NiCu-based catalysts for the low-temperature hydrodeoxygenation of anisole: Effect of the metal ratio on SiO2 and γ-Al2O3 supports

Abstract

The effects of the metal ratio of NiCu catalysts on the low-temperature hydrodeoxygenation (HDO) of anisole were assessed on a neutral SiO₂ and an acidic γ-Al₂O₃ support. The activity of SiO₂-supported catalysts increases with the Ni content in the NiCu phase, related to Ni’s hydrogenation capacity. In contrast, on a γ-Al₂O₃ support, the activity decreases with the Ni content. Overall, Al₂O₃-supported catalysts, exhibiting a smaller NiCu alloy particle size, are more active than SiO₂-supported ones. In terms of selectivity, SiO₂-supported catalysts mainly hydrogenate anisole to methoxycyclohexane, while, particularly at higher conversions, γ-Al₂O₃-supported catalysts are able to further convert methoxycyclohexane to cyclohexane, demonstrating the importance of acid sites for low-temperature HDO. The Ni/Cu ratio also steers the selectivity, but not the catalyst stability. Deactivation phenomena are only support dependent: while on SiO₂-supported catalysts, active site sintering occurs, attributed to weak stabilization of metal particles by the support, acid catalyzed coking is the main cause of deactivation on the γ-Al₂O₃-supported catalysts.