Growth of nitrogen-doped filamentous and spherical carbon over unsupported and Y zeolite supported nickel and cobalt catalysts

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Unsupported and Y zeolite supported nickel and cobalt catalysts have been tested for the growth of nitrogen-doped structured carbon via the chemical vapour decomposition (CVD) of acetonitrile where 550 °C ≤ T ≤ 1150 °C. A range of carbonaceous structures, including carbon filaments with different lattice structures and carbon nanospheres were obtained. The graphitic character of the carbon product has been evaluated by means of temperature-programmed oxidation (TPO) and XRD analyses, surface area and porosity measurements for both catalyst and carbon product are provided and structural/morphological features illustrated by scanning and transmission electron microscopy (SEM and TEM). Carbon yield and morphology were strongly dependent on reaction temperature, the nature of the active metal and the use of a support. Carbon yield increased with increasing temperature (up to 1050 °C) to give maximum values in the order Ni < Co < Ni/Y < Co/Y. The supported catalysts delivered significantly higher carbon yields (up to 35 gcarbon/gmetal) and initiated carbon growth at temperatures up to 300 °C lower than that observed for the bulk metals. Carbon generated over Ni/Y and Co/Y at 750 °C took the form of high aspect ratio nanofibres where the arrangement of graphene layers exhibited a periodic variation at higher reaction temperatures to ultimately result in a predominant production of nanospheres at 1150 °C, rather attributed to a thermal than a catalytic route. Based on TPO analyses, carbon grown from bulk and supported Ni showed a higher degree of structural order compared with the Co promoted growth. An increase in reaction temperature served to enhance graphitic character. XRD analyses were in all the cases consistent with a graphitic product. Elemental (CHN) analysis of the carbon product has revealed a nitrogen content of up to 5 mol%.