Showing papers on "Palladium published in 2018"
TL;DR: A palladium electrocatalyst is developed that shows a high selectivity and activity for N2 reduction to NH3 and outperforming other catalysts including gold and platinum.
Abstract: Electrochemical reduction of N2 to NH3 provides an alternative to the Haber−Bosch process for sustainable, distributed production of NH3 when powered by renewable electricity. However, the development of such process has been impeded by the lack of efficient electrocatalysts for N2 reduction. Here we report efficient electroreduction of N2 to NH3 on palladium nanoparticles in phosphate buffer solution under ambient conditions, which exhibits high activity and selectivity with an NH3 yield rate of ~4.5 μg mg−1Pd h−1 and a Faradaic efficiency of 8.2% at 0.1 V vs. the reversible hydrogen electrode (corresponding to a low overpotential of 56 mV), outperforming other catalysts including gold and platinum. Density functional theory calculations suggest that the unique activity of palladium originates from its balanced hydrogen evolution activity and the Grotthuss-like hydride transfer mechanism on α-palladium hydride that lowers the free energy barrier of N2 hydrogenation to *N2H, the rate-limiting step for NH3 electrosynthesis.
582 citations
TL;DR: P palladium is added into MoS2 materials to activate and stabilize the conductive basal plane to improve the electrocatalytic activity and open the possibility of manipulating the catalytic performance ofMoS2 to rival platinum.
Abstract: Lacking strategies to simultaneously address the intrinsic activity, site density, electrical transport, and stability problems of chalcogels is restricting their application in catalytic hydrogen production. Herein, we resolve these challenges concurrently through chemically activating the molybdenum disulfide (MoS2) surface basal plane by doping with a low content of atomic palladium using a spontaneous interfacial redox technique. Palladium substitution occurs at the molybdenum site, simultaneously introducing sulfur vacancy and converting the 2H into the stabilized 1T structure. Theoretical calculations demonstrate the sulfur atoms next to the palladium sites exhibit low hydrogen adsorption energy at –0.02 eV. The final MoS2 doped with only 1wt% of palladium demonstrates exchange current density of 805 μA cm−2 and 78 mV overpotential at 10 mA cm−2, accompanied by a good stability. The combined advantages of our surface activating technique open the possibility of manipulating the catalytic performance of MoS2 to rival platinum. While water reduction may provide a carbon-neutral means to produce hydrogen gas, there is a scarcity of efficient, earth-abundant electrocatalysts. Here, the authors add palladium into MoS2 materials to activate and stabilize the conductive basal plane to improve the electrocatalytic activity.
427 citations
TL;DR: The chemistry described here provides a practical approach to functionalize common amide and ester functional groups in organic synthesis and establishes straightforward access to acyl-metal intermediates that enable nonconventional cross-coupling strategies.
Abstract: ConspectusTransition-metal-catalyzed cross-coupling reactions represent a most powerful tool for the rapid construction of C–C and C–X bonds available to synthetic chemists. Recently, tremendous progress has been made in the burgeoning area of cross-coupling reactions of amides and esters enabled by regio- and chemoselective acyl C–X (X = N, O) cleavage using well-defined Pd(II)–NHC complexes. The use of N-heterocyclic carbenes as ligands in palladium-catalyzed cross-couplings permits reactions of amides and esters that were previously impossible using palladium or could be achieved only under harsh conditions. These reactions provide an attractive method to synthetic chemists to manipulate the traditionally inert amide and ester bonds with the broad cross-coupling generality inherent to palladium catalysis. Research in the area of cross-coupling of stable acyl electrophiles can be broadly categorized by the type of electrophile undergoing the cross-coupling. Recent studies have shown that cross-coupling ...
283 citations
01 Jul 2018
TL;DR: In this paper, a seed-directed growth technique was used to fix the metal nanoparticles (platinum, palladium, rhodium and silver) with diameters in the range of industrial catalysts (0.8-3.6nm) within zeolite crystals (metal@zeolite).
