Production of syngas from pyrolysis of biomass using Fe/CaO catalysts: Effect of operating conditions on the process

- Calcination temperature affects the physicochemical properties and catalytic activity of the resulting Fe/CaO catalysts.
- Enhanced syngas yield (63.0 wt.%) and hydrogen yield (172 mL/g biomass) were obtained at optimized operating conditions.
- The absorption-enhanced biomass catalytic pyrolysis process is highly dependent on catalytic temperature.
- Partial Fe3+ in Ca2Fe2O5 were in-situ reduced to Fe3O4 by generated syngas (CO/ H2) during pyrolysis process.

This study aimed to further optimize the operating conditions to produce hydrogen-enriched syngas from the catalytic pyrolysis of biomass in a two-stage fixed-bed reaction system with the Fe/CaO catalyst derived from layered double hydroxides (LDHs) precursor. Specifically, the effects of catalyst calcination temperature and catalytic bed temperature on the composition and yield of syngas were investigated. Various characterization techniques such as XRD, SEM, BET, H2-TPR and CO2-TPD were employed to thoroughly characterize the Fe/CaO catalysts both before and after the catalytic reaction. It was found that the catalyst synthesized at a mild temperature of 600 °C performed the best in producing hydrogen-enriched syngas, probably because of its uniform morphology, smaller particle size, superior reducibility and stronger CO2 absorption ability. In addition, higher temperature was found to benefit the syngas production due to the acceleration of reaction rate and promotion of secondary cracking and reforming reactions of heavy organic molecules with the maximum syngas yield of 63.0 wt.% and H2 yield of 172 mL/g biomass obtained at catalytic temperature of 800 °C using Fe/CaO catalyst calcined at 600 °C. Nevertheless, the H2/CO ratio was only at a suboptimal level of 0.99 because the decomposition of CaCO3 at higher catalytic temperature released CO2 and suppressed the water gas shift reaction to produce more H2.