Single Pd Atom Research Articles

Nitrogen-doped carbon black supported synergistic palladium single atoms and nanoparticles for electrocatalytic oxidation of methanol

For commercially viable direct methanol fuel cells, electrocatalysts play a crucial role in motivating the sluggish methanol oxidation reaction (MOR) over anode. Unfortunately, the large-scale applications of current MOR catalysts are hampered by their poor tolerance to poisoning and fast activity degradation. Herein, a unique composite catalyst comprised of partial Pd nanoparticles and partial Pd single atoms (PdNPs/Pd-Nx@C) is developed. The as-fabricated catalyst exhibits remarkable activity of 9.45 mA·cm−2 towards MOR in alkaline solution, which is 7.05 and 3.92 times that of commercial Pd/C and nanoparticle type (PdNPs@C) electrocatalysts, respectively. Impressively, the PdNPs/Pd-Nx@C shows the highest long-time stability with 90.38% and 89.8% of the initial activity retained after 3600 s chronoamperometry (CA) test and 2000 cycles of cyclic voltammetry (CV) measurements with accelerated durability test (ADT), respectively. Combined with high-angle annular darkfield scanning transmission electron microscopy (HAADF-STEM), X-ray adsorption fine structure (XAFS) spectra and X-ray photoelectron spectroscopy (XPS) analyses, the superior performance of PdNPs/Pd-Nx@C can be ascribed to the synergistic effect from the Pd single atoms, N-doped carbon supports and Pd nanoparticles. Notably, the embedded Pd single atoms are liable to transfer electrons to the substrate due to the electronic metal-support interactions (EMSI) and the charge transfer between Pd nanoparticles and carbon supports is suppressed, inducing a weak adsorption strength of poisonous carbonous intermediate species on active Pd nanoparticles and improved poisoning tolerance in MOR process, which is verified by density functional theory (DFT) calculations as well as CO-stripping voltammetry experiments. This work not only contributes the first example of a synergistic catalyst between nanoparticles and single atoms for MOR but also deepens the knowledge on the metal-support interaction.

Single noble metals (Pd, Pt and Ir) anchored Janus MoSSe monolayers: Efficient oxygen reduction/evolution reaction bifunctional electrocatalysts and harmful gas detectors

The binding properties of single noble metal atoms (Pd, Pt and Ir) anchored Janus MoSSe monolayers (MLs), the catalytic activity of Pd- and Pt-MoSSe in oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) as well as the adsorption behaviors of Ir-MoSSe for harmful NO, CO and NH3 molecules are systematically studied from the first-principles calculations. Current results reflect the ascending order (Pd-MoSSe < Pt-MoSSe < Ir-MoSSe) of stability and binding strength as well as the tunable electronic properties of Janus MoSSe ML by anchoring single Pd, Pt and Ir atoms. Pd- and Pt-MoSSe exhibit excellent bifunctional catalytic performance, especially the former having lower overpotentials 0.43 and 0.50 V for ORR and OER, which are better than the well-known Pt (111) (0.45 V) and IrO2 (0.56 V) electrocatalysts, respectively. The adsorption nature for NO, CO and NH3 molecules changes from physisorption (on pristine MoSSe) to chemisorption (on Ir-MoSSe), especially for NO and CO molecules due to their ultra-low adsorption energies (−3.72 and −2.91 eV, respectively). Thus, Pd- and Pt-MoSSe (particularly the former) may act as promising highly-efficient ORR/OER bifunctional electrocatalysts, and Ir-MoSSe may serve as a potential sensitive harmful gas detector for NO and CO molecules.

Single Pd atoms synergistically manipulating charge polarization and active sites for simultaneously photocatalytic hydrogen production and oxidation of benzylamine

Photocatalytic hydrogen production coupled with selective oxidation of organic substances is of significance and remains a grand challenge because of unsatisfied photocatalytic activity and unclear mechanism. Herein, we first design and synthesize atomically dispersed Pd on ZnIn2S4 (PdSA-ZIS) for simultaneously photocatalytic hydrogen production and oxidation of benzylamine. Based on systematic characterization with a combination of theoretical simulations, light irradiation-kelvin probe force microscopy (KPFM) and time-resolved photoluminescence spectrum etc, we demonstrate that Pd single atoms can modulate charge polarization as well as the active sites of ZnIn2S4 to promote spatial charge separation and decrease the energy barriers of reaction. The electrons are enriched around Pd single atoms-ZnS layer with lowest energy barriers of H2 production, while more holes are accumulated on InS2 layer for dehydrogenation of benzylamine. This enables PdSA-ZIS to exhibit remarkable photocatalytic performance for the co-production of N-benzylidenebenzylamine (10.2 mmol g−1 h−1) with selectivity of 100% and H2 (11.1 mmol g−1 h−1) under visible irradiation. Furthermore, by means of controlled experiments, theoretical simulations and in situ electron spin resonance (ESR) spectroscopy, a synergetic photocatalytic redox mechanism on the Pd single atom-ZIS interface for dehydrogenation and coupling of benzylamine and H2 production has been investigated in detail.

