Diverse impact of Α-Fe₂O₃ with nano/micro-sized shapes on the catalytic fast pyrolysis of pinewood: Py-GC/MS study

The feasibility of α-Fe₂O₃ catalyst addition in the in-situ catalytic fast pyrolysis of Pinewood was considered with the focus on the variation in its shape: nano-sized non-ideal spheres, nanotubes, hollow nano/microtubes, and octadecahedral crystals. Nano-sized spheres strongly promoted the formation of acetaldehyde, something that was also observed for the octadecahedral crystals. The formation of acids was primarily facilitated through the addition of nanotube catalysts and octadecahedral crystals. Newly formed alicyclic ketonic compounds were promoted through the addition of nano-sized spheres, hollow nano/microtubes, and octadecahedral crystals. The latter two catalysts also showed a moderate selectivity in the formation of furfural. All applied catalysts showed loss of activity, though at different degrees, on the formation of lignin derived phenolic compounds, which can be primarily attributed to favoring the formation of char with simultaneous release of CO₂. All used α-Fe₂O₃ catalysts with different shapes maintained their original morphology after the rapid heating with the rate of 20 K/ms followed by catalytic fast pyrolysis at 500 °C, indicating that nanomaterials with targeted dimensions can be applied as catalysts in the catalytic fast pyrolysis of biomass to enhance conversion of undesired oxygenated compounds to higher quality bio-oil and valuable chemicals.