Novel coking resistant NiFeAl catalysts for combined dry reforming and partial oxidation of methane: Insights into the mechanism of the function of Fe ions when dispersed in the support

The impact of Fe species as a coking resistance modifier for Ni/γ-Al 2 O 3 catalysts was studied in combined dry reforming and partial oxidation of methane. The main aims of this study were first, to investigate the capability of the Fe-modified catalysts to promote CH 4 reforming with a CO 2 /O 2 mixture and second, to investigate the mechanism of the Fe function as a coking resistance enhancer. Two sets of catalysts were prepared and compared where in one of them Fe ions were dispersed in the support matrix while in the other one Fe ions were co-impregnated along with Ni. The catalysts were characterized by various techniques including XRD, XPS, TGA, H 2 -TPR, Raman spectroscopy, N 2 physisorption, temperature-programmed reduction, and DRIFTS. The Fe ions in the support were partially reduced followed by segregation on the surface where they enhanced the concentration of surface oxygen species and redox sites leading to enhanced oxidation and removal of carbon during reactions. Catalysts with ≤10% showed negligible amounts of crystalline and amorphous carbon during 24 hr reactions at 700 °C and 1 atm. On the contrary, the catalysts where Fe ions were co-impregnated with Ni showed enhanced complete reduction of the Fe ions and alloying with Ni enhancing CH 4 cracking and hence, carbon formation. The textural, structural, and chemical characteristics of both types of catalysts was found to depend on the Fe concentration which should be carefully controlled to avoid the formation of other Fe-based structures such as FeAl 2 O 4 which was found to enhance CH 4 cracking and coke formation.