Abstract: Supported metal nanoparticle catalysts are widely used in industry but suffer from deactivation resulting from metal sintering and coke deposition at high reaction temperatures. Here, we show an efficient and general strategy for the preparation of supported metal nanoparticle catalysts with very high resistance to sintering by fixing the metal nanoparticles (platinum, palladium, rhodium and silver) with diameters in the range of industrial catalysts (0.8–3.6 nm) within zeolite crystals (metal@zeolite) by means of a controllable seed-directed growth technique. The resulting materials are sinter resistant at 600–700 °C, and the uniform zeolite micropores allow for the diffusion of reactants enabling contact with the metal nanoparticles. The metal@zeolite catalysts exhibit long reaction lifetimes, outperforming conventional supported metal catalysts and commercial catalysts consisting of metal nanoparticles on the surfaces of solid supports during the catalytic conversion of C1 molecules, including the water-gas shift reaction, CO oxidation, oxidative reforming of methane and CO2 hydrogenation. Supported metal nanoparticles are indispensable catalysts in industry, yet they are often subjected to severe sintering. Now, a general method based on metal immobilization within zeolite is reported for the preparation of highly sinter-resistant catalysts for a broad range of industrially relevant processes.
259 citations
213 citations
TL;DR: A palladium phosphide electrocatalyst supported on carbon black (PdP2 @CB) shows efficient water splitting in both alkaline and neutral electrolytes and no loss in HER activity is detectable after 5000 potential sweeps.
Abstract: A palladium phosphide electrocatalyst supported on carbon black (PdP2 @CB) shows efficient water splitting in both alkaline and neutral electrolytes Significantly lower overpotentials are required for PdP2 @CB (275 mV in 05 m H2 SO4 ; 354 mV in 1 m KOH; 846 mV in 1 m PBS) to achieve a HER electrocatalytic current density of 10 mA cm-2 compared to commercial Pt/CB (301 mV in 05 m H2 SO4 ; 466 mV in 1 m KOH; 1227 mV in 1 m PBS) Moreover, no loss in HER activity is detectable after 5000 potential sweeps Only 270 mV and 277 mV overpotentials are required to reach a current density of 10 mA cm-2 for PdP2 @CB to catalyze OER in 1 m KOH and 1 m PBS electrolytes, which is better OER activity than the benchmark IrO2 electrocatalyst (301 mV and 313 mV to drive a current density of 10 mA cm-2 ) 159 V and 172 V are needed for PdP2 @CB to achieve stable water splitting catalytic current density of 10 mA cm-2 in 1 m PBS and 50 mA cm-2 in 1 m KOH for 10 h, respectively
205 citations
TL;DR: Dendritic palladium–copper–cobalt trimetallic nanoalloys are synthesized as robust multifunctional electrocatalysts for oxygen reduction and formic acid oxidation as well as alcohol tolerance with high performance and superior durability.
Abstract: Recently, the development of high-performance non-platinum electrocatalysts for fuel cell applications has been gaining attention. Palladium-based nanoalloys are considered as promising candidates to substitute platinum catalysts for cathodic and anodic reactions in fuel cells. Here, we develop a facile route to synthesize dendritic palladium-copper-cobalt trimetallic nanoalloys as robust multifunctional electrocatalysts for oxygen reduction and formic acid oxidation. To the best of our knowledge, the mass activities of the dendritic Pd59Cu30Co11 nanoalloy toward oxygen reduction and formic acid oxidation are higher than those previously reported for non-platinum metal nanocatalysts. The Pd59Cu30Co11 nanoalloys also exhibit superior durability for oxygen reduction and formic acid oxidation as well as good antimethanol/ethanol interference ability compared to a commercial platinum/carbon catalyst. The high performance of the dendritic Pd59Cu30Co11 nanoalloys is attributed to a combination of effects, including defects, a synergistic effect, change of d-band center of palladium, and surface strain.
