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Showing papers on "Palladium published in 2022"


Journal ArticleDOI
TL;DR: In this article , a palladium phosphide (PdxPy) porous nanotubes (PNTs) with different phosphide content (i.e., Pd3P and Pd5P2) are prepared by combining the self-template reduction method of dimethylglyoxime-Pd(II) complex nanorods and succedent phosphating treatment.
Abstract: The development of an efficient catalyst for formic acid electrocatalytic oxidation reaction (FAEOR) is of great significance to accelerate the commercial application of direct formic acid fuel cells (DFAFC). Herein, palladium phosphide (PdxPy) porous nanotubes (PNTs) with different phosphide content (i.e., Pd3P and Pd5P2) are prepared by combining the self-template reduction method of dimethylglyoxime-Pd(II) complex nanorods and succedent phosphating treatment. During the reduction process, the self-removal of the template and the continual inside–outside Ostwald ripening phenomenon are responsible for the generation of the one-dimensional hollow and porous architecture. On the basis of the unique synthetic procedure and structural advantages, Pd3P PNTs with optimized phosphide content show outstanding electroactivity and stability for FAEOR. Importantly, the strong electronic effect between Pd and P promotes the direct pathway of FAEOR and inhibits the occurrence of the formic acid decomposition reaction, which effectively enhances the FAEOR electroactivity of Pd3P PNTs. In view of the facial synthesis, excellent electroactivity, high stability, and unordinary selectivity, Pd3P PNTs have the potential to be an efficient anode electrocatalyst for DFAFC.

93 citations



Journal ArticleDOI
TL;DR: In this article, a gold-palladium modified zirconium metal-organic frameworks (AuPd@UiO-67) nanozyme was employed as signal enhancer for detecting mercury ions (Hg2+) sensitively.

66 citations


Journal ArticleDOI
TL;DR: In this paper , the authors show that separating the gold and palladium components in bimetallic carbon-supported catalysts can almost double the reaction rate compared with that achieved with the corresponding alloy catalyst.
Abstract: In oxidation reactions catalysed by supported metal nanoparticles with oxygen as the terminal oxidant, the rate of the oxygen reduction can be a limiting factor. This is exemplified by the oxidative dehydrogenation of alcohols, an important class of reactions with modern commercial applications1–3. Supported gold nanoparticles are highly active for the dehydrogenation of the alcohol to an aldehyde4 but are less effective for oxygen reduction5,6. By contrast, supported palladium nanoparticles offer high efficacy for oxygen reduction5,6. This imbalance can be overcome by alloying gold with palladium, which gives enhanced activity to both reactions7,8,9; however, the electrochemical potential of the alloy is a compromise between that of the two metals, meaning that although the oxygen reduction can be improved in the alloy, the dehydrogenation activity is often limited. Here we show that by separating the gold and palladium components in bimetallic carbon-supported catalysts, we can almost double the reaction rate compared with that achieved with the corresponding alloy catalyst. We demonstrate this using physical mixtures of carbon-supported monometallic gold and palladium catalysts and a bimetallic catalyst comprising separated gold and palladium regions. Furthermore, we demonstrate electrochemically that this enhancement is attributable to the coupling of separate redox processes occurring at isolated gold and palladium sites. The discovery of this catalytic effect—a cooperative redox enhancement—offers an approach to the design of multicomponent heterogeneous catalysts. ‘Cooperative redox enhancement (CORE) effects, which arise through the coupling of oxidative dehydrogenation and oxygen reduction reactions, can lead to increased rates of reaction over spatially separated bimetallic heterogeneous catalysts.

66 citations


Journal ArticleDOI
TL;DR: In this paper , a gold-palladium modified zirconium metal-organic frameworks (AuPd@UiO-67) nanozyme was employed as signal enhancer for detecting mercury ions (Hg2+) sensitively.

65 citations


Journal ArticleDOI
TL;DR: In this article , single-atomic Pd sites supported by ordered porous N,S-doped carbon are synthesized, exhibiting remarkable alkaline hydrogen oxidation reaction (HOR) performance.
Abstract: Alkaline exchange membrane fuel cells are impeded by the lack of cost-effective, highly efficient catalysts for the sluggish hydrogen oxidation reaction (HOR). Herein, single-atomic Pd sites supported by ordered porous N,S-doped carbon are synthesized, exhibiting remarkable alkaline HOR performance. This catalyst exhibits an ultrahigh anodic current density and mass-specific kinetic current of 2.01 mA cm–2 and 27,719 A gPd–1 (at an overpotential of 50 mV), respectively, not only outperforming the Pt/C counterpart but also making it among the best reported HOR catalysts. Furthermore, this catalyst exhibits a negligible activity decay during long-term electrolysis and a good CO tolerance capability. Experiments and theoretical calculations indicate that the synergistic effect from single Pd sites and heteroatom doping (N and S) weakens the binding energy of Had intermediates, thereby accounting for its superior HOR activity. This study provides a guideline for developing single-atomic site catalysts for highly efficient, stable alkaline HOR.

57 citations


Journal ArticleDOI
TL;DR: In this paper , the evolution of Pd species is investigated on different crystal facets of CeO2, and vastly different behaviors on the single-atomic dispersion of surface Pd atoms are surprisingly discovered.
Abstract: High‐performance, fully atomically dispersed single‐atom catalysts (SACs) are promising candidates for next‐generation industrial catalysts. However, it remains a great challenge to avoid the aggregation of isolated atoms into nanoparticles during the preparation and application of SACs. Here, the evolution of Pd species is investigated on different crystal facets of CeO2, and vastly different behaviors on the single‐atomic dispersion of surface Pd atoms are surprisingly discovered. In situ X‐ray photoelectron spectroscopy (XPS), in situ near‐ambient‐pressure‐XPS (NAP‐XPS), in situ diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS), and X‐ray absorption spectroscopy (XAS) reveal that, in a reducing atmosphere, more oxygen vacancies are generated on the (100) facet of CeO2, and Pd atoms can be trapped and thus feature atomic dispersion; by contrast, on the CeO2 (111) facet, Pd atoms will readily aggregate into clusters (Pdn). Furthermore, Pd1/CeO2(100) gives a high selectivity of 90.3% for the catalytic N‐alkylation reaction, which is 2.8 times higher than that for Pdn/CeO2(111). This direct evidence demonstrates the crucial role of crystal‐facet effects in the preparation of metal‐atom‐on‐metal‐oxide SACs. This work thus opens an avenue for the rational design and targeted synthesis of ultrastable and sinter‐resistant SACs.

46 citations


Journal ArticleDOI
TL;DR: In this paper , a facile Pd II -complex pyrolysis method is applied to synthesize the high-quality one-dimensional heterostructured Pd/PdO nanowires (Pd and PdO H-NWs).