Role of single-atom Pd in Cu/ZrO2 catalysts for CO2 hydrogenation to methanol

This study is to load the sing-atom Pd on Cu/ZrO2 with ion exchange method, and the role of Pd in Cu/ZrO2 for CO2 hydrogenation to methanol is investigated. The exchange of Pd with Cu/ZrO2 increase the methanol production rate from 223 μmol g−1 h−1 to 512 μmol g−1 h−1 at relatively mild conditions (1.5 Mpa, 260 °C). This exchange increases the splitting H adsorptions on Cu species, and strengthen interactions between Cu species and oxygen vacancies at the interface, thus promoting the formations of Cuδ+ species, which is critical to the formation of methanol. This study provides a promising alternative for the understandings the role of exchanged Pd in the Pd-Cu/ZrO2 catalysts for CO2 hydrogenation to methanol.

Ceria-supported Pd catalysts with different size regimes ranging from single atoms to nanoparticles for the oxidation of CO

Supported metal catalysts are the most widely used in industrial processes and the metal particle size plays a crucial factor in determining the catalytic performance. Herein, CeO2-supported Pd catalysts with different Pd size regimes ranging from single atoms, to nanoclusters (1–2 nm), and to nanoparticles (>2 nm) were used for both CO oxidation and preferential oxidation of CO in H2 (CO-PROX). Compared to Pd nanoclusters and nanoparticles, CeO2-supported single Pd atoms (PdSA/CeO2) are the most intrinsically active in CO oxidation, with an apparent activation energy of ca. 40 kJ mol−1. Results of kinetic investigations and in situ diffuse reflectance infrared Fourier transformed spectroscopy demonstrate the CO oxidation proceeding through a Langmuir-Hinshelwood mechanism with the decomposition of formate species acting dominantly as the rate-determining step. The CO reaction rate is exclusively promoted on PdSA/CeO2 catalysts for the CO-PROX reaction, which could be ascribed to a stronger H-spillover effect on isolated Pd sites to produce bridged-OH on CeO2 surface, simultaneously facilitating the consumptions of bicarbonate and formate species. There results greatly deepen the fundamental understanding of the Pd size regimes over Pd/CeO2 catalysts for the oxidation of CO.

Atomic control of active-site ensembles in ordered alloys to enhance hydrogenation selectivity.

Intermetallic compounds offer unique opportunities for atom-by-atom manipulation of catalytic ensembles through precise stoichiometric control. The (Pd, M, Zn) γ-brass phase enables the controlled synthesis of Pd-M-Pd catalytic sites (M = Zn, Pd, Cu, Ag and Au) isolated in an inert Zn matrix. These multi-atom heteronuclear active sites are catalytically distinct from Pd single atoms and fully coordinated Pd. Here we quantify the unexpectedly large effect that active-site composition (that is, identity of the M atom in Pd-M-Pd sites) has on ethylene selectivity during acetylene semihydrogenation. Subtle stoichiometric control demonstrates that Pd-Pd-Pd sites are active for ethylene hydrogenation, whereas Pd-Zn-Pd sites show no measurable ethylene-to-ethane conversion. Agreement between experimental and density-functional-theory-predicted activities and selectivities demonstrates precise control of Pd-M-Pd active-site composition. This work demonstrates that the diversity and well-defined structure of intermetallics can be used to design active sites assembled with atomic-level precision.

