Applied Catalysis A: General, Vol.333, No.1, 11-23, 2007
Catalytic partial oxidation of CH4 to H-2 over cobalt catalysts at moderate temperatures
Catalytic partial oxidation (CPO) of methane has been investigated over Co/Al2O3 catalysts with different metal (0.1 wt.% of Ni, Pt, Rh, Ru or Pd) and oxide (< 4 wt.% Fe3O4/Cr2O3, La2O3, SnO2 or K2O) promoters. A comparison with Ni- and Fe-based catalysts was performed. Methane conversions and selectivities were determined in the temperature range 200-750 degrees C at atmospheric pressure in a continuous fixed-bed quartz reactor. The scope was to identify factors for control of product selectivity and investigate the potential of low temperature operation. The unpromoted 10 wt.% Co/Al2O3 catalyst showed stable steady-state performance at 650 degrees C in the gas hourly space velocity range 15-180 N I CH4/g(cat) h. Equilibrium behaviour was observed during ramping (-1 degrees C/min) until a sudden extinction occurred around 450 degrees C, seemingly coinciding with O-2 breakthrough. Addition of 0.1 wt.% metal promoter, particularly Pt and Rh, caused the activity to be maintained to lower temperatures. While Rh maintained H-2 formation, Pt promoted combustion at low temperatures. Addition of 0.1 wt.% Ni by co-impregnation promoted carbon formation and deactivation. Addition of surface oxides typically promoted instability, deactivation and combustion. While the performance of Ni catalysts was superior to Co catalysts at low temperatures, Fe-based catalysts showed combustion activity in the whole temperature range. A hydrogen yield according to equilibrium predictions seems to be the best possible achievement. (c) 2007 Elsevier B.V. All rights reserved.