40 citations


Journal ArticleDOI
TL;DR: In this paper , three kinds of Pd cocatalysts with various valence distributions were loaded on g-C3N4 nanosheets with the close loading amounts (~ 1 wt%) and uniform sizes (2-3 nm).
Abstract: Nano-structured metal cocatalysts are easy to be oxidized and form mixed valences and interfaces which would facilitate the catalytic performance in previous studies. Herein, as an example in photocatalysis, three kinds of Pd cocatalysts with various valence distributions (PdO70-Pd30/CN, PdO50-Pd50/CN and PdO30-Pd70/CN) were loaded on g-C3N4 nanosheets with the close loading amounts (~1 wt%) and uniform sizes (2–3 nm). Then, the results of the photocatalytic degradation of ciprofloxacin showed that the generated oxidative active species are highly related to the distribution of palladium valence. Pd2+ (PdO) benefits the production of·O2-, while Pd0 benefits the production of h+. The theoretical simulations revealed that surface states e.g., electron distribution and the adsorption ability of O2 on different Pd species determined the production of·O2- and h+. Besides, PdO50-Pd50/CN showed the best performance for degrading ciprofloxacin, due to the joint action of·O2- and h+ in the CIP degradation.

38 citations


Journal ArticleDOI
TL;DR: In this article , a convenient interfacial engineering strategy is developed to the design and construction of quasi-one-dimensional worm-shaped palladium nanocrystals strongly coupled with positively-charged polyelectrolyte-modified Ti3C2Tx MXene via the direct electrostatic attraction.

38 citations


Journal ArticleDOI
TL;DR: In this article , a self-driving laboratory is used to define the Pareto front of conductivities and processing temperatures for palladium films formed by combustion synthesis, which can be used to discover materials that provide optimal trade-offs between conflicting objectives.
Abstract: Useful materials must satisfy multiple objectives, where the optimization of one objective is often at the expense of another. The Pareto front reports the optimal trade-offs between these conflicting objectives. Here we use a self-driving laboratory, Ada, to define the Pareto front of conductivities and processing temperatures for palladium films formed by combustion synthesis. Ada discovers new synthesis conditions that yield metallic films at lower processing temperatures (below 200 °C) relative to the prior art for this technique (250 °C). This temperature difference makes possible the coating of different commodity plastic materials (e.g., Nafion, polyethersulfone). These combustion synthesis conditions enable us to to spray coat uniform palladium films with moderate conductivity (1.1 × 105 S m-1) at 191 °C. Spray coating at 226 °C yields films with conductivities (2.0 × 106 S m-1) comparable to those of sputtered films (2.0 to 5.8 × 106 S m-1). This work shows how a self-driving laboratoy can discover materials that provide optimal trade-offs between conflicting objectives.


Journal ArticleDOI
TL;DR: In this article , an asymmetric salamo-based-Palladium(0) complex grafted on Fe3O4 MNPs was synthesized and characterized using physicochemical methods including FT-IR, XRD, SEM, TEM, EDS, ICP-AES, X-ray mapping, TGA and VSM analyses.

Journal ArticleDOI
06 May 2022-Science
TL;DR: In this article, the authors demonstrate that by using supported gold-palladium (AuPd) alloyed nanoparticles in conjunction with a titanium silicate-1 (TS-1) catalyst, H2O2 can be generated in situ as needed, producing cyclohexanone oxime with >95% selectivity, comparable to the current industrial route.
Abstract: The ammoximation of cyclohexanone using preformed hydrogen peroxide (H2O2) is currently applied commercially to produce cyclohexanone oxime, an important feedstock in nylon-6 production. We demonstrate that by using supported gold-palladium (AuPd) alloyed nanoparticles in conjunction with a titanium silicate-1 (TS-1) catalyst, H2O2 can be generated in situ as needed, producing cyclohexanone oxime with >95% selectivity, comparable to the current industrial route. The ammoximation of several additional simple ketones is also demonstrated. Our approach eliminates the need to transport and store highly concentrated, stabilized H2O2, potentially achieving substantial environmental and economic savings. This approach could form the basis of an alternative route to numerous chemical transformations that are currently dependent on a combination of preformed H2O2 and TS-1, while allowing for considerable process intensification. Description Peroxide as needed Hydrogen peroxide for commercial applications is currently mass produced through an indirect process that involves reduction and reoxidation of a quinone. The trouble with making it straight from the elements is that concentrated mixtures of hydrogen and oxygen are dangerously explosive. Lewis et al. report that direct peroxide synthesis at safe concentrations is compatible with a current industrial method for producing cyclohexanone oxime, a key precursor to nylon. The protocol could potentially offer substantial efficiency advantages for manufacturing a high-volume bulk chemical. —JSY Making hydrogen peroxide in situ could improve overall process efficiency for production of a key nylon precursor.

Journal ArticleDOI
TL;DR: In this paper , the basic perceptions of the green synthesis of metal nanoparticles and their supported-catalyst-based reduction of 4-nitrophenol (4-NP) to 4-aminophenol(4-AP) are discussed.
Abstract: Noble metal (silver (Ag), gold (Au), platinum (Pt), and palladium (Pd)) nanoparticles have gained increasing attention due to their importance in several research fields such as environmental and medical research. This review focuses on the basic perceptions of the green synthesis of metal nanoparticles and their supported-catalyst-based reduction of 4-nitrophenol (4-NP) to 4-aminophenol (4-AP). The mechanisms for the formation of these nanoparticles and the catalytic reduction of 4-NP are discussed. Furthermore, the parameters that need to be considered in the catalytic efficiency calculations and perspectives for future studies are also discussed.

Journal ArticleDOI
TL;DR: In this article , a palladaelectro-catalyzed C-H activation/[3 + 2] spiroannulation of alkynes by 1-aryl-2-naphthols was described.
Abstract: Despite indisputable progress in the development of electrochemical transformations, electrocatalytic annulations for the synthesis of biologically relevant three-dimensional spirocyclic compounds has as of yet not been accomplished. In sharp contrast, herein, we describe the palladaelectro-catalyzed C–H activation/[3 + 2] spiroannulation of alkynes by 1-aryl-2-naphthols. Likewise, a cationic rhodium(iii) catalyst was shown to enable electrooxidative [3 + 2] spiroannulations via formal C(sp3)–H activations. The versatile spiroannulations featured a broad substrate scope, employing electricity as a green oxidant in lieu of stoichiometric chemical oxidants under mild conditions. An array of spirocyclic enones and diverse spiropyrazolones, bearing all-carbon quaternary stereogenic centers were thereby accessed in a user-friendly undivided cell setup, with molecular hydrogen as the sole byproduct.

Journal ArticleDOI
TL;DR: In this paper , the formation mechanism of Pd single atoms on the ultrathin, mesoporous cyano-group-rich graphitic carbon nitride (g-C3N4) nanosheets is proposed, and the synthesis process includes copolymerization of urea-derived supramolecular aggregates and NH4Cl followed by wet impregnation.
Abstract: To improve the photocatalytic hydrogen evolution activity of palladium-assisted graphitic carbon nitride (g-C3N4), here, palladium-single-atom-coordinated cyano-group-rich g-C3N4 (Pd/DN-UCN) are synthesized, and the synthesis process includes copolymerization of urea-derived supramolecular aggregates and NH4Cl followed by wet impregnation. By combining powerful characteristic results and theoretical calculations, the formation mechanism of Pd single atoms on the ultrathin, mesoporous cyano-group-rich g-C3N4 nanosheets is proposed, highlighting that the Pd single atoms are firmly stabilized in the interlayers of g-C3N4 nanosheets caused by the combination of the physical confinement effect of ultrathin, mesoporous g-C3N4 nanosheets and coordination bonding of cyano groups with Pd atoms; additionally, Pd–N3 coordination in the Pd/DN-UCN heterojunctions is confirmed, in which one Pd atom coordinates with one N atom of the cyano group and two sp2-hybridized N atoms in the adjacent layer. The presence of cyano groups and Pd–N coordination in the Pd/DN-UCN induces a midgap state in the band structure of g-C3N4. At optimal Pd loading levels (0.16%), the synthesized 0.16%Pd/DN-UCN0.50 exhibits enhanced photocatalytic hydrogen production activity as compared to electrostatically stabilized Pd single atoms on the “sixfold cavities” of g-C3N4, and apparent quantum yield values at the stationary point of the 0.16%Pd/DN-UCN0.50 concentration (1.2 g L–1) can reach up to 14.6, 15.8, 4.69, and 3.05% under monochromatic light irradiation at 365, 400, 450, and 550 nm, respectively. The cooperation of significantly boosted transfer of photoexcited electrons to atomically dispersed Pd sites via as-built interlayer Pd–N coordination delivery channels and the maximal Pd atom utilization efficiency dominates the enhanced photocatalytic hydrogen evolution activity of Pd/DN-UCN.

