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Single-atom vs. single-superatom as catalysts for ammonia production
A new class of single-superatom catalyst (TiO, ZrO, and WC) supported on graphene is shown to outperform the stability and activity of their corresponding single-atom catalysts (Ni, Pd and Pt) for the electrochemical nitrogen reduction reaction.
Achieving Ultra-High Selectivity to Hydrogen Production from Formic Acid on Pd–Ag Alloys
Palladium-silver based alloy catalysts have a great potential for CO-free hydrogen production from formic acid for fuel cell applications. However, the structural factors affecting the selectivity of formic acid decomposition is still debated. Herein, the decomposition pathways of formic acid on Pd-Ag alloys with different atomic configurations have been investigated to identify the alloy structures yielding high H 2 selectively. Several Pd x Ag 1-x surface alloys with various compositions were generated on a Pd(111) single crystal; their atomic distribution and electronic structure were determined by a combination of infrared reflection absorption spectroscopy (IRAS), X-ray photoelectron spectroscopy (XPS), and density functional theory (DFT). It was established that the Ag atoms with Pd neighbors are electronically altered, and the degree of alteration correlates with the number of nearest Pd. Temperature programmed reaction spectroscopy (TPRS) and DFT demonstrated that the electronically altered Ag domains create a new reaction pathway that selectively dehydrogenates formic acid. In contrast, Pd monomers surrounded by Ag are demonstrated to have a similar reactivity compared to pristine Pd(111), yielding CO and H 2 O in addition to the dehydrogenation products. Furthermore, they bind to the produced CO weaker than pristine Pd, demonstrating an enhancement in resistance to CO poisoning. This work therefore shows that surface Ag domains modified by interaction with subsurface Pd are the key active sites for selective decomposition of formic acid, while surface Pd atoms are detrimental for selectivity. Hence the decomposition pathways can be tailored for CO-free H 2 production on Pd-Ag alloy systems.
PdCu Single Atom Alloys for the Selective Oxidation of Methanol to Methyl Formate at Low Temperatures
The selective catalytic oxidation of methanol to methyl formate (MF) has been considered as an attractive route to produce MF, an important precursor in the chemical industry. Although supported Pd nanoparticles are active for the selective oxidation of methanol to MF, the relatively low MF selectivity and yield remains an unsolved issue. Here in this paper, we show that adding a small amount of Pd into Cu forming PdCu single atom alloy (SAA) catalysts can catalyze the oxidation of methanol to MF selectively at low temperatures, with a high catalyst stability. The atomic dispersion of Pd atoms in the Cu matrix was confirmed by various in-situ characterization techniques. The activity and selectivity of PdCu SAA catalysts were compared to monometallic Cu and Pd catalysts, in a flow reactor at similar conditions. This work may guide the design of new SAA based catalysts for selective oxidation reactions.
