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Stoichiometric synthesis of Fe/CaxO catalysts from tailored layered double hydroxide precursors for syngas production and tar removal in biomass gasification

Zhang, Xiaodong, Yang, Shuangxia, Xie, Xinping, Chen, Lei, Sun, Laizhi, Zhao, Baofeng, Si, Hongyu
Journal of analytical and applied pyrolysis 2016 v.120 pp. 371-378
X-ray diffraction, absorption, active sites, adsorption, alkalinity, biomass, calcium, calcium oxide, carbon dioxide, catalysts, catalytic activity, catalytic cracking, gas chromatography-mass spectrometry, gasification, hydrogen, iron, magnetite, particle size, phenolic compounds, pyrolysis, scanning electron microscopy, synthesis gas
A series of bi-functional Fe/CaxO catalysts with different Ca/Fe molar ratios (2/1, 3/1, 4/1, 5/1) were prepared from tailored single-source CaxFe-LDHs precursors and applied to the thermo-chemical catalytic conversion of biomass. The results of catalyst characterization using XRD, SEM and CO2-TPD techniques indicate that the Fe load has a significantly influence on the composition, particle size, alkalinity and CO2 adsorption capacity of resulting Fe/CaxO materials. As catalysts, the selectivity of H2 was increased and the selectivity of CO was reduced with increasing Fe load. The highest gasification yield of 48.3wt.%, H2 yield of 37.48vol.% and H2/CO ratio of 1.36 were obtained at an optimized composition of Ca/Fe=2/1, with the gasification efficiency as high as 76.4%. GC–MS analysis of the condensable tar indicated that the as-synthesized Fe/CaxO catalysts were capable for selective phenolics production from biomass gasification, with the maximum phenolics yield as high as 90.06%. Moreover, based on the results of structure characteristics and catalytic activities, a synergistic catalytic mechanism was proposed that the Ca2Fe2O5 and Fe3O4 formed by partial reduction of Ca2Fe2O5 during biomass gasification are the main active site for catalytic cracking of tar, which can be further promoted by the in-situ CO2 absorption of CaO.