Journal ArticleDOI
26 May 2022-Science
TL;DR: In this paper , a pair of palladium catalysts assembled with quinoline-pyridone ligands of different chelate ring sizes were used to perform highly site-selective monolactonization reactions with a wide range of dicarboxylic acids, generating structurally diverse and synthetically useful γ- and δ-lactones via site-Selective β- or γmethylene C-H activation.
Abstract: Catalyst-controlled site-selective activation of β- and γ-methylene carbon-hydrogen (C–H) bonds of free carboxylic acids is a long-standing challenge. Here we show that, with a pair of palladium catalysts assembled with quinoline-pyridone ligands of different chelate ring sizes, it is possible to perform highly site-selective monolactonization reactions with a wide range of dicarboxylic acids, generating structurally diverse and synthetically useful γ- and δ-lactones via site-selective β- or γ-methylene C–H activation. The remaining carboxyl group serves as a versatile linchpin for further synthetic applications, as demonstrated by the total synthesis of two natural products, myrotheciumone A and pedicellosine, from abundant dicarboxylic acids. Description Sizing rings with carbon–hydrogen oxidation Catalytic reactions targeting carbon–hydrogen bonds have proliferated in recent years, but selecting a particular site in a hydrocarbon chain remains a great challenge. Chan et al. report that precise optimization of the nitrogen ligands coordinating a palladium catalyst can tune the ring size accessed in lactone formation. More specifically, with reagents comprising a hydrocarbon chain capped at each end by an acid, the choice of ligand determines whether oxidative ring closure will occur two or three carbons away from an end group. —JSY Precise ligand optimization tunes the site selectivity of palladium-catalyzed carbon–hydrogen oxidation to form lactone rings from acids.

Journal ArticleDOI
TL;DR: In this article , a method for a highly regioselective formation of a B-N bond by Pd(II)-catalyzed B(9)-H amination of o- and m-carboranes in hexafluoroisopropanol (HFIP) with different nitrogen sources under air atmosphere is presented.
Abstract: Amination of carboranes has a good application prospect in organic and pharmaceutical synthesis. However, the current methods used for this transformation suffer from limitations. Herein, we report a practical method for a highly regioselective formation of a B-N bond by Pd(II)-catalyzed B(9)-H amination of o- and m-carboranes in hexafluoroisopropanol (HFIP) with different nitrogen sources under air atmosphere. The silver salt and HFIP solvent play critical roles in the present protocol. The mechanistic study reveals that the silver salt acts as a Lewis acid to promote the electrophilic palladation step by forming a heterobimetallic active catalyst PdAg(OAc)3; the strong hydrogen-bond-donating ability and low nucleophilicity of HFIP enhance the electrophilic ability of Pd(II). It is believed that these N-containing carboranes are potentially of great importance in the synthesis of new pharmaceuticals.

Journal ArticleDOI
TL;DR: In this paper , a metal-organic frameworks adsorbent (MOF-AFH) was synthesized to efficiently separate Pd(II) and Au(III) from the water.
Abstract: With the boom of modern industry, the demand for precious metals palladium (Pd) and gold (Au) is increasing. However, the discharge of Pd(II) and Au(III) wastewater has caused environmental pollution and shortage of resources. Here, a new metal-organic frameworks adsorbent (MOF-AFH) was synthesized to efficiently separate Pd(II) and Au(III) from the water. The adsorption behavior of Pd(II) and Au(III) was explored at the same time. When gold and palladium are adsorbed separately, the adsorption capacity of gold and palladium is 389.02 mg/g and 191.27 mg/g, respectively. The equilibration time is 3 h. When gold and palladium coexist, the adsorption capacities of Au(III) and Pd(II) are 238.71 and 115.02 mg/g, respectively. The experimental results show that the adsorption of Pd(II) and Au(III) on MOF-AFH is a single-layer chemical adsorption, which is an endothermic process. MOF-AFH has excellent selectivity and after MOF-AFH is repeatedly used 4 times, the removal effect can still reach more than 90%. The adsorption mechanisms include reduction reaction and chelation with N and O-containing functional groups on the adsorbent. There is also electrostatic interaction for Au(III) adsorption. The adsorbent can be used to efficiently recover gold and palladium from wastewater.

