Simultaneous catalytic H2 production and CO2 capture in steam reforming of toluene as tar model compound from biomass gasification

During biomass gasification in a fast internal circulating fluidized bed (FICFB) reactor hydrogen production is strongly influenced by the physicochemical properties and ability of the catalyst to transform the organic fraction (tar molecules), considered as pollutant and produced along the process. The hydrogen production can be also favored by the sorption of CO2 formed during biomass gasification. In this work, two types of bi-functional sorbents/catalysts were prepared taking into account the high attrition resistance required in this type of reactor. Olivine was chosen as catalyst and support of CaO or CaO–Ca12Al14O33 (CaO–CaAl) used as CO2 sorbent phases. The bi-functional materials and olivine were characterized by SEM, BET, XRD, TPR and Mössbauer spectroscopy. The SEM and BET analyses showed that the higher content of CaO–CaAl on olivine allowed having larger pore volume and smaller pore size than CaO/olivine. XRD and TPR showed that the formation of α-Fe2O3 by oxidation of Fe2+ from the olivine structure is favored in presence of the CaO–Ca12Al14O33 phase which improves iron oxide dispersion.The CaO–CaAl/olivine 1:2 ratio showed the best sorption properties at 700 °C. The CO2 sorption capacity was attributed to the high CaO content and its large pore volume while the presence of Ca12Al14O33 provided CO2 sorption stability during carbonation–decarbonation cycles.The enhancement of catalytic activity in tar conversion for these bi-functional materials compared to olivine was demonstrated and attributed to the presence of well dispersed iron oxides and the high content of sorbent on olivine surface. This work presents the interest of a CaO–CaAl/olivine catalyst for hydrogen production improved by CO2 capture in a fast internal circulating fluidized bed biomass gasifier.

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► Study of calcium oxide based sorbent addition on olivine physicochemical properties.
► Fe3+ formed from olivine structure despite the presence of sorbent phase.
► Mayenite provides sorption stability and favors iron oxide dispersion.
► Bi-functional sorbent/catalyst materials activity studied in tar steam reforming.
► Olivine activity in tar steam reforming enhanced by CaO–Ca12Al14O33 sorbent addition.