A Magnetically Separable Pd Single-Atom Catalyst for Efficient Selective Hydrogenation of Phenylacetylene

MOF-Derived PdCo and PdMn Systems as Versatile Catalysts in Alkyne Semihydrogenation

This study investigates the structure and catalytic properties of bimetallic nanocomposites derived from PdCo- and PdMn-based metal-organic frameworks. These materials, synthesized via chemical (Q) and thermal treatments (T), resulted in PdCo-QT and PdMn-QT catalysts containing Pd-based nanoparticles modified with Co or Mn and supported on N-doped carbon. Detailed characterization techniques confirm these complex structures, including high-resolution transmission electron microscopy, scanning transmission electron microscopy energy-dispersive X-ray spectroscopy, X-ray diffraction, X-ray photoelectron spectroscopy, and X-ray absorption spectroscopy. The catalytic performances of these materials were evaluated for the selective semihydrogenation of phenylacetylene and 4-octyne under soft conditions (1 H2 bar, room temperature) in batch reactors, demonstrating very high selectivity (≥95 mol %) toward alkenes at high conversion levels (≥94 mol %). Moreover, they displayed significant stability after five catalytic cycles with minimal leaching and highly competitive values of alkyne productivity in the semihydrogenation of phenylacetylene. The study also explored the potential of these catalysts in continuous gas-phase reactions, where PdCo-QT demonstrated remarkable catalytic activity and selectivity with a high gas hourly space velocity.

Insight into the mechanism of semi-hydrogenation of phenylacetylene over Pd embedded in thioether functionalized Schiff-base linked covalent organic frameworks

We report a novel catalyst comprising palladium supported on thioether functionalized Schiff-base conjugated covalent organic frameworks, which significantly enhances the semi-hydrogenation conversion and selectivity of phenylacetylene. Theoretical calculations substantiate that the imide and thioether groups modify the electron density around Pd, reducing the energy barriers for phenylacetylene adsorption and styrene desorption, thereby improving the conversion and selectivity of the catalyst.

Spatially Confined Construction of Ultrasmall Pd Clusters Within Nitro-Bonded Covalent Organic Frameworks for Efficient Alkyne Semihydrogenation

Confinement of metal species in porous supports is an effective strategy to optimize hydrogenation performance ascribing to tunable nanopore environments. However, only focusing on the electronic structure modulation for metal species has limited the design of improved catalysts. Herein, spatial confinement strategy is reported for constructing ultrasmall metal clusters in nitro-bonded COF (M@TpPa-NO2, M = Pd, Pt, Ru, Rh, Ir). Thereinto, Pd@TpPa-NO2 can achieve efficient co-catalytic alkyne semi-hydrogenation by the organic nitro units and the Pd clusters, with an outstanding phenylacetylene hydrogenation activity of TOF = 13756 h-1 and a high 94% styrene selectivity under 25 °C and 1 bar H2. In situ diffuse reflectance infrared Fourier transform spectroscopy and density functional theory calculations confirm that the H2 dissociation occurs at Pd clusters and the nitro groups accept spilled H atoms for subsequent semi-hydrogenation. The facile styrene desorption from TpPa-NO2 support contributes to a high semi-hydrogenation selectivity. This work provides new perspectives for designing efficient catalysts with overcoming the activity-selectivity trade-off in selective hydrogenation reactions.

Core-Shell Magnetic Particles: Tailored Synthesis and Applications

Core-shell magnetic particles consisting of magnetic core and functional shells have aroused widespread attention in multidisciplinary fields spanning chemistry, materials science, physics, biomedicine, and bioengineering due to their distinctive magnetic properties, tunable interface features, and elaborately designed compositions. In recent decades, various surface engineering strategies have been developed to endow them desired properties (e.g., surface hydrophilicity, roughness, acidity, target recognition) for efficient applications in catalysis, optical modulation, environmental remediation, biomedicine, etc. Moreover, precise control over the shell structure features like thickness, porosity, crystallinity and compositions including metal oxides, carbon, silica, polymers, and metal-organic frameworks (MOFs) has been developed as the major method to exploit new functional materials. In this review, we highlight the synthesis methods, regulating strategies, interface engineering, and applications of core-shell magnetic particles over the past half-century. The fundamental methodologies for controllable synthesis of core-shell magnetic materials with diverse organic, inorganic, or hybrid compositions, surface morphology, and interface property are thoroughly elucidated and summarized. In addition, the influences of the synthesis conditions on the physicochemical properties (e.g., dispersibility, stability, stimulus-responsiveness, and surface functionality) are also discussed to provide constructive insight and guidelines for designing core-shell magnetic particles in specific applications. The brand-new concept of "core-shell assembly chemistry" holds great application potential in bioimaging, diagnosis, micro/nanorobots, and smart catalysis. Finally, the remaining challenges, future research directions and new applications for the core-shell magnetic particles are predicted and proposed.

