Growth of carbon nanofibers from methane on a hydroxyapatite-supported nickel catalyst

Ewa Miniach,Grażyna Gryglewicz,Adam Moyseowicz,Agata Śliwak

doi:10.1007/s10853-016-9839-1

Ewa Miniach, Grażyna Gryglewicz + Show 2 more

Open Access

https://doi.org/10.1007/s10853-016-9839-1

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Abstract

Carbon nanofibers (CNFs) were grown using catalytic chemical vapor deposition (CCVD) with methane as the carbon source and a hydroxyapatite-supported nickel catalyst (Ni/HAp). The catalyst, which contained approximately 14 wt% Ni, was prepared using the incipient wetness method with an aqueous nickel nitrate solution. Temperature-programmed reduction and X-ray diffraction were used to characterize the active phase of Ni/HAp. Three variables were evaluated to optimize the CNF growth process, including the temperature and the time of catalyst reduction as well as the reaction time, at 650 °C. Regardless of the applied CCVD process conditions, herringbone bamboo-like CNFs were grown during methane decomposition over Ni/HAp, which was confirmed using transmission electron microscopy. A high CNF yield of nearly 10 gCNF g cat −1 was achieved at 650 °C after a reaction time of 3 h when the catalyst was subjected to a reduction at the same temperature for 2 h under a hydrogen flow prior to synthesis. As the reduction temperature increased from 450 to 650 °C, both the yield and diameters of the CNFs increased. The beneficial effects of including hydrogen in the reaction mixture on the catalytic performance of Ni/HAp and the purity of the grown CNFs were demonstrated.

Highlights

Carbon nanofibers (CNFs), which include carbon nanotubes (CNTs), have been synthesized since the 1960s
This study demonstrates that the use of hydroxyapatite as a support for a nickel catalyst results in the production of herringbone bamboo-like CNFs in a high yield with no amorphous carbon by chemical vapor deposition (CCVD) using a mixture of methane and hydrogen as the reactant gas
At a reaction temperature of 650 °C, the growth of CNFs and their diameter distribution strongly depended on the catalyst reduction temperature

Summary

Introduction

Carbon nanofibers (CNFs), which include carbon nanotubes (CNTs), have been synthesized since the 1960s. Affect CNF growth, such as the catalyst composition, reducibility of the catalyst, nature of the metal/support interaction, particle size of the active metal, synthesis temperature, carbon source, and composition of the reaction gas mixture [3,4,5,6]. HAp does not exhibit any catalytic activity during the high-temperature treatment [20] or create spinels that would lead to a reduction in the catalyst reducibility, which is often observed for alumina-supported nickel catalysts [24, 25]. In this study, selected variables of the CCVD process were studied to obtain CNFs with high yield and purity using a Ni/HAp catalyst and methane as the carbon source. CNFs were subsequently cooled to ambient temperature in a nitrogen atmosphere Both the catalyst reduction and the CNF synthesis were performed at atmospheric pressure. Thermogravimetric analysis (TGA) was performed on the purified CNFs using a TGA/DSC1 Mettler Toledo (thermobalance)

Results and discussion

Conclusions

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