Pd Atoms Research Articles

Ultrathin porous Pd metallene as highly efficient oxidase mimics for colorimetric analysis

Pd-based nanomaterials have shown great promise as promising mimic enzymes, but traditional catalysts can only expose only part of the active sites, resulting in low atomic utilization. Herein, we demonstrated that ultrathin Pd metallene with abundant accessible active sites could be served as highly efficient oxidase mimics. Due to their ultrathin porous structure, nearly all the Pd atoms of the Pd metallenezymes could be efficiently utilized during the catalytic process. By using the 3,3′,5,5′-tetramethyl benzidine (TMB) as a typical chromogenic substrate, the Pd metallenezymes with excellent oxidase-like activity are successfully applied for some colorimetric-based analysis applications. Benefiting from the sensitive Pd metallene/TMB detection system, the TAC of some commercial beverages and vitamin C chewable pieces are proved to meet the description and the activity of alkaline phosphatase (ALP) was successfully detected in 0–20 U/L range, achieving a lowest detect limit of 0.41 U/L. This work provides not only one kind of novel nanozymes, but also an effective strategy to maximize the atom utilization as enzyme mimics.

Poly-icosahedral Co–Fe–Pd nanoalloy: Isomerism effect on the structural and magnetic properties from DFT

This study seeks to understand and explain the role of isomerism on the structural and magnetic properties of Co–Fe–Pd nanoalloys. To this end, semiempirical Gupta potential was utilized to identify the first three isomers and the global minimum structures of all compositions, and then these isomers were subject to re-optimization by means of the DFT approach. The structural analysis of Co2FenPd17-n (n = 0–17) nanoalloys revealed that Co atoms prefer locations in the inner sites of the nanoalloys. Fe and Pd atoms occupy the surface for both GM structures and isomers. Our general result shows an increase in the total magnetic moment of the nanoalloys but a decrease in the local magnetic moments of the Co and Fe atoms. Another important result is that the local magnetic moment of the Pd atoms is not zero. These results support the idea that the isomerism effect plays a crucial role in structural and magnetic properties.

NiCoPd Inlaid NiCo-Bimetallene for Efficient Electrocatalytic Methanol Oxidation.

Pd-based metallenes have attracted great attention recently as newly burgeoning two-dimensional (2D) materials, attributed to their significantly increased active surface areas and intrinsic electrocatalytic activities. Therefore, they could be used as a potential candidate as the high-performance electrocatalyst for methanol oxidation reactions (MORs) in the direct methanol fuel cell. Herein, a new strategy is proposed to fabricate NiCoPd inlaid NiCo-bimetallene (NiCoPd/NiCo-bimetallene) by the structure directing effect of 18-crown-6 ether under an ultrasonic-pulse interface together with the HCHO reduction and atom-diffusion-aging process. NiCoPd ternary-alloys with uniformly dispersed Pd active sites are decorated onto NiCo-bimetallenes, achieving remarkably enhancing the effective utilization of Pd atoms. What is more, the intrinsic activity is enhanced by the "bifunctional mechanism" of NiCo-bimetallene adsorption of intermediate species and increased Pd-active sites. Moreover, the anti-CO poisoning ability is optimized through the "alloying ligand effect" of NiCoPd. Therefore, the NiCoPd/NiCo-bimetallene exhibits excellent mass activity for MOR, which is higher than commercial Pd/C. This work suggests a new way of the Pd-based metallenes catalyst approach to the efficient electrocatalytic MOR.