A Tandem Catalysis for Isoindolinone Synthesis over Single-Atom Pd/TiO2 Catalyst

Developing an efficient strategy to replace the conventional synthesis method for producing isoindolinone (IIO) scaffold, a crucial structural motif for constructing pharmaceutical molecules, remains to be a great challenge. Herein, a single-atom Pd/TiO2 tandem catalysis has been developed for the IIO scaffold synthesis by using readily available phthalic anhydride (PA), ammonia, and H2. The single-atom Pd/TiO2 catalyst demonstrates superior catalytic performance, achieving a PA conversion of 99 %, an IIO selectivity of 91 %, and a turnover frequency (TOF) up to 4807 h-1. This exceptional performance can be attributed to the tandem catalysis between TiO2 support and single-atom Pd. The TiO2 efficiently catalyzes the conversion of PA with ammonia to form phthalimide (PAM), subsequently transformed into IIO over TiO2 through the reaction of PAM with NH3 and the spillover hydrogen species derived from single-atom Pd. Notably, NH3 functions not only as a reactant but also as a promoter to accelerate the reduction of amides combined with the Pd/TiO2 catalyst. This tandem catalysis of a single-atom Pd/TiO2 catalyst provides a promising strategy for the synthesis of the crucial IIO platform molecules.

Synergize Strong and Reactive Metal-Support Interactions to Construct Sub-2 nm Metal Phosphide Cluster for Enhanced Selective Hydrogenation Activities

Strong metal-support interactions (SMSI) are crucial for stabilizing sub-2 nm metal sites, e.g. single atom (M1) or cluster (Mn). However, further optimizing sub-2 nm sites to break the activity-stability trade-off due to excessive interactions remains significant challenges. Accordingly, for the first time, we propose synergizing SMSI with reactive metal-support interactions (RMSI). Comprehensive characterization confirms that the SMSI stabilizes the metal and regulates the aggregation of Ni1 into Nin site within sub-2 nm. Meanwhile, RMSI modulates Nin through sufficiently activating P in the support and eventually generates sub-2 nm metal phosphide Ni2P cluster (Ni2Pn). The synergetic metal-support interactions triggered the adaptive coordination and electronic structure optimization of Ni2Pn, leading to the desired substrate adsorption-desorption kinetics. Consequently, the activity of Ni2Pn site greatly enhanced towards the selective hydrogenations of p-chloronitrobenzene and alkynyl alcohol. The formation rates of target products are up to 20.2 and 3.0 times greater than that of Ni1 and Nin site, respectively. This work may open a new direction for metal-support interactions and promote innovation and application of active sites below 2 nm.

Heteroatoms-Stabilized Single Palladium Atoms on Amorphous Zeolites: Breaking the Tradeoff between Catalytic Activity and Selectivity for Alkyne Semihydrogenation

As a fundamental industrial catalytic process, the semihydrogenation of alkynes presents a challenge in striking a balance between activity and selectivity due to the issue of over-hydrogenation. Herein, we develop an efficient catalytic system based on single-atom Pd catalysts supported on boron-containing amorphous zeolites (Pd/AZ-B), achieving the tradeoff breaking between the activity and selectivity for the selective hydrogenation of alkynes. Advanced characterizations and theoretical density functional theory calculations confirm that the incorporated B atoms in the Pd/AZ-B can not only alter the geometric and electronic properties of Pd atoms by controlling the electron migration from Pd but also mitigate the interaction between alkene and the catalyst supports. This boosts the exceptional catalytic efficacy in the semihydrogenation of phenylacetylene to styrene under mild conditions (298 K, 2 bar H2), achieving a recorded turnover frequency (TOF) value of 24198 h-1 and demonstrating 95 % selectivity to styrene at full conversion of phenylacetylene. By comparison, the heteroatom-free amorphous zeolite-anchored Pd nanoparticles and the commercial Lindlar catalyst have styrene selectivities of 73 % and 15 %, respectively, under identical reaction conditions. This work establishes a solid foundation for developing highly active and selective hydrogenation catalysts by controllably optimizing their electronic and steric properties.

Enhancing Electrocatalytic Semihydrogenation of Alkynes via Weakening Alkene Adsorption over Electron-Depleted Cu Nanowires

Electrochemical semihydrogenation (ESH) of alkynes to alkenes is an appealing technique for producing pharmaceutical precursors and polymer monomers, while also preventing catalyst poisoning by alkyne impurities. Cu is recognized as a cost-effective and highly selective catalyst for ESH, whereas its activity is somewhat limited. Here, from a mechanistic standpoint, we hypothesize that electron-deficient Cu can enhance ESH activity by promoting the rate-determining step of alkene desorption. We test this hypothesis by utilizing Cu-Ag hybrids as electrocatalysts, developed through a welding process of Ag nanoparticles with Cu nanowires. Our findings reveal that these rationally engineered Cu-Ag hybrids exhibit a notable enhancement (2-4 times greater) in alkyne conversion rates compared to isolated Ag NPs or Cu NWs, while maintaining over 99% selectivity for alkene products. Through a combination of operando and computational studies, we verify that the electron-depleted Cu sites, resulting from electron transfer between Ag nanoparticles and Cu nanowires, effectively weaken the adsorption of alkenes, thereby substantially boosting ESH activity. This work not only provides mechanistic insights into ESH but also stimulates compelling strategies involving hybridizing distinct metals to optimize ESH activity.

Regulation Lattice Oxygen Mobility via Dual Single Atoms for Simultaneously Enhancing VOC Oxidation and NOx Reduction

Synergistic catalytic removal of multipollutants (e.g., volatile organic compound (VOC) oxidation and nitrogen oxide (NOx) reduction) is highly demanded due to the increasingly strict emission standards. The prevention of the key reactive intermediate species nitrite excessive oxidation over the supported noble-metal catalysts, rather than the traditional low-efficiency transition metal oxide catalysts, remains a great challenge. Herein, a sound strategy of Pd single atoms saturated with acidic transition element ligands is proposed. The coexistence of Pd and V dual single atoms strengthens the adsorption of reactants, while synergistic interaction between dual atoms and surface oxygen weakens activation of lattice oxygen, thus significantly reducing the overoxidation of nitrite. Meanwhile, the neutralization of the active Pd and inert V sites results in a rational decrease in the redox property of Pd and an obvious increase in that of V. The Pd1V1/CeO2 dual single-atom catalyst achieves 90% conversion of NOx and toluene at 238 and 230 °C and has a large temperature window (>150 °C) for NOx reduction. This research makes a breakthrough in the development of efficient supported noble-/transition-metal dual single-atom catalysts for VOC and NOx simultaneous purification.

