Abstract
The identity of active species in supported gold catalysts for low temperature carbon monoxide oxidation remains an unsettled debate. With large amounts of experimental evidence supporting theories of either gold nanoparticles or sub-nm gold species being active, it was recently proposed that a size-dependent activity hierarchy should exist. Here we study the diverging catalytic behaviours after heat treatment of Au/FeOx materials prepared via co-precipitation and deposition precipitation methods. After ruling out any support effects, the gold particle size distributions in different catalysts are quantitatively studied using aberration corrected scanning transmission electron microscopy (STEM). A counting protocol is developed to reveal the true particle size distribution from HAADF-STEM images, which reliably includes all the gold species present. Correlation of the populations of the various gold species present with catalysis results demonstrate that a size-dependent activity hierarchy must exist in the Au/FeOx catalyst.
Highlights
The identity of active species in supported gold catalysts for low temperature carbon monoxide oxidation remains an unsettled debate
We studied Au/FeOx catalysts prepared by two different co-precipitation (CP) methods previously reported by Haruta et al.[1] and Hutchings et al.[16,17]
0 Atoms Clusters 1–3 3–5 5–7 Atoms Clusters 1–3 3–5 5–7 Atoms Clusters 1–3 3–5 5–7 particles are the only active species, the thermal deactivation of the deposition precipitated (DP)-1 catalyst cannot be explained since a larger population of these 1–3 nm particles exists after calcination
Summary
The identity of active species in supported gold catalysts for low temperature carbon monoxide oxidation remains an unsettled debate. Schuth et al.[13] demonstrated that Au/FeOx catalysts prepared by colloid immobilization methods can exhibit high CO oxidation activity while being devoid of any sub-nm clusters These data combined with that of Herzing et al.[11] suggest that there is not just one distinct active site for CO oxidation over supported Au species and that particles existing over a broad size range may be effective for the reaction. We re-visit Au/FeOx catalysts and use a new counting protocol to reveal the true particle size distribution (PSD) from HAADF-STEM images, which reliably includes all the Au species present and we show experimentally that an activity hierarchy does exist
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