AgPd and CuPd Catalysts for Selective Hydrogenation of Acetylene
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36 MATERIALS SCIENCE↗
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Mechanistic Insights into Acetate Selectivity on Intermetallic CuPd(110) in CO Reduction
Experimental studies demonstrate that CuPd(110) uniquely favors acetate formation during CO reduction (CORR), contrasting with the preference for ethylene on Cu surfaces. To elucidate this selectivity, we employed explicit solvation density functional theory (DFT) calculations to investigate the reaction mechanism from both thermodynamic and kinetic angles. Here, our findings reveal that on CuPd(110), the acetate-pathway intermediate H 2 CCO is thermodynamically favored at experimental conditions, while CHCHO─a precursor to ethylene─is preferred on Cu(111). Beyond thermodynamics, we find that H 2 CCO is kinetically accessible under the experimental conditions on CuPd(110), aiding acetate formation. Electron density difference analyses further corroborate distinct protonation preferences supporting this mechanism. We propose a thermodynamic screening parameter based on the Gibbs free energy, G H 2 CCO < G CHCHO , as a guide for designing Cu-based catalysts with enhanced acetate selectivity. These results offer critical mechanistic insights into the CORR product distribution and a rational framework for future catalyst design.
Acetate↗
Atomic Layers of B2 CuPd on Cu Nanocubes as Catalysts for Selective Hydrogenation
The search for highly active and selective catalysts with high precious metal atom utilization efficiency has attracted increasing interest in both the fundamental synthesis of materials and important industrial reactions. Here, in this work, we report the synthesis of Pd–Cu nanocubes with a Cu core and an ordered B2 intermetallic CuPd shell with controllable atomic layers on the surface (denoted as Cu/B2 CuPd), which can efficiently and robustly catalyze the selective hydrogenation of acetylene (C 2 H 2 ) to ethylene (C 2 H 4 ) under mild conditions. The optimized Cu/B2 CuPd with a Pd loading of 9.5 at. % exhibited outstanding performance in the C 2 H 2 semi-hydrogenation with 100% C 2 H 2 conversion and 95.2% C 2 H 4 selectivity at 90 °C. We attributed this outstanding performance to the core/shell structure with a high surface density of active Pd sites isolated by Cu in the B2 intermetallic matrix, representing a structural motif of single-atom alloys (SAAs) on the surface. The combined experimental and computational studies further revealed that the electronic states of Pd and Cu are modulated by SAAs from the synergistic effect between Pd and Cu, leading to enhanced performance compared with pristine Pd and Cu catalysts. This study provides a new synthetic methodology for making single-atom catalysts with high precious metal atom utilization efficiency, enabling simultaneous tuning of both geometric and electronic structures of Pd active sites for enhanced catalysis.
36 MATERIALS SCIENCE↗
The role of surface chemistry in the synthesis of supported CuPd bimetallic/intermetallic catalysts for selective hydrogenation reactions
Understanding and controlling the structure of supported bimetallic/intermetallic catalysts are crucial for many heterogeneous catalytic reactions. However, commonly used synthesis techniques such as coimpregnation and coadsorption often yield nonuniform alloying and phase segregation, largely owing to the lack of interactions between different metal precursors. Here we show that by adopting sequential adsorption of complex metal cations and anions with the assistance of a proper ligand, the interaction between different metal precursors is enhanced, thus resulting in uniformly alloyed intermetallic catalysts. Importantly, the supported CuPd intermetallic catalyst exhibits greatly improved selectivity towards monoolefins in the semihydrogenation of acetylene and butadiene compared to those random CuPd alloys synthesized via coimpregnation and coadsorption methods.
37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
Decoupling size and surface effects of intermetallic CuPd nanocrystals for electrocatalytic nitrate reduction to ammonia
Nitrate pollution poses a major environmental challenge, but its electrochemical conversion to ammonia offers a sustainable waste-to-value solution. Here, in this study, we synthesized monodisperse, size-tunable B2-phase CuPd intermetallic nanocrystals (6–46 nm) and studied their performance in the electrochemical nitrate reduction reaction (eNO 3 RR). By using bromide ions to modulate Pd reduction and applying mild annealing, we achieved phase-pure B2 structures across all sizes. Catalytic testing revealed a volcano-like trend in ammonia yield, peaking at 33 nm nanocubes with a rate of 6.97 mol h −1 g −1 at −0.6 V vs. reversible hydrogen electrode (RHE). This optimum reflects a balance between the increased surface area of smaller particles and the enhanced exposure of active (100) facets in larger ones. Theoretical calculations indicated that the B2-CuPd (100) facet is favorable for nitrate adsorption, thereby supporting the high activity of nanocubes. Our results highlight the critical role of tuning both nanoparticle size and surface structure to maximize eNO 3 RR efficiency.
