Pd catalysts supported on TiO₂ with different crystalline phases were prepared with formaldehyde as reducing agent and examined for hydrodeoxygenation (HDO) of guaiacol. Their properties were characterized by N₂ adsorption, X-ray diffraction, transmission electron microscopy, and X-ray photoelectron spectroscopy. Compared to the carbon-supported Pd catalysts, TiO₂-supported Pd catalysts exhibited higher C–O bond scission ability, which may be attributed to the presence of partially reduced titanium species originating from the reduction of Ti⁴⁺ by spillover hydrogen from Pd at 200 °C on the surface of TiO₂. Guaiacol was hydrogenated on Pd sites to give 2-methoxycyclohexanol, which diffused to partially reduced titanium species and subsequently reacted with hydrogen from Pd to generate cyclohexane. Anatase TiO₂-supported Pd catalyst gave the highest HDO activity of guaiacol among the Pd catalysts supported on three types of TiO₂ (anatase, rutile, and their mix, P25), suggesting that more partially reduced titanium species are in favor of the HDO reaction because anatase is facile to reduce by H₂ at 200 °C. Higher selectivity of cyclohexane for Pd/TiO₂ reduced at 500 °C than that reduced at 200 °C further confirmed that the enhanced C–O bond scission ability of Pd/TiO₂ is mainly attributed to the partially reduced titanium species on the surface of TiO₂.

中文翻译：

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不同二氧化钛载体上钯催化的愈创木酚催化加氢脱氧

以甲醛为还原剂，制备了负载在不同晶相TiO ₂上的Pd催化剂，并研究了愈创木酚的加氢脱氧反应（HDO）。它们的性质通过N ₂吸附，X射线衍射，透射电子显微镜和X射线光电子能谱表征。与碳负载的Pd催化剂相比，TiO ₂负载的Pd催化剂表现出更高的C–O键断裂能力，这可能归因于存在部分还原的钛物种，这是由于在Pd处氢从Pd溢出而导致的Ti ⁴⁺还原^所致。 TiO ₂表面温度200°C。愈创木酚在Pd位点上氢化，得到2-甲氧基环己醇，其扩散至部分还原的钛物种，然后与来自Pd的氢反应生成环己烷。锐钛矿型TiO ₂负载的Pd催化剂在三种类型的TiO ₂（锐钛型，金红石及其混合物P25）上负载的Pd催化剂中，愈创木酚的HDO活性最高。反应是因为锐钛矿很容易在200°C下被H ₂还原。在500°C下降低的环己烷对Pd / TiO _2的选择性高于在200°C下降低的对环己烷的选择性，进一步证实了Pd / TiO ₂的增强的C–O键断裂能力主要是由于TiO ₂表面上部分还原的钛物种。