Computationally assisted, surface energy-driven synthesis of Mn-doped Co3O4 fibers with high percentage of reactive facets and enhanced activity for preferential oxidation of CO in H2

Abstract

Surface engineering is central to heterogeneous catalysis. For Co3O4-based catalysts, the bulk extended Co3O4 {110} surface has been shown to be one of the most active surfaces. However, most available Co3O4 nanocrystals are terminated by the thermodynamically stable {111} and {010} facets, rather than the active {110} facets. The increasing portion of {110}-type facets in the Co3O4-based catalysts correlates with an enhancement of the catalytic activity, and synthesis strategies need to pursue them. Here, with the aid of theoretical calculation, we present doping-assisted growth strategy to modulate the facet termination of Co3O4-based nanocatalysts. Both theoretical and experimental studies demonstrate that Co3O4-based catalysts undergo profound surface termination changes in response to Mn bulk doping. Doping of Mn into Co3O4 lowers the surface energy of {110}-type facets, and reproduces hierarchy of surface energies as {111} > {010} ≈ {110}, providing thermodynamic driving force for morphology change and surface termination transformation. The resulting Mn-doped Co3O4 catalysts are mostly composed of fiber-like shapes, exposing a large fraction of {110} and {010} surfaces. In contrast, Mn-free Co3O4 consists of octahedron-shaped nanoparticles with planar geometries of {111} and {010} as their major and minor specific exposed facets. The Mn-doped Co3O4 catalysts reported herein also show high activity and excellent stability for preferential oxidation of CO in H2 during 40 h of reaction at 60 ℃. We anticipate that our theoretical and experimental findings provide a basis for the design and synthesis of new and high-performance catalysts though surface engineering strategies.