Effects of CeO₂, TiO₂, and TiO₂-CeO₂ Supports on Catalytic Performance of Ni₂P in Hydrodeoxygenation of Anisole

Abstract

This work examined the effects of supports for nickel phosphide (Ni2P) catalysts on anisole hydrodeoxygenation (HDO) using synthesized CeO2, TiO2, and TiO2-CeO2 supports and commercial supports (denoted as CeO2-L and TiO2-L) along with bulk Ni2P. Characterization revealed that Ni2P nanoparticles were well dispersed on the synthesized CeO2. Ni2P/CeO2 exhibited the highest activity on a catalyst weight basis among those Ni2P on synthesized supports as well as the common materials such as SiO2, Al2O3, and activated carbon. Ni2P/TiO2-CeO2 (at a Ti/Ce molar ratio of 0.98) afforded superior reactivity to Ni2P/CeO2 based on turnover frequency (TOF, h–1), which points to more active sites on Ni2P/TiO2-CeO2 than on Ni2P/CeO2. The TOF of anisole on catalysts decreased in the following order: Ni2P/Ti0.98Ce0.02O2 > Ni2P/TiO2 > Ni2P/CeO2 > bulk Ni2P. The type of supports employed for Ni2P also influenced the product distributions and thus HDO pathways. Ni2P/CeO2 favored benzene selectivity, and this may be related to the relative electron enrichment on the Niδ+ site of Ni2P/CeO2 that facilitated benzene desorption from the catalyst surface after demethoxylation of anisole. Ni2P/TiO2-CeO2 exhibited significantly higher cyclohexane selectivity, which may be attributed to the lower electron density on Niδ+ of Ni2P/TiO2-CeO2 and the acidity of binary support, promoting the deep hydrogenation of benzene to cyclohexane. The presence of phenol when Ni2P/TiO2 and Ni2P/TiO2-CeO2 were employed in anisole HDO could be correlated with the acidity of TiO2, which led to methylation of anisole. Adding a small amount of CeO2 in TiO2 and using it as support synergistically improved the TOF and suppressed phenol formation while increasing cyclohexane selectivity. Both Ni2P/CeO2 and Ni2P/TiO2-CeO2 are promising catalysts in anisole HDO for the tunable target products of benzene and cyclohexane, respectively.