Selective Hydrodeoxygenation of Guaiacol to Phenolics by Ni/Anatase TiO2 Catalyst Formed by Cross-Surface Migration of Ni and TiO2

加氢脱氧 愈创木酚 催化作用 锐钛矿 覆盖层 初湿浸渍 无定形固体 金红石 材料科学 化学工程 无机化学 化学 有机化学 选择性 光催化 冶金 物理化学 工程类
作者
Xiaoqiang Zhang,Peifang Yan,Bin Zhao,Kairui Liu,Mayfair C. Kung,Harold H. Kung,Shanyong Chen,Z. Conrad Zhang
出处
期刊:ACS Catalysis [American Chemical Society]
卷期号:9 (4): 3551-3563 被引量:97
标识
DOI:10.1021/acscatal.9b00400
摘要

The catalytic properties of physical mixtures of Ni particles (100–200 nm) with nanoparticles of anatase TiO2 (TiO2-A), ZrO2, Al2O3, rutile TiO2 (TiO2-R), and CeO2 were investigated for the hydrodeoxygenation (HDO) of guaiacol. High selectivities to phenolics were obtained only for Ni mixed with anatase TiO2 (Ni and TiO2-A), while saturated hydrocarbons were the main products for the mixtures with other supports. By thermal treatment in hydrogen gas only at 300 °C or higher and subsequently separating the large Ni particles from the TiO2-A particles with a magnet, it was further discovered that there was migration of TiO2 from TiO2-A onto the large Ni particles, resulting in an amorphous TiO2 overlayer on the Ni particles as evidenced by high-resolution TEM, and vice versa, migration of Ni onto TiO2-A. The TiO2 overlayer rendered the Ni particles completely inactive as a hydrogenation/hydrodeoxygenation catalyst. Conversely, the small amounts of Ni (<1.5 wt %) migrated onto TiO2-A formed highly dispersed Ni, undetectable by high-resolution TEM (<2 nm), that were remarkably highly active for HDO of guaiacol, producing selectively phenolics. Such highly selective HDO catalysts could also be formed by incipient wetness impregnation of Ni in loadings above 2 wt % onto the TiO2-A, but it was essential to pretreat the sample in H2 at 300 °C or higher. Pretreatment in H2 at 200 °C 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. The results suggested that two types of Ni species existed on the TiO2-A surface. One type consisted of a cluster of Ni atoms that were dominant on larger Ni particles that were active in aromatic ring hydrogenation and hydrodeoxygenation. They were readily covered by reducible TiO2-A at 300 °C or higher due to the traditional strong metal support interaction (SMSI) effect and became inactive. Another type was clusters of a very small number of Ni atoms, perhaps one atom, that were present as highly dispersed Ni clusters interacting strongly with the defect sites of TiO2-A. The strong interaction of this type of Ni with the TiO2 defect deterred TiOx migration allowing surface exposed Ni atoms to catalyze the HDO of guaiacol with very high selectivities that were not characteristic of typical Ni particles.
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