Effects of doping a boron atom in g-C3N4 on the catalytic activity of deposited Pd atom for the dehydrogenation of formic acid: A DFT study

The catalytic performance of palladium atom deposited on the cavity of the g-C3N4 sheet for the formic acid (FA) dehydrogenation was investigated using M06-L calculations. For the Pd1/g-C3N4 system, the preferable pathway for H2 production from FA decomposition occurs through the hydrocarboxyl intermediate with Ea of 21.2 kcal mol−1 for the rate-determining step (RDS). For B-doped g-C3N4, two different forms, which are the substitution of a boron atom at the nitrogen or the carbon atom, were used to examine the impact of the support on the catalytic activity of the deposited Pd atom. The boron dopant can enhance the basicity of the g-C3N4. As a result. the deposited Pd atom becomes more positively charged as compared to that on the pristine support. The greater the positive charge of the Pd atom, the stronger interaction with FA is found. Furthermore, the enhancement of basicity of the B-doped g-C3N4 sheet plays a key role in activating the O-H bond of FA as compared to that on the bare support. The reaction mechanism on Pd1/B-doped g-C3N4 favorably proceeds through the formate pathway. The activation energy of RDS is predicted to be 11.4 and 16.4 kcal mol−1 for BN-, BC-doped g-C3N4 supports, respectively.

Surface Structure Engineering of PtPd Nanoparticles for Boosting Ammonia Oxidation Electrocatalysis.

Achieving high catalytic ammonia oxidation reaction (AOR) performance of Pt-based catalysts is of paramount significance for the development of direct ammonia fuel cells (DAFCs). However, the high energy barrier of dehydrogenation of *NH2 to *NH and easy deactivation by *N on the Pt surface make the AOR show sluggish kinetics. Here, we have put forward an alloying and surface modulation tactic to optimize Pt catalysts. Several spherical PtM (M = Co, Ni, Cu, and Pd) binary nanoparticles were controllably loaded on reduced graphene oxide (rGO). Among others, spherical PtPd nanoparticles displayed the most efficient catalytic activity. Further surface engineering of PtPd nanoparticles with a cubic-dominant structure has resulted in dramatic AOR activity improvements. The optimized (100)Pt85Pd15/rGO exhibited a low onset potential (0.467 V vs reversible hydrogen electrode (RHE)) and high peak mass activity (164.9 A g-1), much better than commercial Pt/C. Nevertheless, a short-term stability test along with morphology, structure, and composition characterizations indicate that the leaching of Pd atoms from PtPd alloy nanoparticles, their structure transformations, and the possible poisoning effects by the N-containing intermediates could result in the catalyst's activity loss during the AOR electrocatalysis. A temperature-dependent electrochemical test confirmed a reduced activation energy (∼12 kJ mol-1 decrease) of cubic-dominant PtPd compared to Pt/C. Density functional theory calculations further demonstrated that Pd atoms in Pt decrease the reaction energy barrier of electrochemical dehydrogenation of *NH2 to *NH, resulting in an excellent catalytic activity for the AOR.

Optimizing Oxygen and Intermediate HOO* Adsorption of Cu–Pd Alloy Cocatalyst for Boosting Photocatalytic H2O2 Production of BiVO4

AbstractThe modification of Pd cocatalysts is considered to be an effective strategy to improve H2O2 production of photocatalysts because it can accelerate the reaction rate of O2 reduction. However, the strong adsorption between O2 molecules and Pd atoms is not conducive to the formation of intermediate HOO* and leads to the further reduction of H2O2 to H2O, thus limiting the improvement of H2O2 production. To solve the issue, in this work, Cu–Pd alloy cocatalysts are selectively modified on the electron‐rich facets of BiVO4 via facile photoinduced deposition and subsequent galvanic displacement. DFT calculations indicate that the incorporation of Cu atoms to Pd atoms weakens the oxygen adsorption energy and HOO* binding energy on Pd atom surfaces, thus increasing the activity and selectivity of O2 reduction to H2O2. Further experimental results show that the optimized Cu‐Pd/BiVO4(5:1) photocatalyst exhibits markedly boosted activity for H2O2 production (2189 µmol L‐1), which is 3.2‐fold higher than that of BiVO4 with modification of 0.3 wt% Pd cocatalyst (675 µmol L‐1). Additionally, the incorporation of metal Cu enables the economic utilization of Pd atoms and reduces the expense of the Pd cocatalyst.

