Structural Reversibility and Nickel Particle stability in Lanthanum Iron Nickel Perovskite-Type Catalysts

Significance Statement

Perovskite-type metal oxides are a class of mixed oxides with unique catalytic properties and can be implemented as catalysts without additional functionalization by metals. In addition they can serve as supports for catalytically active metal phases. The resulting interface between the perovskite-type metal oxide and the metal nanoparticles has been found to have a similar nature as that between reducible metal oxides and metals. As opposed to other metal oxides, researchers have shown that precious metals can be segregated reversibly from perovskite-type metals oxide lattices, which is a temperature limited process that enhances the resistance against precious metal sintering.

Analysis through various X-ray based methods on Pd containing perovskite-type metal oxides after isothermal oxidation and reduction treatments has indicated that the fraction of Pd segregating at the perovskite metal oxide surface on reduction, and the fraction dissolving in the perovskite metal oxide lattice on reoxidation increases with increasing temperature. Several researchers have so far tried to explain this.

It is likely that not all of the reduced metal is accessible for catalysis. This is attributed to the stabilization of metals in high oxidation states within the perovskite metal oxide lattices and not all perovskite compositions show the reversible metal segregation at suitable temperatures. A significant benefit of the incorporation of the active metal into a perovskite-type oxide lattice and exploiting the reversible metal segregation is that the active metal contents can be significantly reduced to yield an active but moreover highly redox stable catalyst.

Patrick Steiger and colleagues at Paul Scherrer Institut, EPFL and Zurich University of Applied Sciences in Switzerland, rationalized the required parameters to initiate overall structural reversibility in this form of materials applying a probe reaction catalyzed by nickel, that is carbon dioxide hydrogenation. Their research work is published in ChemSusChem.

The authors explored the parameters of reversible segregation behavior for a typically used catalyst metal (nickel) to avoid nickel sintering that is common on most metal/support type catalyst materials. The researchers used the temperature-programmed reduction, X-ray absorption spectroscopy, and X-ray diffraction, catalytic tests as well as electron microscopy to determine the extent and limits of reversible nickel segregation from the LaFe1-xNixOδ host lattice. The authors exclusively reduced nickel at a reduction temperature of 600 °C and segregated it to the oxide surface at which it developed catalytically active nickel metal particles.

The researchers observed that the extent of nickel reduction from the selected perovskite was dependent on the perovskite B-site composition. The reduction extent also increased from about 35% in the LaFe0.95Ni0.05Oδ perovskite to about 50% in the LaFe0.8Ni0.2Oδ. They realized complete structural reincorporation after oxidation at 650 °C for about 2 h. Reversible nickel segregation was observed to lead to active as well as highly redox stable Nickel catalyst. Nickel particle growth was completely suppressed.

The proposed process offers great potential to reverse particle sintering under conditions that are commonly applied to regenerate coked catalysts. This could enhance the catalytic lifetime as well as cost efficiency.

About the author

Davide Ferri obtained MSc in Technical Chemistry at the University of Milano (Italy) including a stay at the University of Delft (The Netherlands) as Erasmus student, and PhD in Natural Science at ETH Zurich (Switzerland). After a short employment as Sale and Application Manager at Bruker Optics GmbH (Switzerland) he moved back to ETH Zurich as senior scientist in 2006. He held a position of group leader in heterogeneous catalysis at the Swiss Laboratories for Material Science and Technology (Empa, Switzerland) from 2007 to 2012 before moving to the current position as senior scientist at the Paul Scherrer Institut (PSI, Switzerland) since October 2012.

His research interest is centered on the application of advanced in situ and operando spectroscopic techniques to analyse catalytic materials in gas and liquid environment to obtain structure-activity relationships aiding catalyst development. His major areas of research are the abatement of pollutants from exhaust gases, methane oxidation and perovskite-type oxides.

About the author

Patrick Steiger is a PhD student at the École polythechnique fédérale de Lausanne (EPFL) in Switzerland within the school of chemistry and chemical engineering (EDCH). He conducts his research as a member of the biochemistry and catalysis laboratory (LBK) at the Paul Scherrer Institut (PSI) in Villigen (Switzerland). His research is focused on the study of reversible nickel segregation from perovskite-type mixed metal oxides to produce redox stable and completely regenerable nickel catalysts, which can be applied in a variety of processes ranging from CO2 methanation for fuel generation from biogenic feed gases to water gas shift catalysts applied in solid oxide fuel cells. He has a BSc degree in Interdisciplinary Natural Sciences from the Eidgenössisch Technische Hochschule (ETH) in Zurich and an MSc from Imperial College in London UK in Materials Science and Engineering. During his master he specialized in the synthesis and properties of functional ceramics.

Research conducted over the course of this program included the application of zinc oxide nanorods as efficient charge carriers in organic-inorganic hybrid solar cells. His current research at PSI is funded by the Swiss National Science Foundation (SNF) and the Competence Center for Energy and Mobility (CCEM) and is conducted in the context of the Swiss Competence Center for Energy Research (SCCER BIOSWEET).

Reference

Patrick Steiger, Renaud Delmelle, Debora Foppiano, Lorenz Holzer, Andre Heel, Maarten Nachtegaal, Oliver Kröcher, and Davide Ferri. Structural Reversibility and Nickel Particle stability in Lanthanum Iron Nickel Perovskite-Type Catalysts. ChemSusChem 2017, 10, 2505 – 2517.

 

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