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At least 19 records
All sourcesNASA NTRSDOE OSTI
DOE OSTI2021

Mechanistic insights into carbon–carbon coupling on NiAu and PdAu single-atom alloys

Carbon–carbon coupling is an important step in many catalytic reactions, and performing sp 3 –sp 3 carbon–carbon coupling heterogeneously is particularly challenging. It has been reported that PdAu single-atom alloy (SAA) model catalytic surfaces are able to selectively couple methyl groups, producing ethane from methyl iodide. In this work, we extend this study to NiAu SAAs and find that Ni atoms in Au are active for C–I cleavage and selective sp 3 –sp 3 carbon–carbon coupling to produce ethane. Furthermore, we perform ab initio kinetic Monte Carlo simulations that include the effect of the iodine atom, which was previously considered a bystander species. We find that model NiAu surfaces exhibit a similar chemistry to PdAu, but the reason for the similarity is due to the role the iodine atoms play in terms of blocking the Ni atom active sites. Specifically, on NiAu SAAs, the iodine atoms outcompete the methyl groups for occupancy of the Ni sites leaving the Me groups on Au, while on PdAu SAAs, the binding strengths of methyl groups and iodine atoms at the Pd atom active site are more similar. These simulations shed light on the mechanism of this important sp 3 –sp 3 carbon–carbon coupling chemistry on SAAs. Furthermore, we discuss the effect of the iodine atoms on the reaction energetics and make an analogy between the effect of iodine as an active site blocker on this model heterogeneous catalyst and homogeneous catalysts in which ligands must detach in order for the active site to be accessed by the reactants.

77 NANOSCIENCE AND NANOTECHNOLOGY↗
DOE OSTI2022

Dual-step photocarrier injection by mixture layer of ZnO QDs and MoS 2 NPs on hybrid PdAu NPs

Hybrid UV-photodetector (PD) design consisted of various compatible nano-material systems are drawing significant research interests due to their improved device tunability and functionality. A hybrid ZnO–MoS 2 /HNP UV-PD design is demonstrated by the mixture layer of zinc oxide (ZnO) quantum dot (QD) and molybdenum di-sulfate (MoS 2 ) nanoparticles (NPs) on the plasmonic hybrid PdAu NP template. The proposed design exhibits an excellent photocurrent of 1.45×10 -3 A under the 54.9 mW/mm2 at ± 10 V due to a dual step enhancement of photo-carrier injection. It then leads to the significantly improved performance factors of photo-responsivity 1430 mA/mm 2 and detectivity 4.50 × 10 10 jones at 0.34 mW/mm 2 . The rise time (T r ) and fall time (T f ) of 3.37 and 0.35 s are obtained for the ZnO–MoS 2 /HNP PD. Finally, the demonstrated performance factors indicate that the hybrid ZnO–MoS 2 /HNP UV-PD platform is one of the best UV-PDs as summarized in Table 1.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on U2(PdAu)5 by Materials Project

U2(PdAu)5 is Frank-Kasper $\mu$ Phase-derived structured and crystallizes in the monoclinic Cm space group. The structure is three-dimensional. there are two inequivalent U sites. In the first U site, U is bonded in a 12-coordinate geometry to ten Pd and six Au atoms. There are a spread of U–Pd bond distances ranging from 3.16–3.36 Å. There are a spread of U–Au bond distances ranging from 3.17–3.19 Å. In the second U site, U is bonded in a 12-coordinate geometry to seven Pd and nine Au atoms. There are a spread of U–Pd bond distances ranging from 3.18–3.36 Å. There are a spread of U–Au bond distances ranging from 3.17–3.21 Å. There are five inequivalent Pd sites. In the first Pd site, Pd is bonded in a 12-coordinate geometry to three equivalent U, five Pd, and four Au atoms. There are a spread of Pd–Pd bond distances ranging from 2.72–3.19 Å. There are two shorter (2.69 Å) and two longer (2.70 Å) Pd–Au bond lengths. In the second Pd site, Pd is bonded in a 12-coordinate geometry to three U, four Pd, and five Au atoms. There are two shorter (3.18 Å) and one longer (3.19 Å) Pd–Pd bond lengths. There are a spread of Pd–Au bond distances ranging from 2.71–2.73 Å. In the third Pd site, Pd is bonded in a 12-coordinate geometry to three U, four Pd, and five Au atoms. There are two shorter (3.17 Å) and one longer (3.18 Å) Pd–Pd bond lengths. There are a spread of Pd–Au bond distances ranging from 2.71–2.74 Å. In the fourth Pd site, Pd is bonded in a 2-coordinate geometry to four U, three Pd, and nine Au atoms. There are a spread of Pd–Au bond distances ranging from 3.18–3.20 Å. In the fifth Pd site, Pd is bonded in a 10-coordinate geometry to four U, six Pd, and six Au atoms. There are a spread of Pd–Au bond distances ranging from 3.17–3.19 Å. There are three inequivalent Au sites. In the first Au site, Au is bonded to three U, six Pd, and three Au atoms to form a mixture of corner, edge, and face-sharing AuU3Pd6Au3 cuboctahedra. There are two shorter (2.71 Å) and one longer (2.72 Å) Au–Au bond lengths. In the second Au site, Au is bonded to three U, six Pd, and three Au atoms to form a mixture of distorted corner, edge, and face-sharing AuU3Pd6Au3 cuboctahedra. There are a spread of Au–Au bond distances ranging from 2.69–2.74 Å. In the third Au site, Au is bonded to three equivalent U, five Pd, and four Au atoms to form AuU3Pd5Au4 cuboctahedra that share corners with eight AuU3Pd6Au3 cuboctahedra, edges with six equivalent AuU3Pd5Au4 cuboctahedra, and faces with twelve AuU3Pd6Au3 cuboctahedra.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on Fe2(PdAu)3 by Materials Project