Encapsulation of Pd Single-Atom Sites in Zeolite for Highly Efficient Semihydrogenation of Alkynes

Palladium (Pd)-based single-atom catalysts (SACs) have shown outstanding selectivity for semihydrogenation of alkynes, but most Pd single sites coordinated with highly electronegative atoms (such as N, O, and S) of supports will result in a decrease in the electron density of Pd sites, thereby weakening the adsorption of reactants and reducing catalytic performance. Constructing a rich outer-shell electron environment of Pd single-atom sites by changing the coordination structure offers a novel opportunity to enhance the catalytic efficiency with excellent alkene selectivity. Therefore, in this work, we first propose the in situ preparation of isolated Pd sites encapsulated within Al/Si-rich ZSM-5 structure using the one-pot seed-assisted growth method. Pd1@ZSM-5 features Pd-O-Al/Si bonds, which can boost the domination of d-electron near the Fermi level, thereby promoting the adsorption of substrates on Pd sites and reducing the energy barrier for the semihydrogenation of alkynes. In semihydrogenation of phenylacetylene, Pd1@ZSM-5 catalyst performs the highest turnover frequency (TOF) value of 33582 molC═C/molPd/h with 96% selectivity of styrene among the reported heterogeneous catalysts and nearly 17-fold higher than that of the commercial Lindlar catalyst (1992 molC═C/molPd/h). This remarkable catalytic performance can be retained even after 6 cycles of usage. Particularly, the zeolitic confinement structure of Pd1@ZSM-5 enables precise shape-selective catalysis for alkyne reactants with a size less than 4.3 Å.

Pd Catalysts Supported on Mixed Iron and Titanium Oxides in Phenylacetylene Hydrogenation: Effect of TiO2 Content in Magnetic Support Material

Recently, Pd catalysts supported on magnetic nanoparticles (MNPs) have attracted a great attention due to their ability of easy separation with an external magnet. Modification of MNPs is successfully used to obtain Pd magnetic catalysts with enhanced catalytic activity. In this work, we discussed the effect of titania content in TiO2/MNPs support materials on catalytic properties of Pd@TiO2/MNPs catalysts in phenylacetylene hydrogenation. TiO2/MNPs composites were prepared by simple ultrasound-assisted mixing of TiO2 and MNPs, synthesized by co-precipitation method. This was followed by deposition of palladium ions on the mixed metal oxides using NaOH as precipitant. The supports and catalysts were characterized using XRD, BET, STEM, EDX, XPS, and a SQUID magnetometer. Pd nanoparticles (5-6 nm) formed were found to be homogeneously distributed on support materials representing the well-mixed metal oxides with TiO2 content of 10, 30, 50, or 70%wt. Testing of the catalysts in phenylacetylene hydrogenation showed that their activity increased with increasing TiO2 content, and the process was faster in alkali medium (pH = 10). The hydrogenation rates of triple and double C-C bonds on Pd@70TiO2/MNPs achieved 9.3 × 10-6 mol/s and 23.1 × 10-6 mol/s, respectively, and selectivity to styrene was 96%. The catalyst can be easily recovered with an external magnet and reused for 12 runs without significant degradation in the catalytic activity. The improved catalytic properties of Pd@70TiO2/MNPs can be explained by the fact that the surface of the support is mainly composed of TiO2 particles, affecting the state and size of Pd species.

Directional Construction of the Highly Stable Active-Site Ensembles at Sub-2 nm to Enhance Catalytic Activity and Selectivity

Precise control over the size, species, and breakthrough of the activity-selectivity trade-off are great challenges for sub-nano non-noble metal catalysts. Here, for the first time, a "multiheteroatom induced SMSI + in situ P activation" strategy that enables high stability and effective construction of sub-2 nm metal sites for optimizing selective hydrogenation performance is developed. It is synthesized the smallest metal phosphide clusters (<2 nm) including from unary to ternary non-noble metal systems, accompanied by unprecedented thermal stability. In the proof-of-concept demonstration, further modulation of size and species results in the creation of a sub-2 nm site platform, directionally achieving single atom (Ni1), Ni1+metal cluster (Ni1+Nin), or novel Ni1+metal phosphide cluster synergistic sites (Ni1+Ni2Pn), respectively. Based on thorough structure and mechanism investigation, it is found the Ni1+Ni2Pn site is motivated to achieve electronic structure self-optimizing through synergistic SMSI and site coupling effect. Therefore, it speeds up the substrate adsorption-desorption kinetics in semihydrogenation of alkyne and achieves superior catalytic activity that is 56 times higher than the Ni1 site under mild conditions. Compared to traditional active sites, this may represent the highly effective integration of atom utilization, thermal stability, and favorable site requirements for chemisorption properties and reactivities of substrates.

