NiAlCe mixed oxides obtained from layered double hydroxides applied to anisole hydrodeoxygenation

Bio-oil derived from the pyrolysis of lignocellulosic biomass residues cannot be used directly as biofuel due to the high content of oxygenated compounds. As an alternative, bio-oil must undergo a deoxygenation process, such as catalytic hydrodeoxygenation (HDO). In this sense, this work studied the effect of different concentrations of Ce3+ and Ce4+ in layered double hydroxides (LDHs) in order to obtain mixed oxide catalysts containing NiAlCe (NiO-NiAl2O4-CeO2) with low cost and high performance for the hydrodeoxygenation of anisole as a model biooil compound. Mixed oxides were obtained from the thermal decomposition of layered double hydroxides (LDHs) by using terephthalic acid as compensation anion, with molar ratio: Ni2+/(Al3++ M) = 1.0, where M = Ce3+; Ce4+ or Ce3+-Ce4+; and Al/Ce ratios of 9 and 1. Characterization analyses confirmed the formation of LDHs for all materials, although at lower Al/Ce ratio it is observed a loss of crystallinity, due to a greater repulsion and distortion of the layer structure caused by the incorporation, in greater amount, of cations with a high ionic radius. The increase in the content of cerium in mixed oxides also led to an increase in the acidity of the catalysts, in addition to a reduction in the surface area, justified by the pore blockage by CeO2 on the catalyst surface. The greater structural and thermal stability was evidenced in the LDHs derived from Ce4+, as well as a greater dispersion of the NiO phase in the corresponding mixed oxides, and therefore presenting greater anisole conversion. The obtained data indicated that the presence of Ce4+ ions on the catalyst surface was decisive in the conversion of anisole to cyclohexane, the main deoxygenated product, obtained via the direct deoxygenation and hydrogenation mechanism.

Automated summary

This study investigated the effect of different Ce3+ and Ce4+ concentrations in layered double hydroxides (LDHs) to obtain low-cost and high-performance mixed oxide catalysts for the deoxygenation process of high-oxygenated compounds in bio-oil. The presence of Ce4+ ions was found to play a crucial role in the activity of the catalysts. This research provides technical support for the utilization of bio-oil.