190 citations
TL;DR: A material based on palladium and hierarchical zeolite with fully sodium-exchanged acid sites is designed, which improves the support stability and prevents steam-induced palladium sintering under reaction conditions by confining the metal within theZeolite.
Abstract: Increasing the use of natural gas engines is an important step to reduce the carbon footprint of mobility and power generation sectors. To avoid emissions of unburnt methane and the associated severe greenhouse effect of lean-burn engines, the stability of methane oxidation catalysts against steam-induced sintering at low temperatures (<500 °C) needs to be improved. Here we demonstrate how the combination of catalyst development and improved process control yields a highly efficient solution for complete methane oxidation. We design a material based on palladium and hierarchical zeolite with fully sodium-exchanged acid sites, which improves the support stability and prevents steam-induced palladium sintering under reaction conditions by confining the metal within the zeolite. Repeated short reducing pulses enable the use of a highly active transient state of the catalyst, which in combination with its high stability provides excellent performance without deactivation for over 90 h in the presence of steam.
172 citations
TL;DR: In-on-Pd nanoparticles (NPs) showed room-temperature nitrate catalytic reduction activity that varies with volcano-shape dependence on In surface coverage as mentioned in this paper.
Abstract: Nitrate (NO3−) is an ubiquitous groundwater contaminant and is detrimental to human health. Bimetallic palladium-based catalysts have been found to be promising for treating nitrate (and nitrite, NO2−) contaminated waters. Those containing indium (In) are unusually active, but the mechanistic explanation for catalyst performance remains largely unproven. We report that In deposited on Pd nanoparticles (NPs) (“In-on-Pd NPs”) shows room-temperature nitrate catalytic reduction activity that varies with volcano-shape dependence on In surface coverage. The most active catalyst had an In surface coverage of 40%, with a pseudo-first order normalized rate constant of kcat ∼ 7.6 L gsurface-metal−1 min−1, whereas monometallic Pd NPs and In2O3 have nondetectible activity for nitrate reduction. X-ray absorption spectroscopy (XAS) results indicated that In is in oxidized form in the as-synthesized catalyst; it reduces to zerovalent metal in the presence of H2 and reoxidizes following NO3− contact. Selectivity in exces...
170 citations
TL;DR: A scalable protocol is introduced to prepare crystal phase and orientation controlled Pd3S nanoparticles supported on carbon nitride, exhibiting unparalleled semi-hydrogenation performance due to a high density of active and selective ensembles.
Abstract: Ensemble control has been intensively pursued for decades to identify sustainable alternatives to the Lindlar catalyst (PdPb/CaCO3) applied for the partial hydrogenation of alkynes in industrial organic synthesis. Although the geometric and electronic requirements are known, a literature survey illustrates the difficulty of transferring this knowledge into an efficient and robust catalyst. Here, we report a simple treatment of palladium nanoparticles supported on graphitic carbon nitride with aqueous sodium sulfide, which directs the formation of a nanostructured Pd3S phase with controlled crystallographic orientation, exhibiting unparalleled performance in the semi-hydrogenation of alkynes in the liquid phase. The exceptional behavior is linked to the multifunctional role of sulfur. Apart from defining a structure integrating spatially-isolated palladium trimers, the active ensembles, the modifier imparts a bifunctional mechanism and weak binding of the organic intermediates. Similar metal trimers are also identified in Pd4S, evidencing the pervasiveness of these selective ensembles in supported palladium sulfides.
157 citations
TL;DR: The synthesis and evaluation of a highly versatile platform based on diphosphazane monoxide ligands is reported, which mediate the copolymerization of ethylene with a number of fundamental polar monomers.
Abstract: The ability to carry out transition-metal-catalyzed copolymerizations of olefins with polar monomers is a great challenge in the field of olefin polymerization. Palladium has been the dominant player in this field, while its low-cost nickel counterpart has only achieved very limited success. We report the synthesis and evaluation of a highly versatile platform based on diphosphazane monoxide ligands. Both palladium and nickel catalysts bearing these ligands mediate the copolymerization of ethylene with a number of fundamental polar monomers.