Ambient hydrogenation of solid aromatics enabled by a high entropy alloy nanocatalyst

Hydrogenation is a versatile chemical process with significant applications in various industries, including food production, petrochemical refining, pharmaceuticals, and hydrogen carriers/safety. Traditional hydrogenation of aromatics, hindered by the stable π-conjugated phenyl ring structures, typically requires high temperatures and pressures, making ambient hydrogenation a grand challenge. Herein, we introduce a PdPtRuCuNi high entropy alloy (HEA) nanocatalyst, achieving an exceptional 100% hydrogenation of carbon-carbon unsaturated bonds, including alkynyl and phenyl groups, in solid 1,4-bis(phenylethynyl)benzene (DEB) at 25 °C under ≤1 bar H2 and solventless condition. This results in a threefold higher hydrogen uptake for DEB-contained composites compared to conventional Pd catalysts, which can only hydrogenate the alkynyl groups with a ~ 27% conversion of DEB. Our experimental results, complemented by theoretical calculations, reveal that PdPtRu alloy is highly active and crucial in enabling the hydrogenation of phenyl groups, while all five elements work synergistically to regulate the reaction rate. Remarkably, this newly developed catalyst also achieves nearly 100% reactivity for ambient hydrogenation of a broad range of aromatics, suggesting its universal effectiveness. Our research uncovers a novel material platform and catalyst design principle for efficient and general hydrogenation. The multi-element synergy in HEA also promises unique catalytic behaviors beyond hydrogenation applications.

Highly Stable Cesium Molybdenum Chloride Perovskite Nanocrystals for Photothermal Semihydrogenation Applications

Metal halide perovskite materials with excellent carrier transport properties have been regarded as a new class of catalysts with great application potential. However, their development is hampered by their instability in polar solvents and high temperatures. Herein, we report a solution-processed Cs2MoCl6 perovskite nanocrystals (NCs) capped with the Mo6+, showing high thermostability in polar solvents. Furthermore, the Pd single atoms (PdSA) can be anchored on the surface of Cs2MoCl6 NCs through the unique coordination structure of Pd-Cl sites, which exhibit excellent semihydrogenation of different alkyne derivatives with high selectivity at full conversion at room temperature. Moreover, the activity could be improved greatly under Xe lamp irradiation. Detailed experimental characterization and DFT calculations indicate the improved activity under light illumination is due to the synergistic effect of photo-to-heat conversion and photoinduced electron transfer from Cs2MoCl6 to PdSA, which facilitates the activation of the C≡C group. This work not only provides a new catalyst for high selective semihydrogenation of alkyne derivatives but also opens a new avenue for metal halides as photothermal catalysts.

Toward High-Performance Hydrogenation at Room Temperature Through Tailoring Nickel Catalysts Stable in Aqueous Solution

The development of highly active, reusable catalysts for aqueous-phase reactions is challenging. Herein, metallic nickel is encapsulated in a nitrogen-doped carbon-silica composite (SiO2@Ni@NC) as a catalyst for the selective hydrogenation of vanillin in aqueous media. The constructed catalyst achieved 99.8% vanillin conversion and 100% 4-hydroxymethyl-2-methoxyphenol selectivity at room temperature. Based on combined scanning transmission electron microscopy, X-ray photoelectron spectroscopy, and Raman analyses, the satisfactory catalytic performance is attributed to the composite structure consisting of an active metal, carbon, and silica. The hydrophilic silica core promoted dispersion of the catalyst in aqueous media. Moreover, the external hydrophobic NC layer has multiple functions, including preventing oxidation or leaching of the internal metal, acting as a reducing agent to reduce the internal metal, regulating the active-site microenvironment by enriching the concentrations of H2 and organic reactants, and modifying the electronic structure of the active metal via metal-support interactions. Density functional theory calculations indicated that NC facilitates vanillin adsorption and hydrogen dissociation to promote aqueous-phase hydrogenation. This study provides an efficient strategy for constructing encapsulated Ni-based amphiphilic catalysts to upgrade biomass-derived compounds.

Nanoparticles as an antidote for poisoned gold single-atom catalysts in sustainable propylene epoxidation

The development of sustainable and anti-poisoning single-atom catalysts (SACs) is essential for advancing their research from laboratory to industry. Here, we present a proof-of-concept study on the poisoning of Au SACs, and the antidote of Au nanoparticles (NPs), with trace addition shown to reinforce and sustain propylene epoxidation. Multiple characterizations, kinetics investigations, and multiscale simulations reveal that Au SACs display remarkable epoxidation activity at a low propylene coverage, but become poisoned at higher coverages. Interestingly, Au NPs can synergistically cooperate with Au SACs by providing distinct active sites required for H2/O2 and C3H6 activations, as well as hydroperoxyl radical to restore poisoned SACs. The difference in reaction order between C3H6 and H2 (nC3H6-nH2) is identified as the descriptor for establishing the volcano curves, which can be fine-tuned by the intimacy and composition of SACs and NPs to achieve a rate-matching scenario for the formation, transfer, and consumption of hydroperoxyl. Consequently, only trace addition of Au NPs antidote (0.3% ratio of SACs) stimulates significant improvements in propylene oxide formation rate, selectivity, and H2 efficiency compared to SACs alone, offering a 56-fold, 3-fold, and 22-fold increase, respectively, whose performances can be maintained for 150 h.

