Efficient production of hydrogen and carbon nanotubes via the cracking of a waste cooking oil model compound over ordered mesoporous Ni/KIT-6 catalysts

Ni/KIT-6 catalysts were synthesized using ordered mesoporous silica-based KIT-6 molecular sieves as a support in conjunction with an impregnation method. These catalysts were characterized using transmission electron microscopy, X-ray diffraction, N2-Brunauer–Emmett–Teller surface area analysis and hydrogen temperature-programmed reduction. The results showed good dispersion of metallic nickel (Ni) on the surface of the KIT-6 and strong interactions between the metal and carrier. The surface areas of the catalysts were in the range of 387–788 m2/g and the average pore diameters were in the range of 5.5–8.6 nm. Following H2 reduction, these materials were applied to the catalytic cracking of a waste cooking oil model compound to produce hydrogen and carbon nanotubes in a laboratory-scale fixed bed reactor. A catalyst with a Ni loading of 10 wt% showed optimal catalytic activity. Reaction trials using an oil flow rate of 0.04 mL/min at 750 °C provided an instantaneous H2 volume-based proportion of 44.2% with a maximum H2 concentration in the gaseous products of 59.0% after 25 min. Analyses by thermogravimetry and Raman spectroscopy indicated that carbon nanotubes deposited on the spent catalyst had good oxidative stability and a high degree of graphitization.