TL;DR: This mechanistically novel strategy expands the scope of the traditional Pd-catalyzed asymmetric allylic alkylation reaction and serves as its alternative and potential complement.
Abstract: Highly regio- and enantioselective allylic alkylation has been achieved enabled by the merger of photoredox and palladium catalysis. In this dual catalytic process, alkyl radicals generated from 4-alkyl-1,4-dihydropyridines act as the coupling partners of the π-allyl palladium complexes. The generality of this method has been illustrated through the reaction of a variety of allyl esters with 4-alkyl-1,4-dihydropyridines. This mechanistically novel strategy expands the scope of the traditional Pd-catalyzed asymmetric allylic alkylation reaction and serves as its alternative and potential complement.
TL;DR: In this paper, a single-atom catalysts (SAC) with reduced graphene oxide (RGO) as the inner shell and carbon nanospheres as the outer shell is presented.
Abstract: The maximized atomic efficiency of supported catalysts is highly desired in heterogeneous catalysis. Therefore, the design and development of active, stable, and atomic metal-based catalysts remains a formidable challenge. To tackle these problems, it is necessary to investigate the interaction between single atoms and supports. Theoretical calculations indicate that the Pd binding strength is higher on graphene/amorphous carbon (AC) than that on graphene or AC substrate. Based on these predictions, we present a facile confined-interface-directed synthesis route for the preparation of single-atom catalysts (SACs) in which Pd atoms are well-dispersed on the interface of double-shelled hollow carbon nanospheres with reduced graphene oxide (RGO) as the inner shell and AC as the outer shell. Owing to the synergetic effect of the RGO/AC confined interface and the atomically dispersed Pd, the as-made RGO@AC/Pd SAC achieves the maximum atomic efficiency (catalytic activity) of Pd species and exhibits an excellent stability in chemical catalysis. This confined-interface-directed synthesis method provides a novel direction to maximize the atomic efficiency, improve the activity, and enhance the stability of metal-based catalysts.
TL;DR: In this article, a hierarchically porous carbon was prepared from carbonization of a nitrogen-containing metal-organic framework, followed by activation under ultrasonication in aqueous potassium hydroxide (aq KOH).
Abstract: In this work, a hierarchically porous carbon was prepared from carbonization of a nitrogen-containing metal–organic framework, followed by activation under ultrasonication in aqueous potassium hydroxide (aq KOH). The activated carbon was applied as a support for immobilizing ultrafine palladium (Pd) nanoparticles (1.1 ± 0.2 nm). As a result, the as-prepared Pd nanoparticles on N-doped porous carbon with both micro- and mesoporosity exhibit an excellent activity for the dehydrogenation of formic acid, showing a high turnover frequency (TOF, 14 400 h–1) at 60 °C. This activation approach of carbon opens an avenue for the syntheses of highly active supported ultrafine metal NPs for catalysis.
TL;DR: It is reported that Pd(PPh3)2Cl2 in combination with 4,5-bis(diphenylphosphino)-9,9-dimethylxanthene (Xantphos) under irradiation of blue LEDs efficiently catalyzes a decarboxylative Heck reaction of vinyl arenes and vinyl heteroarenes with aliphatic N-(acyloxy)phthalimides at room temperature.
TL;DR: In this paper, a new magnetic interphase palladium catalyst has been synthesized on chitosan-biguanidine coated-magnetic Fe3O4 nanoparticles, which demonstrated high catalytic activity as a recyclable nanocatalyst toward Suzuki-Miyaura crosscoupling reactions, at room temperature.
TL;DR: The development of a method for the Pd-catalyzed electrochemical acetoxylation of C-H bonds is described, developed and optimized with respect to the cell configuration, rate of oxidation, and chemistry at the counter electrode.
TL;DR: In this article, the authors demonstrate that palladium atoms can be effectively isolated on other carbon nitride scaffolds including linear melem oligomers and poly(triazine/heptazine imides).