Ab Initio Studies of Work Function Changes of CO Adsorption on Clean and Pd-Doped ZnGa2O4(111) Surfaces for Gas Sensors

We performed first-principles calculations to study the adsorption of the CO molecules on both clean and Pd-doped ZnGa2O4(111) surfaces. The adsorption reaction and work function of the CO adsorption models were examined. The CO molecules on the clean and Pd-doped ZnGa2O4(111) surfaces exhibit maximum work function changes of −0.55 eV and −0.79 eV, respectively. The work function change of Pd-doped ZnGa2O4(111) for detecting CO is 1.43 times higher than that of the clean ZnGa2O4(111). In addition, the adsorption energy is also significantly reduced from −1.88 eV to −3.36 eV without and with Pd atoms, respectively. The results demonstrate ZnGa2O4-based gas sensors doped by palladium can improve the sensitivity of detecting CO molecules.

Boosting toluene oxidation by the regulation of Pd species on UiO-66: Synergistic effect of Pd species

Supported single-atoms and sub-nanometre clusters have exhibited superb catalytic performance toward many reactions. However, inactivation of single-atom or cluster catalysts in complex reactive conditions poses major challenge for their practical application. Herein, we demonstrate that the prepared Pd-UiO-66 with ultra-low Pd loading (0.05 wt%) contains three robust active Pd species, (isolated Pd atom (Pd1), sub-nanometre Pd clusters (Pdc) and Pd nanoparticles (Pdn)) and presents superb activity for toluene oxidation and water resistance (10.0 vol%). Experiments and theoretical calculations firstly confirm that consecutive H2-O2 and reaction gas treatment (1000 ppm toluene in 20 vol.%O2/Ar) induce residual N species from solvent N, N-dimethylformamide to enter UiO-66 skeleton forming Pd1-N1 structures. DFT calculations reveal that the synergistic effect of Pd species (namely, the enhanced activation of O2 and H2O by Pd1 and the improved adsorption of toluene by Pdc and Pdn) is the main factor for the excellent activity of Pd-U-H-O-reused catalyst.

Role of Titanium replacement with Pd atom on band gap reduction in the anatase Titanium Dioxide: First-Principles calculation approach

Titanium dioxide (TiO2) is one of the highly promising energy materials. Nevertheless, it has a wide energy bandgap that restricts its absorption capacity within the visible light spectrum. To investigate the effects of doping the transition-metal Palladium (Pd) into anatase TiO2, we perform first-principles calculations in the framework of density functional theory (DFT). All calculations are carried out in the scheme of Hubbard potential (U) correction to account for the correlated effects in TiO2. For this purpose, the first-principles calculations are carried out with the CASTEP code in the formalism of GGA + U. The Pd-doped TiO2 was examined in detail for its electronic structure, lattice parameters, E-K representation, the density of states and optical properties. The results showed that lattice parameters of TiO2 changed after doping. The band structure, partial density of state (PDOS), total density of state (TDOS), complex dielectric function, refractive index, optical absorption, and energy loss function of Pd-doped anatase are improved drastically. It was observed that the doping process adds Pd 4d electronic states into different energy ranges and thus reduces middle states within the band gap region. Our electronic structure calculations indicate augmentation of d-states around the Fermi level, induced by doping Pd. Additionally, compared with the undoped TiO2, the absorption edges of Pd-doped TiO2 show a shift from the UV spectrum towards the visible light region. The results indicate that the GGA + U approach is unique in determining the real band structure of semiconductors which is close enough to empirical results.

