The role of metal–support interaction for CO-free hydrogen from low temperature ethanol steam reforming on Rh–Fe catalysts

Abstract

Rh–Fe catalysts supported on Ca–Al₂O₃, MgO and ZrO₂ were evaluated in ethanol steam reforming at 623 K and compared to Rh catalysts on the same supports without iron promotion. The metal–support interaction among the three entities, i.e. Rh ↔ Fe₂O₃ ← support (ZrO₂, MgO and Ca–Al₂O₃) was investigated using H₂-chemisorption, TEM, XPS and in situ techniques such as DRIFTS, temperature-resolved XRD and XAS. As compared to the unpromoted Rh catalysts on the same supports, the CO selectivity is depressed in the presence of iron on Rh/MgO and Rh/Ca–Al₂O₃, the latter being significantly superior. The role of metal–support interaction for CO-free hydrogen generation was unravelled using a combination of techniques. It was found that the reducibility of iron oxide determines the extent of the strong metal support interaction between Rh and Fe₂O₃ and the reducibility of iron oxide was affected by the support. On Rh–Fe/Ca–Al₂O₃, a good balance of the interaction between Rh, Fe₂O₃ and Ca–Al₂O₃ prevents strong metal support interaction between Rh and Fe₂O₃ and thus promotes CO elimination via water–gas-shift reaction on Rh–Fe_xO_y sites.