Abstract: Carbon nitrides integrating macroheterocycles offer unique potential as hosts for stabilizing metal atoms due to their rich electronic structure. To date, only graphitic heptazine-based polymers have been studied. Here, we demonstrate that palladium atoms can be effectively isolated on other carbon nitride scaffolds including linear melem oligomers and poly(triazine/heptazine imides). Increased metal uptake was linked to the larger cavity size and the presence of chloride ions in the polyimide structures. Changing the host structure leads to significant variation in the average oxidation state of the metal, which can be tuned by exchange of the ionic species as evidenced by X-ray photoelectron spectroscopy and supported by density functional theory. Evaluation in the semi-hydrogenation of 2-methyl-3-butyn-2-ol reveals an inverse correlation between the activity and the degree of oxidation of palladium, with oligomers exhibiting the highest activity. These findings provide new mechanistic insights into the influence of the carbon nitride structure on metal stabilization.
01 Jul 2018
TL;DR: In this paper, paired electrolysis of 4-methoxybenzyl alcohol and 1-hexene with the concomitant formation of 1hexene from 1-hexyne in an electrochemical cell is described.
Abstract: Electrosynthesis provides a method of driving organic reaction chemistry under ambient conditions with electricity. Pairing two reactions together enables the synthesis of two valuable chemicals with no waste product. Here we report the paired electrolysis of 4-methoxybenzyl alcohol to 4-methoxybenzaldehyde with the concomitant formation of 1-hexene from 1-hexyne in an electrochemical cell. These reaction chambers are separated by a dense palladium membrane that reduces protons formed at the anode to hydrogen atoms that can permeate through the palladium foil to hydrogenate 1-hexyne. The palladium membrane enables two reactions to be performed in distinct reaction conditions: hydrogenation in organic solvents and electrochemical oxidation in aqueous electrolyte. The starting materials in both chambers react quantitatively over 5 hours of electrolysis, and selectivities ≥95% can be achieved for 4-methoxybenzaldehyde and 1-hexene with control of reaction conditions. Exquisite control of the reaction kinetics and selectivities of each of the individual reactions is demonstrated. Electrolysis uses clean electricity to form chemical products but typical water electrolysis produces hydrogen which is hard to store oxygen which is a waste gas. Here, paired electrolysis is performed with an palladium membrane reactor to carry out two organic reactions simultaneously. The dense palladium membrane enables the two reactions to proceed in different solvents and the reaction rates and selectivities can be independently controlled.
TL;DR: In this article, a green method was developed to prepare palladium/sodium borosilicate nanocomposite by using aqueous extract of the leaves of Euphorbia milii as bioreducing and stabilizing agent.
TL;DR: A novel Pd/g-C3 N4 stabilized Pickering emulsion microreactor is developed, in which alkenes are hydrogenated in the oil phase with hydrogen originating from AB in the water phase, catalysed by the Pd nanoparticles at the interfaces, for more economical hydrogen utilization over conventional systems.
Abstract: Direct hydrogenation of C=C double bonds is a basic transformation in organic chemistry which is vanishing from simple practice because of the need for pressurized hydrogen. Ammonia borane (AB) has emerged as a hydrogen source through its safety and high hydrogen content. However, in conventional systems the hydrogen liberated from the high‐cost AB cannot be fully utilized. Herein, we develop a novel Pd/g‐C3N4 stabilized Pickering emulsion microreactor, in which alkenes are hydrogenated in the oil phase with hydrogen originating from AB in the water phase, catalysed by the Pd nanoparticles at the interfaces. This approach is advantageous for more economical hydrogen utilization over conventional systems. The emulsion microreactor can be applied to a range of alkene substrates, with the conversion rates achieving >95 % by a simple modification.
TL;DR: The fundamental organometallic reactivity of palladium in its 0, I, II, III, and IV oxidation states make it special and useful in challenging carbon-heteroatom bond-formation reactions as mentioned in this paper.
