Microkinetic analysis of CH4 CPO tests with CO2-diluted feed streams Original Research Article

Autothermal CH4 catalytic partial oxidation (CPO) tests were performed in an adiabatic lab-scale reformer over 2 wt% Rh/α-Al2O3 catalysts supported on 600 cpsi cordierite honeycombs. The effect of adding either CO2 or N2 to CH4/air mixtures was investigated at constant O2/CH4 ratio (0.56) and total flow rate (10 Nl/min). At increasing dilution the conversion of CH4 and the gas temperatures decreased. Also, at equal CH4 concentration, the addition of CO2 decreased the temperatures and the conversion of CH4 more importantly than N2. Thus, in line with previous studies from this and other laboratories, no evidence of a direct dry reforming route was found; the observed thermal behavior appeared largely controlled by the heat capacity of the feed streams. However an important chemical effect of CO2 addition, not previously appreciated in the literature, was shown by the evolution of the outlet H2/CO ratio; at increasing N2 dilution, the H2/CO ratio slightly increased from about 2 to 2.5, but at increasing CO2 dilution, the H2/CO ratio decreased from about 1.7 to 0.7. These trends are in line with the thermodynamics of the reverse water gas shift (RWGS) reaction; such a reaction was thus extremely fast in all the experiments with CO2, even at the highest values of dilution, while CH4 conversion did not reach the equilibrium.