Search Menu
DOE PAGES title logo U.S. Department of Energy
Office of Scientific and Technical Information
Search Scholarly Publications

21 Search Results

Sorted by Relevance
Save Results
...

  1. Atom Efficiency of Pd Sites for Methane Combustion: Single Atom Catalysts Versus Nanocatalysts

    Yang, Weiwei ; Zhou, Hua ; Yu, Xinbin ; ... - ACS ES&T Engineering
    Methane combustion is an important reaction for energy production and methane removal from the atmosphere. This reaction highly relies on the use of noble metal Pd-based catalysts, which therefore drives the pursuit of catalysts with high atomic dispersion and activity. In this work, Pd/ceria catalysts dominated with Pd single atoms or nanosized Pd clusters (∼1 nm) are prepared and characterized by combining high-resolution high-angle annular dark-field scanning transmission electron microscopy (HAADF-STEM), in situ diffuse reflectance infrared Fourier-transform spectroscopy (DRIFTS), and Raman and X-ray absorption spectroscopy (XAS) techniques. By comparing the turnover frequencies (TOF; per every Pd atom) of Pd/ceria singlemore » atom catalysts and nanocatalysts, it is found that the atom efficiency of Pd is increased by 10 ∼30 times from single atom catalysts to nanocatalysts. For Pd single atom catalysts, although their activity can be tuned by changing the local structures, the intrinsic activity and number of active sites need to be further improved by engineering the surfaces of supports. For nanosized Pd species, despite the high TOF, the Pd atoms in the bulk structure are not directly participating in the catalytic reaction. Furthermore, this work highlights the importance of increasing the intrinsic activity of individual noble atoms, as well as the homogeneity of their local structures. For Pd/ceria systems reported in this work, our results indicate that from the application point of view, at the current stage, it is not practical to replace Pd nanocatalysts with single atom catalysts for methane combustion.« less

  2. Efficient transfer hydrodehalogenation of halophenols catalyzed by Pd supported on ceria

    Naik, Pranjali J. ; Kunal, Pranaw ; Liu, Da-Jiang ; ... - Applied Catalysis. A, General
    We report the transfer hydrodehalogenation (THD) of halophenols is efficiently catalyzed by palladium supported on high surface area ceria (Pd/CeO2) under mild conditions (65 °C) using isopropanol (iPrOH) as hydrogen source. The reactivity of 4-halophenols (4-X-PhOH) varies in the order 4-F-PhOH > 4-Cl-PhOH > 4-Br-PhOH > > 4-I-PhOH and appears to be controlled by the desorption of halides from the catalyst surface. Kinetic analysis of the reactions and temperature programmed surface reaction (TPSR) experiments indicate that oxidative addition of C-X bonds and H-abstraction from isopropoxide compete for the same active sites on Pd. The catalyst was able to conduct themore » THD of various hazardous pollutants and emerging contaminants (dichlorodiphenyltrichloroethane (DDT), pentachlorophenol, pentafluorophenol and triclosan).« less

  3. Preparation of SBA-15-Supported Metals by Vapor-Phase Infiltration

    Wang, Ching-Yu ; Shen, Kai ; Gorte, Raymond J. ; ... - Inorganics
    A simple method is presented for incorporating various catalytic metals into the pores of SBA-15 using vapor-phase infiltration. The precursors used in Atomic Layer Deposition (ALD) for Pt, Pd, Rh, Ru, and Ni were exposed to an evacuated SBA-15, resulting in monolayer films of the adsorbed precursors inside the mesopores. The metal particles that formed after removal of the precursor ligands remained in the pores and had particle sizes ranging from 3.8 nm for Pt to 5.2 nm for Ni, as determined by Transmission Electron Microscopy (TEM), XRD, and CO chemisorption. Metal loadings for saturation exposures ranged from 5.1-wt% formore » Ni to 9.1-wt% for Pt; however, uniform deposition was demonstrated for lower loadings of Pd by decreasing the amount of precursor. To determine the effect of the surface composition of the mesopores, Pd particles were also added to SBA-15 that was coated with a 0.2-nm film of ZrO2.« less