Abstract: Nitrogen-containing compounds are the most common structural architectures in drug candidates, natural and biological products, and small-molecule therapeutics. Within the body of work of transition-metal-catalyzed direct C–H amination reactions, palladium remains in the forefront and has been established as one of the most useful transition metals for C–N bond formation. The fundamental organometallic reactivity of palladium in its 0, I, II, III, and IV oxidation states make it special and useful in challenging carbon–heteroatom bond-formation reactions. Palladium undergoes facile formation of chelation-assisted palladacycle and palladium-nitrenoid intermediates that open an avenue for new bond formation. It has been utilized in various new synthetic approaches toward both intermolecular and intramolecular C–N bond formation reactions that employ nitrogen sources ranging from free, unprotected amines to electrophilic nitrogen sources. Palladium’s compatibility with various functional groups and oxidants ...
TL;DR: A commercially available dialkyl triarylmonophosphine-supported palladium catalyst is utilized that facilitates a broad range of C-N coupling reactions in the presence of weak, soluble bases and shows extraordinary tolerance for even highly base-sensitive functional groups.
Abstract: Due to the low intrinsic acidity of amines, palladium-catalyzed C–N cross-coupling has been plagued continuously by the necessity to employ strong, inorganic, or insoluble bases. To surmount the many practical obstacles associated with these reagents, we utilized a commercially available dialkyl triarylmonophosphine-supported palladium catalyst that facilitates a broad range of C–N coupling reactions in the presence of weak, soluble bases. The mild and general reaction conditions show extraordinary tolerance for even highly base-sensitive functional groups. Additionally, insightful heteronuclear NMR studies using 15N-labeled amine complexes provide evidence for the key acidifying effect of the cationic palladium center.
TL;DR: It is described that ultrathin Pd nanosheets effectively reduce the onset potential for CO by exposing abundant atoms with comparatively low generalized coordination number in palladium-based catalysts toward CO2 ER.
Abstract: Electrochemical conversion of carbon dioxide (CO2 ) to value-added products is a possible way to decrease the problems resulting from CO2 emission. Thanks to the eminent conductivity and proper adsorption to intermediates, Pd has become a promising candidate for CO2 electroreduction (CO2 ER). However, Pd-based nanocatalysts generally need a large overpotential. Herein we describe that ultrathin Pd nanosheets effectively reduce the onset potential for CO by exposing abundant atoms with comparatively low generalized coordination number. Hexagonal Pd nanosheets with 5 atomic thickness and 5.1 nm edge length reached CO faradaic efficiency of 94 % at -0.5 V, without any decay after a stability test of 8 h. It appears to be the most efficient among all of Pd-based catalysts toward CO2 ER. Uniform hexagonal morphology made it reasonable to build models and take DFT calculations. The enhanced activity originates from mainly edge sites on palladium nanosheets.
TL;DR: The results highlight the contributions of the chelate effect for tailoring and maintaining reactivity at molecular-materials interfaces enabled by surface organometallic chemistry.
Abstract: Reported here is the chelate effect as a design principle for tuning heterogeneous catalysts for electrochemical CO2 reduction. Palladium functionalized with a chelating tris-N-heterocyclic carbene (NHC) ligand (Pd-timtmbMe ) exhibits a 32-fold increase in activity for electrochemical reduction of CO2 to C1 products with high Faradaic efficiency (FEC1 =86 %) compared to the parent unfunctionalized Pd foil (FE=23 %), and with sustained activity relative to a monodentate NHC-ligated Pd electrode (Pd-mimtmbMe ). The results highlight the contributions of the chelate effect for tailoring and maintaining reactivity at molecular-materials interfaces enabled by surface organometallic chemistry.
TL;DR: An unpredicted arrangement of the Pd-O-Ce interface is obtained in which an amorphous shell containing palladium species dissolved in ceria is covering a core of CeO2 particles, which outperforms conventional Pd/CeO2 reference catalysts in methane oxidation by lowering light-off temperature and boosting the reaction rate.