Electro-Catalytic Properties of Palladium and Palladium Alloy Electro-Catalysts Supported on Carbon Nanofibers for Electro-Oxidation of Methanol and Ethanol in Alkaline Medium

Carbon nanofibers (CNFs) supported by Pd and Pd-Sn electro-catalysts were prepared by the chemical reduction method using ethylene glycol as the reducing agent. Their physicochemical characteristics were studied using high resolution-transmission electron microscopy (HR-TEM), Fourier transform infrared spectroscopy (FTIR), X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), thermogravimetric analysis (TGA) and Bruanaer-Emmett-Teller (BET) analysis. FTIR revealed that oxygen, hydroxyl, carboxylic and carbonyl functional groups facilitated the dispersion of Pd and Sn nanoparticles. The doping of Pd with Sn to generate PdSn alloy was also confirmed by XPS data. The amorphous nature of CNFs was confirmed by XRD patterns which exhibited the Pd diffraction peaks. When Sn was added to Pd/CNFs, the diffraction peaks moved to lower angles. HRTEM images revealed that the CNFs with cylindrical shape-like morphology and also Pd-Sn nanoparticles dispersed on carbon support. The catalytic activity and stability towards alcohol electro-oxidation in alkaline medium at room temperature was evaluated using cyclic voltammetry (CV), chronoamperometry (CA) and electrochemical impedance spectroscopy (EIS). The obtained Pd-Sn/CNFs electro-catalyst exhibited a better electro-catalytic activity than Pd/CNFs and Pd/C electro-catalysts for both methanol and ethanol oxidation. The improvement of the electrochemical performance was associated with the synergistic effect via the addition of Sn which modified the Pd atom arrangement, thereby promoting oxidation through a dehydrogenation pathway. Furthermore, SnO2 generates abundant OH species which helps with increasing the rate of the oxidative removal of carbon monoxide (CO) intermediates from Pd sites.

Palladium-rhodium binary oxide composite nanofibers with various composition ratios for highly efficient electrochemical sensing of carbon monoxide in neutral aqueous media

Binary palladium (Pd) and rhodium (Rh) oxide composite nanofibers with diverse atomic ratios (PdxRh1−xOy NFs, x = 0.34, 0.55 and 0.75) were synthesized by electrospinning and post-calcination. The component phases of PdxRh1−xOy NFs varied with the Pd/Rh atomic ratio: PdRhO2 and amorphous RhOy in Pd0.34Rh0.66Oy; mainly PdRhO2 with a slight PdO in Pd0.55Rh0.45Oy; and PdO along with a rather small amount of PdRhO2 in Pd0.75Rh0.25Oy. The electrocatalytic activities of the synthesized materials were characterized for CO oxidation in neutral aqueous solution at room temperature. The anodic current of PdxRh1−xOy NFs increased in a linear proportion to CO concentration change, demonstrating the CO oxidation catalytic activity. For amperometric CO sensing, all the PdxRh1−xOy NFs exhibited considerably enhanced activity and sensitivity compared to the materials containing single metal only (i.e., Rh2O3 NFs and PdO NFs). Pd0.55Rh0.45Oy NFs exhibited the greatest CO sensitivity among the group of PdxRh1−xOy NFs. This high activity of Pd0.55Rh0.45Oy NFs was attributed mainly to the following factors: The similar contents of Pd and Rh in the material can (1) maximize the synergetic effect between Pd and Rh, producing the largest number of Pd atoms adjacent to Rh atoms; and (2) form the greatest amount of highly conductive PdRhO2 delafossite phase. In addition to the high sensitivity of Pd0.55Rh0.45Oy NFs in amperometric CO sensing, the excellent reproducibility, resistance for CO poisoning and selectivity over NO were also verified. This study demonstrates a feasibility of Pd0.55Rh0.45Oy NFs as a promising electrode material for electrochemical CO sensing.

