title: Cooperativity and Dynamics Increase the Performance of NiFe Dry Reforming Catalysts.
abstract: The dry reforming of methane (DRM), i.e., the reaction of methane and CO2to form a synthesis gas, converts two major greenhouse gases into a useful chemical feedstock. In this work, we probe the effect and role of Fe in bimetallic NiFe dry reforming catalysts. To this end, monometallic Ni, Fe, and bimetallic Ni-Fe catalysts supported on a MgxAlyOzmatrix derived via a hydrotalcite-like precursor were synthesized. Importantly, the textural features of the catalysts, i.e., the specific surface area (172-178 m2/gcat), pore volume (0.51-0.66 cm3/gcat), and particle size (5.4-5.8 nm) were kept constant. Bimetallic, Ni4Fe1with Ni/(Ni + Fe) = 0.8, showed the highest activity and stability, whereas rapid deactivation and a low catalytic activity were observed for monometallic Ni and Fe catalysts, respectively. XRD, Raman, TPO, and TEM analysis confirmed that the deactivation of monometallic Ni catalysts was in large due to the formation of graphitic carbon. The promoting effect of Fe in bimetallic Ni-Fe was elucidated by combining operando XRD and XAS analyses and energy-dispersive X-ray spectroscopy complemented with density functional theory calculations. Under dry reforming conditions, Fe is oxidized partially to FeO leading to a partial dealloying and formation of a Ni-richer NiFe alloy. Fe migrates leading to the formation of FeO preferentially at the surface. Experiments in an inert helium atmosphere confirm that FeO reacts via a redox mechanism with carbon deposits forming CO, whereby the reduced Fe restores the original Ni-Fe alloy. Owing to the high activity of the material and the absence of any XRD signature of FeO, it is very likely that FeO is formed as small domains of a few atom layer thickness covering a fraction of the surface of the Ni-rich particles, ensuring a close proximity of the carbon removal (FeO) and methane activation (Ni) sites.
authors.affiliation: Laboratory of Energy Science and Engineering, Department of Mechanical and Process Engineering, ETH Zurich , Leonhardstrasse 21, Zurich 8092, Switzerland.
authors.forename: Sung Min
authors.initials: SM
authors.lastname: Kim
authors.affiliation: Laboratory of Energy Science and Engineering, Department of Mechanical and Process Engineering, ETH Zurich , Leonhardstrasse 21, Zurich 8092, Switzerland.
authors.forename: Paula Macarena
authors.initials: PM
authors.lastname: Abdala
authors.affiliation: Department of Chemistry and Applied Sciences, ETH Zurich , Vladimir Prelog Weg 1-5, Zurich 8093, Switzerland.
authors.forename: Tigran
authors.initials: T
authors.lastname: Margossian
authors.affiliation: Laboratory of Energy Science and Engineering, Department of Mechanical and Process Engineering, ETH Zurich , Leonhardstrasse 21, Zurich 8092, Switzerland.
authors.forename: Davood
authors.initials: D
authors.lastname: Hosseini
authors.affiliation: Department of Chemistry and Applied Sciences, ETH Zurich , Vladimir Prelog Weg 1-5, Zurich 8093, Switzerland.
authors.forename: Lucas
authors.initials: L
authors.lastname: Foppa
authors.affiliation: Laboratory of Energy Science and Engineering, Department of Mechanical and Process Engineering, ETH Zurich , Leonhardstrasse 21, Zurich 8092, Switzerland.
authors.forename: Andac
authors.initials: A
authors.lastname: Armutlulu
authors.affiliation: Swiss-Norwegian Beamlines, European Synchrotron Radiation Facility (ESRF) , BP 220, Grenoble 38043, France.
authors.forename: Wouter
authors.initials: W
authors.lastname: van Beek
authors.affiliation: Department of Chemistry and Applied Sciences, ETH Zurich , Vladimir Prelog Weg 1-5, Zurich 8093, Switzerland.
authors.forename: Aleix
authors.identifier: 0000-0002-7002-1582
authors.initials: A
authors.lastname: Comas-Vives
authors.affiliation: Department of Chemistry and Applied Sciences, ETH Zurich , Vladimir Prelog Weg 1-5, Zurich 8093, Switzerland.
authors.forename: Christophe
authors.identifier: 0000-0001-9660-3890
authors.initials: C
authors.lastname: Copéret
authors.affiliation: Laboratory of Energy Science and Engineering, Department of Mechanical and Process Engineering, ETH Zurich , Leonhardstrasse 21, Zurich 8092, Switzerland.
authors.forename: Christoph
authors.initials: C
authors.lastname: Müller