Electronic States Of Pd Research Articles

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, 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 (C2H2) to ethylene (C2H4) under mild conditions. The optimized Cu/B2 CuPd with a Pd loading of 9.5 at. % exhibited outstanding performance in the C2H2 semi-hydrogenation with 100% C2H2 conversion and 95.2% C2H4 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.

Insights into N dopants during dehydrogenation of formic acid over Pd/N-doped carbon catalysts

Catalytic dehydrogenation of formic acid (FA) is one strategy to generate hydrogen from an easily handled chemical and meet the clean-energy demand simultaneously. The Pd/N-doped carbon catalyst is famous for boosting the activity of active metal in FA dehydrogenation. However, the origin of achieving highly catalytic activity remains controversial. Herein, a variety of Pd/N-doped carbon catalysts were systematically prepared by regulating different N doping content and reduction conditions (H2 and NaBH4) for promoting hydrogen production from FA under ambient conditions without additives. The results showed that N dopants have a great impact on the electronic state and particle size of Pd. Moreover, the electronic state of Pd is also sensitive to the reduction methods. The catalyst with the highest pyridinic-N content presented the best catalytic performance after being reduced in H2 flow at 260 °C, and its initial TOF value is 2656 h−1 without additives at 50 °C. The electronic levels investigation of the active metal can provide new ideas for the design of highly efficient catalysts for FA dehydrogenation.

Evolution of the PVP-Pd Surface Interaction in Nanoparticles through the Case Study of Formic Acid Decomposition.

Palladium nanoparticles (Pd NPs) were synthesized by the reduction-by-solvent method using polyvinylpirrolidone (PVP) as capping agent. The nonstatic interaction between PVP and the metallic surface may change the properties of the NPs due to the different possible interactions, through either the O or N atoms of the PVP. In order to analyze these effects and their repercussions in their catalytic performance, Pd NPs with various PVP/Pd molar ratios (1, 10, and 20) were prepared, deposited on silica, and tested in the formic acid decomposition reaction. The catalytic tests were conducted using catalysts prepared by loading NPs with three different time lapses between their purification and their deposition on the silica support (1 day, 1 month, and 6 months). CO adsorption, FTIR spectroscopy, XPS, and TEM characterization were used to determine the accessibility of the Pd NPs surface sites, the electronic state of Pd, and the average NPs size, respectively. The H2 production from the formic acid decomposition reaction has a strong dependence on the Pd surface features, which in turn are related to the NPs aging time due to the progressive removal of the PVP.

Recent Developments in Palladium‐Based Bimetallic Catalysts

AbstractAs one of the alternative metals to platinum, which supports a wide range of applications in chemistry and catalysis in industry, palladium increasingly receives attention because of its similar physicochemical properties. However, Pd is generally less expensive than Pt and has a richer natural reserve. Herein, some recently developed techniques for the preparation and characterization of Pd‐based bimetallic catalysts are reviewed. The impact on catalytic reactions of interest, including hydrogenation, dehydrogenation, hydrogenolysis, reforming, the oxygen reduction reaction, and hydrodesulfurization are also discussed. It is shown that the catalytic performance of Pd‐based bimetallic catalysts is strongly dependent on the geometric and electronic states of Pd, which can be significantly affected by blended foreign element(s). Rationalization of the structure–activity relationship can provide useful guidelines to the fine tuning of these important catalytic reactions.

The Catalytic Properties of Pd Nanoparticles Modified by Phosphorus in Liquid-phase Hydrogenation of o-chloronitrobenzene

The new Pd-P catalysts for o-CNB hydrogenation obtained by interaction of Pd(acac)2 with white phosphorus in hydrogen, in N,N-dimethylformamide (DMF) under mild conditions were developed and studied. They exhibit higher selectivity to o-chloroaniline (74-94%) compared to Pd-black (56%). The introduction of phosphorus increases selectivity of palladium catalysts, however the activity values and P/Pd ratio are inversely related. The nature and the properties of Pd-P catalysts depend on P/Pd ratio. With the increase of the P/Pd ratio the average size of the particles decreases from 26 nm (for P/Pd = 0) to 5.6 nm (P/Pd = 0.3) and 4.8 nm (P/Pd = 1.0). Nanoparticles formed at P/Pd = 0.3 consist of palladium phosphide Pd6P and clusters Pd(0). Core-shell structure PdxP@Pdn was proposed for them. The Pd(0) clusters in the Pd-P catalyst (P/Pd = 0.3) possess higher electron density (Pd3d5/2 334.52 eV) compared to metallic palladium. With the increase of the P/Pd ratio the fraction of Pd(0) reduces and P-enriched palladium phosphides are formed. The Pd-P catalyst with P/Pd = 1.0 mainly consists of Pd5P2 and PdP2. The Pd(0) content for this catalyst is below 8%. Dimethylammonium dihydro- and hydrophosphates (phosphites) formed via the partial hydrolysis of the solvent – DMF contribute to the stabilization of Pd-P nanoparticles. We suggest that the nature of the catalyst nanoparticles consisting of Pd and PdxP as well as electronic state of Pd(0) clusters are the main factors determining catalytic properties of the Pd-P catalyst in o-CNB hydrogenation. Keywords: о-Chloronitrobenzene, hydrogenation, nanoparticles, palladium, phosphide, phosphorus.

