Applied Catalysis A: General 266 (2004) 155–162 Modelling the activity–stability pattern of Ni/MgO catalysts in the pre-reforming of n-hexane Francesco Arena ∗ , Giuseppe Trunfio, Emanuele Alongi, Davide Branca, Adolfo Parmaliana Dipartimento di Chimica Industriale e Ingegneria dei Materiali, Università degli Studi di Messina, Salita Sperone 31, I-98166 S. Agata Messina, Italy Received 30 October 2003; received in revised form 4 February 2004; accepted 4 February 2004 Available online 15 April 2004 Abstract The activity–stability pattern of a 19 wt.% Ni/MgO catalyst in the pre-reforming (T, 450 ◦ C; P, 10 bar) of n-hexane with steam (S/C, 1.5–3.5) in absence and presence of H 2 (H/C, 2) has been investigated. Deactivation profiles of the kinetics of CH 4 and CO/CO 2 formation indicate that the activity, selectivity and stability are closely related. Hydrogenation of carbon species to methane is a critical step involving the occurrence of coking in the pre-reforming of hexane. Thermodynamic analysis of the outlet reaction stream signals that the net coking rate depends upon the relative kinetics of carbon methanation (MET, C + 2H 2 ⇄CH 4 ) and gasification/water–gas-shift (GAS, C + H 2 O⇄H 2 + CO; WGS, CO + H 2 O⇄CO 2 + H 2 ) reactions, while negligible appears the contribution of the Bouduard reaction path (DISP, 2CO⇄C + CO 2 ). © 2004 Elsevier B.V. All rights reserved. Keywords: Pre-reforming; n-Hexane; Steam; Ni/MgO catalyst; Activity; Stability; Kinetics; Deactivation; Coking 1. Introduction Hydrogen is nowadays one the most important chemical finding an extensive use in a variety of industrial processes going from hydrocracking–hydrotreating in oil refining, to fine chemicals production and also as raw material for am- monia and methanol synthesis [1–5]. Apart from latter, the major users of hydrogen are currently the refineries consum- ing ca. 85% of the total amount produced worldwide, most of which (ca. 65% in US refineries) is available from the catalytic reforming of naphtha [1]. The remainder supply is met by auxiliary production facilities; mostly steam reform- ing (SR) processes, satisfying ca. 90% of the actual extra hydrogen demand [1,2]. However, this scenario is destined to an abrupt change in the next future for two main reasons [3]: first, the need to reduce progressively the aromatics’ content in gasoline, essentially through a lowering of the catalytic reforming severity, will lead to a decreased hy- drogen production [1,2]; and second, the expected break- ∗ Corresponding author. Tel.: +39-090-676-5606; fax: +39-090-391-518. E-mail address: francesco.arena@unime.it (F. Arena). through in the fuel market, imposed by the need of cleaner and more efficient fuels (e.g., hydrogen, synthetic gasoline, dimethylether, etc.) produced from natural gas (GTL) rather than from oil, to attain a definitive reduction of NO x , SO x and CO 2 emissions from mobile sources [4,5], will impose an extraordinary development of the actual syngas produc- tion capacity. On this account, both industrial companies and academic groups are involved since several years in a con- tinuous challenge aimed at upgrading the hydrogen/syngas technology which could result in significant improvements of the overall GTL process economy [1–5]. The exploitation of novel and alternative production routes [3], the engineer- ing of combined and more energy-effective reforming tech- nologies [1–3,6] and the enhancement of SR catalysts’ per- formance [6–10] are the pursued routes. In this context, adi- abatic pre-reforming constitutes an established technology with recognised economic and operational benefits on the overall syngas production, especially as a tool for revamp- ing older SR plants [1,2,6,11]. Indeed, a pre-reforming unit upstream a tubular reformer allows whatever hydrocarbon feed (NG, LPG, VN) being converted into CH 4 and CO x at low temperature, typically in 450–550 ◦ C range, with many practical advantages consisting in: (i) an increased produc- 0926-860X/$ – see front matter © 2004 Elsevier B.V. All rights reserved. doi:10.1016/j.apcata.2004.02.006