Reactivity of pure ethanol and acetaldehyde on Ni/MgO catalyst at different reaction temperatures was investigated confirming that hydrogen production is ascribable to a series of consecutive and/or parallel reactions. FT-IR studies on adsorbed dry molecules (ethanol or acetaldehyde) showed that ethanol decomposition occurs on catalyst surface through formation of acetaldehyde, which is converted to acetates and then to carbonates, or decomposes to CO, C and H-2.