Catalytic partial oxidation of methane over nickel and ruthenium based catalysts under low O2/CH4 ratios and with addition of steam

Catalytic partial oxidation (CPO) of methane to synthesis gas at low O2/CH4 ratios and in the presence of steam was investigated over nickel and ruthenium catalysts supported on hydrotalcite-derived materials. The influence of catalyst properties and composition on activity, temperature profile and deactivation by carbon formation was examined. All catalyst presented high methane conversions, close to the values predicted by thermodynamic equilibrium and such conversions increased in proportion to the metal surface of the catalyst tested. The temperature profiles at O2/CH4 = 0.2 and H2O/CH4 = 0.3 and a constant exit temperature of 700 °C varied depending on the catalyst type; it was possible to examine catalyst deactivation from the change in the shape of the profile of each catalyst. Since the O2/CH4 and H2O/CH4 ratios were low, the risk or potential for carbon formation was thermodynamically favorable along the entire catalytic bed; however, this potential was qualitatively higher when the temperature profile of the catalyst presented a pronounced maximum peak at the inlet of the reactor. During catalytic reaction tests and methane decomposition experiments, the ruthenium catalyst did not formed appreciable amounts of carbon while a bimetallic catalyst (Ni and Ru) form only small amounts (in comparison with the nickel catalysts). For the ruthenium catalyst, a higher O2/CH4 ratio favored conversions closer to the equilibrium value. The observations presented in this work indicate that during the CPO of methane, at low O2/CH4 ratios and in the presence of steam, the catalyst properties and composition will have a substantial influence on the extent of the combustion and reforming reactions along the catalytic bed. This will in turn define the temperature profile, and therefore the risk or potential for carbon formation; this risk might effectively be overcome by the use of ruthenium-containing catalysts.