  4. Surface oxygenation induced strong interaction between Pd catalyst and functional support for zinc–air batteries

    Zhang, Wei ; Chang, Jinfa ; Wang, Guanzhi ; ... - Energy & Environmental Science
    Employing the strong metal-support interaction (SMSI) effect for promoting the catalyst's activity toward the oxygen reduction reaction (ORR) is promising due to the electronic structure optimization and high utilization efficiency of platinum group metal (PGM) catalysts. Metal oxides as alternative supports for PGMs facilitate intrinsic activity and improve durability as compared to conventional carbon supports. However, the restricted mass and electron transfer at the metal/support interface need to be addressed. Herein, to strengthen the interaction at the metal/support interfaces and improve the utilization efficiency of PGM, an ultralow loading of Pd was embedded in a surface-oxygenated PdNiMnO porous film. Themore » Mn-doping was designed to promote surface oxygenation using a facile anodization process that created sufficiently exposed interfaces between Pd and the support, strengthening the SMSI effects at the Pd/oxygenated support interface for enhancing ORR performance. Furthermore, the Ni-containing oxygenated catalyst served as both the active component for the oxygen evolution reaction (OER) and the functional support for stabilizing Pd, making PdNiMnO a bifunctional catalyst for zinc–air flow batteries (ZAFB). As a proof-of-concept, the ZAFB (PdNiMnO) shows a maximal power density of 211.6 mW cm–2 and outstanding cycling stability for over 2000 h with a minimal voltage gap of 0.69 V at a current density of 10 mA cm–2, superior to the state-of-the-art catalysts.« less

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

    Di Lemma, Fidelma Giulia ; Trowbridge, Tammy M. ; Capriotti, Luca ; ... - Journal of Nuclear Materials
    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 anmore » 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.« less

  6. Electronic growth of Pd(111) nanostructures on MoS2

    Kidd, Timothy E. ; Scott, Skylar ; Roberts, Sophie ; ... - Journal of Applied Physics
    Quantum confinement effects can induce the formation of discrete nanostructures with well-defined preferred heights in thin metallic films. In most systems, such electronic growth modes are weak and limited to cryogenic conditions. Recently, however, we have discovered that metals grown upon van der Waals surfaces can exhibit electronic growth at, or even above, room temperature to spontaneously form well-defined and highly stable nanostructures. Here, we explore the initial stages of room temperature deposition of Pd onto MoS2. We found that, even for minimal thicknesses, Pd spontaneously formed discrete islands with three atomic layers. The islands maintained this preferred height formore » nominal coverages below three atomic layers. At higher coverages, the preferred height switched abruptly to six atomic layers. Unlike previous studies using Au or Ag, the islands did not increase laterally with coverage but rather increased in number with lateral size remaining about the same. The preferred heights in Pd/MoS2 correlate to the Pd Fermi surface topography and are also consistent with thicknesses showing minima in the density of states at the Fermi level, which suggest that the electronic growth modes are the driving factors in these self-assembled Pd nanostructures. The Pd system shows a preference for island nucleation compared to Au and Ag which grow laterally with increasing coverage. Furthermore, this is likely related to differences in bonding at the interface as Pd is typically much more reactive than Ag or Au.« less

  7. Coupled uptake and conversion of C12H26 and NO on Pd/SSZ-13: Experiments and modeling

    Ambast, Mugdha ; Malamis, Sotirios A. ; Harold, Michael P. - Chemical Engineering Journal
    The uptake of NO in the presence of C12H26 (dodecane) and H2O over a Pd/SSZ-13 washcoated Passive NOx Adsorber (PNA) monolith is reported. When a co-feed containing C12H26 and NO is supplied to an unsaturated (with C12H26) sample, the NO uptake is unaffected but during the subsequent temperature ramp the release of trapped NO is delayed from 175°C to over 220°C. The release delay is beneficial for PNA performance as the primary NOx aftertreatment technology, Selective Catalytic Reduction (SCR), is not operated below 200°C. However, pre-saturation of C12H26 followed by the same NO and C12H26 co-feed results in a decreasemore » in the NO uptake compared to the NO-only feed. We conjecture that C12H26 pre-adsorbed on the exterior surface of the sample blocks NO access to the pores, decreasing the number of available sites for NO uptake. Oxidation of C12H26 leads to the generation of partial oxidation product CO at lower temperatures (<250°C) and deep oxidation product CO2 at higher temperatures. Carbon monoxide binds strongly to Pd sites with NO and can delay NO release. A Pd/SSZ-13 washcoated monolith model developed in an earlier study [Ambast et al., Appl. Catal. B. Environmental (2021)] is upgraded to include C12H26 storage, release, and conversion. Through a systematic combination of judicious experiments, model tuning, and validation, we provide evidence for the underlying NO uptake and release mechanisms in the presence of C12H26.« less