Journal ArticleDOI
TL;DR: Li et al. as mentioned in this paper presented single-crystalline mesoporous Palladium and Palladium-Copper nanocubes for highly efficient electrochemical CO2 reduction. But the performance of these nanostructures is limited.
Abstract: Open AccessCCS ChemistryRESEARCH ARTICLE1 Apr 2022Single-Crystalline Mesoporous Palladium and Palladium-Copper Nanocubes for Highly Efficient Electrochemical CO2 Reduction Hao Lv†, Fang Lv†, Huaiyu Qin, Xiaowen Min, Lizhi Sun, Na Han, Dongdong Xu, Yanguang Li and Ben Liu Hao Lv† College of Chemistry, Sichuan University, Chengdu 610064 †H. Lv and F. Lv contributed equally to this work.Google Scholar More articles by this author , Fang Lv† Institute of Functional Nano and Soft Materials (FUNSOM), Jiangsu Key Laboratory for Carbon-Based Functional Materials and Devices, Soochow University, Suzhou 215123 †H. Lv and F. Lv contributed equally to this work.Google Scholar More articles by this author , Huaiyu Qin College of Chemistry, Sichuan University, Chengdu 610064 Google Scholar More articles by this author , Xiaowen Min College of Chemistry, Sichuan University, Chengdu 610064 Google Scholar More articles by this author , Lizhi Sun Jiangsu Key Laboratory of New Power Batteries, Jiangsu Collaborative Innovation Center of Biomedical Functional Materials, School of Chemistry and Materials Science, Nanjing Normal University, Nanjing 210023 Google Scholar More articles by this author , Na Han Institute of Functional Nano and Soft Materials (FUNSOM), Jiangsu Key Laboratory for Carbon-Based Functional Materials and Devices, Soochow University, Suzhou 215123 Google Scholar More articles by this author , Dongdong Xu Jiangsu Key Laboratory of New Power Batteries, Jiangsu Collaborative Innovation Center of Biomedical Functional Materials, School of Chemistry and Materials Science, Nanjing Normal University, Nanjing 210023 Google Scholar More articles by this author , Yanguang Li *Corresponding authors: E-mail Address: [email protected] E-mail Address: [email protected] Institute of Functional Nano and Soft Materials (FUNSOM), Jiangsu Key Laboratory for Carbon-Based Functional Materials and Devices, Soochow University, Suzhou 215123 Google Scholar More articles by this author and Ben Liu *Corresponding authors: E-mail Address: [email protected] E-mail Address: [email protected]da.edu.cn College of Chemistry, Sichuan University, Chengdu 610064 Jiangsu Key Laboratory of New Power Batteries, Jiangsu Collaborative Innovation Center of Biomedical Functional Materials, School of Chemistry and Materials Science, Nanjing Normal University, Nanjing 210023 Google Scholar More articles by this author https://doi.org/10.31635/ccschem.021.202100958 SectionsSupplemental MaterialAboutAbstractPDF ToolsAdd to favoritesDownload CitationsTrack Citations ShareFacebookTwitterLinked InEmail Mesoporous single crystals have unique potential in catalysis, but remain unexplored owing to the enormous synthetic challenge that they pose. Herein, we report a facile soft-template method to prepare palladium (Pd) and Pd alloy nanocubes with single-crystallinity and abundant mesoporosity. The successful formation of these exotic nanostructures essentially relies on the cointroduction of cetyltrimethylammonium chloride as the surfactant template and extra Cl− ions as the facet-selective capping agent under well controlled experimental conditions. Thanks to their large surface areas and penetrating mesoporous channels, our products exhibit a great performance for electrochemical CO2 reduction. The best sample from alloying palladium with copper enables the efficient formate production with high selectivity (90∼100%) over a broad potential range, and great stability even under the working potential as cathodic as −0.5 V versus a reversible hydrogen electrode. These performance metrics are far superior to previous Pd-based materials, and underscore the structural advantages of our products. Download figure Download PowerPoint Introduction Single-crystalline mesoporous metals constitute a unique class of materials for catalytic applications. Their ordered mesopores expose large accessible surface areas and active sites, and facilitate the rapid diffusion of reactants and products,1–6 while their single-crystallinity ensures long-range structural coherence and enhances electron transport.7–10 Unfortunately, the combination of ordered mesoporosity and single-crystallinity appears inherently unfavorable. Complete crystallization of mesoporous walls significantly compromises structural stability and integrity, leading to the distortion or even collapse of ordered mesopores and consequently the loss of accessible surface areas and active sites.11–14 Indeed, most mesoporous materials (such as silica, carbon, and metal oxides) are amorphous or poorly crystalline in nature. There are only scarce reports available about single-crystalline mesoporous oxides or nitrides in the literature.14–23 The preparation of single-crystalline mesoporous metals is even more challenging since metals generally have larger surface energy than oxides, and have a greater propensity to minimize their surface areas and form disordered structures.20,24,25 This synthetic obstacle largely precludes their potential application at the current stage. One of the emerging catalytic processes is the electrochemical CO2 reduction reaction (CO2RR). It converts CO2 to value-added industrial chemicals or fuels, and is an essential step to close the artificial carbon cycle. Most CO2RR electrocatalysts are composed of metals.26–29 Depending on the selection of catalysts and experimental conditions, different reduction products can be attained from CO2 reduction, of which formic acid or formate is recommended as the most economically viable.30,31 Pd is so far the only known candidate capable of selectively reducing CO2 to formate at close-to-zero overpotential in aqueous solution.32–35 It unfortunately suffers from severe CO poisoning and is subject to rapid selectivity and stability loss with increasing overpotential.36–38 To this end, efforts have been made through nanostructural engineering and/or compositional regulation to enhance the operational stability of Pd-based materials. The performance gain, however, remains limited. In this contribution, we develop a facile aqueous method to prepare single-crystalline mesoporous Pd (s-mesoPd) and Pd alloy nanocubes in the copresence of a suitable quaternary ammonium surfactant and extra Cl− ions. The product exhibits uniform nanocubic morphology with the {100} enclosure, and features abundant mesoporous channels and single-crystallinity. When investigated for CO2 reduction in an aqueous solution, the best catalyst achieved unprecedented selectivity and stability for the formate production at the cathodic potential that was previously believed to cause quick catalyst deactivation. Experimental Methods Synthesis of s-mesoPd nanocubes and other nanocrystals Synthesis of s-mesoPd nanocubes In a typical synthesis of s-mesoPd nanocubes, 0.325 mg of cetyltrimethylammonium chloride (CTAC) was first dissolved in 5.0 mL of deionized H2O, followed by the addition of 0.24 mL of 80 mM KCl and 0.25 mL of 10 mM H2PdCl4. After incubation at 50 °C for 30 min, 0.50 mL of 0.30 M freshly prepared l-ascorbic acid (AA) was rapidly injected into the above solution with gentle shaking. The color of the solution gradually changed from orange to dark brown. After another 30 min, the product was collected by centrifugation and washed several times with ethanol and H2O. The surfactant type and/or KCl concentration were varied under otherwise identical conditions to investigate their effects on the product morphology and crystallinity. The size of s-mesoPd nanocubes was adjusted by varying the added amount of H2PdCl4 under otherwise identical conditions. Synthesis of p-mesoPd nanoparticles In a typical synthesis of p-mesoPd nanoparticles, 0.325 mg of CTAC was first dissolved in 5.0 mL of deionized H2O, followed by the addition of 0.25 mL of 10 mM H2PdCl4. After incubation at 50 °C for 30 min, 0.50 mL of 0.30 M freshly prepared AA was rapidly injected into the above solution with gentle shaking. After another 30 min, the product was collected by centrifugation and washed several times with ethanol and H2O. Synthesis of s-mesoPdCu nanocubes In a typical synthesis, 0.325 mg of CTAC was first dissolved in 5.0 mL of deionized H2O, followed by the addition of 0.24 mL of 80 mM KCl, 0.25 mL of 10 mM H2PdCl4, and 0.125 mL of 10 mM Cu(NO3)2. After incubation at 50 °C for 30 min, 0.50 mL of 0.30 M freshly prepared AA was rapidly injected into the above solution with gentle shaking. After another 30 min, the product was collected by centrifugation and washed several times with ethanol and H2O. Synthesis of s-mesoPdRh nanocubes In a typical synthesis, 0.325 mg of CTAC was first dissolved in 5.0 mL of deionized H2O, followed by the addition of 0.24 mL of 80 mM KCl, 0.25 mL of 10 mM H2PdCl4, and 0.125 mL of 10 mM (NH4)3RhCl6. After incubation at 50 °C for 30 min, 0.50 mL of 0.30 M freshly prepared AA was rapidly injected into the above solution with gentle shaking. After another 30 min, the product was collected by centrifugation and washed several times with ethanol and H2O. Synthesis of Pd nanoparticles In a typical synthesis, 13.0 mg of cetylpyridinium bromide was dissolved in 5.0 mL of H2O, followed by the addition of 0.25 mL of 10 mM H2PdCl4. After incubation at 50 °C for 30 min, 0.50 mL of 0.30 M freshly prepared AA was rapidly injected into the above solution with gentle shaking. After another 30 min, the product was collected by centrifugation and washed several times with ethanol/H2O. Electrochemical measurements Electrochemical CO2RR was carried out in a gas-tight H-cell controlled by the standard three-electrode system as reported in our previous work.38 To prepare the working electrodes, 1.00 mg of the catalyst powders under investigation and 0.50 mg of Ketjenblack carbon were added to 6.0 μL of 5 wt % Nafion solution and 250 μL of ethanol, and sonicated for >30 min to form a uniform dispersion. This catalyst ink was then dropped onto a 1 × 1 cm2 glassy carbon plate to achieve a catalyst loading of 1 mg cm−2 and dried under ambient conditions. For CO2RR measurements, the working electrode and a saturated calomel reference electrode (SCE) were placed in the cathodic compartment. A graphitic rod counter electrode was placed in the anodic compartment. These two compartments were separated by a Nafion-117 membrane, and each filled with 30 mL 0.10 M KHCO3 electrolyte presaturated with CO2 (pH = 6.8). All the potential readings in our study were measured against SCE and converted with respect to a reversible hydrogen electrode (RHE) with ∼90% iR compensation. Only geometric current densities were reported. Polarization curves were recorded from the cathodic sweeping of the working electrode at the scan rate of 10 mV s−1. Chronoamperometric analysis was carried out at a few selected potential points for the selectivity and stability assessment. At the end of the chronoamperometric study, formate accumulated in the catholyte was analyzed using ion chromatography (Dionex ICS-600; Thermo Scientific, USA) by comparing with the calibration curve from a series of standard formate solutions. Characterizations Scanning electron microscopy (SEM) images were collected using a JSM-7600F field emission scanning electron microscope (JEOL, Japan). SEM samples were prepared by dropcasting a suspension of the sample powder onto a silicon wafer. Transmission electron microscopy (TEM) studies were carried out using a JEM-F200 field emission transmission electron microscope (JEOL, Japan) with an accelerating voltage of 200 kV. TEM samples were prepared by dropcasting a diluted suspension of the sample powder onto a carbon coated copper grid (300 mesh). Scanning TEM (STEM) images were collected on a Talos F200X scanning/transmission electron microscope (Thermo Scientific, USA) operating at an accelerating voltage of 200 kV and equipped with an energy-dispersive X-ray spectroscopy (EDS) detector for elemental mapping analysis. Small-angle X-ray scattering (SAXS) patterns were measured using an Anton Paar SAXSess mc2 instrument (Austria). Powder X-ray diffraction (XRD) patterns were recorded on powder samples using a D/max 2500 VL/PC diffractometer (Japan) equipped with graphite-monochromatized Cu Kα radiation in 2θ ranging from 30° to 90°. The working voltage and current were 40 kV and 100 mA, respectively. X-ray photoelectron spectroscopy (XPS) was performed on a Thermo ESCALAB 250Xi X-ray photoelectron spectrometer (Thermo Scientific, USA) using Al Kα radiation. The binding energy of the C 1s peak (284.8 eV) was employed as a standard to calibrate the binding energies of other elements (Pd and Cu). Results and Discussion s-mesoPd nanocubes were prepared via a facile one-step soft-template method by reducing PdCl42− with AA in the presence of CTAC as the surfactant template and KCl as the facet-selective capping agent (Figure 1a). The cointroduction of CTAC and extra Cl− ions holds the decisive key to the successful formation of s-mesoPd nanocubes. The SAXS pattern of the final product shows a well-defined peak at 1.04 nm−1, suggesting mesoporous structure with an average periodicity of 6.04 nm (Figure 1b). The powder XRD pattern of s-mesoPd displays a set of diffraction peaks in the 2θ range of 30–90° assignable to face-centered cubic (fcc) Pd (JCPDS: 05-0681), evidencing that it is crystalline at the atomic scale (Figure 1c). Under SEM, the product is observed to have a cubic morphology with rounded edges and corners and an average size of ∼100 nm (Figure 1d). Figure 1e depicts an individual nanocube viewed perpendicular to its face, edge, or corner. Careful examination reveals that the nanocube surface is riddled with mesopores, which become more evident under STEM and TEM imaging (Figures 1f and 1g and Supporting Information Figure S1). They extend from the center and form cylindrical mesoporous channels radially penetrating the entire nanocube. The meopore size and framework thickness are measured to be 2.7 and 3.2 nm, respectively, consistent with the average periodicity derived from the above SAXS