Fatty acid decarboxylation reaction kinetics and pathway of co-conversion with amino acid on supported iron oxide catalysts

Abstract

Fe₂O₃/Al-MCM-41 nanocomposite catalysts were designed and fabricated to upgrade microalgae hydrothermal liquefaction (HTL)-derived biocrude and its model compounds (palmitic acid and glutamic acid) in the absence of hydrogen. The Fe₂O₃/Al-MCM-41 catalysts were prepared by encapsulating Fe₂O₃ particles on highly stable pure silica MCM-41 and Al-MCM-41. XRD, TEM, N₂ adsorption isotherms, XPS, and UV-Vis characterizations of the catalysts revealed that 10–30 nm γ-Fe₂O₃ particles were well dispersed on the mesoporous support. In the range of 320–350 °C and under subcritical water, palmitic acid conversion was improved by 43–54% by the Fe₂O₃/Al-MCM-41 catalyst. The overall reaction rate was first order to palmitic acid for non-catalytic and catalytic conversions, and the activation energy was 336.76 kJ mol⁻¹ for Fe₂O₃/Al-MCM-41. In situ DRIFTS reaction test demonstrated that the initiation temperature for the catalytic decarboxylation of palmitic acid was decreased to 195 °C, and desorption of the produced CO₂ occurred at 255 °C. Based on the GC-MS results of the HTL products, the reaction pathway of the binary mixture of palmitic acid and glutamic acid was elucidated, and the chemical origins of amide, pyrrolidinone, hydroxy-butanoic acid, and pentadecane were proposed.