Activation of Methane by Rhodium Clusters on a Model Support C<sub>20</sub>H<sub>10</sub>
Xi‐Guan Zhao, Zhongpu Zhao, Yan‐Xia Zhao, Sheng‐Gui He
Abstract
Supported metals represent an important family of catalysts for the transformation of the most stable alkane, methane, under mild conditions. Here, using state-of-the-art mass spectrometry coupled with a newly designed double ion trap reactor that can run at high temperatures, we successfully immobilize a series of Rh n – ( n = 4–8) cluster anions on a model support C 20 H 10 . Reactivity measurements at room temperature identify a significantly enhanced performance of large-sized Rh 7,8 C 20 H 10 – toward methane activation compared to that of free Rh 7,8 – . The “support” acting as an “electron sponge” is emphasized as the key factor to improve the reactivity of large-sized clusters, for which the high electron-withdrawing capability of C 20 H 10 dramatically shifts the active Rh atom from the apex position in free Rh 7 – to the edge position in “supported” Rh 7 – to enhance CH 4 adsorption, while the flexibility of C 20 H 10 to release electrons further promotes subsequent C–H activation. The Rh atoms in direct contact with the support serve as electron-relay stations for electron transfer between C 20 H 10 and the active Rh atom. This work not only establishes a novel approach to prepare and measure the reactivity of “supported” metal clusters in isolated gas phase but provides useful atomic-scale insights for understanding the chemical behavior of carbon (e.g., graphene)-supported metals in heterogeneous catalysis.