Monoatomically dispersed Pd/TiO₂ catalyst effective for epoxidation of propylene at ambient temperature in the presence of H₂ and O₂

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• 作者：Susumu Hikazudani^a ; Tatsuya Mochida^b ; Naofumi Matsuo^b ; Katsutoshi Nagaoka^b ; Tatsumi Ishihara^c ; Hisayoshi Kobayashi^d ; Yusaku Takita^b ; ^{takita@cc.oita-u.ac.jp}
• 关键词：Propylene epoxidation ; Pd/TiO2 ; Monoatomically supported Pd ; Reaction mechanism ; Oxidation in the presence of H2
• 刊名：Journal of Molecular Catalysis A ; Chemical
• 出版年：2012
• 期刊代码：57_13811169
• 类别：ch
• 出版时间：June, 2012
• 卷：358
• 期：Complete
• 页码：89-98
• 文件大小：1492 K

摘要

The catalytic activity of monoatomically dispersed Pd supported on TiO₂ toward propylene epoxidation in the presence of H₂ and O₂ was studied at ambient temperature, and both propylene oxide (PO) and propane were obtained. Short-chain alkanes also reacted but epoxide formation was not observed in those reactions except in the case of isobutane, which formed isobutylene oxide at a low rate. The optimum surface concentration of Pd on TiO₂ was 0.005-0.01 atom/nm²; because the supported amount of Pd is extremely small relative to the surface area of the support, the supported Pd is thought to be monoatomically dispersed. Pd/TiO₂ catalysts prepared from a tetraphenylporphyrin-Pd chloride complex showed almost the same product distribution for propylene epoxidation as did catalysts prepared from Pd(NO₃)₂. Isotope exchange between H₂ and D₂ proceeded over Pd/TiO₂ with a low surface concentration (0.0001 atom-Pd/nm²), and chemical potential calculations suggested that H₂ molecules could dissociatively adsorb onto the monoatomically dispersed Pd/TiO₂. A PO formation mechanism over the catalyst is proposed on the basis of these results. The results presented here may provide the first clear evidence of catalysis by monoatomically dispersed noble metals.