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At least 1,045 records · Page 58
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DOE OSTI2020

Pd3Ag(111) as a Model System for Hydrogen Separation Membranes: Combined Effects of CO Adsorption and Surface Termination on the Activation of Molecular Hydrogen

Abstract The co-adsorption of hydrogen and carbon monoxide on Pd 3 Ag(111) alloy surfaces has been studied as a model system for Pd-Ag alloys in membrane and catalysis applications using periodic density functional theory calculations (PW91-GGA). We explored the effects of Pd–Ag surface composition, since segregation of silver towards and away from the surface has been suggested to explain the experimentally observed changes in H 2 activation, CO inhibition and reactivity. We found that CO pre-adsorbed on the surface weakens the adsorption of H on Pd 3 Ag(111) alloy surfaces irrespective of whether the surface termination corresponds to the bulk Pd 3 Ag composition, or is purely Pd-terminated. A higher coverage of H with CO present is obtained for the Pd-terminated surface; this surface also exhibits a larger range of chemical potentials for co-adsorbed hydrogen and CO. The barrier for H 2 activation increases with increasing CO coverage, but the surface composition has the largest impact on H 2 activation at intermediate CO coverage. The results imply that Pd-based membranes with typically ~ 23 wt% Ag are less prone to CO poisoning if the surface becomes Pd-terminated.

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

Deactivation trends of Pd/SSZ-13 under the simultaneous presence of NO, CO, hydrocarbons and water for passive NO x adsorption

Pd-functionalized chabazite (Pd/SSZ-13) was evaluated for passive NO x adsorption (PNA) using low temperature combustion with diesel (LTC-D) reaction feed of the “United States Driving Research and Innovation for Vehicle efficiency and Energy sustainability” (U.S.DRIVE) protocol. Notably as per the protocol conditions, 12% O 2 + 6% CO 2 + 6% H 2 O was flown in all cases. NO-uptake studies in the presence of the LTC-D feed showed a systematic decline with (NO:Pd)molar changing from 0.5 to 0.4 after 10 trials. Control experiments showed more pronounced decline for NO + CO case, with appreciable intial (NO:Pd)molar value of 0.4 yet comparable-to-the-LTC-D-feed decline after 8 trials. CO-induced particle formation and larger extent of particle sintering was also evident from TEM analysis. Other controls did not exhibit trial-dependent deactivation as(NO:Pd)molar values were constant, at 0.3, 0.2, 0.5 and 0.2 for the NO, NO+H 2 , NO + unsaturated hydrocarbon (C 2 H 4 , C 3 H 6 ) and NO + saturated HC (C 3 H 8 , C 10 H 22 ) feeds respectively. In addition to these quantitative differences, desorption behaviors are qualitatively different. While only one major desorption event is observed for the full LTC-D, NO+ CO and NO+ unsaturated HC-controls, desorption occurs in two distinct stages for NO, NO + saturated HCs and initial-NO+H 2 trials. This arises due to inherent differences in Pd sites while exposed to these chemically distinct feeds. Furthermore, presence of reducing agents such as CO and unsaturated HCs in the feed result in almost complete elimination of lower, sub-200 °C desorption peak. The higher temperature desorption peaks, at > 300 °C is associated with NO strongly bound to ionic Pd sites and are prevalent under reducing conditions. Using DRIFTS also, three complexes leading to PNA are assigned, [O = N–Pd 2 +(OH)–Z], [O = N–Pd 2 +(Z2)] and [O = N–Pd 2 +(H 2 O)y–Z] with the latter being clearly observed upon water exposure. Pd/SSZ-13 showed higher hydrocarbon trapping than the SSZ-13 counterpart.

