (2) to γ—Fe 2 O 3 between 310 and 325 °C; and 3. (3) to α—Fe 2 O 3 between 325 and 400 °C. For mineral pyrite, the oxidation has been found to be dependent on the particle size and results in the formation of iron sulphates and α—Fe 2 O 3 . From the amount of conversion of pyrite in the IL6 coal (almost 100%) and the mineral pyrite (maximum of 7 ± 2%) it has been concluded that the oxidation of the two types of pyrite is entirely different and the oxidation of pyrite in coal is highly influenced by the coal constituents.

Hydrocracking of diphenyl ether and diphenylmethane in the presence of iron sulphides and hydrogen sulphide

Abstract The reactions of diphenyl ether (DPE) and diphenylmethane (DPM) with hydrogen, hydrogen sulphide and combinations thereof in stainless steel reactors are described. The use of hydrogen or hydrogen sulphide alone produces little cleavage of these compounds after 1 h at 450 °C. Both DPE and DPM are extensively converted when hydrogen and hydrogen sulphide are used in tandem. DPE mainly produces phenol and benzene with smaller amounts of cyclohexane and methylcyclopentane. Reactions of benzene and phenol indicate phenol to be the major precursor of the hydrogenated products. DPM produces benzene and toluene. The reactivity of the H2H2S system is ascribed to the formation of iron sulphides on the stainless steel reactor surface followed by the hydrocracking of the organic compounds over this activated surface. The reaction rates of DPE and DPM with H2 and H2H2S were shown to depend on the concentration of the organic substrate raised to the first power. Activation energies for these reactions are dependent upon the presence of H2S: H2DPE 45 kcal/mol, H2H2SDPE 31 kcal/mol, H2DPM 50 kcal/mol, H2H2SDPM 37 kcal/mol. Pyrrhotite was added to the DPE and DPM reactions and its activity determined as a function of hydrogen sulphide pressure. Comparison of these results to in situ Mossbauer analyses of the added pyrrhotite allowed the correlation of the sulphide catalyst composition to reactivity. For both DPE and DPM, the highest catalytic activity was reached at 5% partial pressure of hydrogen sulphide. At this partial pressure, pyrrhotite is the dominant form of iron sulphide present in the catalyst.

Mössbauer and auger spectroscopic studies of supported and sulfided FeMo hydrodesulfurization catalysts

In this study a series of Fe-Mo/Al/sub 2/O/sub 3/ catalysts with different atomic ratios, R = Mo/Mo + Fe, of 0.05, 0.25, 0.50, 0.75, 0.90, and 0.95 were prepared and characterized by x-ray diffraction and Moessbauer and Auger spectroscopic techniques. The percentage conversions of coal liquids soluble in tetrahydrofuran (THF), ethyl acetate, and pentane as a function of R values were also determined. Evidence of the interaction between the support and the active components of the catalysts was observed. Additional evidence of the variation in the amount of different species in the catalyst with the change in the concentration of iron atoms was also found. The activity of the Mo/Al/sub 2/O/sub 3/ catalyst was highly influenced by the presence of Fe atoms in the samples.