Effects of various carbon-supported iron catalysts on tar removal efficiency and syngas yield during catalytic biomass gasification

Raw biomass, biochar, and activated carbon (AC) were used to produce carbon supported iron catalysts for catalytic biomass gasification. K2CO3 was used to activate the biochar and provide the K promoter of the catalysts. The results showed that the catalyst prepared by co-impregnating and calcining Fe and K on the raw biomass (B-Fe-K) could remove 80.23 % tar, which was much higher than 73.73 % for the catalyst of B-Fe without the K promoter, and 76.25 % for the catalyst by co-impregnating and calcining Fe and K on the biochar (C-Fe-K). The supports of AC and biochar themselves could also remove 63.16 % and 37.23 % tar, respectively. The use of B-Fe-K almost doubled the syngas yield to 473.79 ml/g (including 243.56 ml/g CO, 198.25 ml/g H2, and 31.98 ml/g CO2), compared to 241.37 ml/g syngas (including 108.98 ml/g CO, 66.41 ml/g H2, and 65.987 ml/g CO2) produced by the pyrolysis of biomass without a catalyst. The addition of biochar during the pyrolysis slightly increased the syngas yield to 248.96 ml/g (117.36 ml/g CO, 74.22 ml/g H2, and 57.38 ml/g CO2) while the use of AC could significantly increase the syngas yield to 347.60 ml/g (179.39 ml/g CO, 124.22 ml/g H2, and 43.99 ml/g CO2). It was found that the porosity, dispersion of active sites and the oxidation state of iron oxide are substantial factors determining the performance of catalysts in tar removal efficiency. The addition of potassium and enhancing the porosity of the catalysts enhanced the reducibility of iron resulted in increasing the tar removal efficiency and gas yield.