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Three Ni/Al2O3 catalysts prepared by co-precipitation, impregnation and sol-gel methods were investigated for the pyrolysis-steam reforming of waste plastics. The influence of Ni loading method on the physicochemical properties and the catalytic activity towards hydrogen and carbon monoxide production were studied. Three different plastic feedstocks were used, high density polyethylene (HDPE), polypropylene (PP) and polystyrene (PS), and compared in relation to syngas production. Results showed that the overall performance of the Ni catalyst prepared by different synthesis method was found to be correlated with the porosity, metal dispersion and the type of coke deposits on the catalyst. The porosity of the catalyst and Ni dispersion were significantly improved using the sol-gel method, producing a catalyst surface area of 305.21 m2/g and average Ni particle size of 15.40 nm, leading to the highest activity among the three catalysts investigated. The least effective catalytic performance was found with the co-precipitation prepared catalyst which was due to the uniform Ni dispersion and the amorphous coke deposits on the catalyst. In regarding to the type of plastic, polypropylene experienced more decomposition reactions at the conditions investigated, resulting in higher hydrogen and coke yield. However, the catalytic steam reforming ability was more evident with polystyrene, producing more hydrogen from the feedstock and converting more carbon into carbon monoxide gases. Overall the maximum syngas production was achieved from polystyrene in the presence of the sol-gel prepared Ni/Al2O3 catalyst, with production of 62.26 mmol H2 g−1plastic and 36.10 mmol CO g−1plastic.
Yao et al. (Sun,) studied this question.