Efficient Alkyne Semihydrogenation Catalysis Enabled by Synergistic Chemical and Thermal Modifications of a PdIn MOF

Recently, there has been a growing interest in using MOF templating to synthesize heterogeneous catalysts based on metal nanoparticles on carbonaceous supports. Unlike the common approach of direct pyrolysis of PdIn-MOFs at high temperatures, this work proposes a reductive chemical treatment under mild conditions before pyrolysis (resulting in PdIn-QT). The resulting material (PdIn-QT) underwent comprehensive characterization via state-of-the-art aberration-corrected electron microscopy, N2 physisorption, X-ray absorption spectroscopy, Raman, X-ray photoelectron spectroscopy, and X-ray diffraction. These analyses have proven the existence of PdIn bimetallic nanoparticles supported on N-doped carbon. In situ DRIFT spectroscopy reveals the advantageous role of indium (In) in regulating Pd activity in alkyne semihydrogenation. Notably, incorporating a soft nucleation step before pyrolysis enhances surface area, porosity, and nitrogen content compared to direct MOF pyrolysis. The optimized material exhibits outstanding catalytic performance with 96% phenylacetylene conversion and 96% selectivity to phenylethylene in the fifth cycle under mild conditions (5 mmol phenylacetylene, 7 mg cat, 5 mL EtOH, R.T., 1 H2 bar).

Graphene Chainmail Shelled Dilute Ni─Cu Alloy for Selective and Robust Aqueous Phase Catalytic Hydrogenation

Cost-effective non-noble metal-based catalysts for selective hydrogenation with excellent activity, selectivity, and durability are still the holy grail. Herein, an oxygen-doped carbon (OC) chainmail encapsulated dilute Cu-Ni alloy is developed by simple pyrolysis of Cu/Ni-metal-organic framework. The CuNi0.05@OC catalyst displays superior performance for atmospheric pressure transfer hydrogenation of p-chloronitrobenzene and p-nitrophenol, and for hydrogenation of furfural, all in water and with exceptional durability. Comprehensive characterizations confirm the close interactions between the diluted Ni sites, the base Cu, and optimized three-layered graphene chainmail. Theoretical calculations demonstrate that the properly tuned lattice strain and Schottky junction can adjust electron density to facilitate specific adsorption on the active centers, thus enhancing the catalytic activity and selectivity, while the OC shell also offers robust protection. This work provides a simple and environmentally friendly strategy for developing practical heterogeneous catalysts that bring the synergistic effect into play between dilute alloy and functional carbon wrapping.

Mediating trade-off between activity and selectivity in alkynes semi-hydrogenation via a hydrophilic polar layer

As a crucial industrial process for the production of bulk and fine chemicals, semi-hydrogenation of alkynes faces the trade-off between activity and selectivity due to undesirable over-hydrogenation. By breaking the energy linear scaling relationships, we report an efficient additive-free WO3-based single-atom Pd catalytic system with a vertical size effect of hydrogen spillover. Hydrogen spillover induced hydrophilic polar layer (HPL) with limited thickness on WO3-based support exhibits unconventional size effect to Pd site, in which over-hydrogenation is greatly suppressed on Pd1 site due to the polar repulsive interaction between HPL and nonpolar C=C bonds, whereas this is invalid for Pd nanoparticles with higher altitudes. By further enhancing the HPL through Mo doping, activated Pd1/MoWO3 achieves recorded performance of 98.4% selectivity and 10200 h-1 activity for semi-hydrogenation of 2-methyl-3-butyn-2-ol, 26-fold increase in activity of Lindlar catalyst. This observed vertical size effect of hydrogen spillover offers broad potential in catalytic performance regulation.

Pd-Mn/NC Dual Single-Atomic Sites with Hollow Mesopores for the Highly Efficient Semihydrogenation of Phenylacetylene

The direct pyrolysis of metal-zeolite imidazolate frameworks (M-ZIFs) has been widely recognized as the predominant approach for synthesizing atomically dispersed metal-nitrogen-carbon single-atom catalysts (M/NC-SACs), which have exhibited exceptional activity and selectivity in the semihydrogenation of acetylene. However, due to weak adsorption of reactants on the single site and restricted molecular diffusion, the semihydrogenation of large organic molecules (e.g., phenylacetylene) was greatly limited for M/NC-SACs. In this work, a dual single-atom catalyst (h-Pd-Mn/NC) with hollow mesopores was designed and prepared using a general host-guest strategy. Taking the semihydrogenation of phenylacetylene as an example, this catalyst exhibited ultrahigh activity and selectivity, which achieved a turnover frequency of 218 molC═CmolPd-1 min-1, 16-fold higher than that of the commercial Lindlar catalyst. The catalyst maintained high activity and selectivity even after 5 cycles of usage. The superior activity of h-Pd-Mn/NC was attributed to the 4.0 nm mesopore interface of the catalyst, which enhanced the diffusion of macromolecular reactants and products. Particularly, the introduction of atomically dispersed Mn with weak electronegativity in h-Pd-Mn/NC could drive the electron transfer from Mn to adjacent Pd sites and regulate the electronic structure of Pd sites. Meanwhile, the strong electronic coupling in Pd-Mn pairs enhanced the d-electron domination near the Fermi level and promoted the adsorption of phenylacetylene and H2 on Pd active sites, thereby reducing the energy barrier for the semihydrogenation of phenylacetylene.