Materials Data on Mg29Pd4 by Materials Project
Mg29Pd4 crystallizes in the cubic F-43m space group. The structure is three-dimensional. there are eleven inequivalent Mg sites. In the first Mg site, Mg is bonded in a distorted single-bond geometry to two equivalent Mg and one Pd atom. Both Mg–Mg bond lengths are 3.21 Å. The Mg–Pd bond length is 2.80 Å. In the second Mg site, Mg is bonded in a distorted linear geometry to two equivalent Pd atoms. Both Mg–Pd bond lengths are 2.90 Å. In the third Mg site, Mg is bonded in a 2-coordinate geometry to two equivalent Pd atoms. Both Mg–Pd bond lengths are 3.12 Å. In the fourth Mg site, Mg is bonded in a distorted single-bond geometry to one Pd atom. The Mg–Pd bond length is 2.94 Å. In the fifth Mg site, Mg is bonded in a tetrahedral geometry to four equivalent Mg atoms. All Mg–Mg bond lengths are 2.95 Å. In the sixth Mg site, Mg is bonded in a 2-coordinate geometry to two Pd atoms. There are one shorter (2.74 Å) and one longer (2.97 Å) Mg–Pd bond lengths. In the seventh Mg site, Mg is bonded in a 2-coordinate geometry to two Pd atoms. There are one shorter (2.80 Å) and one longer (2.99 Å) Mg–Pd bond lengths. In the eighth Mg site, Mg is bonded in a 10-coordinate geometry to ten Mg atoms. All Mg–Mg bond lengths are 2.96 Å. In the ninth Mg site, Mg is bonded in a distorted single-bond geometry to one Mg and one Pd atom. The Mg–Pd bond length is 2.88 Å. In the tenth Mg site, Mg is bonded in a distorted trigonal non-coplanar geometry to three equivalent Pd atoms. All Mg–Pd bond lengths are 2.86 Å. In the eleventh Mg site, Mg is bonded in a bent 150 degrees geometry to two equivalent Pd atoms. Both Mg–Pd bond lengths are 2.73 Å. There are three inequivalent Pd sites. In the first Pd site, Pd is bonded in a 9-coordinate geometry to nine Mg atoms. In the second Pd site, Pd is bonded to twelve Mg atoms to form corner-sharing PdMg12 cuboctahedra. In the third Pd site, Pd is bonded to twelve Mg atoms to form a mixture of face and corner-sharing PdMg12 cuboctahedra.
Ligand-coordination effects on the selective hydrogenation of acetylene in single-site Pd-ligand supported catalysts
The selective hydrogenation of acetylene to ethylene is a critical step in the synthesis of polyethylenes. Achieving high conversion to ethylene without over-hydrogenation to ethane is a challenge that requires control of the transition metal site, which we achieve through a ligand-coordinated supported catalyst (LCSC) strategy. Using Pd catalysts coordinated to 1,10-phenanthroline-5,6-dione (PDO) ligands on CeO2 supports, we have discovered that the reaction selectivity depends strongly on the ligand:metal ratio with higher selectivity when more ligand is present in the catalyst. Catalyst structure was examined by extended X-ray absorption fine structure spectroscopy, transmission electron microscopy, and CO adsorption, which indicate single-atom character of the Pd. The ligand:metal ratio is determined by Xray photoelectron spectroscopy measurements and correlated with hydrogenation reactions under steady-state flow conditions to examine trends in hydrogenation activity and selectivity. Those trends can be better understood by density functional theory calculations that indicate hydrogen binding on the ligand to guide reaction selectivity toward the desired ethylene hydrogenation product. Here these results demonstrate the importance of considering the dynamic character of LCSCs and inform the design of future single-site heterogeneous catalysts.
Materials Data on Bi2Pd3S2 by Materials Project
Pd3Bi2S2 crystallizes in the monoclinic C2/m space group. The structure is zero-dimensional and consists of four bismuth molecules, four palladium molecules, and two PdS2 clusters. In each PdS2 cluster, Pd is bonded in a linear geometry to two equivalent S atoms. Both Pd–S bond lengths are 2.11 Å. S is bonded in a single-bond geometry to one Pd atom.
Materials Data on Mg5Pd2 by Materials Project
Mg5Pd2 crystallizes in the hexagonal P6_3/mmc space group. The structure is three-dimensional. there are three inequivalent Mg sites. In the first Mg site, Mg is bonded in a distorted single-bond geometry to three equivalent Pd atoms. There are one shorter (2.63 Å) and two longer (3.13 Å) Mg–Pd bond lengths. In the second Mg site, Mg is bonded in a distorted single-bond geometry to three Pd atoms. There are one shorter (2.42 Å) and two longer (2.95 Å) Mg–Pd bond lengths. In the third Mg site, Mg is bonded in a 6-coordinate geometry to six equivalent Pd atoms. All Mg–Pd bond lengths are 2.75 Å. There are two inequivalent Pd sites. In the first Pd site, Pd is bonded in a 10-coordinate geometry to ten Mg atoms. In the second Pd site, Pd is bonded in a distorted trigonal planar geometry to three equivalent Mg atoms.
