The deposition of coke on the Ni/Al2O3 catalyst used in the pyrolysis/gasification of biomass and plastics was determined by temperature-programme oxidation (TPO). This coke blocks the pores and poisons the active sites, which gives way to a loss of activity in the catalyst, and consequently hydrogen production is reduced. Figs. 3 and 4 display the results of TGATPO for the catalysts used with different polypropylene/ biomass ratios and different types of plastics. In both cases, the overall coke deposition is very low (less than 1 wt.%). Figs. 3 and 4 reveal that there is amass loss between 0 and 150 C in all cases. This is likely to be due to the vaporization of the moisture contained in each coked catalyst, with mass loss being in all the cases of around 2e3 wt.%. The mass loss around 350e400 C is due to coke combustion. The addition of steam during the gasification stage as well as the high temperature in the second reactor (800 C) reduce the final coke deposition on the catalyst because the carbon atoms generated react with the steam introduced at that temperature. The TGA-TPO results for different biomass/polypropylene ratios (Fig. 3) reveal that the lowest coke deposition in the catalyst was obtained when only biomass was present in the reactor. Coke deposition on the catalyst is hardly affected by the plastic content in the plastic/biomass mixture since all the coke percentages are similar and low. Fig. 4 shows the TGA-TPO mass loss results for the different types of plastics/biomass mixtures. The lowest coke formation was observed for the catalyst used in for the pyrolysis/ gasification of biomass and polypropylene. The amount of coke increased slightly when other plastics were introduced in the pyrolysis stage. However, the amount was so small in all cases that catalyst deactivation was not observed. Several researchers have reported the deactivation of Ni/ Al2O3 catalysts by coke in the steam gasification of biomass and plastics [39,40,13]. For example, Kimura et al. [34] obtained a maximum of 5 wt.% coke deposition on a Ni/Al2O3 catalyst (12 wt.% Ni) by operating with a temperature between 600 and 650 C in the steam gasification process. Wu et al. [13