Methane Reaction with NO over Alumina-Supported Ru Nanoparticles

The reaction between NO (1%) and CH4 (0.55%) over alumina supported Ru nanoparticles is analyzed from NO abatement, methane partial oxidation, and structural sensitivity points of view. The 6 and 12 wt% Ru/Al2O3 catalysts were prepared by deposition of well-defined colloidal Ru nanoparticles on alumina. The NO was selectively converted to N2 starting from 450°C. Methane conversion to COx, H2, and H2O proved to be structure sensitive at 450°C and structure insensitive at T>450°C. Methane was selectively converted to CO2 at 450°C over the 12% Ru/Al2O3 catalyst having larger average Ru particle size (average particle size, 5.8 nm). Methane was oxidized to CO and CO2 over the 6% Ru/Al2O3 catalyst with smaller Ru nanoparticles (average particle size, 4.8 nm). It is concluded that, at low temperature (450°C), methane is preferentially converted to CO and H2 over small Ru nanoparticles. The highest reaction selectivity to CO (≈80%) and H2 (≈78%) was observed at 600°C for both catalysts investigated. Ru/Al2O3 catalysts showed high and stable catalytic activity in time (i.e., 96 h), even at high reaction temperature (600°C). A selectivity to CO and H2 of almost 100% was observed at 600°C for both a stoichiometric mixture of NO/CH4 and one with an excess of methane. The catalyst with smaller Ru nanoparticles (6% Ru/Al2O3) was rapidly deactivated either by O2 or by NO, whereas the catalyst with larger Ru particles (12% Ru/Al2O3) proved to be more resistant to oxygen poisoning. Both catalysts were rapidly reactivated in pure CH4. A reaction mechanism is proposed in light of the experimental results.