Catalytic Synergies in Bimetallic RuPt Single–Atom Catalysts via Speciation Control

Abstract

Bimetallic single-atom catalysts (b-SACs) have recently gained prominence by virtue of the unique catalytic cooperative interactions they can exhibit, intertwining electronic and geometric effects. To date, research efforts have exclusively focused on direct mechanisms such as electron density transfer or sequential reactivity. Herein, the first study on indirect, coordination-induced catalytic synergies in carbon-supported RuPt SACs is conducted. To this end, a holistic approach is developed, combining i) precision synthesis, ii) advanced characterization, iii) exploration of single-site adsorption properties via the hydrogen evolution reaction, and iv) modeling through density functional theory. Despite the lack of both intermetallic coordination in the first or second shell and charge redistribution effects, the RuPt SACs exhibit a H 2 formation rate enhanced up to 15-fold compared with their monometallic counterparts. To unfold the origin of the intermetallic cooperativity, modifications of the structural and catalytic properties induced by the integration of a second metal species are investigated. Thus, Pt atoms are found to selectively occupy the most energeticallyfavorable cavities in the support, prompting Ru atoms to assume a distinct, more active, configuration. This contribution unveils a novel principle of bimetallic cooperativity, demonstrating the key role of integrative experimental and computational analyses in studying b-SACs.

Selectivity Control in Palladium-Catalyzed CH2Br2 Hydrodebromination on Carbon-Based Materials by Nuclearity and Support Engineering

“…To represent the wide range of possible chemical environments in NC, speciation analysis of Pd over the NC cavities is conducted by calculating Boltzmann distributions of the chlorinated Pd species, deriving from the H 2 PdCl 4 precursor employed in the synthetic procedure (Tables S5 and S6). To this end, tri-pyrrolic (3 × N5) and tetra-pyridinic (4 × N6) sites are selected as representatives of trigonal and square-planar geometries (Figure S19), respectively, in line also with literature-reported studies. , The calculated distribution demonstrates that chlorinated species (PdCl x , x = 1–4) tend to adsorb on 3 × N5 sites (41–94% of the Boltzmann population), although upon thermal treatment, Pd SAs are preferably stabilized on square-planar 4 × N6 sites, reflected by a significant reduction in the calculated Boltzmann population (up to 8%). While the EXAFS analysis of Pd SA /NC (Pd-N CN = 4.4, Table S1) derived from EXAFS fitting would suggest stabilization of the Pd atoms on 4 × N6 sites, the square-planar geometry of this configuration leads to virtually inactive metal sites (Table S7).…”

“…For the simulation of the SACs, a Pd atom was placed on the N-cavity of the selected carbon-based hosts. Tri-pyrrolic (3 × N5) and tetra-pyridinic (4 × N6) sites are selected as representatives of trigonal and square-planar geometries, respectively, in agreement also with literature-reported studies . Speciation analysis of Pd over the distinct cavities of NC was performed via Boltzmann distribution calculations taking into account different degrees of chlorination of the Pd atom, in order to simulate the synthetic conditions .…”

Challenges and Opportunities in Engineering the Electronic Structure of Single-Atom Catalysts

“…Although the number of studies covering the integration of multiple metal sites is rapidly increasing, reporting diverse electronic cooperative mechanisms between metal centers, general geometry-electronic property relations have not yet been unraveled. While the intersite distance has been proposed as a descriptor to quantitatively evaluate the electronic metal–metal interactions, 84 , 87 , 88 rationalization of intermetallic catalytic synergies should not overlook other structural features, such as local coordination, 73 , 89 for accurate analysis of orbital hybridization and charge transfer effects.…”

Electronic and Structural Engineering of Atomically Dispersed Isolated Single‐Atom and Alloy Architectures

“…Precise regulation and an in-depth understanding of the atom-scale effect suggested that the heteronuclear dual SA and SA dimers exhibit an improved atomic interface (Figure 12d) for electrochemical energy generation and reduction processes. [144,207,208] The dynamic atomiclevel structure under conditions of alkaline HER is influenced by the electrochemical properties of the active sites, which are a result of coordination engineering. The dynamic structure results from surface self-reconstruction and is possible to track by using atomic level identification by XANES spectral analysis.…”