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.