  8. Optimizing the lean hydrocarbon NOx trap: Sequential and dual-layer configurations

    Malamis, Sotirios A. ; Harold, Michael P. - Catalysis Today
    Vehicular emission control catalysts are ineffective in eliminating CO, hydrocarbons, and NOx during engine cold-start when exhaust temperatures are below 200 °C. In this study the performance of coupled low temperature NOx, n-C12H26 (C12), and C3H6 trapping, release and conversion for a series of model Lean Hydrocarbon NOx Trap (LHCNT) catalysts are examined. Pd and Pt supported on small-pore (SSZ-13) and large-pore (BEA) zeolites are selected based on the performance during transient NO and C12 uptake, release and conversion experiments. These catalysts are combined into sequential (Pt + Pd/BEA → Pd/SSZ-13; Pd/SSZ-13 → Pt + Pd/BEA) and dual-layer (Pt +more » Pd/BEA top, Pd/SSZ-13 bottom) configurations in an attempt to improve the trapping and conversion performance. While all three configurations trap between 75 and 100 μmolNOx/g-cat, the Pd/SSZ-13 → Pt + Pd/BEA sequential configuration is most effective in simultaneously trapping C12 and NO in the presence of H2O, resulting in excellent NO and C12 storage below 100 °C with release and/or conversion at or above 200 °C. For each configuration, C12 oxidation lights-off below 300 °C and NO oxidation achieves ~35 % conversion in the absence of C12. Neither the presence of C12 nor the order of the sequential configuration has a significant impact on NO uptake. C12 significantly delays NO and NO2 desorption to temperatures exceeding 300 °C. The more compact dual-layer catalyst is most effective in forming NO2 as the release temperature lines up with the maximum NO conversion temperature but traps less C12 than the sequential configurations. The addition of C3H6 in the feed on the dual-layer catalyst leads to further delay in the NOx desorption as well as increased NO and C12 conversion at high temperatures. Here, the overall findings provide guidance in the optimizing LHCNT configuration for realistic feeds.« less

  9. NOx adsorption with CO and C2H4 on Pd/SSZ-13: Experiments and modeling

    Ambast, Mugdha ; Gupta, Abhay ; Rahman, Bhuiyan Mushfikur ; ... - Applied Catalysis. B, Environmental
    A transient monolith model containing microkinetic schemes for NO uptake and release over Pd/SSZ-13 without and with reductants CO or C2H4 is presented. The scheme involves three cationic Pd species (Z–[PdOH]+, Z–Pd2+Z–, Z–Pd+) as the active sites during uptake of NO, CO and C2H4, and their desorption and conversion at higher temperature. Kinetic parameters are estimated through a combination of density functional theory (DFT) estimates and a fit of uptake, desorption and conversion data. The tuned model is validated at different uptake temperatures, ramp rates, and flowrates. A “degree of uptake control” parameter is defined that helps to identify themore » step(s) that are uptake controlling. The model helps to interpret the data features and is used to identify operating conditions to meet application-relevant performance metrics, including NO trapping efficiency and NO release temperature. Furthermore, the model demonstrates higher NO uptake on Pd/SSZ-13 compared to Pd/ZSM-5.« less

  10. A Review of Microwave-Assisted Synthesis-Based Approaches to Reduce Pd-Content in Catalysts

    Kunal, Pranaw ; Toops, Todd J. - Catalysts
    This review article focuses on the latest advances in the synthesis of inorganic nano-catalysts using microwave heating, which has progressed significantly since its initial implementation in the mid-1980s. Over the years, nanoparticles (NPs), which inherently offer better surface accessibility for heterogeneous catalysis, have been synthesized using a wide array of heating methods. Microwave heating is one such method and employs a unique heating mechanism that can have several benefits for catalysis. When compared to conventional form of heating which relies on inter-layer mixing via convection, microwave heating operates through the chemical polarity in the target chemicals leading to an “inside-out”more » mode of heating. This heating mechanism is more targeted and therefore results in rapid synthesis of catalytically active NPs. Platinum group metals (PGM) have classically been the focus of nano-catalysis; however, recent efforts have also applied non-PGM group metals with the goals of lower costs, and ideally, improved catalytic reactivity and durability. This is especially of interest with respect to Pd because of its current historically high cost. Investigations into these new materials have primarily focused on new/improved synthetic methods and catalytic compositions, but it is important to note that these approaches must also be economic and scalable to attain practical relevance. With this overarching goal in mind, this review summarizes notable recent findings with a focus on Pd-dilution and microwave heating in a chronological fashion.« less
...
Search for:
All Records
Subject
Pd
Refine by:
Article Type
Availability
Journal
more less
Creator / Author
more less
Publication Date
Research Organization
more less