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

以NaY分子筛超笼内合成的羰基簇合物Rh_&lt；6-X&gt；Ir_X(CO)_&lt；16&gt；(X=0-6)和[Fe_2Rh_4(CO)_&lt；16&gt；]^&lt；2-&gt；为原料，制备了一系列金属/双金属催化剂。用FTIR、~(129)&GT；Xe~(2+)和CO/H化学吸附等方法对羰基簇合物中NaY掺杂的Rh_6、Ir_6、Rh_4Ir_2、Rh_3Ir_3和Rh_2Ir_4微晶的金属结构和电子态进行了表征。结果表明，NaY沸石中的还原微晶由金属组成受控的团簇组成，并通过氧化、还原和烷烃氢解等几个步骤达到了较好的稳定性。作为试验反应，进行了正丁烷和乙烷的加氢反应和苯加氢反应。值得注意的是，通过增加活性Rh系综中适度Ir原子的数量，整个原子团簇的氢解活性急剧下降了四个数量级，而苯加氢活性略有增强。对于丁烷氢解，双金属团簇中较小的Rh系综对中心C-C键断裂的选择性最高，生成C_2H_6。

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.