Effect of structural promoters on the catalytic performance of cobalt-based catalysts during natural gas decomposition to hydrogen and carbon nanotubes

Abstract

ABSTRACTCatalytic thermal decomposition of natural gas to CO/CO2-free hydrogen production was studied over cobalt catalysts supported on Al2O3, MgO, and SiO2. The physico-chemical properties of the fresh catalysts were investigated by X-ray diffraction (XRD), temperature-programmed reduction (TPR), and surface area. In addition, the morphological structure of as-deposited carbon over the spent catalysts was characterized by transmission electron microscope (TEM), Raman spectroscopy, thermogravimetric analysis, and XRD. The obtained results proved that the catalytic activity and longevity of the cobalt-based catalysts strongly depended on the nature of the applied support. Among the catalysts tested, the Co/Al2O3 catalyst exhibited the highest activity and stability due to the higher dispersion and stabilization of cobalt particles because of formation of CoAl2O3 spinel phase. The lower activity of Co/SiO2 catalyst is mainly attributed to the aggregation of cobalt metal particles because of weak metal–support interaction. It was observed that both type and morphological structure of deposited carbon were strictly depended on the nature of the support. TEM images revealed that multi-walled carbon nanotubes were produced over Al2O3- and MgO-supported catalysts, whereas both carbon nanofibers and amorphous carbon were formed over the Co/SiO2 catalyst.