investigated a Ni/Al2O3 catalyst (10 wt.% Ni) in the steam pyrolysis/ gasification of polypropylene and showed that the catalyst was effective for the production of hydrogen even though a high coke deposition occurred (11 wt.%). However, no studies have been carried out on the catalyst deactivation in the copyrolysis/ gasification of biomass and plastics. Fig. 5 shows the scanning electron micrographs (SEM) of the used catalysts used for the pyrolysis/gasification ofbiomass, a mixture of 90 wt.% biomass and 10 wt.% of polypropylene and for 80 wt.% biomass and 20 wt.% polypropylene. The SEM analysis confirmed the presence of filamentous type carbon deposits on the catalyst surface. As observed in Fig. 5, when plastic was introduced to the biomass/plastic feed, hydrogen production was increased and coke deposition on the catalyst increased slightly. These results are consistent with those obtained in the TPO (Figs. 3 and 4), in which the lowest hydrogen and coke yields have been obtained for the pyrolysis/gasification of 100 wt.% biomass. Hence, when the percentage of plastic in the mixture was increased to 10 wt.% of polypropylene, coke deposition also increased. However, when 20 wt.% of polypropylene was added to the biomass, the coke yield in the catalyst remains almost constant.