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

PdCu Electrocatalysts for Selective Nitrate and Nitrite Reduction to Nitrogen

Electrocatalytic conversion of nitrate in waste can enable efficient waste remediation (NO 3 - to N 2 ) or waste valorization (NO 3 - to NH 4 + ) depending on the selectivity of the catalyst. Palladium and copper electrocatalysts typically exhibit ideal nitrate and nitrite binding properties, allowing for effective destruction of nitrate. However, rational steering of selectivity through material design remains a critical challenge for PdCu electrocatalyst. Here, we use the electrochemical underpotential deposition method to synthesize palladium nanocube electrocataysts with controlled copper surface coverage (e.g., partial and full copper coatings). We then examine the potential for NO 3 - destruction (conversion) and NO 2 - reduction reaction. We identify that partial copper-coated Pd nanocubes not only effectively facilitate the reduction of 95% of NO 3 - but also increase the reduction of NO 2 - to N 2 with 89% selectivity over 20 consecutive cycles (80 h). We also show that under these conditions, the Pd(100) surface facet is exposed. Complete copper-covered Pd nanocubes effectively facilitate the reduction of ~99% of NO 3 - . Complete coverage of copper; however, prevented exposure of Pd(100) surface facet, promoting the selective reduction of NO 2 - to NH 4 + with a 70% selectivity over 20 consecutive cycles (80 h). Density functional theory (DFT) calculations show that NO 3 - and NO 2 - adsorb more strongly on the Cu(100) surface compared to the Pd(100) surface, while the NO* intermediate generated from NO 3 - or NO 2 - reduction adsorbs more strongly on the Pd surface. Furthermore, barrier calculations show that NO* can readily migrate from the Cu domain to the Pd domain and that the N–N coupling barrier on Pd is significantly diminished at high NO* coverage. Together, these results suggest that the high N 2 selectivity observed on the PdCu electrocatalyst is caused by the spillover of NO* from the Cu domains to the Pd domains.

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↗
DOE OSTI2022

A P-61 Black Widow Inspired Palladium Biladiene Complex for Efficient Sensitization of Singlet Oxygen Using Visible Light

Photodynamic therapy (PDT) is a promising treatment option that ablates cancerous cells and tumors via photoinduced sensitization of singlet oxygen. Over the last few decades, much work has been devoted to the development of new photochemotherapeutic agents for PDT. A wide variety of macrocyclic tetrapyrrole based photosensitizers have been designed, synthesized and characterized as PDT agents. Many of these complexes have a variety of issues that pose a barrier to their use in humans, including biocompatibility, inherent toxicity, and synthetic hurdles. We have developed a non-traditional, non-cyclic, and non-aromatic tetrapyrrole ligand scaffold, called the biladiene (DMBil1), as an alternative to these traditional photosensitizer complexes. Upon insertion of a heavy atom such as Pd 2+ center, Pd[DMBil1] generates singlet oxygen in substantial yields (Φ Δ = 0.54, λ exc = 500 nm) when irradiated with visible light. To extend the absorption profile for Pd[DMBil1] deeper into the phototherapeutic window, the tetrapyrrole was conjugated with alkynyl phenyl groups at the 2- and 18-positions (Pd[DMBil2-PE]) resulting in a significant redshift while also increasing singlet oxygen generation (Φ Δ = 0.59, 600 nm). To further modify the dialkynyl-biladiene scaffold, we conjugated a 1,8-diethynylanthracene with to the Pd[DMBil1] tetrapyrrole in order to further extend the compound’s π-conjugation in a cyclic loop that spans the entire tetrapyrrole unit. This new compound (Pd[DMBil2-P61]) is structurally reminiscent of the P61 Black Widow aircraft and absorbs light into the phototherapeutic window (600–900 nm). In addition to detailing the solid-state structure and steady-state spectroscopic properties for this new biladiene, photochemical sensitization studies demonstrated that Pd[DMBil2-P61] can sensitize the formation of 1 O 2 with quantum yields of Φ Δ = 0.84 upon irradiation with light λ = 600 nm. These results distinguish the Pd[DMBil2-P61] platform as the most efficient biladiene-based singlet oxygen photosensitizer developed to date. When taken together, the improved absorption in the phototherapeutic window and high singlet oxygen sensitization efficiency of Pd[DMBil2-P61] mark this compound as a promising candidate for future study as an agent of photodynamic cancer therapy.