Palladium Nanoparticles Supported on Nitrogen‐Doped Carbon Nanofibers: Synthesis, Microstructure, Catalytic Properties, and Self‐Sustained Oscillation Phenomena in Carbon Monoxide Oxidation

AbstractThe oxidation of CO over Pd nanoparticles supported on carbon nanofibers (CNFs) and N‐doped carbon nanofibers (N‐CNFs) has been studied. Investigation by scanning transmission electron microscopy together with electron energy‐loss spectroscopy revealed that Pd nanoparticles are located on the N‐CNFs surface patches that have a high concentration of N atoms. The N‐doping of CNFs was shown to change the electric conductivity of N‐CNFs and redox properties of Pd, which thus determines the self‐oscillatory behavior of the catalysts during CO oxidation, the type of oscillations, and the conditions of their generation. Mechanisms that underlie the effect of N in N‐CNFs on the electronic state of Pd as well as the occurrence of two types of oscillation mechanisms—the known redox mechanism and the mechanism related to Pd intercalation into graphene layers—are discussed.

Investigation of Electronic States of Pd in 4H-SiC by Means of Radiotracer-DLTS

Investigation of Electronic States of Pd in 4H-SiC by Means of Radiotracer-DLTS

Active States of Pd and Cu in Carbon-Supported Wacker-Type Catalysts for Low-Temperature CO Oxidation

Carbon-supported Wacker-type catalysts that showed high activities in CO oxidation at low temperatures were characterized with X-ray diffraction (XRD) and X-ray absorption fine structure (XAFS) techniques in order to correlate the catalytic activity with the structures and electronic states of Pd and Cu. The active states of palladium and copper were found to be a molecular Pd(II) species coordinated with chlorine ions and Cu(II) compounds, respectively, with solid Cu2Cl(OH)3 being the particularly effective copper species. A larger than stoichiometric amount of CuCl2 was required for high activity over the carbon support. The presence of chlorine ion was essential to sustain these active palladium and copper species. The solid copper phase of Cu2Cl(OH)3 was superior to traditional CuCl2·2H2O for reoxidizing the reduced palladium species via Wacker chemistry. The chemical environment of copper appeared to have crucial effects in sustaining the active Pd(II) species, which is required for high activities i...

Electronic states of Pd +3

Complete active space self-consistent field (CASSCF) followed by multi-reference singles+doubles CI (MRSDCI) which included up to 2.3 million configurations are made on eight electronic states of Pd + 3. All eight states of Pd + 3 were found to exhibit only slight Jahn-Teller distortion from ideal equilateral triangular structures. The ground state of Pd + 3 was found to be 4B 2 with near-equilateral triangle geometry. Seven excited states within 5 kcal/mol of the ground state were also found.

Magnetic Susceptibility and Electronic Specific Heat of Transition Metals and Alloys II. Pd Metal and Pd-Ag and Pd-Rh Alloys

Electronic specific heat of Pd is deduced from the experimental data. Using the density of electronic states of Pd which has been determined from the low temperature specific heat data of Pd–Ag and Pd–Rh alloys and Ru metal by assuming the rigid band model, the electronic specific heat and the spin paramagnetic susceptibility of Pd are calculated at arbitrary temperatures. The calculated result for the temperature dependence of the electronic specific heat of Pd satisfactorily agrees with the experimental result, whereas the calculated values for spin paramagnetic susceptibility are considerably smaller than the observed values. The main difference will be attributable to the effect of the molecular field. The maximum in observed magnetic susceptibility at about 80°K can be explained by considering a peculiar band shape. Similar calculations to those for Pd metal are performed for Pd–Ag and Pd–Rh alloys.