Mesoporous α-Al2O3-supported PdCu bimetallic nanoparticle catalyst for the selective semi-hydrogenation of alkynes

The selective hydrogenation of alkynes to alkenes is widely applied in the chemical industry; nevertheless, achieving highly selective hydrogenation with high catalytic activity is considerably challenging. Herein, ultrafine PdCu bimetallic nanoparticles encapsulated by high-surface-area mesoporous α-Al2O3 were prepared by high-temperature calcination-reduction using a porous organic framework (POF) as the template. As-obtained PdCu@α-Al2O3 exhibited a high selectivity of 95% for the semi-hydrogenation of phenylacetylene as a probe reaction under mild reaction conditions. The separation of continuous Pd atoms and modification of the Pd electronic state by Cu atoms suppressed β-hydride formation and alkene adsorption, contributing to high selectivity for the catalytic hydrogenation of alkynes. The catalytic activity was maintained after 7 cycles due to the strong interaction between the PdCu bimetallic nanoparticles and α-Al2O3 as well as the encapsulation effect of mesoporous α-Al2O3. Thus, the current work provides a facile strategy for fabricating high-surface-area mesoporous α-Al2O3-supported catalysts for industrial catalysis applications.

Hydrogen Spillover-Driven Dynamic Evolution and Migration of Iron Oxide for Structure Regulation of Versatile Magnetic Nanocatalysts

Magnetic nanocatalysts with properties of easy recovery, induced heating, or magnetic levitation play a crucial role in advancing intelligent techniques. Herein, we report a method for the synthesis of versatile core-shell-type magnetic nanocatalysts through "noncontact" hydrogen spillover-driven reduction and migration of iron oxide with the assistance of Pd. In situ analysis techniques were applied to visualize the dynamic evolution of the magnetic nanocatalysts. Pd facilitates the dissociation of hydrogen molecules into activated H*, which then spills and thus drives the iron oxide reduction, gradual outward split, and migration through the carbonaceous shell. By controlling the evolution stage, nanocatalysts having diverse architectures including core-shell, split core-shell, or hollow type, each featuring Pd or PdFe loaded on the carbon shell, can be obtained. As a showcase, a magnetic nanocatalyst (Pd-loaded split core-shell) can hydrogenate crotonaldehyde to butanal (26 624 h-1 in TOF, ∼100% selectivity), outperforming reported Pd-based catalysts. This is due to the synergy of the enhanced local magnetothermal effect and the preferential adsorption of -C═C on Pd with a small d bandwidth. Another catalyst (PdFe-loaded split core-shell) also delivers a robust performance in phenylacetylene semihydrogenation (100% conversion, 97.5% selectivity) as PdFe may inhibit the overhydrogenation of -C═C. Importantly, not only Pd, other noble metals (e.g., Pt, Ru, and Au) also showed a similar property, revealing a general rule that hydrogen spillover drives the dynamic reduction, splitting, and migration of encapsulated nanosized iron oxide, resulting in diverse structures. This study would offer a structure-controllable fabrication of high-performance magnetic nanocatalysts for various applications.

Few-Atomic Zero-Valent Palladium Ensembles for Efficient Reductive Dehydrogenation and Dehalogenation Catalysis

Single-atom catalysts (SACs) offer immense potential in heterogeneous catalysis due to their maximized atomic utilization and high selectivity but suffer the problem of low reactivity in catalytic reductive reactions due to their high-valent state. Here, we demonstrate that supported palladium (Pd) ensembles consisting of a few zero-valent Pd atoms (Pd1+c-red/CN) exhibit exceptional reactivity in formic acid (FA) dehydrogenation and 4-chlorophenol (4-CP) dechlorination. The initial FA dehydrogenation and 4-CP dechlorination rates of Pd1+c-red/CN are 42-104 and 16-210 times higher than that of supported Pd SACs (Pd1-ox/CN), respectively. Experimental results and density functional theory (DFT) calculations reveal that optimal adsorption sites of Pd1+c-red/CN stimulate the formation of H*, which is indispensable for 4-CP dechlorination. Moreover, direct electron transfer from Pd atoms to FA with a high electron density on Pd1+c-red/CN also contributes to the rapid 4-CP dechlorination. The superior dehalogenation capability of Pd1+c-red/CN for organohalides of great environmental and health concerns suggested its immense application potential in environmental remediation. This work highlights the pivotal roles of the structure and valence state of Pd ensembles in catalytic reductive reactions and provides a strategy to broaden the application of Pd-based catalysts for dehydrogenation and dehalogenation.

Encapsulation of Palladium Carbide Subnanometric Species in Zeolite Boosts Highly Selective Semihydrogenation of Alkynes

The selective hydrogenation of alkynes to alkenes is a crucial step in the synthesis of fine chemicals. However, the widely utilized palladium (Pd)-based catalysts often suffer from poor selectivity. In this work, we demonstrate a carbonization-reduction method to create palladium carbide subnanometric species within pure silicate MFI zeolite. The carbon species can modify the electronic and steric characteristics of Pd species by forming the predominant Pd-C4 structure and, meanwhile, facilitate the desorption of alkenes by forming the Si-O-C structure with zeolite framework, as validated by the state-of-the-art characterizations and theoretical calculations. The developed catalyst shows superior performance in the selective hydrogenation of alkynes over mild conditions (298 K, 2 bar H2 ), with 99 % selectivity to styrene at a complete conversion of phenylacetylene. In contrast, the zeolite-encapsulated carbon-free Pd catalyst and the commercial Lindlar catalyst show only 15 % and 14 % selectivity to styrene, respectively, under identical reaction conditions. The zeolite-confined Pd-carbide subnanoclusters promise their superior properties in semihydrogenation of alkynes.

