Catalysis Today 207 (2013) 21–27 Contents lists available at SciVerse ScienceDirect Catalysis Today jou rn al h om epage: www.elsevier.com/locate/cattod Inhibition of carbon formation during steam reforming of methane over ethyldisulfide-impregnated metallic nickel catalysts Kandaiyan Shanmuga Priya, Nicolas Abatzoglou ∗ , Sonia Blais Department of Chemical & Biotechnological Engineering, Université de Sherbrooke, 2500 boul. de l’Université, Sherbrooke, Quebec J1K 2R1, Canada a r t i c l e i n f o Article history: Received 27 January 2012 Received in revised form 6 June 2012 Accepted 23 July 2012 Available online 17 August 2012 Keywords: Unsupported nickel catalyst Steam reforming of methane Graphitic carbon Ethyldisulfide Impregnation a b s t r a c t This paper describes the surface modification of unsupported micrometric nickel powder with ethyld- isulfide and its use as a catalyst in steam reforming of methane (SRM). It reports on catalytic activity and inhibition of carbon formation due to unsupported Ni catalyst alterations with varying ethyldisulfide molar ratios. Methane conversion was investigated by mass spectrometry under time-on-stream con- ditions during SRM reactions at a temperature = 700 ◦ C for 12 h at methane/steam molar ratio = 1:2 and gas hourly space velocity = 19,600 ml g -1 h -1 ; selectivity toward hydrogen production and CO and CO 2 formation was calculated. The nature and relative quantities of carbon species formed on the surface of spent catalysts were studied by X-ray photoelectron spectroscopy analysis. A preliminary mechanistic explanation regarding the inhibition of C formation over the used modified catalysts is provided with. © 2012 Elsevier B.V. All rights reserved. 1. Introduction Steam reforming of methane (SRM) is the main commercial technology for hydrogen and synthesis gas production [1,2]. Among transition metals, nickel (Ni) is the dominant catalyst in indus- trial steam reforming processes because of its reasonable catalytic activity and low cost. The main technological drawback of Ni cat- alysts is that, during SRM, the efficiency of catalytic activity is significantly inhibited by the growth of carbonaceous deposits. This carbon (C) species formation is attributed to the fact that Ni cat- alyzes both steam reforming and C formation reactions. Thus, it is highly desirable to control/minimize the rate of C C bond forma- tion, maintaining catalyst stability and prolonging its lifespan. Numerous works have been published, mainly in the last 3 decades, on means aimed at enhancing the catalytic activity of Ni during SRM and subsequently curtailing C formation [3–8]. Rostrup-Nielsen [9] investigated the surface passivation of cata- lysts by sulfur (S) moieties, employed for SRM, and reported that steam reforming involves ensembles (clusters) of 3–4 Ni atoms, while graphite formation requires 6 or 7 atoms. Chemisorbed S con- tributes to decreasing the surface density of C nucleation sites, thus reducing the C formation rate more than the reforming rate. Ben- gaard et al. [3] performed density function theory (DFT) calculations and concluded that promoters, such as S, K, and Au bound prefer- entially to the step edges of Ni, considered being the most reactive ∗ Corresponding author. Tel.: +1 819 821 7904; fax: +1 819 821 7955. E-mail address: Nicolas.Abatzoglou@USherbrooke.ca (N. Abatzoglou). sites for both CH 4 activation and graphite nucleation. Step sites are often more active and have been proposed as nucleation sites for graphene formation [3,10,11]. Abild-Pedersen et al. [10] studied step deactivation in the presence of C and S, and emphasized that the amount of deposited C decreased rapidly with increasing S cov- erage, up to the 0.06 monolayer, after which the effect of additional S was less pronounced. They established that the small amount of S on the surface does not lead to deactivation and that the opti- mal quantity is the one which is sufficient to block the steps. The basic idea behind these experiments was to pre-sulfide the catalyst surface under controlled process conditions in such a way that the modified surface served as a C-tolerant catalyst with stable catalytic activity in SRM. Most researchers have focused on close-packed surfaces for steam-reforming activity, but it has been found that corrugated surfaces are more reactive for SRM [12]. A recent study further con- firmed the existence of a similar barrier to both C gasification and C deposition processes on monometallic Ni [5]. Moreover, the pos- sibility of utilizing unsupported micrometric Ni-255 as catalyst in SRM under process conditions circumvents the complexities of sup- porting catalysts [13]. T255 TM is a high purity nickel powder with a fine, 3D chain-like structure and spiky surface; it is recognized as an industry standard feed for the production of sintered rechargeable battery electrodes. More physical properties are found in [13]. Since this material is destined for use in catalyst-supported solid oxide fuel cells (SOFCs), the use of pure metallic nickel is technically less cumbersome and trouble-free. There are two main advantages: one phase which means higher thermal resistance; easier deposition- anode fabrication. 0920-5861/$ – see front matter © 2012 Elsevier B.V. All rights reserved. http://dx.doi.org/10.1016/j.cattod.2012.07.009