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

The simultaneous production of H-2 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 H-2 -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 H-2 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 H-2 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 H-2 production. Raman spectroscopy and XRD analyses demonstrated the formation of the best quality CNMs using the 20NiCu/SBA15 catalyst. (C) 2019 Hydrogen Energy Publications LLC. Published by Elsevier Ltd. All rights reserved.