Synergy of Pd atoms and oxygen vacancies on In2O3 for methane conversion under visible light

Methane (CH4) oxidation to high value chemicals under mild conditions through photocatalysis is a sustainable and appealing pathway, nevertheless confronting the critical issues regarding both conversion and selectivity. Herein, under visible irradiation (420 nm), the synergy of palladium (Pd) atom cocatalyst and oxygen vacancies (OVs) on In2O3 nanorods enables superior photocatalytic CH4 activation by O2. The optimized catalyst reaches ca. 100 μmol h−1 of C1 oxygenates, with a selectivity of primary products (CH3OH and CH3OOH) up to 82.5%. Mechanism investigation elucidates that such superior photocatalysis is induced by the dedicated function of Pd single atoms and oxygen vacancies on boosting hole and electron transfer, respectively. O2 is proven to be the only oxygen source for CH3OH production, while H2O acts as the promoter for efficient CH4 activation through ·OH production and facilitates product desorption as indicated by DFT modeling. This work thus provides new understandings on simultaneous regulation of both activity and selectivity by the synergy of single atom cocatalysts and oxygen vacancies.

High C1 selectivity in alkaline ethanol oxidation reaction over stable Lewis pairs of Pd-MxC@CNT (M = W, Mo and Cr)

Pd-based catalysts have been widely studied as electrocatalysts for ethanol oxidation reaction (EOR) because of their higher oxygenophilic properties. However, there are still some disadvantages such as low activity, poor stability and poor selectivity, which hinder the development of EOR. Herein, a method through strong metal-support interaction (SMSI) and heterostructure of Pd-MxC@CNT (M = W, Mo and Cr) to construct a stable Lewis acid-base pair is proposed. Pd-W2C@CNT nanomaterial showed the highest mass activity (13.9 A mgPd−1), C1 selectivity (74.15%) and stability, better than Pd Black (3.5 A mgPd−1, 7.2%) and Pd@CNT (4.1 A mgPd−1, 7.6%). Ex situ and in situ electrochemical experiments reveal that the introduction of W2C became a stable electron donor for Pd, increasing the electron density of Pd atoms and forming a stable Lewis acidity Pd atoms to weaken the adsorption of intermediates. Reducing the electron density of W2C and forming a stable Lewis basicity W2C to provide sufficient OH adspecies for the reaction, thereby increasing the selectivity of the C1 pathway. Furthermore, the Pd-MxC@CNT synthesized by this method also exhibited excellent EOR activity, stability and C1 selectivity and glycerol oxidation reaction (GOR) performance.

Glucose electrooxidation modelling studies on carbon nanotube supported Pd catalyst with response surface methodology and density functional theory

In this study, carbon nanotube supported Pd catalysts (Pd/CNT) are synthesized at different weight percentages by the sodium borohydride (NaBH4) reduction method to investigate catalytic performance of glucose electrooxidation reaction. 0.5% Pd/CNT, 3% Pd/CNT, and 7% Pd/CNT catalysts are characterized by using X-ray diffraction (XRD), electron microscopy with energy dispersive X-ray (SEM-EDX), and N2 adsorption-desorption measurements. The average particle size and surface area of 3% Pd/CNT catalyst are determined as 46.33 nm and 129.48 m2/g, respectively. Characterization results indicate that Pd/CNT catalysts are successfully prepared by NaBH4 reduction method. Cyclic voltammetry measurements are performed to investigate the effect of Pd loading for the glucose electrooxidation. CV results reveal that 3% Pd/CNT catalyst exhibits best glucose electrooxidation activity. Following this, experimental optimization is performed to obtain maximum glucose electrooxidation activity via response surface methodology (RSM). Estimated and experimental specific activities at optimum experimental conditions are assigned as 6.186 and 5.832 mA/cm2, respectively. To understand the glucose electrooxidation activity on the surface of Pd/CNT, surface modeling is also performed with density functional theory (DFT) method to investigate adsorption of glucose molecule on CNT supported Pd surface. The DFT results emphasize that the addition of Pd atom to the CNT structure significantly improves the catalytic performance in glucose electrooxidation.

