Co-production of hydrogen and carbon nanomaterials using NiCu/SBA15 catalysts by pyrolysis of a wax by-product: Effect of Ni–Cu loading on the catalytic activity

Abstract

The simultaneous production of H2 and carbon nanomaterials (CNMs) over NiCu/SBA15 catalysts with different Ni–Cu contents (10, 20, 30, 40 and 50 wt%) was investigated using the pyrolysis-catalysis process of paraffin wax. The fresh and spent catalysts were characterized by various techniques including H2-TPR, XRD, TEM, Raman spectroscopy and BET surface area. TEM observations showed that broad particle size distributions were formed in fresh 40NiCu/SBA15 and 50NiCu/SBA15 catalysts, while catalysts with smaller Ni–Cu contents displayed better metals dispersion. We found that the catalyst activity is related to the type of carbon nanomaterials, catalyst particle size, and catalyst loading with Ni–Cu. Also, the largest yield of H2 and CNMs was achieved using the 30NiCu/SBA15 catalyst. NiCu/SBA15 catalysts with Ni-Cu contents of 30–50 wt% exhibited good catalytic stability and similar activity in terms of H2 yield, especially at reaction time above 225 min. Small diameters carbon nanofibers (CNFs) were produced over the 10NiCu/SBA15 catalyst, while a mixture of CNFs and carbon nano-onions (CNOs) was produced using catalysts with Ni-Cu loadings of 20–50 wt%. The generation of octopus-like CNFs over large catalyst particles was associated with the observed catalytic stability of H2 production. Raman spectroscopy and XRD analyses demonstrated the formation of the best quality CNMs using the 20NiCu/SBA15 catalyst.