Fe2(PdAu)3 crystallizes in the orthorhombic Pmmm space group. The structure is three-dimensional. Fe is bonded to six Pd and six Au atoms to form FePd6Au6 cuboctahedra that share corners with twelve equivalent FePd6Au6 cuboctahedra, edges with twelve PdFe4Pd4Au4 cuboctahedra, edges with twelve AuFe4Pd6Au2 cuboctahedra, faces with six equivalent FePd6Au6 cuboctahedra, faces with six PdFe4Pd4Au4 cuboctahedra, and faces with six AuFe4Pd6Au2 cuboctahedra. There are four shorter (2.74 Å) and two longer (2.83 Å) Fe–Pd bond lengths. There are four shorter (2.82 Å) and two longer (2.83 Å) Fe–Au bond lengths. There are three inequivalent Pd sites. In the first Pd site, Pd is bonded to four equivalent Fe, four equivalent Pd, and four equivalent Au atoms to form distorted PdFe4Pd4Au4 cuboctahedra that share corners with four equivalent PdFe4Pd4Au4 cuboctahedra, corners with eight equivalent AuFe4Pd4Au4 cuboctahedra, edges with eight equivalent FePd6Au6 cuboctahedra, edges with eight equivalent PdFe4Au8 cuboctahedra, edges with eight equivalent AuFe4Pd6Au2 cuboctahedra, faces with four equivalent FePd6Au6 cuboctahedra, faces with six AuFe4Pd6Au2 cuboctahedra, and faces with eight PdFe4Pd4Au4 cuboctahedra. All Pd–Pd bond lengths are 2.82 Å. All Pd–Au bond lengths are 2.77 Å. In the second Pd site, Pd is bonded to four equivalent Fe and eight Au atoms to form PdFe4Au8 cuboctahedra that share corners with twelve PdFe4Au8 cuboctahedra, edges with eight equivalent FePd6Au6 cuboctahedra, edges with eight equivalent PdFe4Pd4Au4 cuboctahedra, edges with eight equivalent AuFe4Pd6Au2 cuboctahedra, faces with four equivalent FePd6Au6 cuboctahedra, faces with six PdFe4Au8 cuboctahedra, and faces with eight AuFe4Pd6Au2 cuboctahedra. There are four shorter (2.80 Å) and four longer (2.82 Å) Pd–Au bond lengths. In the third Pd site, Pd is bonded to four equivalent Fe, four equivalent Pd, and four equivalent Au atoms to form distorted PdFe4Pd4Au4 cuboctahedra that share corners with twelve PdFe4Au8 cuboctahedra, edges with eight equivalent FePd6Au6 cuboctahedra, edges with sixteen AuFe4Pd6Au2 cuboctahedra, faces with four equivalent FePd6Au6 cuboctahedra, faces with four equivalent AuFe4Pd6Au2 cuboctahedra, and faces with ten PdFe4Pd4Au4 cuboctahedra. All Pd–Au bond lengths are 2.77 Å. There are two inequivalent Au sites. In the first Au site, Au is bonded to four equivalent Fe, six Pd, and two equivalent Au atoms to form distorted AuFe4Pd6Au2 cuboctahedra that share corners with twelve equivalent AuFe4Pd6Au2 cuboctahedra, edges with four equivalent AuFe4Pd4Au4 cuboctahedra, edges with eight equivalent FePd6Au6 cuboctahedra, edges with twelve PdFe4Pd4Au4 cuboctahedra, faces with four equivalent FePd6Au6 cuboctahedra, faces with six PdFe4Pd4Au4 cuboctahedra, and faces with eight AuFe4Pd6Au2 cuboctahedra. Both Au–Au bond lengths are 2.80 Å. In the second Au site, Au is bonded to four equivalent Fe, four equivalent Pd, and four equivalent Au atoms to form distorted AuFe4Pd4Au4 cuboctahedra that share corners with four equivalent AuFe4Pd4Au4 cuboctahedra, corners with eight equivalent PdFe4Pd4Au4 cuboctahedra, edges with eight equivalent FePd6Au6 cuboctahedra, edges with eight equivalent PdFe4Pd4Au4 cuboctahedra, edges with eight equivalent AuFe4Pd6Au2 cuboctahedra, faces with four equivalent FePd6Au6 cuboctahedra, faces with six PdFe4Pd4Au4 cuboctahedra, and faces with eight AuFe4Pd6Au2 cuboctahedra.