Engineering Ultrathin Alloy Shell in Au@AuPd Core-Shell Nanoparticles for Efficient Plasmon-Driven Photocatalysis
Bimetallic core-shell nanoparticles (NPs) possessing a synergetic coupling of plasmonic and catalytic metals have emerged as promising prototypes for efficient plasmon-driven photocatalysis. Here, Au@AuPd core-shell NPs composed of Au core NP and ultrathin AuPd shell are introduced to acquire improved light utilization efficiency in photocatalytic selective oxidation. With systematical control of the composition of the ultrathin alloy shell, it reveals that the Au@AuPd core-shell NPs with 10 at% Pd (in the single-atom alloy regime) is an effective nanostructure capable of maximizing the quantum yield of plasmon-induced light absorption and optimizing the surface electronic structure for catalytic reactions. This controlled system provides new insights into shell engineering for enhancing photocatalytic performance via the regulation of energy funneling processes in core-shell nanocatalysts.
Selective acetylene hydrogenation over single metal atoms supported on Fe 3 O 4 (001): A first-principle study
Supported single-atom catalysts (SACs) have gained increasing attention for improved catalytic activity and selectivity for industrially-relevant reactions. In this study, we explore the hydrogenation of acetylene over single Pt, Ru, Rh, Pd, and Ir atoms supported on the Fe 3 O 4 (001) surface using density functional theory (DFT) calculations. The thermodynamic profile of H diffusion is significantly changed with the type of single metal atoms used and suggests that H spillover from the single atom dopant to the Fe 3 O 4 (001) surface is favored and will likely lead to high H coverages in the functioning catalyst. Correspondingly, as the surface H coverage increases, the important desorption step of ethylene becomes energetically competitive against the detrimental hydrogenation steps of ethylene to ethane. Overall, we show herein that the selectivity of SACs towards ethylene production can be tuned by considering the proper type of metal and controlling the redox state of the support.
Method for preparation of nanoceria supported atomic noble metal catalysts and the application of platinum single atom catalysts for direct methane conversion
Described are methods for converting methane to olefins, aromatics, or a combination thereof using a single atom catalyst comprising CeO2 nanoparticles impregnated with individual atoms of noble metals including Pt, Pd, Rh, Ru, Ag, Au, Ir, or a combination thereof. These single atom catalysts of the present invention are heated with methane to form olefins and aromatics.
Investigation of the structure and chemical nature of Pd fission product agglomerations in irradiated TRISO particle SiC
Tristructural-isotropic (TRISO)-coated fuel particles are used in high-temperature gas-cooled nuclear reactors. Although the polycrystalline 3C-SiC layer acts as the main barrier to fission product release, post-irradiation examinations have shown that certain metallic fission products are found outside of the TRISO coated particle, with no observable micro-cracks or other mechanical failure feature. In this study, an atomic resolution transmission electron microscopy investigation of a SiC layer of a neutron irradiated (19.38% fissions per initial metal atom average burnup; 1072°C time-averaged temperature) TRISO-coated particle from the first advanced gas reactor experiment at Idaho National Laboratory containing mainly Pd and U was conducted. The fission product Pd was found to be present at dislocation cores associated with twins, stacking faults, and their intersections. The Pd present at the dislocation cores were bonded to Si, suggesting that the diffusion of Pd along the SiC dislocation cores involves the formation of Pd-Si bonds. Evidence of single atom grain boundary migration was also found. Fission product agglomerations at grain boundaries most likely consist of a random solid solution containing Si-FP, Si-C, and C-C type bonding arrangements. No difference in the Si- or C-bonding environment is found for the unoccupied grain boundary adjacent to a fission product agglomeration compared to the bulk SiC.
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.
