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The catalytic conversion of biomass-derived tars over char during long tests (over 6 hours) is studied. The syngas is generated in a steam-blown fluidized-bed gasifier employing wood pellets and conducted to a second tubular reactor where non-activated char particles are fluidized. The gasifier operated at 750 °C whereas the temperature of the secondary reactor was varied between 750 °C and 875 °C. The evolution of the tar conversion, gas composition and internal structure of the used catalysts were studied. At 750 °C, the initial catalytic activity of the char was low and deactivation occurs rapidly. However, as the reactor temperature increased, the catalytic activity of the char improved significantly. At 875 °C, the initial conversion of tar was above 70 % and over 64 % after 5 h of operation. Moreover, the conversion of the heaviest tars was above 80 % during the entire test. At this temperature, the decrease in tar conversion is attributed to the consumption of the char by steam gasification since its catalytic activity increased during of the test. In these conditions the char bed with an initial weight of 32 g converted approximately 12 g of tars (benzene not included) after 5 h of operation. 1-IntroductionGasification is a thermo-chemical route for conversion of solid fuels, such as biomass and wastes, into a syngas that can be used in a variety of applications [1,2]. Fluidized bed (FB) gasification has several advantages over that in fixed/moving bed or entrained-flow for distributed energy production [3]. However, in all types of FB gasifiers the process temperature must be kept relatively low to prevent agglomeration and sintering of bed material. The low temperature results in incomplete carbon conversion and a high concentration of heavy tars in the gas. The condensation of heavy tars in downstream equipment is the main bottleneck for the use of the syngas in any application where the gas needs to be cooled down.

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