Size-Dependent Activity of Iron Nanoparticles in Both Thermal and Plasma Driven Catalytic Ammonia Decomposition

Water-dispersible Fe(3)O(4 )nanoparticles with diame-ters of 4.2 +/- 0.6, 6.1 +/- 0.8, 8.1 +/- 1, and 10.4 +/- 1 nm were prepared through the polyol method and employed as the precursors of Fe3O4/Al2O3 catalysts to study the size-dependent activity. We identified that the activity of the catalysts in NH3 decomposition (driven by both thermal and dielectric barrier discharge plasma) increased with increasing Fe3O4 particle size. The turnover frequencies (TOFs) were increased from 0.9 to 5.8 s-1 with an increasing Fe3O4 precursor size from 4.2 to 10.4 nm during the thermocatalytic decomposition. A quite similar "particle size effect " was also observed for the plasma catalytic decomposition, although lower TOF was observed. Additionally, reaction-induced catalyst reconstruction was identified during the early-stage of the catalytic decomposition and can be attributed to the nitridation of FeOx to FexN. Our results provide new evidence for the "structure-sensitivity " of the catalytic NH3 decomposition.