Direct strain correlations at the single-atom level in three-dimensional core-shell interface structures
Abstract Nanomaterials with core-shell architectures are prominent examples of strain-engineered materials. The lattice mismatch between the core and shell materials can cause strong interface strain, which affects the surface structures. Therefore, surface functional properties such as catalytic activities can be designed by fine-tuning the misfit strain at the interface. To precisely control the core-shell effect, it is essential to understand how the surface and interface strains are related at the atomic scale. Here, we elucidate the surface-interface strain relations by determining the full 3D atomic structure of Pd@Pt core-shell nanoparticles at the single-atom level via atomic electron tomography. Full 3D displacement fields and strain profiles of core-shell nanoparticles were obtained, which revealed a direct correlation between the surface and interface strain. The strain distributions show a strong shape-dependent anisotropy, whose nature was further corroborated by molecular statics simulations. From the observed surface strains, the surface oxygen reduction reaction activities were predicted. These findings give a deep understanding of structure-property relationships in strain-engineerable core-shell systems, which can lead to direct control over the resulting catalytic properties.
Materials Data on Ti3Pd5 by Materials Project
Pd5Ti3 crystallizes in the tetragonal P4/mmm space group. The structure is three-dimensional. there are two inequivalent Ti sites. In the first Ti site, Ti is bonded in a distorted linear geometry to two equivalent Pd atoms. Both Ti–Pd bond lengths are 2.83 Å. In the second Ti site, Ti is bonded in a 5-coordinate geometry to five Pd atoms. There are four shorter (2.64 Å) and one longer (2.70 Å) Ti–Pd bond lengths. There are three inequivalent Pd sites. In the first Pd site, Pd is bonded in a 10-coordinate geometry to ten Pd atoms. There are eight shorter (2.77 Å) and two longer (2.97 Å) Pd–Pd bond lengths. In the second Pd site, Pd is bonded in a 10-coordinate geometry to five Ti and one Pd atom. In the third Pd site, Pd is bonded in a distorted single-bond geometry to one Ti and four equivalent Pd atoms.
Materials Data on Rb3Pd by Materials Project
Rb3Pd crystallizes in the cubic Im-3 space group. The structure is three-dimensional and consists of two Rb3Pd frameworks. Rb is bonded in a distorted single-bond geometry to two Pd atoms. There are one shorter (3.25 Å) and one longer (4.23 Å) Rb–Pd bond lengths. There are two inequivalent Pd sites. In the first Pd site, Pd is bonded in a cuboctahedral geometry to twelve equivalent Rb atoms. In the second Pd site, Pd is bonded in a square co-planar geometry to four equivalent Rb atoms.
Materials Data on Ba4Pd by Materials Project
Ba4Pd is Iron carbide-like structured and crystallizes in the cubic Fd-3m space group. The structure is zero-dimensional and consists of eight Ba4Pd clusters. Ba is bonded in a single-bond geometry to one Pd atom. The Ba–Pd bond length is 2.98 Å. Pd is bonded in a tetrahedral geometry to four equivalent Ba atoms.
Materials Data on Rb3Pd by Materials Project
Rb4PdRb8Pd3 crystallizes in the tetragonal I4/mmm space group. The structure is two-dimensional and consists of two Rb4Pd clusters and two Rb8Pd3 sheets oriented in the (0, 0, 1) direction. In each Rb4Pd cluster, Rb is bonded in a single-bond geometry to one Pd atom. The Rb–Pd bond length is 3.16 Å. Pd is bonded in a square co-planar geometry to four equivalent Rb atoms. In each Rb8Pd3 sheet, Rb is bonded in a water-like geometry to two Pd atoms. There are one shorter (3.56 Å) and one longer (3.72 Å) Rb–Pd bond lengths. There are two inequivalent Pd sites. In the first Pd site, Pd is bonded in a body-centered cubic geometry to eight equivalent Rb atoms. In the second Pd site, Pd is bonded in a 4-coordinate geometry to four equivalent Rb atoms.