Dilute PdAu alloys are promising catalysts for selective oxidation with high activity and high selectivity. The promotional effect of Pd for selective alcohol oxidation is strongly dependent on the alkyl chain length. Whereas Pd substantially promotes the selective oxidation of methanol, there is essentially no promotion of oxidation of longer-chain alcohols (C2–C4) for Pd₃Au₉₇ RCT-SiO₂ compared to pure Au RCT-SiO₂. The lack of promotion of selective oxidation of higher alcohols by Pd is attributed to their over-oxidation on the Pd₃Au₉₇ RCT-SiO₂ catalyst, yielding strongly bound carboxylates that poison the Pd sites. The longer-chain carboxylates are stable on the surface under reaction conditions whereas formate, which would form from over-oxidation of methanol, decomposes. The surface carboxylate was identified for 1-propanol oxidation as propionate using in situ Fourier transform infrared (FTIR) spectroscopy. Further evidence for poisoning by carboxylates is the production of CO₂ in temperature programmed oxidation following catalyst use. The poisoned catalyst can be regenerated in a flowing methanol/oxygen mixture, restoring the promotional effect of Pd for methanol oxidation. The residual activity of the Au and of the poisoned Pd/Au catalysts may be due to the migration of hydroxyl from the silica support to the nanoparticle. A reservoir of hydroxyl groups on the RCT-SiO₂ is identified using FTIR. Hydroxyls on Au are known to spontaneously disproportionate to adsorbed oxygen atoms and water. These results demonstrate the sensitivity of dilute alloy catalyst reactivity to molecular structure.

中文翻译：

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直链醇的选择性氧化：水对稀 PdAu 催化剂的促进作用和羧酸盐的抑制作用

稀PdAu合金是具有高活性和高选择性的有前途的选择性氧化催化剂。 Pd 对选择性醇氧化的促进作用很大程度上取决于烷基链长度。虽然 Pd 显着促进甲醇的选择性氧化，但与纯 Au RCT-SiO ₂相比， Pd ₃ Au ₉₇ RCT-SiO ₂基本上没有促进长链醇（C2-C4）的氧化。 Pd 对高级醇选择性氧化缺乏促进的原因是它们在 Pd ₃ Au ₉₇ RCT-SiO ₂催化剂上过度氧化，产生强结合的羧酸盐，使 Pd 位点中毒。长链羧酸盐在反应条件下在表面上稳定，而甲醇过度氧化形成的甲酸盐会分解。使用原位傅立叶变换红外 (FTIR) 光谱将表面羧酸盐鉴定为丙酸盐，用于 1-丙醇氧化。羧酸盐中毒的进一步证据是使用催化剂后在程序升温氧化中产生CO ₂ 。中毒的催化剂可以在流动的甲醇/氧气混合物中再生，恢复钯对甲醇氧化的促进作用。 Au 和中毒的 Pd/Au 催化剂的残余活性可能是由于羟基从二氧化硅载体迁移到纳米颗粒。使用 FTIR 识别RCT-SiO ₂上的羟基库。已知金上的羟基会自发歧化为吸附的氧原子和水。这些结果证明了稀合金催化剂反应性对分子结构的敏感性。