(682c) Selective Hydrodeoxygenation of Guaiacol to Phenolics By Anatase TiO2 supported Ni Atoms

Guaiacol (2-methoxyphenol) is a model compound for representative products from lignin-derived bio-oils. The performance in hydrodeoxygenation of guaiacol is widely used to evaluate catalysts for their potential industrial use. In this work, we report that highly selective hydrodeoxygenation of guaiacol to phenol, without saturated hydrocarbons and aromatics, was obtained with Ni supported on anatase TiO₂prepared by incipient wetness impregnation of Ni onto the TiO₂-A, but it was essential to pretreat the sample in H₂at 300 ^oC or higher. Pretreatment in H₂at 200 ^oC generated catalysts that produced saturated ring products. The activity of the impregnated catalysts, as measured by guaiacol conversion, increased linearly with Ni loading below 0.5 wt%. The activity continued to increase with Ni loading but more slowly up to 2 wt%, beyond which there was little further change. Large Ni particles were formed at high Ni loadings, but the large Ni particles are covered by a layer of TiOx which are verified to be totally inactive for hydrogenation of guaiacol. Highly dispersed Ni with very small number of Ni atoms, perhaps one atom interacts strongly with the defect sites of TiO₂-A. The strong interaction of this type of Ni with the TiO₂defect deterred TiO_xmigration allowing surface exposed Ni atoms to catalyze the HDO of guaiacol with very high selectivities that were not characteristic of typical Ni particles. In contrast, Ni supported on rutile TiO₂ catalyzes the saturation of the aromatic ring due to the poor reducibility of rutile TiO₂, and thus weak interaction of the support with Ni particles.