Evaluation of anisole hydrodeoxygenation reaction pathways over a Ni/Al2O3 catalyst

Abstract

Anisole is a model molecule for studying hydrodeoxygenation (HDO) of lignin -derived oxygenates. Here we elucidate its HDO pathway over 10 % Ni/Al2O3 catalyst. Adsorption experiments showed that anisole is adsorbed on the acidic sites of the Al2O3 . Anisole adsorption at 200 -300 degrees C is reactive in nature, and results in its demethylation. The catalyst was tested at 100 -300 degree celsius, 5 -40 bar H-2 pressure. Conversion of 78 % was obtained at 5 bar and 300 degrees C, restricted by hydrogenation -dehydrogenation equilibrium. HDO mainly starts through the ringhydrogenation pathway. This is followed by demethoxylation beyond 180 degree celsius. At 5 -12 bar, cyclohexane dehydrogenates to benzene. This was confirmed by conducting an HDO experiment with methoxycyclohexane. At lower pressure deoxygenation is favored; and demethylation is accompanied with methylation of the aromatic ring, for temperature >260 degree celsius Investigation of the initial reaction stages showed that anisole HDO on Ni/Al2O3 catalyst proceeds via two independent pathways i.e., reactive adsorption/(de)methylation and aromatic ring hydrogenation.