36 MATERIALS SCIENCE↗
DOE OSTI2021

Directing reaction pathways via in situ control of active site geometries in PdAu single-atom alloy catalysts

Abstract The atomic scale structure of the active sites in heterogeneous catalysts is central to their reactivity and selectivity. Therefore, understanding active site stability and evolution under different reaction conditions is key to the design of efficient and robust catalysts. Herein we describe theoretical calculations which predict that carbon monoxide can be used to stabilize different active site geometries in bimetallic alloys and then demonstrate experimentally that the same PdAu bimetallic catalyst can be transitioned between a single-atom alloy and a Pd cluster phase. Each state of the catalyst exhibits distinct selectivity for the dehydrogenation of ethanol reaction with the single-atom alloy phase exhibiting high selectivity to acetaldehyde and hydrogen versus a range of products from Pd clusters. First-principles based Monte Carlo calculations explain the origin of this active site ensemble size tuning effect, and this work serves as a demonstration of what should be a general phenomenon that enables in situ control over catalyst selectivity.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2021

Quantifying oxygen induced surface enrichment of a dilute PdAu alloy catalyst

Dilute PdAu alloys are promising catalysts for selective oxidation and hydrogenation reactions. However, the surface composition and active site density of the minority metal, Pd, is unknown. Here, we quantitatively determine a three-fold increase in the Pd site density on the surface of a dilute Pd 0.08 Au 0.92 alloy catalyst after oxygen activation by titrating the oxidized surface with quantified pulses of CO.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2025

Partial PdAu nanoparticle embedding into TiO 2 support accentuates catalytic contributions from the Au/TiO 2 interface

Despite the broad catalytic relevance of metal–support interfaces, controlling their chemical nature, the interfacial contact perimeter (exposed to reactants), and consequently, their contributions to overall catalytic reactivity, remains challenging, as the nanoparticle and support characteristics are interdependent when catalysts are prepared by impregnation. Here, we decoupled both characteristics by using a raspberry-colloid-templating strategy that yields partially embedded PdAu nanoparticles within well-defined SiO 2 or TiO 2 supports, thereby increasing the metal–support interfacial contact compared to nonembedded catalysts that we prepared by attaching the same nanoparticles onto support surfaces. Between nonembedded PdAu/SiO 2 and PdAu/TiO 2 , we identified a support effect resulting in a 1.4-fold higher activity of PdAu/TiO 2 than PdAu/SiO 2 for benzaldehyde hydrogenation. Notably, partial nanoparticle embedding in the TiO 2 raspberry-colloid-templated support increased the metal–support interfacial perimeter and consequently, the number of Au/TiO 2 interfacial sites by 5.4-fold, which further enhanced the activity of PdAu/TiO 2 by an additional 4.1-fold. Theoretical calculations and in situ surface-sensitive desorption analyses reveal facile benzaldehyde binding at the Au/TiO 2 interface and at Pd ensembles on the nanoparticle surface, explaining the connection between the number of Au/TiO 2 interfacial sites (via the metal–support interfacial perimeter) and catalytic activity. Our results demonstrate partial nanoparticle embedding as a synthetic strategy to produce thermocatalytically stable catalysts and increase the number of catalytically active Au/TiO 2 interfacial sites to augment catalytic contributions arising from metal–support interfaces.

