Influence of silica–alumina support ratio on H₂ production and catalyst carbon deposition from the Ni-catalytic pyrolysis/reforming of waste tyres

The influence of catalyst support alumina–silica in terms of different Al₂O₃ to SiO₂ mole ratios containing 20 wt.% Ni on the production of hydrogen and catalyst coke formation from the pyrolysis-catalysis of waste tyres is reported. A two-stage reactor system was used with pyrolysis of the tyres followed by catalytic reaction. There was only a small difference in the total gas yield and hydrogen yield by changing the Al₂O₃ to SiO₂ mole ratios in the Ni-Al₂O₃/SiO₂ catalyst. The 1:1 ratio of Al₂O₃:SiO₂ ratio produced the highest gas yield of 27.3 wt.% and a hydrogen production of 14.0 mmol g-1tyre. Catalyst coke formation decreased from 19.0 to 13.0 wt.% as the Al₂O₃:SiO₂ ratio was changed from 1:1 to 2:1, with more than 95% of the coke being filamentous-type carbon, a large proportion of which was multi-walled carbon nanotubes. Further experiments introduced steam to the second-stage reactor to investigate hydrogen production for the pyrolysis-catalytic steam reforming of the waste tyres using the 1:1 Al₂O₃/SiO₂ nickel catalyst. The introduction of steam produced a marked increase in total gas yield from ~27 wt. % to ~58 wt.%; in addition, hydrogen production was increased to 34.5 mmol g‾¹ and there was a reduction in catalyst coke formation to 4.6 wt.%