Ultrathin covalent organic overlayers on metal nanocrystals for highly selective plasmonic photocatalysis

Metal nanoparticle-organic interfaces are common but remain elusive for controlling reactions due to the complex interactions of randomly formed ligand-layers. This paper presents an approach for enhancing the selectivity of catalytic reactions by constructing a skin-like few-nanometre ultrathin crystalline porous covalent organic overlayer on a plasmonic nanoparticle surface. This organic overlayer features a highly ordered layout of pore openings that facilitates molecule entry without any surface poisoning effects and simultaneously endows favourable electronic effects to control molecular adsorption-desorption. Conformal organic overlayers are synthesised through the plasmonic oxidative activation and intermolecular covalent crosslinking of molecular units. We develop a light-operated multicomponent interfaced plasmonic catalytic platform comprising Pd-modified gold nanoparticles inside hollow silica to achieve the highly efficient and selective semihydrogenation of alkynes. This approach demonstrates a way to control molecular adsorption behaviours on metal surfaces, breaking the linear scaling relationship and simultaneously enhancing activity and selectivity.

Design of Hollow Nanoreactors for Size- and Shape-Selective Catalytic Semihydrogenation Driven by Molecular Recognition

Mimicking the structures and functions of cells to create artificial organelles has spurred the development of efficient strategies for production of hollow nanoreactors with biomimetic catalytic functions. However, such structure are challenging to fabricate and are thus rarely reported. We report the design of hollow nanoreactors with hollow multishelled structure (HoMS) and spatially loaded metal nanoparticles. Starting from a molecular-level design strategy, well-defined hollow multishelled structure phenolic resins (HoMS-PR) and carbon (HoMS-C) submicron particles were accurately constructed. HoMS-C serves as an excellent, versatile platform, owing to its tunable properties with tailored functional sites for achieving precise spatial location of metal nanoparticles, internally encapsulated (Pd@HoMS-C) or externally supported (Pd/HoMS-C). Impressively, the combination of the delicate nanoarchitecture and spatially loaded metal nanoparticles endow the pair of nanoreactors with size-shape-selective molecular recognition properties in catalytic semihydrogenation, including high activity and selectivity of Pd@HoMS-C for small aliphatic substrates and Pd/HoMS-C for large aromatic substrates. Theoretical calculations provide insight into the pair of nanoreactors with distinct behaviors due to the differences in energy barrier of substrate adsorption. This work provides guidance on the rational design and accurate construction of hollow nanoreactors with precisely located active sites and a finely modulated microenvironment by mimicking the functions of cells.

Palladium particles dispersed on hollow structural support improve CO2 conversion

Herein, an effective Pd/NHS catalyst has been designed and facilely synthesized with extraordinary CO2 fixation performance, which is superior to that of Pd/NS catalysts, owing to the hollow structures facilitating mass transfer and product release.

A Heterogeneous Single Atom Cobalt Catalyst for Highly Efficient Acceptorless Dehydrogenative Coupling Reactions

A fundamental understanding of metal active sites in single-atom catalysts (SACs) is important and challenging in the development of high-performance catalyst systems. Here, a highly efficient and straightforward molten-salt-assisted approach is reported to create atomically dispersed cobalt atoms supported over vanadium pentoxide layered material, with each cobalt atom coordinated with four neighboring oxygen atoms. The liquid environment and the strong polarizing force of the molten salt at high temperatures potentially favor the weakening of VO bonding and the formation of CoO bonding on the vanadium oxide surface. This cobalt SAC achieves extraordinary catalytic efficiency in acceptorless dehydrogenative coupling of alcohols with amines to give imines, with more than 99% selectivity under almost 100% conversion within 3 h, along with a high turnover frequency (TOF) of 5882 h^-1 , exceeding those of previously reported benchmarking catalysts. Moreover, it delivers excellent recyclability, reaction scalability, and substrate tolerance. Density functional theory (DFT) calculations further confirm that the optimized coordination environment and strong electronic metal-support interaction contribute significantly to the activation of reactants. The findings provide a feasible route to construct SACs at the atomic level for use in organic transformations.

Boosting Chemoselective Hydrogenation of Nitroaromatic via Synergy of Hydrogen Spillover and Preferential Adsorption on Magnetically Recoverable Pt@Fe2 O3

It is highly desired but challenging to design high performance catalyst for selective hydrogenation of nitro compounds into amino compounds. Herein, a boosting chemoselective hydrogenation strategy on Pt@Fe₂ O₃ is proposed with gradient oxygen vacancy by synergy of hydrogen spillover and preferential adsorption. Experimental and theoretical investigations reveal that the nitro is preferentially adsorbed onto oxygen vacancy of Pt@Fe₂ O₃ , meanwhile, the H₂ dissociated on Pt nanoparticles and then spillover to approach the nitro for selective hydrogenation (>99% conversion of 4-nitrostyrene, > 99% selectivity of 4-aminostyrene, TOF of 2351 h^-1 ). Moreover, the iron oxide support endows the catalyst magnetic retrievability. This high activity, selectivity, and easy recovery strategy provide a promising avenue for selective hydrogenation catalysis of various nitroaromatic.