36 MATERIALS SCIENCE↗
Breaking adsorption-energy scaling limitations of electrocatalytic nitrate reduction on intermetallic CuPd nanocubes by machine-learned insights
The electrochemical nitrate reduction reaction (NO 3 RR) to ammonia is an essential step toward restoring the globally disrupted nitrogen cycle. In search of highly efficient electrocatalysts, tailoring catalytic sites with ligand and strain effects in random alloys is a common approach but remains limited due to the ubiquitous energy-scaling relations. With interpretable machine learning, we unravel a mechanism of breaking adsorption-energy scaling relations through the site-specific Pauli repulsion interactions of the metal d-states with adsorbate frontier orbitals. The non-scaling behavior can be realized on (100)-type sites of ordered B2 intermetallics, in which the orbital overlap between the hollow *N and subsurface metal atoms is significant while the bridge-bidentate *NO 3 is not directly affected. Among those intermetallics predicted, we synthesize monodisperse ordered B2 CuPd nanocubes that demonstrate high performance for NO 3 RR to ammonia with a Faradaic efficiency of 92.5% at –0.5 V RHE and a yield rate of 6.25 mol h –1 g –1 at –0.6 V RHE . This study provides machine-learned design rules besides the d-band center metrics, paving the path toward data-driven discovery of catalytic materials beyond linear scaling limitations.
37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
Materials Data on CuPd by Materials Project
PdCu is Tetraauricupride structured and crystallizes in the cubic Pm-3m space group. The structure is three-dimensional. Pd is bonded in a body-centered cubic geometry to eight equivalent Cu atoms. All Pd–Cu bond lengths are 2.61 Å. Cu is bonded in a body-centered cubic geometry to eight equivalent Pd atoms.
36 MATERIALS SCIENCE↗
Materials Data on CuPd by Materials Project
PdCu crystallizes in the orthorhombic Cmmm space group. The structure is two-dimensional and consists of two PdCu sheets oriented in the (0, 1, 0) direction. Pd is bonded in a 4-coordinate geometry to four equivalent Cu atoms. All Pd–Cu bond lengths are 2.59 Å. Cu is bonded in a 4-coordinate geometry to four equivalent Pd atoms.
36 MATERIALS SCIENCE↗
Materials Data on CuPd by Materials Project
PdCu crystallizes in the trigonal R-3m space group. The structure is three-dimensional. there are two inequivalent Pd sites. In the first Pd site, Pd is bonded to six equivalent Pd and six Cu atoms to form distorted PdCu6Pd6 cuboctahedra that share corners with twelve PdCu6Pd6 cuboctahedra, edges with twelve PdCu6Pd6 cuboctahedra, edges with twelve CuCu6Pd6 cuboctahedra, faces with six equivalent PdCu6Pd6 cuboctahedra, and faces with twelve CuCu6Pd6 cuboctahedra. All Pd–Pd bond lengths are 2.74 Å. All Pd–Cu bond lengths are 2.65 Å. In the second Pd site, Pd is bonded to ten equivalent Pd and six Cu atoms to form distorted PdCu6Pd10 cuboctahedra that share corners with ten CuCu6Pd6 cuboctahedra, corners with twelve PdCu6Pd6 cuboctahedra, edges with eight CuCu6Pd6 cuboctahedra, edges with sixteen PdCu6Pd6 cuboctahedra, faces with sixteen equivalent PdCu6Pd10 cuboctahedra, and faces with eighteen CuCu6Pd6 cuboctahedra. There are a spread of Pd–Pd bond distances ranging from 2.74–5.48 Å. All Pd–Cu bond lengths are 2.65 Å. There are three inequivalent Cu sites. In the first Cu site, Cu is bonded to six equivalent Pd and six equivalent Cu atoms to form distorted CuCu6Pd6 cuboctahedra that share corners with twelve CuCu6Pd6 cuboctahedra, edges with twelve equivalent PdCu6Pd6 cuboctahedra, edges with twelve CuCu6Pd6 cuboctahedra, faces with six equivalent CuCu6Pd6 cuboctahedra, and faces with twelve equivalent PdCu6Pd6 cuboctahedra. All Cu–Cu bond lengths are 2.74 Å. In the second Cu site, Cu is bonded to six Pd and six equivalent Cu atoms to form distorted CuCu6Pd6 cuboctahedra that share corners with five equivalent PdCu6Pd10 cuboctahedra, corners with twelve CuCu6Pd6 cuboctahedra, edges with ten PdCu6Pd6 cuboctahedra, edges with twelve CuCu6Pd6 cuboctahedra, faces with six equivalent CuCu6Pd6 cuboctahedra, and faces with fifteen PdCu6Pd6 cuboctahedra. All Cu–Pd bond lengths are 2.65 Å. All Cu–Cu bond lengths are 2.74 Å. In the third Cu site, Cu is bonded to six Pd and six equivalent Cu atoms to form distorted CuCu6Pd6 cuboctahedra that share corners with five equivalent PdCu6Pd10 cuboctahedra, corners with twelve CuCu6Pd6 cuboctahedra, edges with ten PdCu6Pd6 cuboctahedra, edges with twelve CuCu6Pd6 cuboctahedra, faces with six equivalent CuCu6Pd6 cuboctahedra, and faces with fifteen PdCu6Pd6 cuboctahedra. All Cu–Cu bond lengths are 2.74 Å.
