Carbon formation and its influence on ethanol steam reforming over Ni/Al2O3 catalysts

Ethanol steam reforming was studied over Ni/Al2O3 catalysts. The effect of support (α- and γ-Al2O3), metal loading and a comparison between conventional H2 reduction with an activation method employing a CH4/O2 mixture was investigated. The properties of catalysts were studied by N2 physisorption, X-ray diffraction (XRD) and temperature programmed reduction (TPR). After activity tests, the catalysts were analyzed by scanning electron microscopy (SEM) and thermogravimetric analysis (TG/DTA). Ni supported on γ-Al2O3 was more active for H2 production than the catalyst supported on α-Al2O3. Metal loading did not affect the catalytic performance. The alternative activation method with CH4/O2 mixture affected differently the activity and stability of the Ni/γ-Al2O3 and the Ni/α-Al2O3 catalyst. This activation method increased significantly the stability of Ni/α-Al2O3 compared to H2 reduction. SEM and TG/DTA analysis indicate the formation of filamentous carbon during the CH4/O2 activation step, which is associated with the increasing catalyst activity and stability. The effect of temperature on the type of carbon formed was investigated; indicating that filamentous coke increased activity while encapsulating coke promoted deactivation. A discussion about carbon formation and the influence on the activity is presented.