Barbaro Pierluigi, Bianchini Claudio, Dal Santo Vladimiro, Meli Andrea, Moneti Simonetta, Psaro Rinaldo, Scaffidi Adriana, Sordelli Laura, Vizza Francesco
ICCOM-CNR, Area di Ricerca CNR di Firenze, Via Madonna del Piano 10, 50019 Sesto Fiorentino, Florence, Italy.
J Am Chem Soc. 2006 May 31;128(21):7065-76. doi: 10.1021/ja060235w.
The complex Rh(cod)(sulfos) (Rh(I); sulfos = (-)O(3)S(C(6)H(4))CH(2)C(CH(2)PPh(2))(3); cod = cycloocta-1,5-diene), either free or supported on silica, does not catalyze the hydrogenation of benzene in either homogeneous or heterogeneous phase. However, when silica contains supported Pd metal nanoparticles (Pd(0)/SiO(2)), a hybrid catalyst (Rh(I)-Pd(0)/SiO(2)) is formed that hydrogenates benzene 4 times faster than does Pd(0)/SiO(2) alone. EXAFS and DRIFT measurements of in situ and ex situ prepared samples, batch catalytic reactions under different conditions, deuterium labeling experiments, and model organometallic studies, taken together, have shown that the rhodium single sites and the palladium nanoparticles cooperate with each other in promoting the hydrogenation of benzene through the formation of a unique entity throughout the catalytic cycle. Besides decreasing the extent of cyclohexa-1,3-diene disproportionation at palladium, the combined action of the two metals activates the arene so as to allow the rhodium sites to enter the catalytic cycle and speed up the overall hydrogenation process by rapidly reducing benzene to cyclohexa-1,3-diene.
配合物Rh(cod)(sulfos)（Rh(I)；sulfos = (-)O(3)S(C(6)H(4))CH(2)C(CH(2)PPh(2))(3)；cod = 环辛-1,5-二烯），无论是游离态还是负载在二氧化硅上，在均相或非均相体系中均不能催化苯的氢化反应。然而，当二氧化硅负载有钯金属纳米颗粒（Pd(0)/SiO(2)）时，会形成一种混合催化剂（Rh(I)-Pd(0)/SiO(2)），其氢化苯的速度比单独的Pd(0)/SiO(2)快4倍。原位和非原位制备样品的扩展X射线吸收精细结构（EXAFS）和漫反射红外傅里叶变换光谱（DRIFT）测量、不同条件下的间歇催化反应、氘标记实验以及模型有机金属研究综合表明，铑单中心与钯纳米颗粒在整个催化循环中通过形成独特的实体相互协作促进苯的氢化反应。除了降低钯上1,3-环己二烯歧化反应的程度外，两种金属的协同作用还活化了芳烃，从而使铑中心能够进入催化循环，并通过将苯快速还原为1,3-环己二烯来加速整个氢化过程。
