Study of Ni–M/MgO and Ni–M–Mg/Al (M=Fe or Cu) catalysts in the CH4–CO2 and CH4–H2O reforming

The catalysts Ni–M/MgO prepared by impregnation of the MgO support and (Ni–M–Mg)2Al by co-precipitation method using NH4OH as precipitating agent (M=Cu or Fe), were characterized by BET surface area, X-ray diffraction (XRD), temperature programmed reduction (TPR), temperature programmed oxidation (TPO), Transmission electronic microscopy (TEM) and tested in CH4/CO2 and CH4/H2O reactions. XRD analysis showed the presence of NixMg1 − xO (x = 0.05 or 0.1), NiAl2O4 and/or MgAl2O4 solid solutions. NiO was not observed on all catalysts what could confirm the formation of solid solutions. The reducibility of the catalysts increased in the presence of Cu or Fe due to the reduction assistance of these elements. The reactivity results showed very high performances (with CH4 conversion and yields of H2 and CO up to 90%) and a good resistance for coke formation. For the CO2 reforming of methane, the TPO profiles and TEM analysis showed mainly four types of coke: CHx species, surfaces carbon, nickel carbide and carbon nanotubes. However, for the H2O reforming, the nanotubes carbon was not detected. The coke deposit decreased in the presence of Fe or Cu species due probably to the formation of Ni–Fe or Ni–Cu alloys where in the active phase is highly dispersed. In this work, we observed also that the presence of Mg, basic element, in the catalyst composition decreased coke formation in the form of nanotube. In the other hand, the deactivation of catalysts in the case of H2O reforming is more related to actives sites oxidation.