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.