1 research outputs found
Role of Coating-Metallic Support Interaction in the Properties of Electrosynthesized Rh-Based Structured Catalysts
Rh-structured catalysts for the catalytic
partial oxidation of
CH<sub>4</sub> to syngas were prepared by electrosynthesis of Rh-containing
hydrotalcite-type (HT) compounds on FeCrAlloy foams followed by calcination
at 900 °C. During the calcination the simultaneous decomposition
of the layered HT structure and formation of the protective FeCrAlloy
outer shell in alumina occurred. Here, we studied the role of the
coating-metallic support interaction in the properties of the catalysts
after calcination, H<sub>2</sub> reduction, and catalytic tests, by
a combination of electron (FEG-SEM/EDS) and synchrotron X-ray (XRF/XRPD
and XRF/XANES) microscopic techniques. The characterization of crystalline
phases in the metallic support and coating and distribution of Rh
active species was carried out on several samples prepared by modifying
the Rh content in the electrolytic solution (Rh/Mg/Al = 11.0/70.0/19.0,
5.0/70.0/25.0, 0/70.0/30.0 atomic ratio). A sample was also prepared
with no aluminum in the electrolytic solution (Rh/Mg/Al = 13.6/86.4/0.0
atomic ratio) and calcined at 550 and 900 °C. The interaction
between the elements of the metallic support and the catalytic coating
increased the film adhesion during the thermal treatment and catalytic
tests and modified the catalyst crystalline phases. A chemical reaction
between Al coming from the foam and Mg in the coating occurred during
calcination at high temperature leading to the formation of spinel
phases in which rhodium is solved, together with some Rh<sub>2</sub>O<sub>3</sub> and Rh<sup>0</sup>. The metallic support was oxidized
forming the corundum scale and chromium oxides, moreover ι-Al<sub>2</sub>O<sub>3</sub> was identified. For the Rh<sub>11.0</sub>Mg<sub>70.0</sub>Al<sub>19.0</sub> catalyst the inclusion of Rh in the spinel
phase decreased its reducibility in the H<sub>2</sub> pretreatment.
The reduction continued during catalytic tests by feeding diluted
CH<sub>4</sub>/O<sub>2</sub>/He gas mixtures, evidenced by the catalyst
activation. While under concentrated gas mixtures the deactivation
occurred, probably by oxidation