Institute for Chemical and Bioengineering, Department of Chemistry and Applied Biosciences, ETH Zurich, Hönggerberg, Wolfgang-Pauli-Str. 10, CH-8093 Zürich, Switzerland.
Phys Chem Chem Phys. 2010;12(20):5307-16. doi: 10.1039/b926833b.
Modification of 5 wt% Pt/Al(2)O(3) by Bi (0.9 wt%) affords a drastic improvement of catalytic activity in the liquid phase aerobic oxidation of benzyl alcohol. The nature of the solvent employed, cyclohexane or toluene, seems to influence the catalytic activity as well. We have investigated the catalysts under working conditions using in situ X-ray absorption spectroscopy (XAS) and attenuated total reflection infrared spectroscopy (ATR-IR), aiming at uncovering the roles of the metal promoter and the reaction medium. XAS confirms that Bi is oxidized more easily than Pt, maintaining the catalytic activity of the metallic Pt sites for a longer period of time. Interestingly, toluene contrary to cyclohexane reduced Pt to a large extent. The freshly reduced noble metal sites seem to directly interact with the solvent, inducing an immediate poisoning of the material and limiting its performance. This behaviour is not observed in the presence of Bi, whose geometric effect (site blocking) is interpreted as additionally limiting the adsorption of toluene and the premature deactivation of Pt. ATR-IR spectroscopy during CO adsorption on Pt and during reaction indicates that Bi is located rather on extended surfaces than on step or kink sites. Side products, CO and benzoate species, appearing during the reaction reveal that the geometric suppression of undesired reactions does not occur to the same extent on Pt-based catalysts as on Pd, suggesting that decarbonylation of the produced aldehyde on Pt may occur also on sites other than the (111) terraces.
改性 5wt%Pt/Al(2)O(3)负载 0.9wt%Bi 显著提高了苯甲醇液相氧化的催化活性。所用溶剂环己烷或甲苯的性质似乎也影响了催化活性。我们在工作条件下使用原位 X 射线吸收光谱 (XAS) 和衰减全反射红外光谱 (ATR-IR) 对催化剂进行了研究，旨在揭示金属助催化剂和反应介质的作用。XAS 证实 Bi 比 Pt 更容易氧化，从而使金属 Pt 位的催化活性保持更长的时间。有趣的是，甲苯与环己烷相反，大量还原了 Pt。新鲜还原的贵金属位似乎直接与溶剂相互作用，导致材料立即中毒，并限制了其性能。在 Bi 的存在下没有观察到这种行为，其几何效应（位阻）被解释为进一步限制了甲苯的吸附和 Pt 的过早失活。在 Pt 上吸附 CO 和反应过程中的 ATR-IR 光谱表明，Bi 主要位于扩展表面而不是台阶或扭结位。反应过程中出现的副产物 CO 和苯甲酸表明，在 Pt 基催化剂上，对不需要的反应的几何抑制程度不如 Pd 那么大，这表明在 Pt 上可能在除 (111) 平台之外的其他位置也发生了产生的醛的脱羰反应。
