Liquid Phase Conversion of Phenols into Aromatics over Magnetic Pt/NiO–Al₂O₃@Fe₃O₄ Catalysts via a Coupling Process of Hydrodeoxygenation and Dehydrogenation

Magnetic colloidal sol was first prepared and added in the mixed solution of Ni(NO 3 ) 2 and Al(NO 3 ) 3 . After the constant-pH coprecipitation and calcination, magnetic NiO–Al 2 O 3 @Fe 3 O 4 mixed oxides were formed and used as supports for Pt-based catalysts. The activities of these magnetic Pt/NiO–Al 2 O 3 @Fe 3 O 4 catalysts were tested in the hydrodeoxygenation (HDO) of phenols such as 4-ethylphenol, 4-methylphenol, and guaiacol. These exhibited high HDO activity, and aromatic hydrocarbons were produced through a coupling process of hydrodeoxygenation and dehydrogenation. The addition of Fe enhanced both the conversion and aromatic hydrocarbons selectivity, which was attributed to the electron transfer between metallic Pt and Fe. For example, after the liquid phase HDO of 4-ethylphenol at 300 °C and 2.0 MPa for 1.5 h, 97.9% conversion and 18.3% toluene selectivity were obtained. When the reaction time was prolonged to 8 h, ethylbenzene selectivity increased to 88.0%. Moreover, these Pt/NiO–Al 2 O 3 @Fe 3 O 4 catalysts were easily recycled from the liquid reaction mixture by employing an external magnet, but the dehydrogenation stability needs to be further improved.