Tuning Reaction Pathways of Electrochemical Conversion of CO2 by Growing Pd Shells on Ag Nanocubes.

The electrochemical carbon dioxide reduction reaction (CO2RR) has been studied on Ag, Pd, Ag@Pd1-2L nanocubes using a combination of in situ characterization and density functional theory calculations. By manipulating the deposition and diffusion rates of Pd atoms on Ag nanocubes, Ag@Pd core-shell nanocubes with a shell thickness of 1-2 atomic layers have been successfully synthesized for CO2RR. Pd nanocubes produce CO with high selectivity due to the transformation of Pd to Pd hydride (PdH) during CO2RR. In contrast, PdH formation becomes more difficult in Ag@Pd1-2L core-shell nanocubes, which inhibits CO production from the *HOCO intermediate and thus tunes the reaction pathway toward HCOOH. Ag nanocubes exhibit high selectivity toward H2, and there is no phase transition during CO2RR. The results demonstrate that the CO2RR reaction pathways can be manipulated through engineering the surface structure of Pd-based catalysts by allowing or preventing the formation of PdH.

The importance of Brønsted acid sites on C[sbnd]O bond rupture selectivities during hydrogenation and hydrogenolysis of esters

Esters represent an important class of reagents and intermediates for the production of fine chemicals and polymers. In prior studies of homogeneous catalysis, molecular complexes have been reported to selectively cleave either carbonyl CO or acyl CO bonds of ester to ether or alcohols, respectively. In contrast, reactions of esters and H2 upon heterogeneous catalysts typically cleave acyl CO bonds and produce alcohols. Here, we demonstrate that the proximity of Brønsted acid sites to Pd nanoparticles and the thermodynamic strength of these Brønsted acid sites influence the rates and selectivities toward CO bond cleavage pathways either to ethers or alcohols during reactions of esters over bifunctional solid catalysts. The combined results from rate measurements as functions of H2 pressure, ester conversion, and methods to combine Pd nanoparticles and acidic supports; kinetic isotope effects; in situ Brønsted acid site titrations; and calorimetric assessments of Brønsted acid strength provide evidence for bifunctional pathways that require proximity between Brønsted acid sites and Pd atoms to form ethers. These findings suggest that Brønsted acid sites near Pd nanoparticles and with lower deprotonation energies promote the direct reduction of esters to ethers by cleaving the carbonyl CO bond. Taken together, these data indicate that direct reduction of esters to ethers involves the hydrogenation of the ester reactant to form hemiacetal at Pd nanoparticles, followed by dehydration of the hemiacetal at proximal acid sites, and subsequent hydrogenation of the enol ether. In comparison, hydrogenolysis of acyl CO bonds of the ester reactant involves the reaction of a hydrogenated intermediate (plausibly hemiacetal) upon Pd nanoparticles to form the corresponding alcohol and aldehyde products. Among the materials examined, Pd nanoparticles supported on WO3 catalyze the direct reduction of esters and lactones to corresponding ethers and remain stable over extended periods of time on stream (∼42 h). These findings offer a foundation for further design and improvement of heterogeneous catalysts for the selective reduction of esters and other challenging hydrogenations.

Breaking scaling relationships in alkynol semi-hydrogenation by manipulating interstitial atoms in Pd with d-electron gain

Pd catalysts are widely used in alkynol semi-hydrogenation. However, due to the existence of scaling relationships of adsorption energies between the key adsorbed species, the increase in conversion is frequently accompanied by side reactions, thereby reducing the selectivity to alkenols. We report that the simultaneous increase in alkenol selectivity and alkynol conversion is achieved by manipulating interstitial atoms including B, P, C, S and N in Pd catalysts. A negative linear relationship is observed between the activation entropies of 2-methyl-3-butyn-2-ol and 2-methyl-3-buten-2-ol which is highly related to the filling of d-orbital of Pd catalysts by the modification of p-block elements. A catalyst co-modified by B and C atoms has the maximum d charge of Pd that achieves a 17-fold increase in the turn-over frequency values compared to the Lindlar catalysts in the semi-hydrogenation of 2-methyl-3-butyn-2-ol. When the conversion is close to 100%, the selectivity can be as high as 95%.

