HZSM-5 supported with N-doped Fe for microwave catalytic pyrolysis of lignin

Microwave catalytic pyrolysis of lignin is one of emerging technologies for efficiently converting lignin into fuels and chemicals. Molecular sieves (HZSM-5) are widely used as carriers to load metallic components for biomass pyrolysis but often encounter challenges such as high diffusion resistance and insufficient acidity of acidic sites. Traditionally, HZSM-5 is directly modified to enhance the activity of the acidic sites, but this modification is ineffective in improving the metallic components’ activity. Instead, we made nitrogen doping on Fe and then supported on HZSM-5 to construct Fe-N 25 /HZSM-5 catalysts for microwave catalytic pyrolysis of lignin. The N-doped Fe has the effect of “killing two birds with one stone” on enhancing the catalytic activity. The characterization results indicated that N replaced C of the graphitic carbon network to form carbon nitride structure, and further combined with Fe to generate Fe-N bonds, improving the electronegativity of the metallic component. Besides, the loading of N-doped Fe increased the acidity of the catalyst. The utilization of 1.00Fe-N 25 /HZSM-5 obtained the greatest bio-gas yield (35.2 wt%), a hydrogen yield of 27.8 mL/min, bio-oil yield (36.4 wt%) and phenol selectivity of 46.2 %. The likely pathway of microwave catalytic pyrolysis on Fe-N 25 /HZSM-5 was proposed through DFT calculation, using guaiacol as a model compound. The results suggested that N-doped Fe on HZSM-5 8 T tended to break the side-chain methoxy during pyrolysis of guaiacol, with energy barrier of 0.14 eV. This paper provides a promising strategy for modification of microwave pyrolysis catalysts.