Abstract
Despite their high atomic dispersion, single site catalysts with Pt supported on CeO2 were found to have a low activity during oxidation reactions. In this study, we report the behavior of Pt/CeO2 single site catalyst under more complex gas mixtures, including CO, C3H6 and CO/C3H6 oxidation in the absence or presence of water. Our systematic operando high-energy resolution-fluorescence-detected X-ray absorption near-edge structure (HERFD-XANES) spectroscopic study combined with multivariate curve resolution with alternating least squares (MCR-ALS) analysis identified five distinct states in the Pt single site structure during CO oxidation light-off. After desorption of oxygen and autoreduction of Pt4+ to Pt2+ due to the increase of temperature, CO adsorbs and reduces Pt2+ to Ptδ+ and assists its migration with final formation of PtxΔ+ clusters. The derived structure–activity relationships indicate that partial reduction of Pt single sites is not sufficient to initiate the conversion of CO. The reaction proceeds only after the regrouping of several noble metal atoms in small clusters, as these entities are probably able to influence the mobility of the oxygen at the interface with ceria.
Highlights
In recent years, single atom catalysts (SACs) have attracted increased interest
Our systematic operando high-energy resolutionfluorescence-detected X-ray absorption near-edge structure (HERFD-X-ray absorption near edge structure (XANES)) spectroscopic study combined with multivariate curve resolution with alternating least squares (MCR-ALS) analysis identified five distinct states in the Pt single site structure during CO oxidation light-off
In line with our previous investigations [14], no Pt nanoparticles could be identified in the TEM micrographs (Figure 1) obtained for the Pt/CeO2 catalyst (0.94 wt.% noble metal loading found by inductively coupled plasma-optical emission spectroscopy, ICP-OES, analysis) upon the hydrothermal treatment in 10% O2, 10% H2O/N2 at 800 ◦C for 16 h
Summary
Single atom catalysts (SACs) have attracted increased interest. Especially when noble metals are the active components, an atomically dispersed catalyst would maximize their efficient use. It has been observed that the CO conversion rate increases by treating the SAC with steam at high temperature [10] This treatment was shown to lead to the formation of Ce1-XPtO2-XH–OH species, apparently more active than Ce1-XPtO2-Y. Gänzler et al demonstrated that a careful reductive treatment leads to the formation of small Pt nanoparticles and significantly improves the low-temperature oxidation activity of highly dispersed Pt/CeO2 based catalysts [5]. This outcome has been confirmed by other recent studies [10,12]
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