Computational Design of Pd Nanoclusters and Pd Single-Atom Catalysts Supported on O-Functionalized Graphene

Abstract

A crucial step in the preparation of supported metal catalysts is related to the choice of support, since it regulates the anchoring of the metal species in an environment of strong interactions. In this sense, the binding on the support, which may present defects, as well as induced modifications of the electronic structure, helps to determine efficient metal/support combinations for catalysis applications. In this work, first-principles studies have been carried out to model and describe the geometric and electronic properties of O-functionalized graphene as a model carbon support, in addition to a single Pd atom and Pd 13 nanocluster (experimentally observed on various carbon supports) as supported metal catalysts. The carbon-based nanomaterial includes experimentally probed abundant oxygen functional groups and point defects, demonstrating high thermal stability at room temperature. The characterization confirms the structural motifs presented in the model, distinguishing the organic functionalities and various defects using spectroscopy techniques. Interestingly, the oxygenated carbon-based support presents a metallic character when the formal charges in the embedded Pd atom and nanocluster have been determined to be [Pd] + and [Pd 13 ] 3+ . The hydrogenation process of the adsorbed cluster is also presented, with the determination of a ratio between the adsorbed hydrides and the surface metal atoms close to unity at room temperature, thanks to ab initio molecular dynamics.

Adjustment of the Single Atom/Nanoparticle Ratio in Pd/CNT Catalysts for Phenylacetylene Selective Hydrogenation

“…[22] The second doublet with a Pd 3d 5/2 BE between at 337.2-337.9 eV can be safely attributed to electron-deficient Pd SA, [23] experiencing significant charge transfer from the metal to the support. [24] As expected, the peak corresponding to Pd SA is increasing from catA to catD, whereas the peak corresponding to Pd NP is simultaneously decreasing (Figure 3). The atomic percentage of Pd SA determined by XPS followed the order: catA (21.4 %) < catB (35.0 %) < catC (45.5 %) < catD (62.5 %).…”

“…Partial occupancies were estimated with a Gaussian smearing (σ) of 0.05 eV during all relaxations and extrapolating the energies to σ=0.00 eV. As recently computationally modeled and described by some of us, [24a] the supported metal catalyst consists of an O‐functionalized graphene (including experimentally probed abundant oxygen functional groups and point defects) as carbon support, together with a single Pd atom in a single vacancy and an ultra‐small Pd 13 nanoparticle as supported metal catalysts, the latter being hydrogenated with a ratio between adsorbed hydrides and surface metal atoms above unity. Γ‐Centered (3×3×1) k ‐point mesh generated using the Monkhorst‐Pack method was employed [46] .…”

Photoinduced loading of electron-rich Cu single atoms by moderate coordination for hydrogen evolution

“…The SACs possess distinct active sites or catalytic pathways different from those of conventional metal catalysts, exhibiting superior activity and selectivity towards oxygen reduction 6 – 8 , CO oxidation 1 , 9 , hydrogenation reactions 5 , 10 , and other important reactions 11 – 16 . During the past decade, various concepts for atomic dispersion of metals on solid supports have emerged, such as the utilization of vacancy defects on supports 17 – 19 , fabrication of metal-organic frameworks (MOFs) 20 , 21 , spatial confinement in zeolites 22 , 23 , and enhancement of the metal-support interactions 3 , 24 – 26 . However, these routes involve fussy synthetic steps and sensitive conditions, including adsorption and reduction of metal precursors 27 , 28 .…”

Structure–Activity Relationship of Continuous Transformed Palladium Nanoclusters and Single Atoms for Selective Phenylacetylene Hydrogenation

“…Unfortunately, the highly selective hydrogenation of phenylacetylene to styrene remains a tremendous challenge, because phenylacetylene is prone to be further hydrogenated to phenylethane. − Until now, Pd-based ADCs are the most applicable catalysts in this reaction. − However, the ambiguous understanding of their specific active site structures and working mechanism leads to controversial findings. While some studies claim that Pd nanoclusters (NCs), Pd nanoparticles (NPs), and Pd-based alloy NPs perform better than Pd single atoms in selective phenylacetylene hydrogenation, − Pd single atoms have also been reported to possess superior ability of catalyzing semi-hydrogenation of phenylacetylene than Pd NCs and Pd NPs. , The dispute of this issue partly results from the lack of studies that synthesize Pd-based NCCs and SACs with the same chemical procedures and systematically unveil their structure–activity relationship. Moreover, the steric hindrance caused by additional functional groups of phenylacetylene is often ignored …”