Dual production of turquoise hydrogen and hybrid carbon nano materials from plastic waste over Co-Mo/Al-Mg catalysts

Abstract An optimized Co–Mo/Al₂O₃–MgO catalyst composition was developed to achieve stable and prolonged catalytic performance for the production of turquoise hydrogen from low-density polyethylene (LDPE) waste while simultaneously tailoring the morphology of the resulting carbon nanomaterials. To investigate the influence of support composition on catalytic performance, a series of Al₂O₃–MgO binary oxide supports with different weight ratios (Al75:Mg25, Al50:Mg50, and Al25:Mg75) were synthesized. The prepared supports and their corresponding fresh and spent catalysts were comprehensively characterized using FTIR, Raman spectroscopy, X-ray diffraction (XRD), BET surface area analysis, transmission electron microscopy (TEM), and thermogravimetric analysis (TGA). Among the Al₂O₃–MgO mixed-oxide-supported catalysts, Co–Mo/Al 25 –Mg 75 exhibited the highest hydrogen concentration and produced well-graphitized multi-walled carbon nanotubes (MWCNTs). In contrast, Co–Mo/Al 75 –Mg 25 exhibited the lowest hydrogen production and promoted the formation of turbostratic carbon, graphitic flakes, carbon nanofibers (CNFs), dense graphene layers, and carbon nano-onions (CNOs) encapsulating Co particles. Although CoMo/MgO exhibited the highest hydrogen concentration overall among all the investigated catalysts, Co–Mo/Al 25 –Mg 75 provided the best overall catalytic performance when hydrogen production was considered together with the yield and graphitization quality of the carbon nanomaterials. These findings demonstrate that optimizing the Al₂O₃–MgO support composition effectively balances hydrogen production and carbon nanomaterial growth during catalytic conversion of plastic waste.