Abstract
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 alumina-supported 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.
Highlights
Production of substitute natural gas (SNG) from coal, biomass or other carbonaceous sources is gaining great attention in areas located far from natural gas or shale gas CO + 3H2 → CH4 + H2O (ΔH◦ = −206 kJ/mol)CO2+4H2 → CH4+2H2O(ΔH◦ = − 165 kJ/mol)These reactions are thermodynamically favored at low temperature and high pressure [6]
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 objective of the present work is to evaluate the effect of different structural promoters on carbon formation and thermal sintering under relevant methanation conditions
Summary
Alumina-supported nickel catalysts are usually employed in this application due to their high activity, selectivity to methane and relatively low price [7] 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].
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