Abstract
Local structure of Pd1 single sites on the surface of Pd1In1 intermetallic nanoparticles supported on α-Al2O3 was investigated by the combination of CO-DRIFTS spectroscopy and DFT. CO-DRIFTS spectra of PdIn/Al2O3 catalyst exhibit only one asymmetric absorption band of linearly adsorbed CO comprising two peaks at 2065 and 2055 cm−1 attributable to CO molecules coordinated to Pd1 sites located at (110) and (111) facets of PdIn nanoparticles. The absence of bridged or hollow-bonded CO bands indicates that multipoint adsorption on PdIn nanoparticles is significantly hindered or impossible. DFT results show that on (110) facet multipoint CO adsorption is hindered due to large distance between neighboring Pd atoms (3.35 Å). On (111) facet multipoint CO adsorption on surface palladium atoms is impossible, since adjacent Pd atoms are located below the surface plane.
Highlights
Single-atom alloys (SAA) is an important class of so-called single-site catalysts widely used in state-of-the-art catalysis [1,2,3,4]
Local structure of Pd1 single sites on the surface of Pd1In1 intermetallic nanoparticles supported on α-Al2O3 was investigated by the combination of CO-DRIFTS spectroscopy and density functional theory (DFT)
It is of interest to analyze the DRIFTS data on CO adsorption on the surface of intermetallic nanoparticles by DFT calculations in two aspects: (1) the absence of signals from multiply coordinated CO species, and (2) the position of absorption bands and the adsorption energy of linear forms of adsorbed CO
Summary
Single-atom alloys (SAA) is an important class of so-called single-site catalysts widely used in state-of-the-art catalysis [1,2,3,4]. Theoretical analysis of formic acid decomposition over SAA-like CuPt catalysts revealed intermetallic Cu3Pt as a promising material for this process [13], since its surface structure exhibits only Pt1 sites isolated by Cu component This conclusion is in agreement with the results reported elsewhere [14,15,16]. This is due to the fact that CO is adsorbed only by surface atoms, and it is possible to distinguish isolated Pd1 and multiatomic Pdm (m > 1) centers by the presence of linear-, bridge- or threefold hollow-bonded CO bands. Since CODRIFTS provides information only on the upper surface layer, the combination with DFT modeling can be an informative method for revealing the local atomic surroundings of Pd1 surface sites
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