Non-oxidative conversion of real low density polyethylene waste into hydrogen and carbon nanomaterials over MgO supported bimetallic Co-Mo catalysts with different total Co-Mo contents

Abstract A series of bimetallic CoMo/MgO catalysts with different total metal contents from 10 up to 60 wt% and a fixed Co/Mo weight ratio of 4/1 were prepared and employed for the first time to transform real low-density polyethylene (LDPE) waste into hydrogen and carbon nanomaterials through a two-stage process. The waste was thermally cracked at 500 oC to non-condensable gases which then decomposed over CoMo/MgO catalysts at 700 oC to obtain the desired products. Both fresh and spent CoMo/MgO catalysts were characterized by XRD, H2-TPR, FTIR, Raman, BET, TEM, and TGA techniques. The results showed that the catalytic activity and stability were increased with the successive increase of CoMo content up to 40 wt%. Both 30CoMo/MgO and 40CoMo/MgO catalysts exhibited higher catalytic activity where more than 90% H2 yield was obtained. This behavior could be attributed to the excessive formation of different types of mixed oxide species such as MgCoOx, CoMoOx and MgMoOx as shown from XRD, TPR and Raman results. In fact, the presence of these species enhances the dispersion and stabilization of Co and Mo particles in the catalyst matrix, resulting in improved catalyst performance. TEM, Raman spectra, and TGA results showed that high-quality CNMs with various structures such as regular, bamboo, cup stacked carbon nanotubes were deposited over all CoMo/MgO catalysts depending on the CoMo content.