A novel Ni-Mg-Al-CaO catalyst with the dual functions of catalysis and CO₂ sorption for H₂ production from the pyrolysis-gasification of polypropylene

A novel Ni-Mg-Al-CaO catalyst/sorbent has been prepared by integration of the catalytic and CO₂ absorbing properties of the material to maximise the production of hydrogen. The prepared catalyst was tested for hydrogen production from the pyrolysis-gasification of polypropylene by using a two-stage fixed-bed reaction system. X-ray diffraction (XRD), thermogravimetric analysis (TGA) and scanning electron microscopy (SEM)-energy dispersive X-ray spectrometry (EDXS) were used to characterize the prepared Ni-Mg-Al-CaO catalyst/sorbent. Ni-Mg-Al-CaO and calcined dolomite showed a stable carbonation conversion after several cycles of carbonation/calcination, while CaO showed a certain degree of decay. The calcined dolomite showed low efficiency for hydrogen production from pyrolysis-gasification of polypropylene. Increasing the gasification temperature resulted in a decrease of H₂/CO ratio for the Ni-Mg-Al catalyst mixed with sand; however, a stable H₂/CO ratio (around 3.0) was obtained for the Ni-Mg-Al-CaO catalyst. An increased Ni-Mg-Al-CaO catalyst/polypropylene ratio promoted the production of hydrogen from the pyrolysis-gasification of polypropylene. Approximately 70 wt.% of the potential H₂ production was obtained, when the Ni-Mg-Al-CaO catalyst/polypropylene ratio and gasification temperature were 5 and 800 °C, respectively.