Molecular Design of Cluster Catalysts in Micropore and Selective Activation of Alkanes

在NaY沸石超笼内合成了羰基团簇Rh_<6-X>、Ir_X(CO)_<16> (X=0-6)和[Fe_2Rh_4(CO)_<16>]^<2->，制备了一系列金属/双金属催化剂。用FTIR、^<129>Xe NMR和CO/H化学吸附对羰基团簇的金属结构和电子态进行了表征，得到了稀土包裹的Rh_6、Ir_6、Rh_4Ir_2、Rh_3Ir_3和Rh_2Ir_4晶体。结果表明，NaY沸石内部的还原晶系为金属成分可控的簇系，经过氧化、还原和烷烃氢解等一系列反应，形成了较为稳定的晶系。试验反应为正丁烷和乙烷的加氢反应和苯的加氢反应。有趣的是，通过增加活性Rh系簇中适度的Ir原子的数量，可以观察到整个簇的氢解活性急剧下降了四个数量级，而苯的加氢活性则略有增强。对于丁烷氢解，双金属簇中较小的Rh系综对中心C-C键断裂产生C_2H_6具有最大的选择性。

A series of metal/bimetal catalysts have been prepared from the carbonyl clusters such as Rh_<6-X>Ir_X(CO)_<16> (X=0-6) and [Fe_2Rh_4(CO)_<16>]^<2-> which were synthesized inside NaY zeolite supercages. NaY-entrapped Rh_6, Ir_6, Rh_4Ir_2, Rh_3Ir_3, and Rh_2Ir_4 crystallites derived from the carbonyl clusters have been well characterized by FTIR, ^<129>Xe NMR, and CO/H chemisorption on their metallic structure and electronic states. The results suggested that the reduced crystallites inside NaY zeolite consisted of the cluster ensemble with the controlled metal compositions and fairly stabilized through several sequence of oxidation, reduction, and alkane hydrogenolysis. As the test reactions, hydrogenlysis of n-butane and ethane, and benzene hydrogenation were conducted. It is of interest to observe the dramatic decrease of hydrogenolysis activity by four order of magnitude across the series of clusters by increasing the number of modest Ir atoms in the active Rh ensembles, while a slight enhanacement activity for the benzene hydrogenation. For butane hydrogenolysis, the smaller Rh ensembles in the bimetallic clusters gave the maximum selectivities towards the central C-C bond scission to give C_2H_6.