Formation of carbon nanofibers with Ni catalyst supported on a micro-mesoporous glass

M.A Mazo,J Rubio,I Martín-Gullón,J Sanguino

doi:10.1016/j.micromeso.2021.111168

Abstract

The Ni/SiO2 system is one of the most interesting to produce COx-free H2 and valuable carbon nanofibers (CNFs) by the catalytic decomposition of CH4. SiO2 is one of the most effective support while Ni catalyst displays long life and high activity. We studied the catalytic chemical vapor deposition (CCVD) process of CH4 within Ni/glass system at relatively low temperature (600 °C) during long times (3 h), varying the amount of the catalyst (2.3–17.8% Ni(%)) and the carbon source (100:200 to 100:0, CH4:N2). As the amount of Ni and CH4 increases, the formation of CNFs is enhanced giving as a result CNFs/glass materials with more amount, longer and thicker CNFs. The initial microstructure of the glass support and the way of Ni catalyst is deposited play a decisive role. Pristine porous glass displays a microstructe of interconnected mesopores which are progressively filled with Ni, producing ink-bottle pores with open ends. After the CCVD process as the amount of Ni or CH4 increases, the porosity of the Ni-doped glass is reduced due to the progressively filling of the mesopores (4 nm) with CNFs. Furthermore, due to the formation of large entanglements of CNFs new pores appear (20–70 nm) depending on the processing conditions. Fish-bone with hollow core and bamboo-like CNFs are found over the surface and also inside the porous glass support. It is observed a base-growth mechanism due to the strong interaction between the catalyst and the support, which prevents the Ni deactivation enhancing its activity for long times.

Highlights

Carbon nanomaterials (CNs) such as carbon nanotubes (CNTs), car bon nanofibers (CNFs) and opened CNs have received much attention since the publication of Ijima’s works [1,2]
In the tip-growth mechanism, the deactivation of the Ni catalyst occurs by the deposition of certain amount of carbon at the tips of the CNFs [27]
In the case of the base-growth mechanism, the metal parti cles remain on the glass and this fact does not occur, offering new and very interesting possibilities of these materials, for example enhancing the time of catalytic life of Ni and so the formation of CNFs and COx-free H2 [30]

Summary

Introduction

Carbon nanomaterials (CNs) such as carbon nanotubes (CNTs), car bon nanofibers (CNFs) and opened CNs have received much attention since the publication of Ijima’s works [1,2]. Afterwards, many efforts have been made to solve this problem and, the proposed solutions included sonication, use of sur factants, purification and subsequent functionalization of CNs and the employment of the sol-gel method which enhances the dispersion and improves the interaction between the matrix and the reinforcement, [20,21,22]. All of these processes make the route longer, more expensive and include impurities which can directly affect the sintering pro cess and the final properties of the composites.

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