36 MATERIALS SCIENCE↗
Interpreting the Operando X-ray Absorption Near-Edge Structure of Supported Cu and CuPd Clusters in Conditions of Oxidative Dehydrogenation of Propane: Dynamic Changes in Composition and Size
Supported subnano-cluster catalysts are highly dynamic, developing true active sites only under the pressures and temperatures of reaction conditions. Operando X-ray absorption near-edge structure (XANES) spectroscopy can track changes in the oxidation state and the local environment of cluster atoms, providing insight into the development of these active sites. While bulk metal, oxide, and hydroxide standards are often used for fitting experimental XANES spectra to obtain average oxidation states, we recently showed that computed cluster standards of relevant compositions are a more suitable basis, producing more accurate fits. Here, we theoretically interpret the operando XANES of supported Cu 3 Pd and Cu 4 clusters during temperature-programmed reaction (TPRx) of oxidative dehydrogenation of propane. We use an expanded basis set including both globally optimized computed clusters and bulk standards. Not only can we track reversible composition/oxidation state change with temperature, but also the irreversible growth of the bulk fraction upon heating, which we attribute to cluster sintering. This has important implications for the mechanism of the catalyzed reaction and the nature of the available active sites. Here, we propose that operando XANES provides most significant insight into the nature of supported cluster catalysts in reaction conditions when interpreted using mixed computed cluster and bulk standards.
37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
Correlating binding energies of adsorbed CO and H on model surfaces with CO/H 2 selectivity from co-electrolysis of CO 2 and H 2 O over copper–palladium bimetallic catalysts
Binding energies of adsorbed CO and H are key descriptors governing the activity and selectivity of the co-electrolysis of CO 2 and H 2 O to produce syngas with desired CO/H 2 ratios. Palladium hydride (PdH), which forms in situ at negative overpotentials, has been identified as the active Pd phase for CO 2 reduction to syngas. Herein, binding energies of CO and H are determined using temperature programmed desorption (TPD) of CO and H 2 from Pd(111), PdH/Pd(111), and Cu/PdH/Pd(111) under ultra-high vacuum (UHV) conditions. TPD results reveal that desorption of H 2 from subsurface PdH occurs at 460 K, while desorption from surface PdH is more facile at 320 K. CO desorption temperatures shift 20 K lower on PdH/Pd(111) compared to on Pd(111). The presence of 0.7 ML Cu further increases the desorption temperature of H 2 by 30 K while simultaneously reducing CO desorption temperatures by 70 K. Density functional theory (DFT) calculations show that CO adsorption onto Pd sites is hindered on the 0.7 ML Cu/PdH/Pd(111) surface while the kinetic barrier for H 2 desorption is increased. The trends in the binding energies of CO and H on model surfaces are consistent with electrochemical measurements of CuPd powder catalysts in a membrane electrode assembly (MEA), where H 2 evolution is reduced while CO production is enhanced compared to unmodified Pd catalysts. Overall, the results from model surface studies (TPD and DFT) provide a prediction and explanation for the activity and CO/H 2 ratios observed in electrochemical experiments. This study also demonstrates that CuPd is a promising catalyst with reduced Pd-loading to produce CO-rich syngas.
36 MATERIALS SCIENCE↗
Oxidative dehydrogenation of cyclohexene on atomically precise subnanometer Cu 4− n Pd n (0 ≤ n ≤ 4) tetramer clusters: the effect of cluster composition and support on performance
High fidelity selectivity tuning of the oxidative dehydrogenation of cyclohexene was achieved through the control of the atomic composition of CuPd clusters and their interactions with the support.
37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
Atomistic Modeling of Surface and Bulk Properties of Cu, Pd and the Cu-Pd System
The BFS (Bozzolo-Ferrante-Smith) method for alloys is applied to the study of the Cu-Pd system. A variety of issues are analyzed and discussed, including the properties of pure Cu or Pd crystals (surface energies, surface relaxations), Pd/Cu and Cu/Pd surface alloys, segregation of Pd (or Cu) in Cu (or Pd), concentration dependence of the lattice parameter of the high temperature fcc CuPd solid solution, the formation and properties of low temperature ordered phases, and order-disorder transition temperatures. Emphasis is made on the ability of the method to describe these properties on the basis of a minimum set of BFS universal parameters that uniquely characterize the Cu-Pd system.
Bozzolo, Guillermo↗