Characterization and evaluation of Ni/SiO₂ catalysts for hydrogen production and tar reduction from catalytic steam pyrolysis-reforming of refuse derived fuel

A series of Ni/SiO₂ catalysts have been prepared and investigated for their suitability for hydrogen production and tar reduction in a two-stage pyrolysis-reforming system, using refuse derived fuel (RDF) as the raw material. Experiments were conducted at a pyrolysis temperature of 600°C, and a reforming temperature of 800°C. The product gases were analysed by gas chromatography (GC) and the condensed fraction was collected and quantified using gas chromatography-mass spectrometry (GC-MS). The effects of the catalyst preparation method, nickel content and the addition of metal promoters (Ce, Mg, Al), were investigated. Catalysts were characterised using BET surface area analysis, temperature programmed oxidation (TPO), and scanning electron microscopy (SEM). The TPO and SEM analysis of the reacted catalysts showed that amorphous type carbons tended to be deposited over the Ni/SiO₂ catalysts prepared by impregnation, while filamentous type carbons were favoured with the sol-gel prepared catalysts. The influence of catalyst promoters (Ce, Mg, Al) added to the Ni/SiO₂ catalyst prepared by the sol-gel method was found not to be significant, as the H₂ production was not increased and the tar formation was not reduced with the metal-added catalyst. The highest H₂ concentration of 57.9vol.% and lower tar amount produced of 0.24mg_tar/g_RDF; were obtained using the 20wt.% Ni/SiO₂ catalyst prepared by sol-gel. On the other hand a low catalytic activity for H₂ production and higher tar produced were found for the impregnated series of catalysts, which might be due to the smaller surface area, pore size and due to the formation of amorphous carbons on the catalyst surface. Alkenes and alcohol functional groups were mainly found in the analysed tar samples, with major concentrations of styrene, phenol, indene, cresols, naphthalene, fluorene, and phenanthrene.