Single-atom Pd catalysts as oxidase mimics with maximum atom utilization for colorimetric analysis

Single-atom Pd catalysts as oxidase mimics with maximum atom utilization for colorimetric analysis

A density functional theory study on the catalytic performance of metal (Ni, Pd) single atom, dimer and trimer for H2 dissociation

• H 2 dissociation on transition metal (TM = Ni, Pd) single atom, dimer and trimer doped on Au substrate have been studied. • The H 2 dissociation in the form of Ni, Pd trimer exhibited the best catalytic performance. • The H 2 dissociation process follow the BEP relation on different structural units. Elucidating the effect of different structural units in the catalyst on catalytic performance was very important for the development of the excellent heterogeneous catalyst. This work used density functional theory (DFT) approach to investigate H 2 dissociation over transition metal (TM = Ni, Pd) single atom, dimer and trimer doped on Au substrate. The influence of different structural units toward the catalytic performance was elucidated. The results showed that the catalytic performance of Ni, Pd trimer was stronger than those of Ni, Pd single atom and dimer. Therefore, it was proposed that for the H 2 dissociation, the structural units in the form of Ni, Pd trimer exhibited the best catalytic performance. It was also obtained that the H 2 dissociation process followed the BEP relation on different structural units. This work provides insights about structural units for the reasonable design of the excellent heterogeneous catalysts toward dissociation reactions.

Pd speciation on black phosphorene in a CO and C2H4 atmosphere: a first-principles investigation.

Deposited transition metal clusters and nanoparticles are widely used as catalysts and have long been thought stable in reaction conditions. We investigated the electronic structure and stability of freestanding and black phosphorene supported small Pd clusters containing 1 to 6 atoms in a CO or C2H4 atmosphere by extensive first-principles based calculations. We showed that, driven by the thermodynamics, subnanometric Pd clusters and single Pd atom on phosphorene may evolve for a better balance among metal-metal, metal-support and metal-adsorbate interactions, etc., resulting in atomic dispersion of Pd in reaction conditions. The strong interfacial Pd-P interactions would deform preformed Pd clusters into atomic strips of various lengths with enhanced stability comparable to bulk Pd. The diffusion barriers of terminal Pd atoms in the zigzag direction on phosphorene are small (<0.3 eV) and vary within ∼0.1 eV with the length of these atomic strips. Further adsorption of CO or C2H4 alters the Pd-P and Pd-Pd interactions and forms thermodynamically stable surface Pd species with decreased diffusion barriers, suggesting that atomic dispersion of Pd can be achieved on phosphorene, especially in a CO or C2H4 atmosphere. The current work may help to understand the superior catalytic performance of supported subnanometric transition metal catalysts in reaction conditions and pave the way for fabrication of single atom catalysts with the desired performance.

Insights into Synergistic Effect of Pd Single Atoms and Sub-Nanoclusters on Tio2 for Enhanced Photocatalytic H2 Evolution

Insights into Synergistic Effect of Pd Single Atoms and Sub-Nanoclusters on Tio2 for Enhanced Photocatalytic H2 Evolution

Mechanistic Insight into Surface Oxygen Species of the Polyoxometalate-Supported Pd Single-Atom Catalysts for Highly Efficient Co Oxidation

Mechanistic Insight into Surface Oxygen Species of the Polyoxometalate-Supported Pd Single-Atom Catalysts for Highly Efficient Co Oxidation

Pd/Fe2O3 with Electronic Coupling Single-Site Pd-Fe Pair Sites for Low-Temperature Semihydrogenation of Alkynes.

Dispersing single palladium atoms on a support is promising to minimize the usage of palladium and improve the selectivity for alkyne semihydrogenation, but its activity is often very low as a result of unfavorable H2 activation. Here, we load palladium onto α-Fe2O3(012) to construct highly active and stable single-site Pd-Fe pairs with luxuriant d-electron domination near the Fermi level driven by strong electronic coupling and prove that Pd-Fe pairs cooperatively adsorb H2 and dissociate an H─H bond, whereas solo Pd sites enable preferential desorption of C═C intermediate, thus achieving both high activity and high selectivity for alkyne hydrogenation. This catalyst exhibits state-of-the-art performance in purifying acetylene of ethylene stream, with 99.6% and 100% conversion and 96.7% and 94.7% selectivity at 353 and 393 K, respectively, and excellent stability with negligible activity decay after a 200 h test. This single-site pair inherits the advantage but overcomes the weakness of both Pd ensemble and single Pd atoms, enabling ultralow-Pd-loading catalysts for selective hydrogenation.

