Influence of silica–alumina support ratio on H(2) 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 Al(2)O(3) to SiO(2) 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 Al(2)O(3) to SiO(2) mole ratios in the Ni-Al(2)O(3)/SiO(2) catalyst. The 1:1 ratio of Al(2)O(3):SiO(2) ratio produced the highest gas yield of 27.3 wt.% and a hydrogen production of 14.0 mmol g(-1)(tyre). Catalyst coke formation decreased from 19.0 to 13.0 wt.% as the Al(2)O(3):SiO(2) 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 Al(2)O(3)/SiO(2) 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.%.