analysis. Surprisingly, we find that each nanocube is a single crystal despite its abundant mesoporosity. The selected area electron diffraction (SAED) pattern of the nanocube shown in Figure 1h only exhibits a single set of bright spots along the [100] zone direction of fcc Pd (Figure 1i). High-resolution TEM imaging of four randomly selected regions of the nanocube discloses the same lattice orientation and an identical d-spacing of 0.196 nm from the (200) plane (Figure 1j). These results unambiguously confirm that s-mesoPd nanocubes are single-crystalline and enclosed with six {100} facets. Figure 1 | Synthesis and characterizations of s-mesoPd nanocubes. (a) Schematic synthetic procedure. (b) SAXS analysis. (c) XRD pattern. (d and e) SEM images, inset in (d) illustrates the nanocube size distribution. (f) STEM image, inset shows the {100} enclosure of a nanocube. (g) TEM image. (h) TEM image of a nanocube and corresponding (i) SAED pattern and (j) high-resolution TEM images from different regions in (h). Download figure Download PowerPoint Here, the combination of the overall nanocubic morphology, abundant mesoporosity and single-crystallinity is highly unusual, and not available in previous literature to the best of our knowledge. We believe that CTAC and Cl− ions play important roles in precisely regulating the nanocrystal growth. In what follows, a series of control experiments are carried out to elucidate their effects. We first explored the effect of the surfactant template on the product structure and morphology (Figure 2a). In the absence of any surfactant, the product consists of concave nanocubes free of any mesoporous channels ( Supporting Information Figures S2a–S2c). When shorter-chained octyltrimethylammonium chloride (C8TAC) or dodecyltrimethylammonium chloride (C12TAC) are used instead of CTAC under otherwise identical conditions, resultant nanocubes become smaller in size and have less ordered mesoporous channels ( Supporting Information Figures S2d–S2i). When longer-chained behenyltrimethylammonium chloride (C22TAC) is used, two-dimensional (2D) Pd nanosheets are yielded, presumably from templating the lamellar mesophase of C22TAC in solution ( Supporting Information Figures S2j–S2l and S3).39 Figure 2 | Exploration of different experimental parameters. (a) TEM images of products prepared with no surfactant or in the presence of quaternary ammonium surfactants with different chain lengths under otherwise identical conditions. (b) TEM images of products prepared with no extra Cl− or different Cl− concentrations as indicated under otherwise identical conditions. (c) TEM images showing the structural evolution of s-mesoPd nanocubes with the reaction time. Download figure Download PowerPoint We then investigated the effect of Cl− ions during the synthesis of s-mesoPd nanocubes (Figure 2b). In the absence of extra Cl− ions from KCl, the product consists of spherical polycrystalline mesoporous Pd (p-mesoPd) nanoparticles ( Supporting Information Figures S4a–S4c). With the extra addition of Cl− ions, the overall product morphology gradually evolves from spheres to cubes. The optimal Cl− concentration is found to be 4.0 mM, giving rise to s-mesoPd nanocubes with the {100} enclosure as characterized in detail above. EDS and XPS analyses reveal the presence of Cl residue on the product surface after the synthesis ( Supporting Information Figure S5). Adding too many Cl− ions (16 mM) affords smaller polycrystalline nanocubes albeit with the same {100} enclosure ( Supporting Information Figures S4d–S4f). It should be noted that K+ cations do not play a role in the facet selection as replacing KCl with an equimolar amount of NaCl, CaCl2 or NH4Cl results in similar s-mesoPd nanocubes ( Supporting Information Figure S6). However, replacing Cl− ions with Br− ions or adding OH− compromises the nanocubic morphology ( Supporting Information Figure S7). Based on the above experimental observations, we propose that s-mesoPd nanocubes are formed through a concurrent surfactant-templating and facet-selective growth mechanism. CTAC is directly responsible for the formation of abundant mesoporous channels. During the reaction, amphiphilic CTAC molecules interact with PdCl42− through the Coulombic attraction, self-assemble to one-dimensional (1D) cylindrical micelles that further organize into a three-dimensional (3D) mesophase. The reduction of PdCl42− by AA gives rise to the templated growth of metallic Pd nanocrystals on the surfactant micelles, creating ordered mesoporous channels upon the surfactant removal. In the meantime, Cl− ions strongly bind to Pd(100) and selectively stabilize this facet.40,41 Such a facet-selective capping effect ultimately results in overall nanocubic morphology of our product. It is the copresence of CTAC and extra Cl− ions that collectively makes possible the successful growth of our s-mesoPd nanocubes in solution. To lend further support to the proposed mechanism, we track the time-dependent nanocube growth under TEM (Figure 2c). Upon the injection of AA, single-crystalline dendritic nanoparticles of 10–25 nm are formed immediately ( Supporting Information Figures S8a–S8c). They grow bigger and gradually evolve into nanocubes in the next 60 s ( Supporting Information Figures S8d–S8i). The nanocubic morphology is maintained throughout the rest of the reaction. Finally, s-mesoPd nanocubes were obtained in 10 min. Our solution synthetic strategy is versatile. For example, by increasing the amount of the PdCl42− precursor under otherwise identical conditions, the size of s-mesoPd nanocubes can be systematically varied from 31 to 132 nm, all of which are single-crystalline and mesoporous (Figures 3a–3d and Supporting Information Figure S9). More interestingly, this method can be extended to the preparation of single-crystalline mesoporous nanocubes of bimetallic alloys (s-mesoPdM nanocubes) such as s-mesoPdCu (Figures 3e–3i) and s-mesoPdRh ( Supporting Information Figure S10). Taking s-mesoPdCu nanocubes (with a nominal Pd/Cu molar ratio of 2) as an example, we find that the coreduction of PdCl42− and Cu2+ does not noticeably alter the templating effect of CTAC and facet-selective capping effect of Cl− ions. Resultant nanocubes are observed to have a similar morphology as that of s-mesoPd nanocubes, while the EDS elemental mapping of Pd and Cu clearly evidences their uniform spatial distribution and attests to the alloy formation instead of phase segregation. Their SAXS and XRD measurements also support the formation of the bimetallic PdCu alloy with ordered mesopores ( Supporting Information Figure S11). XPS analysis evidences the electron transfer from Cu to Pd in the alloy ( Supporting Information Figure S12). The compositional tunability in s-mesoPdM nanocubes provides an additional opportunity to tailor their electronic structures and thereby their catalytic properties. Figure 3 | Size and composition control of s-mesoPd and s-mesoPdM nanocubes. (a–d) TEM images of s-mesoPd nanocubes prepared with different CTAC concentrations. (e) STEM image of s-mesoPdCu nanocubes. (f) TEM image of a s-mesoPdCu nanocube and corresponding (g) SAED pattern and (h) high-resolution TEM image. (i) STEM image of a s-mesoPdCu nanocube and corresponding elemental mapping. Download figure Download PowerPoint The unique combination of mesoporosity and single-crystallinity renders our materials promising candidates for many applications. As a proof of concept, we here investigated the electrocatalytic performances of s-mesoPd and s-mesoPdCu nanocubes for CO2RR to formate, and compared them with p-mesoPd nanoparticles and regular Pd nanoparticles (Pd NPs). Pd is the only known material that can enable the selective CO2 reduction to formate at close-to-zero overpotential, but unfortunately suffers from very limited selectivity and stability under increasing overpotential (η > 200 mV) due to CO poisoning.34,36,38 We reason that this longstanding challenge might be alleviated by taking advantage of the large electrochemical surface areas and rich undercoordinated sites of single-crystalline mesoporous nanocubes as well as the electronic effect from alloying Pd and Cu. Figure 4a depicts the polarization curves of s-mesoPdCu nanocubes in N2- or CO2-saturated 0.1 M KHCO3. These two curves bifurcate at ∼0 V, which signals the CO2RR onset. The cathodic current density quickly rises beyond the onset potential in the presence of CO2, and reaches 8.2 mA cm−2 at −0.3 V, which is over three times larger than that measured in N2 (2.6 mA cm−2). Polarization curves of other samples are shown in Supporting Information Figures S13a–S13c. Figure 4 | Electrocatalytic CO2RR performances. (a) Polarization curves of s-mesoPdCu in N2- and CO2-saturated 0.1 M KHCO3. (b) Chronoamperometric curves of s-mesoPdCu nanocubes at different potentials under CO2. (c) Potential-dependent formate selectivity and Faradaic efficiency of s-mesoPdCu. (d) Comparison of the formate selectivity of s-mesoPdCu, s-mesoPd, p-mesoPd, and Pd NPs. (e) Long-term chronoamperometric stability of s-mesoPdCu, s-mesoPd, p-mesoPd, and Pd NPs at −0.4 V. Download figure Download PowerPoint For the product analysis and quantification, we performed chronoamperometric (i∼t) analysis at a few selected working potentials between 0 and −0.5 V for different catalyst samples under study. It is worth highlighting that s-mesoPdCu exhibits stable chronoamperometric responses over the potential regime examined (Figure 4b). Negligible gas products (H2 and CO) are detected. Formate is identified to be the only product from CO2 reduction. Its Faradaic efficiency is analyzed to be 80% at 0 V, which grows to and maintains >90% between −0.1 and −0.5 V (Figure 4c). Corresponding formate partial current density is calculated to increase from 0.3 mA cm−2 at 0 V to 8.1 mA cm−2 at −0.49 V. In stark contrast, we find that the cathodic current density starts to decline once the working potential is biased <−0.2 V for Pd NPs and p-mesoPd, and <−0.3 V for s-mesoPd owing to the catalyst poisoning by trace CO from CO2RR ( Supporting Information Figures S13d–S13f). Figure 4d compares the formate Faradaic efficiency of four different electrocatalysts under study within their respective stable potential windows. Even though all of them exhibit more or less comparable selectivity (and activity as shown in Supporting Information Figure S13g–S13i) in the low overpotential regime, our s-mesoPdCu clearly stands out for its unique capability to maintain the selectivity and stability under working potential as cathodic as −0.5 V—well beyond the conventional stable region for CO2RR on Pd-based materials and far superior to any close competitors reported in the literature ( Supporting Information Table S1). To better demonstrate the performance advantage of s-mesoPdCu, long-term stability was assessed at −0.4 V for 15,000 s, as shown in Figure 4e. The cathodic current density of Pd NPs quickly drops from 5 to 0 mA cm−2 within the first 4000 s, in agreement with the previous observations.36,42,43 The introduction of mesoporosity significantly promotes the CO tolerance and working stability, thanks to the enlarged catalyst surface areas that dilute CO coverage. At the end of 15,000 s, s-mesoPd and p-mesoPd retain the current density of 1.9 and 1.3 mA cm−2, respectively. Their average formate Faradaic efficiency is measured to be 100% and 94%, respectively. The slightly improved stability and selectivity of s-mesoPd over p-mesoPd is attributed to its single-crystalline nature that benefits the charge transfer during electrocatalysis. Finally, alloying Pd with Cu further enhances the stability. s-mesoPdCu still delivers 5.7 mA cm−2 even after 15,000 s with 100% average formate selectivity. We believe that in addition to its advantageous nanostructure, the electronic effect from alloying Pd and Cu is responsible for the observed enhancement. The introduction of a secondary metal with low work function such as Cu is expected to lower the Pd d-band center (in line with the electron transfer from Cu to Pd as revealed from XPS), consequently weakening the CO binding on the alloy catalyst and dramatically promoting its CO tolerance and catalytic stability. After the stability test, s-mesoPdCu is observed to preserve the single-crystalline mesoporous structure as well as the bimetallic nature ( Supporting Information Figure S14). The Pd/Cu molar ratio is measured to only slightly increase to 2.13. Conclusion Here, we developed a facile solution method for the preparation of s-mesoPd and s-mesoPdM nanocubes. The products featured abundant mesoporous channels and, very surprisingly, single-crystallinity throughout each nanocube. We proposed that this unique nanostructure was formed as the collective result of the templating effect of CTAC and the facet-selective capping effect of Cl− ions as supported by a range of control experiments. The large surface areas and penetrating mesoporous channels of our products greatly benefited their catalytic applications. In CO2-saturated 0.1 M KHCO3, the best sample—s-mesoPdCu-catalyzed electrochemical CO2 reduction to formate with great selectivity (>90%) and stability even under the working potential as cathodic as −0.5 V, which was previously believed to be too harsh for Pd-based CO2RR. The electronic effect from alloying Pd and Cu was found to play an additional role in stabilizing the catalyst. Our study demonstrates the great potential and new opportunity for single-crystalline and mesoporous metallic nanostructures. Supporting Information Supporting Information is available and includes schematic self-assembled structures of different surfactants; STEM images, TEM images, SAED patterns, EDS mapping, SAXS patterns, XRD patterns, and XPS spectra of different samples; polarization curves, chronoamperometric responses, and potential-dependent formate selectivity of different samples; and comparison of the formate Faradaic efficiency of our best sample with literature results. Conflict of Interest There is no conflict of interest to report. Funding Information B.L. thanks the Natural Science Foundation of Jiangsu Province (no. BK20180723), the Open Project of State Key Laboratory of Supramolecular Structure and Materials (no. sklssm20