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

Postirradiation characterization of palladium as an additive for fuel cladding chemical interaction mitigation in metallic fuel

This work describes the microstructural and elemental characterization of irradiated metallic fuels containing palladium as an additive. The use of additives has been proposed to control Fuel-Cladding Chemical Interaction (FCCI) and thus to promote higher fuel utilization (i.e., higher burnup). In this work, Pd has been investigated as a potential additive to metallic fuel to bind lanthanides, impeding their migration and attack on the cladding. The influence of Pd on the microstructure, chemistry and performance of metallic fuel has been characterized via scanning electron microscopy for two metallic fuel designs—namely, annular and solid fuel. Pd was observed to play an important role in the chemistry of the fuel. Indeed, the addition of Pd leads to the formation of new phases. Pd was detected to combine not only with the lanthanides, as intended, but also with Zr, a main element of the fuel matrix. While Pd proved to be effective in preventing lanthanide migration and their attack on the cladding, the Pd-Zr compound may potentially lead to other unexpected fuel-performance issues, such as the formation of low-melting point phases and increased unalloyed U available for FCCI interaction with Fe in the cladding. Even the increase of Zr to 13wt%. did not completely mitigate this adverse phenomenon generated by the Pd-Zr interaction. Furthermore, the efficacy of using this additive needs further investigation.

11 NUCLEAR FUEL CYCLE AND FUEL MATERIALS↗
DOE OSTI2020

Materials Data on Nb5(PPd)4 by Materials Project

Nb5Pd4P4 crystallizes in the tetragonal I4/m space group. The structure is three-dimensional. there are two inequivalent Nb sites. In the first Nb site, Nb is bonded in a 4-coordinate geometry to four equivalent Pd and five equivalent P atoms. There are a spread of Nb–Pd bond distances ranging from 2.90–3.07 Å. There are a spread of Nb–P bond distances ranging from 2.59–3.00 Å. In the second Nb site, Nb is bonded in a square co-planar geometry to four equivalent P atoms. All Nb–P bond lengths are 2.62 Å. Pd is bonded in a 12-coordinate geometry to four equivalent Nb, five equivalent Pd, and three equivalent P atoms. There are four shorter (2.87 Å) and one longer (3.14 Å) Pd–Pd bond lengths. There are two shorter (2.38 Å) and one longer (2.49 Å) Pd–P bond lengths. P is bonded in a 9-coordinate geometry to six Nb and three equivalent Pd atoms.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on HfSiPd by Materials Project

HfPdSi crystallizes in the orthorhombic Pnma space group. The structure is three-dimensional. Hf is bonded in a 11-coordinate geometry to six equivalent Pd and five equivalent Si atoms. There are a spread of Hf–Pd bond distances ranging from 2.99–3.14 Å. There are a spread of Hf–Si bond distances ranging from 2.74–2.83 Å. Pd is bonded in a 12-coordinate geometry to six equivalent Hf, two equivalent Pd, and four equivalent Si atoms. Both Pd–Pd bond lengths are 2.87 Å. There are a spread of Pd–Si bond distances ranging from 2.49–2.59 Å. Si is bonded in a 9-coordinate geometry to five equivalent Hf and four equivalent Pd atoms.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on Yb2Ge6Pd by Materials Project