Abstract: By carefully mixing Pd metal nanoparticles with CeO2 polycrystalline powder under dry conditions, an unpredicted arrangement of the Pd-O-Ce interface is obtained in which an amorphous shell containing palladium species dissolved in ceria is covering a core of CeO2 particles. The robust contact that is generated at the nanoscale, along with mechanical forces generated during mixing, promotes the redox exchange between Pd and CeO2 and creates highly reactive and stable sites constituted by PdOx embedded into CeO2 surface layers. This specific arrangement outperforms conventional Pd/CeO2 reference catalysts in methane oxidation by lowering light-off temperature by more than 50°C and boosting the reaction rate. The origin of the outstanding activity is traced to the structural properties of the interface, modified at the nanoscale by mechanochemical interaction.
TL;DR: In this paper, a highly atropo-enanti-selective palladium(0)-catalyzed methodology was proposed to obtain axially chiral dibenzazepinones.
Abstract: Atropo-enantioselective C-H functionalization reactions are largely limited to the dynamic kinetic resolution of biaryl substrates through the introduction of steric bulk proximal to the axis of chirality. Reported herein is a highly atropo-enantioselective palladium(0)-catalyzed methodology that forges the axis of chirality during the C-H functionalization process, enabling the synthesis of axially chiral dibenzazepinones. Computational investigations support experimentally determined racemization barriers, while also indicating C-H functionalization proceeds by an enantio-determining CMD to yield configurationally stable eight-membered palladacycles.
TL;DR: In this article, the electronic structure of several representative single atom alloys of gold, silver and copper doped with single atoms of platinum, palladium, iridium, rhodium and nickel in the context of the d-band model of Hammer and Norskov.
Abstract: Single atom alloys are gaining importance as atom-efficient catalysts which can be extremely selective and active towards the formation of desired products. They possess such desirable characteristics because of the presence of a highly reactive single atom in a less reactive host surface. In this work, we calculated the electronic structure of several representative single atom alloys. We examined single atom alloys of gold, silver and copper doped with single atoms of platinum, palladium, iridium, rhodium and nickel in the context of the d-band model of Hammer and Norskov. The reactivity of these alloys was probed through the dissociation of water and nitric oxide and the hydrogenation of acetylene to ethylene. We observed that these alloys exhibit a sharp peak in their atom projected d-band density of states, which we hypothesize could be the cause of high surface reactivity. We found that the d-band centers and d-band widths of these systems correlated linearly as with other alloys, but that the energy of adsorption of a hydrogen atom on these surfaces could not be correlated with the d-band center, or the average reactivity of the surface. Finally, the single atom alloys, with the exception of copper–palladium showed good catalytic behavior by activating the reactant molecules more strongly than the bulk atom behavior and showing favorable reaction pathways on the free energy diagrams for the reactions investigated.
TL;DR: In this paper, the in situ encapsulation of sub-nanometric palladium species within MFI-type zeolites, which exhibit high activity and good stability in the hydroconversion of furfural as a model reaction of biomass upgrading, was investigated.
Abstract: Metal nanoparticles encapsulated in zeolite have been recently developed as a special type of catalyst that shows significant advantages in activity, shape-selectivity, and stability over conventional supported catalysts. The selectivity modulation of encapsulated nanoparticle catalysis by the zeolite microenvironment is theoretically possible but not addressed yet. Here, we report the in situ encapsulation of sub-nanometric palladium species within MFI-type zeolites, which exhibit high activity and good stability in the hydroconversion of furfural as a model reaction of biomass upgrading. Remarkably, different products, e.g., furan, furfural alcohol, and 1,5-pentanediol, from furfural hydroconversion can be obtained when silicalite-1, Na-ZSM-5, and H-ZSM-5 are employed as hosts of palladium nanoparticles, respectively. Density functional theory calculations and spectroscopy investigations reveal that both the adsorption of furfural and the activation of hydrogen are significantly affected by the zeolite ...