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Abstract: Currently, catalytically transferable carbenes are limited to electron-deficient and neutral derivatives, and electron-rich carbenes bearing an alkoxy group (i.e., Fischer-type carbenes) cannot be used in catalytic cyclopropanation because of the lack of appropriate carbene precursors. We report herein that acylsilanes can serve as a source of electron-rich carbenes under palladium catalysis, enabling cyclopropanation of a range of alkenes. This reactivity profile is in sharp contrast to that of metal-free siloxycarbenes, which are unreactive toward normal alkenes. The resulting siloxycyclopropanes serve as valuable homoenolate equivalents, allowing rapid access to elaborate β-functionalized ketones.

Journal ArticleDOI
TL;DR: In this article , a facile method for the complete transformation of Palladium nanocubes into a stable phase made of PdH0.706 by treating them with aqueous hydrazine at a concentration as low as 9.2 mM was reported.
Abstract: Palladium is one of the few metals capable of forming hydrides, with the catalytic properties being dependent on the elemental composition and spatial distribution of H atoms in the lattice. Herein, we report a facile method for the complete transformation of Pd nanocubes into a stable phase made of PdH0.706 by treating them with aqueous hydrazine at a concentration as low as 9.2 mM. Using formic acid oxidation (FAO) as a model reaction, we systematically investigated the structure-catalytic property relationship of the resultant nanocubes with different degrees of hydride formation. The current density at 0.4 V was enhanced by four times when the nanocubes were completely converted from Pd to PdH0.706. On the basis of a set of slab models with PdH(100) overlayers on Pd(100), we conducted density functional theory calculations to demonstrate that the degree of hybrid formation could influence both the activity and selectivity toward FAO by modulating the relative stability of formate (HCOO) and carboxyl (COOH) intermediates. This work provides a viable strategy for augmenting the performance of Pd-based catalysts toward various reactions without altering the loading of this scarce metal.