Pd single-atom decorated CdS nanocatalyst for highly efficient overall water splitting under simulated solar light

Solar-induced overall water splitting to produce hydrogen is inspiring towards energy sustainability, but it is also formidable due to its limited efficiency seriously hindering its scale up for practical application. CdS is an important transition metal sulfide with low-work-function. However, its photostability is often deteriorated due to photocorrosion influence. To overcome this issue, single-atom Pd was employed here to decorate CdS to form a CdS-Pd nanocatalyst through a simple and controllable photoinduced reduction strategy. The synergetic semiconductor (CdS)-metal (Pd) interaction promotes the fast bulk-to-surface electron migration, thereby the resultant CdS-Pd (3.83‰) nanocatalyst shows considerable structural stability and dramatically improved solar-induced HER activity in overall water splitting, about 110-fold higher than that of pristine CdS. Meanwhile, high apparent quantum yields (AQYs) of 4.47%/1.81% and 33.92%/27.49% were respectively achieved with this decorated nanocatalyst under the light of 420 nm/500 nm in absence and presence of scavenger, demonstrating the high-efficiency under broadband light illumination. Density functional theory (DFT) calculation supports that the easy formation of H* intermediates on the decorated nanocatalyst due to low energy barriers accounts for the internal promoted mechanism for hydrogen production. This study provides important insight to gain stable CdS-based photocatalysts for high-efficient hydrogen production by overall water splitting.

Bioadhesive injectable hydrogel with phenolic carbon quantum dot supported Pd single atom nanozymes as a localized immunomodulation niche for cancer catalytic immunotherapy

Immunotherapy is a powerful way to treat cancer, however, systemic treatment-associated adverse effects remain a major concern. In this study, a bioadhesive injectable hydrogel is developed to provide localized immune niches for tumor microenvironment immunomodulation and cancer catalytic immunotherapy. First, a phenolic single atom nanozyme (SAN) was developed by in situ synthesis of Pd single atom on catechol-grafted carbon-quantum-dot (DA-CQD@Pd) templates. Then, the bioadhesive injectable hydrogel consisting of DA-CQD@Pd SAN and immune adjuvant CpGODN was formed through SAN-catalyzed free-radical polymerization. The SAN exhibited peroxidase-like activity to generate ROS and kill tumor cells through catalytic therapy. The hydrogel locally released CpGODN in a sustained manner, which limited the risk of systemic exposure, reducing the impact of CpGODN toxicity, and protecting CpGODN from degradation. The bioadhesive hydrogel immobilized around solid tumor to provide an immune response site after injection. When combined it with the administration of immune checkpoint inhibitor anti-PD-L1, the hydrogel realized localized immunomodulation, maximized therapeutic efficacy and prevents tumor metastasis via a catalytic immunotherapy.

Atomic-level insights into the steric hindrance effect of single-atom Pd catalyst to boost the synthesis of dimethyl carbonate

Atomic-level insight into the unique catalytic capability of single-atom catalysts that distinguished from nanometer-sized counterparts is highly desirable for catalyst design and catalysis research. By synthesizing single Pd atoms supported on TiO2 as a catalyst, here we demonstrate a steric hindrance effect of single atoms induced by the unique isolation of single-atom active sites to achieve a remarkable enhancement on catalytic performance in the synthesis of dimethyl carbonate. Experimental results and density functional theory calculations reveal that such steric hindrance effect of single atoms favors the yield of the desired product dimethyl carbonate against further reacting with intermediates to form byproduct, because no extra Pd species around single Pd atoms provide active sites to further adsorb and activate substrates directly. The discovery of such steric hindrance effect is a valuable supplement to single-atom catalysis, and may promote single-atom catalysts to be widely applied in selective catalytic reactions.

Control of Local Electronic Structure of Pd Single Atom Catalyst by Adsorbate Induction.

Aiming at regulating and controlling the localized electronic states while maintaining the metal atoms in the isolation form, an in situ adsorbate induced strategy is proposed at a programmed temperature to activate Zr-based metal-organic framework (MOF) supported single Pd atom catalyst. It is discovered that in situ treatment environments trigger the change of lattice parameters in MOF materials by reaction heat effect, observed by in situ X-ray diffraction, spherical aberration-corrected electron microscope, and X-ray adsorption fine structure (XAFS). The as-obtained electron-deficient Pd single atoms are critical to the high intrinsic activity (turnover frequency of 0.132 s-1 ) and selectivity of 93% with the long-term stability in the semihydrogenation of acetylene, which can be comparable to the state-of-the-art Pd catalysts. This superior catalytic behavior correlates with the reduced C2 H4 desorption energy and the activation barriers for the hydrogenation, confirmed by density functional theory calculation.