Pyridinic Nitrogen Sites Dominated Coordinative Engineering of Subnanometric Pd Clusters for Efficient Alkynes' Semihydrogenation

Supported metal catalysts have played an important role in optimizing selective semihydrogenation of alkynes for fine chemicals. There into, nitrogen-doped carbons, as a type of promising support materials, have attracted extensive attentions. However, due to the general phenomenon of random doping for nitrogen species in the support, it is still atremendous challenge to finely identify which nitrogen configuration dominates the catalytic property of alkynes' semihydrogenation. Herein, it is reported that uniform mesoporous N-doped carbon spheres derived from mesoporous polypyrrole spheres are used as supports to immobilized subnanometric Pd clusters, which provide a particular platform to research the influence of nitrogen configurations on the alkynes' semihydrogenation. Comprehensive experimental results and density functional theory calculation indicate that pyridinic nitrogen configuration dominates the catalytic behavior of Pd clusters. The high contents of pyridinic nitrogen sites offer abundant coordination sites, which greatly reduces the energy barrier of the rate-determining reaction step and makes Pd clusters own high catalytic activity. The electron effect between pyridinic nitrogen sites and Pd clusters makes the reaction highly selective. Additionally, the good mesostructures also promote the fast transport of substrate. Based on the above, catalyst Pd@PPy-600 exhibits high catalytic activity (99%) and selectivity (96%) for phenylacetylene (C₈ H₆ ) semihydrogenation.

Enhanced Alkene Selectivity for Transfer Semihydrogenation of Alkynes over Electron-Deficient Pt Nanoparticles Encapsulated in Hollow Silica Nanospheres

In this work, we report that Pt nanoparticles confined in hollow porous silica nanospheres (Pt@HPSNs) function as highly selective catalysts for the transfer hydrogenation of phenylacetylene to styrene with ammonia borane. Relative to the deep hydrogenation of phenylacetylene to ethylbenzene over the supported Pt/SiO2, Pt@HPSNs exhibit above 88% of styrene selectivity at nearly 100% of phenylacetylene conversions, and the high selectivity of Pt@HPSNs can be maintained even at high ammonia borane/phenylacetylene ratios and longer reaction time. The Pt 4f X-ray photoelectron spectrum of Pt@HPSNs shows a remarkable ∼1.5 eV shift to high binding energy, proving the nature of electron deficiency of such encapsulated Pt nanoparticles. Combined with extremely minor transfer hydrogenation of styrene to ethylbenzene when styrene as substrates, the enhanced styrene selectivity of Pt@HPSNs is ascribed to the electron deficiency of encapsulated Pt nanoparticles, which leads to the fast desorption of styrene and thus avoids deep hydrogenation.

Tripodal Pd metallenes mediated by Nb2C MXenes for boosting alkynes semihydrogenation

2D metallene nanomaterials have spurred considerable attention in heterogeneous catalysis by virtue of sufficient unsaturated metal atoms, high specific surface area and surface strain. Nevertheless, the strong metallic bonding in nanoparticles aggravates the difficulty in the controllable regulation of the geometry of metallenes. Here we propose an efficient galvanic replacement strategy to construct Pd metallenes loaded on Nb₂C MXenes at room temperature, which is triggered by strong metal-support interaction based on MD simulations. The Pd metallenes feature a chair structure of six-membered ring with the coordination number of Pd as low as 3. Coverage-dependent kinetic analysis based on first-principles calculations reveals that the tripodal Pd metallenes promote the diffusion of alkene and inhibit its overhydrogenation. As a consequence, Pd/Nb₂C delivers an outstanding turnover frequency of 10372 h^-1 and a high selectivity of 96% at 25 ^oC in the semihydrogenation of alkynes without compromising the stability. This strategy is general and scalable considering the plentiful members of the MXene family, which can set a foundation for the design of novel supported-metallene catalysts for demanding transformations.

Ni-Pd-Incorporated Fe3O4 Yolk-Shelled Nanospheres as Efficient Magnetically Recyclable Catalysts for Reduction of N-Containing Unsaturated Compounds

The use of metal-based heterogeneous catalysts for the degradation of N-containing organic dyes has attracted much attention due to their excellent treatment efficiency and capability. Here, we report the synthesis of heterometals (Ni and Pd)-incorporated Fe3O4 (Ni-Pd/Fe3O4) yolk-shelled nanospheres for the catalytic reduction of N-containing organic dyes using a facile combination of solvothermal treatment and high-temperature annealing steps. Benefiting from the magnetic properties and the yolk-shelled structure of the Fe3O4 support, as well as the uniformly dispersed active heterometals incorporated in the shell and yolk of spherical Fe3O4 nanoparticles, the as-prepared Ni-Pd/Fe3O4 composite shows excellent recyclability and enhanced catalytic activity for three N-containing organic dyes (e.g., 4-nitrophenol, Congo red, and methyl orange) compared with its mono metal counterparts (e.g., Ni/Fe3O4 and Pd/Fe3O4). In the 4-nitrophenol reduction reaction, the catalytic activity of Ni-Pd/Fe3O4 was superior to many Fe3O4-supported nanocatalysts reported within the last five years. This work provides an effective strategy to boost the activity of iron oxide-based catalytic materials via dual or even multiple heterometallic incorporation strategy and sheds new light on environmental catalysis.

Semi-Encapsulated PdRh Alloy Heterojunction for the Selectively Catalytic Hydrogenation of Nitrophenylacetylene to Nitrostyrene

Semi-hydrogenation usually requires an effective catalyst to ensure selectivity, especially when reducible groups coexist in a molecule. Pd is widely used in the semi-hydrogenation of alkynes to synthesize alkenes, but...

Ultrafine PdCo bimetallic nanoclusters confined in N-doped porous carbon for the efficient semi-hydrogenation of alkynes

Ultrafine PdCo bimetallic nanoclusters with Co atom-modified Pd active sites were highly dispersed and confined in an m-NC material for selective semi-hydrogenation of alkynes to alkenes.