Partial oxidation of methane over supported ruthenium catalysts R. Lanza a,b , S.G. Ja ¨ra ˚s a , P. Canu b, * a KTH, Royal Institute of Technology, Department of Chemical Engineering and Technology, Chemical Technology, SE-100 44 Stockholm, Sweden b Universita ` di Padova, Dipartimento di Principi e Impianti di Ingegneria Chimica, Via Marzolo 9, IT-35131 Padova, Italy Received 13 December 2006; received in revised form 7 March 2007; accepted 8 March 2007 Available online 12 March 2007 Abstract Partial oxidation of methane (POM) to synthesis gas was studied over Ru catalysts (1% (w/w)) supported on silica, alumina and ceria–zirconia. Catalyst samples were prepared by incipient wetness and characterized by BET area, XRD, ESEM–EDS, and TPR–TPO analyses. Ru on silica deactivated very fast, while Ru supported on alumina has good activity and selectivity. The mixture CeO 2 –ZrO 2 led to low selectivity towards POM, with a higher selectivity towards complete combustion, common to all the catalysts at lower temperature. Both reduced and non-reduced catalysts were tested resulting in different behaviour in the same temperature range. We investigated the effect of different GHSVs, heating rates and also sequences of heating and cooling cycles. This allowed gaining insight into the sequence of reactions taking place in the reactor and revealed hysteresis for all reaction conditions. This can be explained through a cycling between Ru oxidation states on the surface. # 2007 Elsevier B.V. All rights reserved. Keywords: Methane; Partial oxidation; Syngas; Ruthenium; Activity; Hysteresis 1. Introduction During last few years an increasing interest in partial oxidation of methane (POM) has developed. The reaction: CH 4 þð1=2ÞO 2 ! CO þ 2H 2 ; DH 298 ¼35:7 kJ=mol allows to produce syngas in the correct proportion to be used to synthesize several chemicals via the Fischer–Tropsh process. NO x forms in very low concentrations (less than 5 ppm) if a catalyst is used, allowing to carry out the reaction at low temperature. Several catalysts are available for this reaction: Ni is an inexpensive material, but it shows a tendency to sintering and needs to be stabilized with small amounts of CaO, potassium oxide and silica [1]. Noble metals are much more active [1] and even if they are more expensive, they are widely used because of their better performance [1]. Ru is the least expensive among the noble metals [2] and seems to be stable and very active and selective, other choices are obviously Pt and Pd, but also Rh and Ir are valid catalysts [3,4]. With this work, we present original results using ruthenium on different supports: SiO 2 , Al 2 O 3 and ZrO 2 with 17.5% CeO 2 added. Ru is commonly supported on alumina and on silica showing high activity at low concentrations [5] and at low temperatures [3]. Yan et al. [6] reached almost 100% CH 4 conversion with 1% Ru on silica with selectivity values over 95% towards H 2 and CO at 750–800 8C. Ru has been investigated quite extensively [1,6–8], but only a few works used the catalyst supported on monoliths [9]. There are various advantages of an open structured monolith (or honeycomb) compared with conventional particle catalysts. These include: high specific surface, small pressure drop (that allows reactions with short contact times, so side product formation is reduced) [1], good interphase mass transfer, negligible resistance to mass transfer by intraphase diffusion through the catalytic layer (which is usually very thin), good thermal and mechanical properties, simple scale-up and other advantages which make them superior related to conventional catalysts [10]. Further, it is easier to model results obtained with a honeycomb-supported catalyst because of the regularity of the geometry and then the flow patterns. We thoroughly investigated the catalyst behaviour, progres- sively increasing the operating temperature, as common practice, but then also cooling down the reactor at a controlled rate. This evidenced marked hysteresis with a better activity at lower temperatures. www.elsevier.com/locate/apcata Applied Catalysis A: General 325 (2007) 57–67 * Corresponding author at: Universita ` di Padova, Dipartimento di Principi e Impianti di Ingegneria Chimica, Via Marzolo 9, IT-35131 Padova, Italy. E-mail address: paolo.canu@unipd.it (P. Canu). 0926-860X/$ – see front matter # 2007 Elsevier B.V. All rights reserved. doi:10.1016/j.apcata.2007.03.005