CNR ExploRA

Articolo in rivista, 2018, CPE, 10.1021/acscatal.8b01039

Fe-Containing Magnesium Aluminate Support for Stability and Carbon Control during Methane Reforming

Theofanidis, Stavros Alexandros; Galvita, Vladimir V.; Poelman, Hilde; Dharanipragada, N. V. R. Aditya; Longo, Alessandro; Meledina, Maria; Van Tendeloo, Gustaaf; Detavernier, Christophe; Marin, Guy B.

Univ Ghent; European Synchrotron; UOS Palermo; Univ Antwerp; Univ Ghent, ISMN-CNR

We report a MgFexAl2-xO4 synthetic spinel, where x varies from 0 to 0.26, as support for Ni-based catalysts, offering stability and carbon control under various conditions of methane reforming. By incorporation of Fe into a magnesium aluminate spine!, a support is created with redox functionality and high thermal stability, as concluded from temporal analysis of products (TAP) experiments and redox cycling, respectively. A diffusion coefficient of 3 x 10(-17) m(2) s(-1) was estimated for lattice oxygen at 993 K from TAP experiments. X-ray diffraction (XRD) and extended X-ray absorption fine structure (EXAFS) modeling identified that the incorporation of iron occurs as Fe3+ in the octahedral sites of the spinel lattice, replacing aluminum. Simulation of the X-ray absorption near edge structure (XANES) spectrum of the reduced support showed that 60 +/- 10% of iron was reduced from 3+ to 2+ at 1073 K, while there was no formation of metallic iron. A series of Ni/MgFexAl2-xO4 catalysts, where x varies from 0 to 0.26, was synthesized and reduced, yielding a supported Ni-Fe alloy. The evolution of the catalyst structure during H-2 temperature-programmed reduction (TPR) and CO2 temperature-programmed oxidation (TPO) was examined using time-resolved in situ XRD and XANES. During reforming, iron in both the support and alloy keeps control of carbon accumulation, as confirmed by O-2-TPO on the spent catalysts. By fine tuning the amount of Fe in MgFexAl2-xO4, a supported alloy was obtained with a Ni/Fe molar ratio of similar to 10, which was active for reforming and stable. By comparison of the performance of Ni-based catalysts with Fe either incorporated into or deposited onto the support, the location of Fe within the support proved crucial for the stability and carbon mitigation under reforming conditions.

ACS catalysis 8 (7), pp. 5983–5995