Yb2PdGe6 crystallizes in the orthorhombic Cmce space group. The structure is three-dimensional. Yb is bonded to two equivalent Pd and ten Ge atoms to form a mixture of distorted corner, edge, and face-sharing YbGe10Pd2 cuboctahedra. There are one shorter (3.13 Å) and one longer (3.14 Å) Yb–Pd bond lengths. There are a spread of Yb–Ge bond distances ranging from 3.06–3.41 Å. Pd is bonded in a 9-coordinate geometry to four equivalent Yb and five Ge atoms. There are a spread of Pd–Ge bond distances ranging from 2.49–2.57 Å. There are five inequivalent Ge sites. In the first Ge site, Ge is bonded in a 8-coordinate geometry to six equivalent Yb and two Ge atoms. There are one shorter (2.49 Å) and one longer (2.53 Å) Ge–Ge bond lengths. In the second Ge site, Ge is bonded in a 1-coordinate geometry to two equivalent Yb, one Pd, and three Ge atoms. There are one shorter (2.55 Å) and two longer (2.58 Å) Ge–Ge bond lengths. In the third Ge site, Ge is bonded in a 1-coordinate geometry to two equivalent Yb, one Pd, and three Ge atoms. Both Ge–Ge bond lengths are 2.58 Å. In the fourth Ge site, Ge is bonded in a 9-coordinate geometry to six equivalent Yb, one Pd, and two Ge atoms. The Ge–Ge bond length is 2.49 Å. In the fifth Ge site, Ge is bonded in a 6-coordinate geometry to two equivalent Yb, one Pd, and three Ge atoms. The Ge–Ge bond length is 2.52 Å.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on Ce2CdPd2 by Materials Project

Ce2Pd2Cd crystallizes in the tetragonal P4/mbm space group. The structure is three-dimensional. Ce is bonded in a 6-coordinate geometry to six equivalent Pd and four equivalent Cd atoms. There are two shorter (2.91 Å) and four longer (3.07 Å) Ce–Pd bond lengths. All Ce–Cd bond lengths are 3.47 Å. Pd is bonded in a 9-coordinate geometry to six equivalent Ce, one Pd, and two equivalent Cd atoms. The Pd–Pd bond length is 2.89 Å. Both Pd–Cd bond lengths are 3.07 Å. Cd is bonded to eight equivalent Ce and four equivalent Pd atoms to form a mixture of face and corner-sharing CdCe8Pd4 cuboctahedra.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on Ni(TePd)2 by Materials Project

Pd2NiTe2 crystallizes in the orthorhombic Ibam space group. The structure is three-dimensional. Pd is bonded in a 10-coordinate geometry to three equivalent Pd, two equivalent Ni, and five equivalent Te atoms. There are one shorter (2.93 Å) and two longer (3.09 Å) Pd–Pd bond lengths. Both Pd–Ni bond lengths are 2.93 Å. There are a spread of Pd–Te bond distances ranging from 2.67–3.03 Å. Ni is bonded in a 10-coordinate geometry to four equivalent Pd, two equivalent Ni, and four equivalent Te atoms. Both Ni–Ni bond lengths are 2.58 Å. All Ni–Te bond lengths are 2.54 Å. Te is bonded in a 7-coordinate geometry to five equivalent Pd and two equivalent Ni atoms.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on Co(PdSe)2 by Materials Project

Pd2CoSe2 crystallizes in the orthorhombic Ibam space group. The structure is three-dimensional. Co is bonded to four equivalent Pd and four equivalent Se atoms to form distorted face-sharing CoPd4Se4 tetrahedra. All Co–Pd bond lengths are 2.86 Å. All Co–Se bond lengths are 2.34 Å. Pd is bonded in a 4-coordinate geometry to two equivalent Co, three equivalent Pd, and five equivalent Se atoms. There are one shorter (2.83 Å) and two longer (2.93 Å) Pd–Pd bond lengths. There are a spread of Pd–Se bond distances ranging from 2.52–2.88 Å. Se is bonded in a 7-coordinate geometry to two equivalent Co and five equivalent Pd atoms.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on Co(TePd)2 by Materials Project

Pd2CoTe2 crystallizes in the orthorhombic Ibam space group. The structure is three-dimensional. Co is bonded in a 10-coordinate geometry to two equivalent Co, four equivalent Pd, and four equivalent Te atoms. Both Co–Co bond lengths are 2.63 Å. All Co–Pd bond lengths are 2.92 Å. All Co–Te bond lengths are 2.49 Å. Pd is bonded in a 10-coordinate geometry to two equivalent Co, three equivalent Pd, and five equivalent Te atoms. There are one shorter (2.91 Å) and two longer (3.12 Å) Pd–Pd bond lengths. There are a spread of Pd–Te bond distances ranging from 2.68–2.96 Å. Te is bonded in a 7-coordinate geometry to two equivalent Co and five equivalent Pd atoms.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on Fe(PdSe)2 by Materials Project

