Aqueous-phase hydrodeoxygenation of bio-derived phenols to cycloalkanes

The kinetics of the catalytic hydrodeoxygenation of phenol and substituted phenols has systematically been investigated on the dual-functional catalyst system Pd/C and H₃PO₄ in order to better understand the elementary steps of the overall reaction. The reaction proceeds via stepwise hydrogenation of the aromatic ring, transformation of the cyclic enol to the corresponding ketone, hydrogenation of the cycloalkanone to the cycloalkanol and its subsequent dehydration as well as the hydrogenation of the formed cycloalkene. The presence of dual catalytic functions is indispensible for the overall hydrodeoxygenation. The dehydration reaction is significantly slower than the hydrogenation reaction and the keto/enol transformation, requiring a significantly larger concentration of Brønsted acid sites compared to the available metal sites for hydrogenation.