Surface composition changes of CuNi-ZrO2 during methane decomposition: An operando NAP-XPS and density functional study

Abstract

Bimetallic CuNi nanoparticles of various nominal compositions (1:3, 1:1, 3:1) supported on ZrO 2 were employed for operando spectroscopy and theoretical studies of stable surface compositions under reaction conditions of catalytic methane decomposition up to 500 C. The addition of Cu was intended to increase the coke resistance of the catalyst. After synthesis and (in situ) reduction the CuNi nanoparticles were characterized by HR-TEM/EDX, XRD, FTIR (using CO as probe molecule) and NAP-XPS, all indicating a Cu rich surface, even when the overall nanoparticle composition was rich in Ni. Density functional (DF) theory modelling, applying a recently developed computational protocol based on the construction of topological energy expressions, confirmed that in any studied composition Cu segregation on surface positions is an energetically favourable process, with Cu preferentially occupying corner and edge sites. Ni is present on terraces only when not enough Cu atoms are available to occupy all surface sites.