Ordered phases of reduced ceria as inverse model catalysts

Abstract

Inverse model catalysts represent valuable systems for studying metal-oxide interactions and finite size effects in heterogeneous catalysis. To maximize the potential of model catalytic studies, high level of control over model catalyst properties is desirable. Here we introduce experimental approaches for obtaining inverse ceria/copper model catalysts of well-defined crystallographic phases CeO2, ι-Ce7O12, CeO1.67, and c-Ce2O3 supported on Cu(1 1 1). The presented cerium oxide thin films are ultrathin (2 monolayers), discontinuous, and feature highly defined stoichiometry and crystallographic structure with characteristic (1 × 1), (√7×√7)R19°, (3 × 3), or (4 × 4) electron diffraction patterns. Compared to thicker films and bulk ceria, the prepared ultrathin cerium oxides exhibit a distinctly different dependence of the lattice constant on the stoichiometry, and show activation barrier preventing their complete oxidation. These phenomena illustrate that metal-oxide interactions and finite size effects strongly influence the behavior of the presented inverse model catalysts indicating their prospective use in disentangling complex functionalities of ceria/copper catalytic systems.