Energy & Fuels 1994,8, 53-55
53
Complex Iron Catalytic Systems: Relative Catalytic Activity of Various Components? Malvina Farcasiu,* Patricia A. Eldredge,$ and Steven C. Petrosiud Pittsburgh Energy Technology Center, U.S. Department of Energy, P.O. Box 10940, Pittsburgh, Pennsylvania 15236 Received July 12, 1993. Revised Manuscript Received October 7, 199P
Fine-particle (6-8 nm) iron-sulfur systems with complex chemical compositions are formed when a 3-nm iron oxide is heated with sulfur in the presence of 9,lO-dihydrophenanthrenefor 1h. These systems form small-particle pyrrhotite when heated at 320 "C. The fine-particle pyrrhotites are very active hydrocracking catalysts but agglomerate rapidly during reaction at 320 "C.
Introduction The use of iron-based catalysts in reactions of interest for direct coal liquefaction usually involves the addition of iron compounds to the reaction mixture and the in situ activation of the iron compounds to iron catalysts. The composition of active iron-based catalysts has been a subject of considerable interest. The forms of iron usually associated with the catalytic activity in reactions of interest to fossil fuels processing are iron-sulfur systems. It has been reported that the hydrocracking of monoaromatic model compounds at temperatures of 425-435 "C is catalyzed by iron-sulfur systems in the presence of hydrogen sulfide. The catalytic activity has been tentatively explained by an interaction of pyrite with pyrrhotite and hydrogen sulfide.1p2 We report here the catalytic activity in selective hydrocracking reactions of iron-sulfur catalytic systems formed in the reaction of fine-particle iron oxides with elemental sulfur and a hydrogen donor, 9,lO-dihydrophenanthrene (9,10-DHP),at low temperatures (200-320 "C). It was found that the iron-sulfur systems formed under these conditions are very active in low-temperature selective hydrocracking of C-C and C-0 bonds. The compositions of these iron-sulfur systems and the variations in their compositions as a function of time under various reaction conditions have been studied by a variety of methods. This paper discusses our findings concerning the catalytically active components in the above-described iron-sulfur system.
Experimental Section
determination by the BET method. Compound I was available from our previous work.3 The reactions were conducted in sealed 7 mm 0.d. heavy-walled glass tubes (Corning Glass) which were heated in a Lindberg Type 59344 muffle furnace equipped with a thermocouple and temperature controller. Chromatographic analyses were conducted on a HewlettPackard Model 5890 Series I1 gas chromatograph equipped with a split-vent injector and connected to a HP 3396A integrator, using a J&W 30 m X 0.248 mm fused silica capillary column coated with 0.25-pm silicone SE-52, with a head pressure of 20 psi. The column temperature was increased from 80 to 310 OC at a rate of 8 OC/min. Identification of the components was described in a previous p~blication.~Mass balances for the reactions typically were 95% or higher and the reproducibility of conversion results was f 2 5%. Catalyst Preparation and Testing, Iron-Sulfur System. In a typical experiment, ferrihydrite (2.5 mg, dried as indicated above), sulfur (2.5 mg), and 9,10-dihydrophenanthrene(100 mg) were loaded into a glass tube which was sealed without excluding the air. The length of the sealed tube was ca. 14 cm. The tube was heated at the desired temperature for the duration indicated below, and then it was cooled and stored at room temperature. For catalyst testing, the tube was cracked open (CAUTION: pressure buildup in the tube occurs,particularly for experiments at higher temperatures), 25 mg of the reactant, 4-(l-naphthylmethy1)bibenzyl (compound I), was added and the tube was resealed and heated as indicated.
I
General. Reagent grade chemicals and HPLC grade solvents were used as purchased unless stated otherwise. Methylene chloride was dried over 4-A molecular sieves. Ferrihydrite (5FezOs.9HzO), obtained from Mach I, Inc. King of Prussia, PA, was vacuum dried for ca. 3 h a t 150 OC, then stored in a desiccator. The particle size reported by the vendor (3-5 nm) was confirmed by microscopic analysis and is consistent with the surface area t Published in part inPrepr. Pap.-Am. Chem. SOC., Diu. Fuel Chem. 1993,38,53. t Oak Ridge Institute for Science and Education Appointee, Post-
graduate Training Program. 0 Abstract published in Advance ACS Abstracts, November 15,1993. (1)Trawhella,M.J.;Grint,A.Fuel1987,66,1316andreferenceatherein. (2)Narain, N. K.; Cillo, D. L.; Stiegel, G.J.; Tisher, R. E. In Coal Science and Chemistry; Volborth, A., Ed.; Elsevier Science Publishers B.V.: Amsterdam, 1987; pp 111-149 and the references therein.
This article not subject to U.S.Copyright.
In an alternative procedure, compound I was added together with the catalyst precursors such that catalyst preparation and reaction of I were conducted in one operation. For product analysis, the tube was cooled to room temperature and carefully opened, and the organic materials were dissolved in a small amount of methylene chloride ( -0.5-1.0 mL) and fiitered through a layer of anhydrous MgSOd (ca. 0.3 g) supported on glass wool in a micropipet. The tube was rinsed twice with methylene chloride (ca. 0.5 mL each time) and the washings were filtered through the same microcolumn for drying. The combined solution was concentrated to
