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(1)In catalytic coal-oil coprocessing, three Argonne coals of different ranks resulted in much higher conversions in the presence of an Fe(C0I6 catalyst precursor (at 0.5 wt 9c Fe) than in its absence (thermal background). The high conversions and oil yields were due chiefly to the departure from bulk properties, especially in surface energetics, as the particle size of the Fe catalyst produced in situ from Fe(CO), was reduced to less than about 12 nm. (2) The effect of the Mo catalyst, added as Mo(CO)~, plus an Fe(CO), precursor, was to increase conversions while also increasing the hydrogen content of the liquid product. This is in contrast to the Fe catalyst, which was active for conversion, but not as active as Mo for hydrogenation. (3) The soluble catalytic precursors of Fe and Mo, added together, are converted to fine grain sizes (20-50 nm) of sulfided phases such as Fel-,$ and probably MoS2, respectively, under reaction conditions. (4) The sulfated oxides of iron and tin were active catalysts for coprocessing reactions both at 400 and 425 "C. These catalysts gave greater conversions and oil yields at 400 "C than a t 425 "C, probably due to coking reactions of the heavy petroleum-derived oils coprocessed with bituminous coals at the higher temperature. ( 5 ) Incorporation of small amounts of molybdenum (2G100 ppm with respect to the reaction mixture) on the sulfated iron oxides enhanced total coal conversions as well as the oil yields in coprocessing. It is likely that the hydrogenation function of Mo helps improve product quality over that obtained with sulfated iron oxides in the absence of Mo. The amount of molybdenum used in our catalytic systems was limited to 100 ppm on the higher side keeping in mind its relative cost as compared to iron and its economically viable use as a disposable catalyst.
(6) The sulfated iron oxides (with or without Mo) were found to be more active for conversion of coal (in coprocessing) to lighter products at 400 "C than the soluble precursors of the same metals (Fe(C0I6 and Mo(CO),) added at the same metal loadings. (7) The catalytic activity of the sulfated oxides is the result of several factors: the fine grain size is undoubtedly of the greatest importance but it is possible that the superacidity of the starting catalysts may play a part during the initial phases of the reaction. In the case of Mo/ Fe2O3/S0t-, the hydrogenation ability of Mo comes into play. (8) There is still much to be learned about the mechanisms involved in these types of reactions. With these superacidic sulfated metal oxides as catalysts, the chemistry of the reactions in coal liquefaction could be different from what is known so far (such as possible involvement of radical ion intermediatesm). In any case, these finely divided solid catalyst precursors show great promise for application in hydroprocessing reactions.
Acknowledgment. We gratefully acknowledge the contributions of the Argonne Coal Sample Bank for providing the coal samples, C. van Ormer and J. R. Blachere for the transmission electron microscopy, the donation of Maya crude by CITGO, and funding support from the U.S. Department of Energy under grant No. DE-FC2288PC8806. Registry No. Fe(C0)5,13463-40-6; MO(CO)~,13939-06-5; Fe203,1309-37-1;Sn02, 18282-10-5;Mo, 7439-98-7. (20) Farcasiu, M.; Smith, C.; Wender, I.; Pradhan, V. R. Submitted for publication in Energy Fuels.
Surface Composition of Iron and Inorganic Sulfur Forms in Argonne Premium Coals by X-ray Photoelectron Spectroscopy S. R. Kelemen,* M. L. Gorbaty, G. N. George, and P. J. Kwiatek Exxon Research and Engineering Company, Annandale, New Jersey 08801 Received April 15, 1991. Revised Manuscript Received June 19, 1991
X-ray photoelectron spectroscopy (XPS) has been used in the study of the surface composition of iron and inorganic sulfur forms in coals from the Argonne Premium Sample Program. The concentration of iron at the coal surface can be very different than the bulk average. XPS and elemental analysis of selected particle size distributions show that the differencea at the surface cannot be explained solely on the basis of particle size effects. In every case the XPS iron 2p and sulfur 2p results indicate the presence of iron oxides or oxyhydroxides. No evidence was found for the presence of pyritic iron at the surface of any sample other than Illinois No. 6 coal. The results indicate that the initial surface oxidation of pyrite is very rapid and unavoidable even in carefully handled samples. Sulfate sulfur was identified as a surface oxidation product after several days' exposure to ambient air. Introduction X-ray photoelectron spectroscopy (XPS) and X-ray absorption near edge structure (XANES)spectroscopy are two techniques which have been applied recently for the 0887-0624/91/2505-0720$02.50/0
direct speciation and approximate quantification of organicdy bound forms in carbonaceous materials.1-8 XPS (1) George, G. N.; Gorbaty, M. L. J . Am. Chem. SOC. 1989,111,3182.
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Surface Composition of Coals
Table I. Comparison of the Calculated Bulk Total Iron to Carbon Atom Ratio, Pyritic Iron to Carbon Atom Ratio, and XPS Total Iron to Carbon Atom Ratio for Argonne Premium Coals iron/carbon (X100) total pyritic total total XPS bulkb coal bulP bulkb 0.08 0.44 Upper Freeport 0.48 0.46 Wyodak 0.11 0.19