First-principle investigation of CO adsorption on Pd-loaded VO2 monolayer

Using the first principle calculation based on density functional theory, the CO adsorption on pure VO2 monolayer and Pd-loaded VO2 monolayer (Pd/VO2) investigated systematically. The electronic structure and properties of the most energetic configuration are analyzed in terms of density of states and charge density difference. The results showed that the adsorption energy of CO on pure VO2 monolayer was −0.239 eV, and the length of V–O bond did not change obviously, which indicated physisorption. Further studies showed that the adsorption energy of CO adsorption on Pd/VO2 surface was −2.010 eV, and the length of V–O bond changed significantly, indicating that CO can be chemically adsorbed on Pd/VO2 surface. Finally, the calculation of optical properties showed that the absorption of visible light by CO adsorption on VO2 monolayer can be substantially improved due to the supported Pd atom. Therefore, the supported Pd atom can effectively improve the adsorption effect of pure VO2 monolayer, providing an promising method to promote the practical application of VO2 monolayer.

Di-chlorido-(4-methyl-aniline-κN)[N-(4-methyl-phen-yl)-1-(thio-phen-2-yl)methanimine-κN]palladium(II).

The structure of a mono-amine PdII complex, [PdCl2(C7H9N)(C12H11NS)], which crystallizes in the triclinic space group, P , is reported. The primary geometry around the PdII atom closely resembles square planar (τ4' = 0.069). In the (E)-1-(thio-phen-2-yl)-N-(p-tol-yl)methanimine ligand, the phenyl and thio-phene rings are not coplanar, subtending a dihedral angle of 38.5 (1)° because of steric effects. The PdCl2N2 coordination plane is almost perpendicular to the planes of the coordinated o-toluidine and the NC2 fragment [dihedral angles of 84.7 (1) and 72.50 (4)°, respectively]. The Pd-NH2 length of 2.040 (2) Å is slightly shorter than the observed mean value for other complexes involving a Pd atom attached to the nitro-gen of an aniline derivative. The mol-ecules display an inter-esting supra-molecular synthon based on reciprocal inter-molecular N-H⋯Cl hydrogen-bonding inter-actions of the p-toluidine amine fragment, which results in centrosymmetric dimeric units. These units are further linked by C-H⋯Cl inter-actions, resulting in chains in the c-axis direction where the mean-planes of the repeating fragment are oriented in the (110) plane.

Regioselective hydrogenation of alkenes over atomically dispersed Pd sites on NHC-stabilized bimetallic nanoclusters

<h2>Summary</h2> A catalyst containing atomically dispersed Pd sites on N-heterocyclic carbene (NHC)-stabilized Au nanoclusters, with the precise formula of PdAu₉(NHC^Bn)₇X₂ (NHC^Bn is dibenzylbenzimidazolin-2-ylidene, X is Br or Cl), has been developed for the regioselective hydrogenation of alkenes. Each Pd site is encircled by an Au₉ ring protected by seven NHC and two halide ligands. Such an encirclement arrangement and open stereochemical framework endow the single Pd atom with the power to activate molecular hydrogen and catalyze the hydrogenation of alkenes efficiently. Interestingly, it otherwise exhibits much lower activity toward the crowded alkenes, owing to the inherent and highly stringent steric requirement of NHC ligands, as also visualized by the theory. As such, these clusters are demonstrated to be a highly efficient (653 h⁻¹ of turnover frequency) and highly selective (97%) catalyst in the regioselective hydrogenation of linalool, an important synthetic perfume and a key intermediate in the synthesis of vitamin A.