reserves [1,2]. The SNG production process involves two steps: gasification of the carbon-containing feedstock and subsequent catalytic methanation of the resulting synthesis gas. Methanation of synthesis gas involves the two following reactions [3][4][5]:These reactions are thermodynamically favored at low temperature and high pressure [6]. It is therefore that the methanation process is designed to effectively remove the heat of reaction and thus maximize the methane yield [1,7]. There are currently two main methanation concepts: single fluidized bed reactors and series of adiabatic fixed bed reactors with intercooling [1]. The latter, also known as high temperature methanation, has already found commercial application [8,9].Alumina-supported nickel catalysts are usually employed in this application due to their high activity, selectivity to methane and relatively low price [7]. However, their stability is threatened by the severe conditions of the high temperature methanation process [10,11]. In this process, the catalyst at the inlet of the reactor is exposed to low temperatures and high CO partial pressures, fact that favors the formation of polymeric carbon and sintering via nickel carbonyl formation [4,[12][13][14]. The exothermic reactions cause a significant temperature rise. As a result, the major part of the catalyst in these reactors is exposed to high temperatures and high steam partial pressures fact that promotes sintering of the nickel nanoparticles and the support [11,15]. In order to limit the temperature rise and thus, catalyst deactivation, a high gas recycle is used in these reactors. Catalysts with improved stability at low andAbstract Catalyst deactivation is one of the major concerns in the production of substitute natural gas (SNG) via CO methanation. Catalysts in this application need to be active at low temperatures, resistant to polymeric carbon formation and stable at high temperatures and steam partial pressures. In the present work, a series of aluminasupported nickel catalysts promoted with Zr, Mg, Ba or Ca oxides were investigated. The catalysts were tested under low temperature CO methanation conditions in order to evaluate their resistance to carbon formation. The catalysts were also exposed to accelerated ageing conditions at high temperatures in order to study their thermal stability. The aged catalysts lost most of their activity mainly due to sintering of the support and the nickel crystallites. Apparently, none of these promoters had a satisfactory effect on the thermal resistance of the catalyst. Nevertheless, it was found that the presence of Zr can reduce the rate of polymeric carbon formation.

No abstract