Computational Design of Pd Nanoclusters and Pd Single-Atom Catalysts Supported on O-Functionalized Graphene

A crucial step in the preparation of supported metal catalysts is related to the choice of support, since it regulates the anchoring of the metal species in an environment of strong interactions. In this sense, the binding on the support, which may present defects, as well as induced modifications of the electronic structure, helps to determine efficient metal/support combinations for catalysis applications. In this work, first-principles studies have been carried out to model and describe the geometric and electronic properties of O-functionalized graphene as a model carbon support, in addition to a single Pd atom and Pd13 nanocluster (experimentally observed on various carbon supports) as supported metal catalysts. The carbon-based nanomaterial includes experimentally probed abundant oxygen functional groups and point defects, demonstrating high thermal stability at room temperature. The characterization confirms the structural motifs presented in the model, distinguishing the organic functionalities and various defects using spectroscopy techniques. Interestingly, the oxygenated carbon-based support presents a metallic character when the formal charges in the embedded Pd atom and nanocluster have been determined to be [Pd]+ and [Pd13]3+. The hydrogenation process of the adsorbed cluster is also presented, with the determination of a ratio between the adsorbed hydrides and the surface metal atoms close to unity at room temperature, thanks to ab initio molecular dynamics.

The Dehydrogenation of H-S Bond into Sulfur Species on Supported Pd Single Atoms Allows Highly Selective and Sensitive Hydrogen Sulfide Detection.

The supported metal catalysts on scaffolds usually reveal multiple active sites, resulting in the occurrence of side reaction and being detrimental to the achievement of highly consistent catalysis. Single atom catalysts (SACs), possessed with highly consistent single active sites, have great potentials for overcoming such issues. Herein, the authors used SACs to modulate kinetic process of gas sensitive reaction. The supported Pd SACs, established by a metal organic frameworks-templated approach, promoted greatly the detection capacity to hydrogen sulfide (H2 S) gas with a very high sensitivity and selectivity. Density functional theory calculations show that the supported Pd SACs not only increased the number of electrons transferring from H2 S molecules to Pd SACs, but strengthened surface affinity to H2 S. Moreover, the HS bonds of H2 S molecules absorbed on Pd atomic sites are more likely to be dehydrogenated directly into sulfur species. Significantly, quasi in situ XPS analysis confirmed the presence of sulfur species during H2 S detection process, which may be a major cause for such detection signal. Based on these results, a suitable sensing principle for H2 S gas driven by Pd SACs was put forward. This work will enrich catalytic electronics in chemiresistive gas sensing.

Tuning the selectivity of catalytic nitriles hydrogenation by structure regulation in atomically dispersed Pd catalysts

The product selectivity in catalytic hydrogenation of nitriles is strongly correlated with the structure of the catalyst. In this work, two types of atomically dispersed Pd species stabilized on the defect-rich nanodiamond-graphene (ND@G) hybrid support: single Pd atoms (Pd1/ND@G) and fully exposed Pd clusters with average three Pd atoms (Pdn/ND@G), were fabricated. The two catalysts show distinct difference in the catalytic transfer hydrogenation of nitriles. The Pd1/ND@G catalyst preferentially generates secondary amines (Turnover frequency (TOF@333 K 709 h−1, selectivity >98%), while the Pdn/ND@G catalyst exhibits high selectivity towards primary amines (TOF@313 K 543 h−1, selectivity >98%) under mild reaction conditions. Detailed characterizations and density functional theory (DFT) calculations show that the structure of atomically dispersed Pd catalysts governs the dissociative adsorption pattern of H2 and also the hydrogenation pathway of the benzylideneimine (BI) intermediate, resulting in different product selectivity over Pd1/ND@G and Pdn/ND@G, respectively. The structure-performance relationship established over atomically dispersed Pd catalysts provides valuable insights for designing catalysts with tunable selectivity.

Ga-doped Pd/CeO[formula omitted] model catalysts for CO oxidation reactivity: A density functional theory study

Ceria-supported Pd single-atom catalysts (SACs) are important catalysts to catalyze the CO oxidation, often used in three-way catalysts to treat automobile exhaust gases. This paper uses density functional theory (DFT) calculations and transition state theory to systematically study the effect of Ga atom doping on the performance of the Pd/CeO2 SACs system. Noticeably, the results of DFT calculations reveal that the stability of Pd single atoms supported on the surface of CeO2(111) was significantly augmented by doping Ga. An oxygen vacancy generated easily near the Ga and Pd site will act as a crucial role for activating the adsorbed oxygen molecule. Most importantly, the climbing image nudged elastic band (CINEB) calculations show that the doping of Ga remarkably reduces the highest energy barrier during the CO oxidation reaction, meaning that the catalytic performance of the CO oxidation reaction is promoted effectively. This work provides a new perspective for SACs modification.