A quantitative electron tomography study of ruthenium particles on the interior and exterior surfaces of carbon nanotubes.

The efficiency of filling carbon nanotubes (CNTs) by ultrasound-assisted wet impregnation is quantified by electron tomography (ET). For image analysis, a method that combines edge detection with single-value thresholding is proposed and validated. A high proportion (80 wt %) of the ruthenium was deposited inside the tube at an average particle size of 2-4 nm. Particles located on the outer surface of the CNT had a size of 1-3 nm. The local ruthenium loading measured by ET (3.2 wt %) closely matched the value from elemental analysis (3.5 wt %). In addition, a few 1 nm-sized ruthenium particles were detected inside the carbon wall, which contained pores/cracks. Direct imaging and quantification is a powerful tool to understand and possibly model the unique properties of CNT-based catalysts.