Lim, Kang Rui Garrick (ORCID:0000000321599844)↗
DOE OSTI2020

Materials Data on PdAu by Materials Project

AuPd 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 Au atoms to form distorted PdPd6Au6 cuboctahedra that share corners with twelve PdPd6Au6 cuboctahedra, edges with twelve PdPd6Au6 cuboctahedra, edges with twelve AuPd6Au6 cuboctahedra, faces with six equivalent PdPd6Au6 cuboctahedra, and faces with twelve AuPd6Au6 cuboctahedra. All Pd–Pd bond lengths are 2.89 Å. All Pd–Au bond lengths are 2.86 Å. In the second Pd site, Pd is bonded to ten equivalent Pd and six Au atoms to form distorted PdPd10Au6 cuboctahedra that share corners with ten AuPd6Au6 cuboctahedra, corners with twelve PdPd6Au6 cuboctahedra, edges with eight AuPd6Au6 cuboctahedra, edges with sixteen PdPd6Au6 cuboctahedra, faces with sixteen equivalent PdPd10Au6 cuboctahedra, and faces with eighteen AuPd6Au6 cuboctahedra. There are a spread of Pd–Pd bond distances ranging from 2.89–5.78 Å. All Pd–Au bond lengths are 2.86 Å. There are three inequivalent Au sites. In the first Au site, Au is bonded to six equivalent Pd and six equivalent Au atoms to form distorted AuPd6Au6 cuboctahedra that share corners with twelve AuPd6Au6 cuboctahedra, edges with twelve equivalent PdPd6Au6 cuboctahedra, edges with twelve AuPd6Au6 cuboctahedra, faces with six equivalent AuPd6Au6 cuboctahedra, and faces with twelve equivalent PdPd6Au6 cuboctahedra. All Au–Au bond lengths are 2.89 Å. In the second Au site, Au is bonded to six Pd and six equivalent Au atoms to form distorted AuPd6Au6 cuboctahedra that share corners with five equivalent PdPd10Au6 cuboctahedra, corners with twelve AuPd6Au6 cuboctahedra, edges with ten PdPd6Au6 cuboctahedra, edges with twelve AuPd6Au6 cuboctahedra, faces with six equivalent AuPd6Au6 cuboctahedra, and faces with fifteen PdPd6Au6 cuboctahedra. All Au–Au bond lengths are 2.89 Å. In the third Au site, Au is bonded to six Pd and six equivalent Au atoms to form distorted AuPd6Au6 cuboctahedra that share corners with five equivalent PdPd10Au6 cuboctahedra, corners with twelve AuPd6Au6 cuboctahedra, edges with ten PdPd6Au6 cuboctahedra, edges with twelve AuPd6Au6 cuboctahedra, faces with six equivalent AuPd6Au6 cuboctahedra, and faces with fifteen PdPd6Au6 cuboctahedra. All Au–Pd bond lengths are 2.86 Å. All Au–Au bond lengths are 2.89 Å.

36 MATERIALS SCIENCE↗
DOE OSTI2022

Dynamical Study of Adsorbate-Induced Restructuring Kinetics in Bimetallic Catalysts Using the PdAu(111) Model System

The dynamic restructuring of bimetallic catalysts plays a crucial role in their catalytic activity and selectivity. In particular, catalyst pretreatment with species such as carbon monoxide and oxygen has been shown to be an effective strategy for tuning the surface composition and morphology. Mechanistic and kinetic understanding of such restructuring are fundamental to the chemistry and engineering of surface active sites but have remained challenging due to the large structural, chemical, and temporal degrees of freedom. Here, we combine time-resolved temperature-programmed infrared reflection absorption spectroscopy, ab initio thermodynamics, and machine-learning molecular dynamics to uncover previously unidentified timescale and kinetic parameters of in situ restructuring in Pd/Au(111), a highly relevant model system for dilute Pd-in-Au nanoparticle catalysts. The key innovation lies in utilizing CO not only as a chemically sensitive probe of surface Pd, but also as an agent that induces restructuring of the surface. Upon annealing in vacuum, as-deposited Pd islands became encapsulated by Au and partially dissolved into the subsurface, leaving behind isolated Pd monomers on the surface. Subsequent exposure to 0.1 mbar CO enabled Pd monomers to repopulate the surface up to 373 K, above which complete Pd dissolution occurred by 473 K, with apparent activation energies of 0.14 and 0.48 eV, respectively. Furthermore, these restructuring processes occurred over the span of ~1000 s at a given temperature. Such a minute-timescale dynamics not only elucidates the fluxional nature of alloy catalysts but also presents an opportunity to fine-tune the surface at moderate temperature and pressure conditions.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2025

