Catalysis for synthesis gas formation from reforming of methane Mahesh V. Iyer a, *, Lawrence P. Norcio a , Alex Punnoose b , Edwin L. Kugler a , Mohindar S. Seehra b , and Dady B. Dadyburjor a, ** a Department of Chemical Engineering, West Virginia University, P.O. Box 6102, Morgantown, WV 26506-6102 b Department of Physics, West Virginia University, P.O. Box 6102, Morgantown, WV 26506-6102 Cobalt–tungsten g-carbide [Co 6 W 6 C] is the precursor for a novel stable and active catalyst for ‘‘dry’’ reforming of methane with carbon dioxide to produce synthesis gas. Once the catalyst is pretreated, the catalyst activity is unchanged after 150 h on stream, and the H 2 /CO ratio is maintained close to unity. X-ray diffraction patterns show the formation of a WC phase, Co and carbon in the stabilized catalyst. Carbon deposition, which leads to severe problems for commercial nickel catalysts, actually helps in the creation of the stable catalyst. KEY WORDS: methane; carbon dioxide; dry reforming; synthesis gas; cobalt tungsten carbide. 1. Introduction Existing processes use methane as a primary feed- stock for producing synthesis gas (syngas), a mixture of carbon monoxide and hydrogen, which serves as the feedstock for a variety of downstream processes [1–4]. Reforming of methane to syngas can be carried out [1–3,5] by steam reforming, dry reforming using carbon dioxide, partial oxidation using oxygen, and auto- thermal reforming using air and steam. Dry reforming: CH 4 þ CO 2 ! 2CO þ 2H 2 ð1Þ has been proposed as a promising technology due to the use of the greenhouse gas CO 2 . Besides, dry reforming can be employed in those natural-gas fields where there is an abundance of CO 2 [5,6]. Finally, dry reforming has been evaluated [3] to have the lowest operating costs, about 20% lower than those of the other reforming processes. Metal catalysts are suitable for methane reforming, with nickel-based catalysts preferred commercially over noble metals due to the inherent availability and low costs of the former. However, nickel also catalyzes the formation of coke, unsaturated polyaromatic hydrocarbons with H/C ratios less than unity, via methane decomposition and/or CO disproportionation [1–3,5]. Coke may form on the catalyst surface and/or the tubes of the reformer, and leads to deactivation of the catalyst and plugging of the tubes. Hence coke formation is one of the major problems associated with dry reforming using these catalysts [3,7]. There has been considerable interest in the catalytic properties of metal carbides. These materials are abun- dant and may be effective enough to replace noble metals as catalysts. Carbides of molybdenum and tungsten, in particular, have been identified as ‘‘magic catalysts’’ for this millennium [6]. Recently, there have been reports of application of these metal carbide catalysts for dry reforming of methane [6,8–12]. These carbides are stable at elevated pressures and are mod- erately resistant to carbon deposition. However, addi- tion of a second metal could result in further improvements in activity and stability. In the present work, we have investigated the performance of a potential bimetallic carbide catalyst prepared from a cobalt–tungsten eta-carbide [Co 6 W 6 C] precursor, for the dry reforming of methane to produce syngas. Future work will concentrate on the kinetics and reactor design of these catalysts. 2. Experimental The catalyst-testing unit is computer controlled with four lines for gas feeds, each being independently controlled by a Brooks mass-flow controller. The reactor consists of a silica-lined stainless-steel tube of nominal outer diameter of 0.5 in. and nominal length of 25 in., placed in a 18 in. single-zone furnace from Applied Test Systems. The stainless-steel reactor was lined with silica (at Restek Corp.) to ensure that the reactor material itself did not contribute to any catalytic activity. The catalyst is placed in the center of the reactor, with quartz chips placed upstream and down- stream of the catalyst. The products are analyzed on-line by a computer-controlled Hewlett-Packard 5890 gas chromatograph (GC), which provides quantitative analysis for He, H 2 , CO, CH 4 , CO 2 and H 2 O. The unsupported cobalt–tungsten eta-carbide [Co 6 W 6 C] precursor was obtained from Nanodyne Inc. and had an initial BET surface area of about 5 m 2 /g. *Present address: Department of Chemical Engineering, The Ohio State University, Columbus, OH 43210. **To whom correspondence should be addressed. E-mail: dady.dadyburjor@mail.wvu.edu Topics in Catalysis Vol. 29, Nos. 3–4, June 2004 (Ó 2004) 197 1022-5528/04/0600–0197/0 Ó 2004 Plenum Publishing Corporation