Impact of Iron Species Dispersion on Fe/ZSM‐5 Catalyst Performance for Methane Dehydroaromatization (MDA)

Abstract

Methane dehydroaromatization (MDA) is one of the most promising technologies for directly transforming methane into aromatics. Unlike the extensively investigated Mo/ZSM‐5 catalysts, the structure and, consequently, the catalytic activity of Fe/ZSM‐5 are markedly influenced by the method of preparation, as shown here. In this study, we prepared 2% and 4% Fe/ZSM‐5 catalysts via wet impregnation (WI) and incipient wetness impregnation (IWI). Characterizations (XRD, STEM, UV‐Vis, NH3‐TPD and H2‐TPR) reveal that 2%Fe‐WI mainly possesses isolated or low‐polymerized Fe species within zeolite channels, leading to a rapid activation and a higher benzene yield due to the faster reduction to iron suboxides under MDA conditions. In contrast, 2%Fe‐IWI contains bulk iron oxide aggregates, resulting in a slower activation as these aggregates transform into iron carbide through successive reduction and carbonization. A deactivation kinetic study applied to the 2% catalysts further demonstrates the quantitative relation between Fe site isolation and catalytic activity. Although both 4% catalysts inevitably form sizable iron oxide clusters and particles due to the high Fe/Al ratio, similar trends were noted, with the WI catalysts exhibiting a shorter induction/activation period and a higher yield of benzene, paralleling observations made with 2% catalysts.