The tendency of coke formation was investigated using nickel catalysts supported on calcium and barium hexaaluminates, compared with a commercial catalyst of natural gas steam reforming. It was developed a methodology in a microactivity unit using cyclohexane as model compound and hydrogen as gas carrier, at low temperature (300-500 A degrees C). After the coking tests, the catalysts were characterized by elemental analysis (CHN) and thermogravimetric analysis using air and steam. 6NiO-BaAl presented the lowest coke removal rate with air. After that, the methodology was modified for ethanol and acetic acid, important model compounds used in studies of biofuels, steam reforming and bio-oil pyrolysis. All model compounds lead to carbon formation with the same chemical nature, as indicated by the temperature of the oxidation peak. So, the methodology can be used as a tool for selection of catalysts. Additionally, cyclohexane and acetic acid are ideal model compounds, because of the lowest and highest coke removal rates with air. [GRAPHICS]