Flame pyrolysis prepared catalysts for the steam reforming of ethanol: effect of support basicity

A set of Ni catalysts supported over ZrO2 for the steam reforming of ethanol were prepared by two different procedures to evaluate the influence of the preparation method on the catalytic performance. Flame pyrolysis (FP) is a one step high temperature synthesis and usually imparts a strong metal-support interaction, besides high thermal resistance. It was compared with traditional precipitation/impregnation method (multistep synthesis). The samples were thoroughly characterized by AAS, XRD, N2 adsorption-desorption, TPR, SEM, TEM and FT-IR. Activity testing for the steam reforming of ethanol was performed after activation at 500°C in H2 flow by means of a continuous micropilot plant, by feeding a 3:1 (mol:mol) mixture of water/ethanol. Testing has been carried out at 500°C, 400°C and 300°C for 8 h-on-stream. Spent catalysts were characterized by TPO, TEM, FE-SEM and Raman analysis. Very high activity has been observed at high reaction temperature (>600°C), but it would be interesting to operate under milder conditions, in order to lower the energy input to the process and to improve H2 productivity by favoring the water gas shift reaction. The main issue at low operating temperature is coke accumulation, which leads to fast catalyst deactivation. The catalytic performances, in terms of stability towards coking, were related to the metal–support interaction. Acidity was tuned by doping ZrO2 with alkali and alkali-earth oxides, helping to prevent ethanol dehydration and coking by ethylene polymerization. The FP method allowed to prepare samples very resistant to coking, and alkali doping was a successful strategy to improve catalyst life.