Pd2FeSe2 crystallizes in the orthorhombic Ibam space group. The structure is three-dimensional. Fe is bonded in a 4-coordinate geometry to four equivalent Pd and four equivalent Se atoms. All Fe–Pd bond lengths are 2.86 Å. All Fe–Se bond lengths are 2.33 Å. Pd is bonded in a 2-coordinate geometry to two equivalent Fe, three equivalent Pd, and five equivalent Se atoms. There are one shorter (2.78 Å) and two longer (2.92 Å) Pd–Pd bond lengths. There are a spread of Pd–Se bond distances ranging from 2.51–2.93 Å. Se is bonded in a 4-coordinate geometry to two equivalent Fe and five equivalent Pd atoms.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on Er2InPd2 by Materials Project

Er2Pd2In crystallizes in the tetragonal P4/mbm space group. The structure is three-dimensional. Er is bonded in a 6-coordinate geometry to six equivalent Pd and four equivalent In atoms. There are two shorter (2.84 Å) and four longer (2.98 Å) Er–Pd bond lengths. All Er–In bond lengths are 3.39 Å. Pd is bonded in a 9-coordinate geometry to six equivalent Er, one Pd, and two equivalent In atoms. The Pd–Pd bond length is 2.79 Å. Both Pd–In bond lengths are 3.03 Å. In is bonded to eight equivalent Er and four equivalent Pd atoms to form a mixture of face and corner-sharing InEr8Pd4 cuboctahedra.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on Lu2InPd2 by Materials Project

Lu2Pd2In crystallizes in the tetragonal P4/mbm space group. The structure is three-dimensional. Lu is bonded in a 6-coordinate geometry to six equivalent Pd and four equivalent In atoms. There are two shorter (2.82 Å) and four longer (2.95 Å) Lu–Pd bond lengths. All Lu–In bond lengths are 3.37 Å. Pd is bonded in a 9-coordinate geometry to six equivalent Lu, one Pd, and two equivalent In atoms. The Pd–Pd bond length is 2.79 Å. Both Pd–In bond lengths are 3.01 Å. In is bonded to eight equivalent Lu and four equivalent Pd atoms to form a mixture of corner and face-sharing InLu8Pd4 cuboctahedra.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on Pr2CdPd2 by Materials Project

Pr2Pd2Cd crystallizes in the tetragonal P4/mbm space group. The structure is three-dimensional. Pr is bonded in a 6-coordinate geometry to six equivalent Pd and four equivalent Cd atoms. There are two shorter (2.97 Å) and four longer (3.12 Å) Pr–Pd bond lengths. All Pr–Cd bond lengths are 3.52 Å. Pd is bonded in a 9-coordinate geometry to six equivalent Pr, one Pd, and two equivalent Cd atoms. The Pd–Pd bond length is 2.83 Å. Both Pd–Cd bond lengths are 3.10 Å. Cd is bonded to eight equivalent Pr and four equivalent Pd atoms to form a mixture of face and corner-sharing CdPr8Pd4 cuboctahedra.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on Sm2CdPd2 by Materials Project

Sm2Pd2Cd crystallizes in the tetragonal P4/mbm space group. The structure is three-dimensional. Sm is bonded in a 6-coordinate geometry to six equivalent Pd and four equivalent Cd atoms. There are two shorter (2.92 Å) and four longer (3.06 Å) Sm–Pd bond lengths. All Sm–Cd bond lengths are 3.47 Å. Pd is bonded in a 9-coordinate geometry to six equivalent Sm, one Pd, and two equivalent Cd atoms. The Pd–Pd bond length is 2.82 Å. Both Pd–Cd bond lengths are 3.06 Å. Cd is bonded to eight equivalent Sm and four equivalent Pd atoms to form a mixture of face and corner-sharing CdSm8Pd4 cuboctahedra.

36 MATERIALS SCIENCE↗