Reduced graphene aerogel-supported Ir(C2H4)2 complexes at an exceptional Ir loading of 23.8 wt%: Confirming site-isolation by combining XAS and STEM

Abstract

Atomically dispersed supported metal catalysts offer significant opportunities when compared to conventional analogues. They provide maximum utilization of expensive noble metals, interesting catalytic properties, and understanding of structure-catalytic activity relationships [1]. These novel catalysts consist of supported single metal atoms bonded to ligands as well as clusters incorporating only a few metal atoms. However, they face certain challenges hindering their industrial use. The main challenges are their limited stability and limited metal loading. Typical metal loadings are limited with <1 wt.%. The support material is crucial in overcoming these challenges. Here, we used reduced graphene aerogel (rGA) as a novel support for Ir(C2H4)2 complexes and assessed the maximum metal loading we can reach. Thanks to the outstanding properties of rGA, such as excellent electronic properties, high porosity and surface area, and multiple bonding sites for Ir atoms, an exceptionally high Ir loading of 23.8 wt% was obtained. Aberration-corrected scanning transmission electron microscopy (STEM) images and X-ray absorption spectroscopy (XAS) data confirmed the site-isolation of Ir atoms at this exceptional loading. Figure 1 shows the STEM images of rGA-supported Ir(C2H4)2 complexes at an Ir loading of 23.8 wt%, a challenging sample because of the three-dimensional multilayer wrinkled-sheet structure of rGA. Besides, these images are one of the first atomic resolution images obtained on a Hitachi HF5000 Cs-corrected cold FEG STEM in Koç University. Results demonstrate the potential of rGA as a superior support material for expensive noble metal complexes to reach exceptional loadings.