High combustion activity of methane induced by reforming gas over Ni/Al2O3 catalysts

During the reactions related to oxidative steam reforming and combustion of methane over alpha-alumina-supported Ni catalysts, the temperature profiles of the catalyst bed were studied using an infrared (IR) thermograph. IR thermographical images revealed an interesting result: that the temperature at the catalyst bed inlet is much higher under CH4/H2O/o(2)/Ar = 20/10/20/50 than under CH4/H2O/O-2/Ar = 10/0/20/70; the former temperature is comparable to that over noble metal catalysts such as Pt and Pd. Based on the temperature-programmed reduction and oxidation measurements over fresh and used catalysts, the metallic Ni is recognized at the catalyst bed inlet under CH4/H2O/O-2/ Ar = 20/10/20/50, although it is mainly oxidized to NiAl2O4 under CH4/H2O/O-2/Ar = 10/0/20/70. This result indicates that the addition of reforming gas (CH4/H2O = 10/10) to the combustion gas (CH4/O-2 = 10/20) can stabilize Ni species in the metallic state even under the presence of oxygen in the gas phase. This would account for its extremely high combustion activity. (c) 2005 Elsevier B.V. All rights reserved.