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?°C is reactive in nature, and results in its demethylation. The catalyst was tested at 100–300?°C, 5–40?bar H2 pressure. Conversion of 78?% was obtained at 5?bar and 300?°C, restricted by hydrogenation-dehydrogenation equilibrium. HDO mainly starts through the ring-hydrogenation pathway. This is followed by demethoxylation beyond 180?°C. 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?°C. 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.