Nanoscale wetting controls reactive Pd ensembles in synthesis of dilute PdAu alloy catalysts

The performance of bimetallic dilute alloy catalysts is largely determined by the size of minority metal ensembles on the nanoparticle surface. By analyzing the synthesis of catalysts comprising Pd 8 Au 92 nanoparticles supported on silica using surface-sensitive techniques, we report that whether Pd overgrowth occurs before or after Au nanoparticle deposition onto the support controls the surface Pd ensemble size and abundance. These differences in Pd ensembles influence catalytic reactivity in H 2 –D 2 isotope exchange and benzaldehyde hydrogenation, which, in correlation with theoretical calculations, is used to elucidate the active site(s) in each reaction. To clarify how the synthetic sequence controls the formation of Pd ensembles, we combine numerical wetting calculations and molecular dynamics simulations (with a machine-learned force field) to visualize Pd deposition and migration on the nanoparticle surface, respectively. Our results suggest that the nanoparticle–support interface restricts nanoparticle accessibility to Pd deposition, which consequently controls the Pd ensemble size, illustrating the critical role of nanoscale wetting phenomena during bimetallic catalyst preparation.

36 MATERIALS SCIENCE↗
DOE OSTI2022

Replication Data for: Efficient and selective carbon-carbon coupling on coke-resistant PdAu single-atom alloys

The data underlying this published work have been made publicly available in this repository as part of the IMASC Data Management Plan. This work was supported as part of the Integrated Mesoscale Architectures for Sustainable Catalysis (IMASC), an Energy Frontier Research Center funded by the U.S. Department of Energy, Office of Science, Basic Energy Sciences under Award # DE-SC0012573.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2022

Replication Data for: Mechanistic insights into carbon-carbon coupling on NiAu and PdAu single-atom alloys

The data underlying this published work have been made publicly available in this repository as part of the IMASC Data Management Plan. This work was supported as part of the Integrated Mesoscale Architectures for Sustainable Catalysis (IMASC), an Energy Frontier Research Center funded by the U.S. Department of Energy, Office of Science, Basic Energy Sciences under Award # DE-SC0012573.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2022

Replication Data for: Quantifying oxygen induced surface enrichment of a dilute PdAu alloy catalyst

The data underlying this published work have been made publicly available in this repository as part of the IMASC Data Management Plan. This work was supported as part of the Integrated Mesoscale Architectures for Sustainable Catalysis (IMASC), an Energy Frontier Research Center funded by the U.S. Department of Energy, Office of Science, Basic Energy Sciences under Award # DE-SC0012573.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2024

Impact of Particle Size on the Vapor-Phase Oxidative Coupling of Methanol and Dimethylamine over Palladium–Gold Nanoparticles

Oxidative coupling of methanol and dimethylamine in the presence of O 2 in the vapor phase over dilute Pd in Au bimetallic catalysts occurs via the dissociation of O 2 on Pd and selective oxidation of methanol on Au. Here, we synthesize a series of silica-supported PdAu alloy nanoparticle catalysts of varied Pd:Au ratios with ~5 nm particle diameter and show that these catalysts have increased selectivity to dimethylformamide across all Pd:Au ratios (~95%), distinct from observations over larger PdAu nanoparticles (~15–25 nm diameter) of similar Pd:Au ratios. Small monometallic Pd particles are more selective than large monometallic Pd particles, and small Au nanoparticles are reactive and selective for oxidative coupling (while large Au nanoparticles are inactive). Rates per surface metal atom were similar over PdAu nanoparticles of all sizes and increased monotonically with increasing Pd content for the small nanoparticles. Further, apparent reaction kinetics demonstrate distinct apparent methanol reaction order and apparent activation energy relative to those reported over larger nanoparticles of similar Pd:Au ratios. Unlike larger PdAu nanoparticles, the rate of dimethylformamide formation is not promoted by cofed water over small PdAu nanoparticles. The results of the kinetic studies are used to propose a series of elementary steps, derive a plausible rate expression, and regress rate and equilibrium constants. These results suggest high coverages of surface methoxy species and low coverages of adsorbates derived from dimethylamine. Taken together, these results demonstrate the sensitivity of the rates, selectivities, and kinetics of oxidative coupling reactions to the size of bimetallic nanoparticles.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