Design of Silica Nanoparticles-Supported Metal Catalyst by Wet Impregnation with Catalytic Performance for Tuning Carbon Nanotubes Growth

Tairan Da Cunha,Alberto Maulu,Didier Arl,Yves Fleming,Jérôme Guillot,Damien Lenoble,Benoit Duez

doi:10.3390/catal11080986

Abstract

The catalytic activity of cobalt and iron nanoparticles for the growth of carbon nanotubes (CNTs) was studied by a specific reproducible and up-scalable fabrication method. Co and Fe catalysts were deposited over SiO2 nanoparticles by a wet-impregnation method and two different annealing steps were applied for the catalyst formation/activation. The samples were calcined at an optimal temperature of 450 °C resulting in the formation of metal oxide nano-islands without the detection of silicates. Further reduction treatment (700 °C) under H2 successfully converted oxide nanoparticles to Co and Fe metallic species. Furthermore, the catalytic efficiency of both supported-metal nanoparticles at 2 and 5% in weight of silica was evaluated through the growth of CNTs. The CNT structure, morphology and size dispersion were tailored according to the metal catalyst concentration.

Highlights

The range of temperatures and/or pressures is driving the decomposition of the precursor as the strength of interaction between the metal ion and the ligands is modified [37]
The thermal decomposition of organometallic precursors used for the wet impregnation of SiO2 is a critical step to maximise the chemisorption/physisorption on 3D supports [38]
We further investigate the thermal decomposition behaviour of the samples by coupling thermogravimetric analyses (TGA) under argon with a mass spectrometer (TGA-mass spectroscopy (MS)) in order to obtain a molecular fingerprint of the released species as a function of the temperature

Summary

Introduction

Transition metals are widely used as a catalyst for the CNT growth [15] This group of metals presents a specific electronic structure, where the increase of unfilled d-orbitals enhances the bonding with carbon. Au or Pd (fully filled d-orbitals) present a low affinity with carbon, while elements with vacant d-orbitals such as Ti and Nb tend to form carbides (strong bond) [16]. For this reason, Fe and Co stand out as commonly used metal catalyst for CNT growth relying on their high solubility of carbon as well the high diffusion rate of carbon in these elements [17]

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Conclusion