Journal ArticleDOI
TL;DR: In this paper , a self-driving laboratory is used to define the Pareto front of conductivities and processing temperatures for palladium films formed by combustion synthesis, which can be used to discover materials that provide optimal trade-offs between conflicting objectives.
Abstract: Useful materials must satisfy multiple objectives, where the optimization of one objective is often at the expense of another. The Pareto front reports the optimal trade-offs between these conflicting objectives. Here we use a self-driving laboratory, Ada, to define the Pareto front of conductivities and processing temperatures for palladium films formed by combustion synthesis. Ada discovers new synthesis conditions that yield metallic films at lower processing temperatures (below 200 °C) relative to the prior art for this technique (250 °C). This temperature difference makes possible the coating of different commodity plastic materials (e.g., Nafion, polyethersulfone). These combustion synthesis conditions enable us to to spray coat uniform palladium films with moderate conductivity (1.1 × 105 S m-1) at 191 °C. Spray coating at 226 °C yields films with conductivities (2.0 × 106 S m-1) comparable to those of sputtered films (2.0 to 5.8 × 106 S m-1). This work shows how a self-driving laboratoy can discover materials that provide optimal trade-offs between conflicting objectives.


Journal ArticleDOI
TL;DR: In this article , the authors summarize the pioneering work on asymmetric Suzuki-Miyaura cross-couplings and cover the implementations via homogeneous and heterogeneous catalysis reported during recent years.
Abstract: Although Suzuki–Miyaura cross-coupling is one of the most convenient and well-developed cross-coupling reactions, its applications to the asymmetric version to deliver highly functionalized atropisomers or nonracemic coupling products have been less explored. Besides some excellent work reported intermittently, the asymmetric Suzuki–Miyaura reaction remains a significant challenge, particularly for preparing highly functionalized heterocyclic atropisomers. A concise but critical knowledge on this topic may further inspire researchers across various subdisciplines to develop innovative and practical solutions to tackle this problem. Therefore, this concise Review aims to summarize the pioneering work on asymmetric Suzuki–Miyaura cross-couplings and cover the implementations via homogeneous and heterogeneous catalysis reported during recent years. Most notably, the use of transition metals other than palladium is also described.

