Effect of P on hydrodeoxygenation performance of Ni–P/SiO2 catalysts for upgrading of m-cresol

Abstract

To deeply understand the role of P in hydrodeoxygenation (HDO), SiO₂-supported Ni and Ni–P catalysts with different P/Ni ratios (x) were prepared. The as-prepared samples were characterized by various characterization methods. The HDO activity and product distribution over the Ni/SiO₂ and N–P/SiO₂-x were compared and the effects of x on the structure, acidity, formation mechanism of active phases and HDO performance were studied taking m-cresol HDO as a model reaction. The results showed that the introduction of P promotes the formation of smaller active sites and contributes to the creation of weak and medium strength acid sites through the formation of P–OH groups and Ni^δ+ in Ni₂P. HDO over the Ni/SiO₂ catalyst occurs mainly via the hydrogenation (HYD) route with 3-methyl-cyclohexanol (3-MCHnol) as the main product. However, for Ni–P/SiO₂-x catalysts, methyl-cyclohexane (MCH) selectivity increases first and then decreases with the increase of x, reaching a maximum of 95% at x = 1. The acidity generated by the introduction of P contributes to increased MCH selectivity, while the dehydration of 3-MCHnol to MCH occurs mainly on acid sites. However, the excessively high P content (x ≥ 2.0) leads to a significant increase of MB (toluene) selectivity, which is associated with the increase in Ni(I) sites. About 100% m-cresol conversion was achieved with Ni–P/SiO₂-1.0 when the m-cresol (g)/catalyst (g) ratio was 3, with MCH (99.4%) as the major product, showing great promise for deep HDO catalysis.