Journal ArticleDOI
01 May 2022-CheM
TL;DR: Wang et al. as discussed by the authors presented an interlayer synergistic binding strategy, a metal recognition manner deviating from chelation within a single ligand molecule in solvent extraction, for selective palladium chelation in a covalent organic framework.
Abstract: •An interlayer synergistic binding mode for Pd recognition is achieved in a COF•COF-TzDa shows ultrahigh uptake selectivity and capacity toward Pd•One-round enrichment and purification of Pd from the nuclear waste is realized Separation of palladium isotopes from used nuclear fuel is of high significance but faces notable challenges, due to the the harsh fuel reprocessing condition with combined high acidity, strong radiation, and vast interfering ions. Compared with the proposed solvent extraction method, where the extractants suffer from limited stability and efficiency, covalent organic frameworks are shown as a new generation of solid extractant not only because of their elevated stability in acids and resistance to radiations but also because they exhibit a distinct interlayer synergistic binding mode, markedly deviating from chelation within a single ligand molecule, with notably enhanced selectivity for Pd extraction. This leads to previously unachieved one-round enrichment and purification of Pd from the simulated high-level nuclear waste solution. This strategy, in general, opens a new avenue to remedy various types of pollutants and to extract many strategic resources in complex conditions. Palladium isotopes as fission products in used nuclear fuel represent precious alternative resources besides its natural reserves and therefore have a high extraction value. The practical use of currently proposed solvent extraction is challenging, originating from the limited stability and separation selectivity of the extractants under harsh reprocessing conditions. Herein, we present an interlayer synergistic binding strategy, a metal-recognition manner deviating from chelation within a single ligand molecule in solvent extraction, for selective palladium chelation in a covalent organic framework. The experimental, structural, and theoretical analyses corroborate that the enol-to-keto tautomerization leads to selective synergistic chelation of Pd2+ instead of other undesired metal ions, where two oxygen donors from adjacent layers and two free nitrate ions work together in a planar tetracoordination model. Fast adsorption kinetics, high adsorption capacity, and one-round enrichment of Pd2+ from the simulated high-level nuclear waste solution are unprecedentedly achieved in the dynamic breakthrough experiment. Palladium isotopes as fission products in used nuclear fuel represent precious alternative resources besides its natural reserves and therefore have a high extraction value. The practical use of currently proposed solvent extraction is challenging, originating from the limited stability and separation selectivity of the extractants under harsh reprocessing conditions. Herein, we present an interlayer synergistic binding strategy, a metal-recognition manner deviating from chelation within a single ligand molecule in solvent extraction, for selective palladium chelation in a covalent organic framework. The experimental, structural, and theoretical analyses corroborate that the enol-to-keto tautomerization leads to selective synergistic chelation of Pd2+ instead of other undesired metal ions, where two oxygen donors from adjacent layers and two free nitrate ions work together in a planar tetracoordination model. Fast adsorption kinetics, high adsorption capacity, and one-round enrichment of Pd2+ from the simulated high-level nuclear waste solution are unprecedentedly achieved in the dynamic breakthrough experiment. 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COF-TzDa indeed touches our expectation to bind Pd2+ via interlayer coordination with a much higher propensity than intralayer coordination, which contributes to a maximum adsorption capacity (265.4 mg g−1) close to the theoretical value (290.5 mg g−1). Our work has demonstrated the reasonability and feasibility of the interlayered synergetic coordination strategy deriving from rigid framework coupled with local self-adaptive fragments to design a new generation of metal adsorbents. COF-TzDa was synthesized via solvothermal condensation of 4,4′,4′′-(1,3,5-triazine-2,4,6-triyl)trianiline (Tz) and 2,5-dihydroxyterephthalaldehyde (Da) in the mixed solvent of o-dichlorobenzene (o-DCB)/n-butanol (3/1, v/v) at 120°C for 72 h yielding crimson crystallites (Scheme S1). The crystalline structure of COF-TzDa was characterized by powder X-ray diffraction (PXRD) analysis. As shown in Figures 1B and S1, the measured PXRD pattern exhibits several dominant intense diffraction peaks at 2.69°, 4.77°, 5.50°, 7.37°, and 9.73°, which are assigned to [100], [110], [200], [210], and [220] Bragg planes, respectively.38Mu M. Wang Y. Qin Y. Yan X. Li Y. Chen L. Two-dimensional imine-linked covalent organic frameworks as a platform for selective oxidation of olefins.ACS Appl. Mater. Interfaces. 2017; 9: 22856-22863Crossref PubMed Scopus (106) Google Scholar A broad peak at 26.01° was also observed, corresponding to the interlayered π-π stacking of the 2D COF. The structural simulation indicates that COF-TzDa possesses a preferably serrated AA-stacking arrangement (Figure 1C). We constructed the serrated stacking model for COF-TzDa via shifting neighboring layers approximately 1.422 Å with respect to each other (see more details in CIF), which partially minimizes the repulsion between the adjacent layers. 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Journal ArticleDOI
TL;DR: In this article , an effort has been given to recover palladium (Pd(II)) from ceramic capacitor using solvent-ligand process with a focus on environmental sustainability, the use of 3−(((5−ethoxybenzenethiol)imino)methyl)−salicylic acid as a ligand to recover Pd (II) from ceramic capacitance was investigated.

Journal ArticleDOI
TL;DR: In this article , the authors describe a straightforward high-temperature quenching approach to precisely construct isolated palladium atoms supported over cubic indium oxide, with individual palladium atom coordinated with four neighboring oxygen atoms.
Abstract: The realization of efficient and fully controllable synthesis of single atom catalysts is an exciting frontier, yet still challenging in the modern catalysis field. Here we describe a straightforward high-temperature quenching approach to precisely construct isolated palladium atoms supported over cubic indium oxide, with individual palladium atoms coordinated with four neighboring oxygen atoms. This palladium catalyst achieves exceptional catalytic efficiency in the selective hydrogenation of nitrobenzene to aniline, with more than 99% chemoselectivity under almost 100% conversion. Moreover, it delivers excellent recyclability, anti-CO poisoning ability, storage stability, and substrate tolerance. DFT calculations further reveal that the high catalytic activity stems from the optimized electronic structure and the charge states of palladium atoms in the defect-containing indium oxide. Our findings provide an effective approach to engineering single atom catalysts at the atomic level and open the door to a wide variety of catalytic reactions. • Pd single atoms supported over In 2 O 3 was created by a quenching approach. • DFT calculations reveal the support can provide anchoring sites for Pd atoms. • This catalyst shows high catalytic efficacy in hydrogenation of nitrobenzene. • The high catalytic activity stems from the unique coordination environment.

Journal ArticleDOI
TL;DR: In this paper , the atomistic details of how a palladium electrocatalyst inhibits CO poisoning during both formic acid oxidation to carbon dioxide and carbon dioxide reduction to formic acids are elucidated.
Abstract: Development of reversible and stable catalysts for the electrochemical reduction of CO2 is of great interest. Here, we elucidate the atomistic details of how a palladium electrocatalyst inhibits CO poisoning during both formic acid oxidation to carbon dioxide and carbon dioxide reduction to formic acid. We compare results obtained with a platinum single-crystal electrode modified with and without a single monolayer of palladium. We combine (high-scan-rate) cyclic voltammetry with density functional theory to explain the absence of CO poisoning on the palladium-modified electrode. We show how the high formate coverage on the palladium-modified electrode protects the surface from poisoning during formic acid oxidation, and how the adsorption of CO precursor dictates the delayed poisoning during CO2 reduction. The nature of the hydrogen adsorbed on the palladium-modified electrode is considerably different from platinum, supporting a model to explain the reversibility of this reaction. Our results help in designing catalysts for which CO poisoning needs to be avoided.