Ag10Ti28‐Oxo Cluster Containing Single‐Atom Silver Sites: Atomic Structure and Synergistic Electronic Properties

Supported single‐atom catalysts have been emerging as promising materials in a variety of energy catalysis applications. However, studying the role of metal–support interactions at the molecular level remains a major challenge, primarily due to the lack of precise atomic structures. In this work, by replacing the frequently used TiO₂ support with its molecular analogue, titanium‐oxo cluster (TOC), we successfully produced a new kind of Ti‐O material doped with single silver sites. The as‐obtained Ag₁₀Ti₂₈ cluster, containing four exposed and six embedded Ag sites, is the largest noble‐metal‐doped Ti‐O cluster reported to date. Density functional theory (DFT) calculations show that the Ag₁₀Ti₂₈ core exhibits properties distinct from those of metallic Ag‐based materials. This Ti‐O material doped with single Ag sites presents a high ?_d and moderate CO binding capacity comparable to that of metallic Cu‐based catalysts, suggesting that it might display different catalytic performance from the common Ag‐based catalysts, for example, for CO₂ reduction. These results prove that the synergism of active surface metal atoms and the Ti‐O cluster support result in unique physical properties, which might open a new direction for single‐atom‐included catalysts.     

Understanding the Origin of Highly Selective CO2 Electroreduction to CO on Ni,N‐doped Carbon Catalysts

Ni,N‐doped carbon catalysts have shown promising catalytic performance for CO₂ electroreduction (CO₂R) to CO; this activity has often been attributed to the presence of nitrogen‐coordinated, single Ni atom active sites. However, experimentally confirming Ni?N bonding and correlating CO₂ reduction (CO₂R) activity to these species has remained a fundamental challenge. We synthesized polyacrylonitrile‐derived Ni,N‐doped carbon electrocatalysts (Ni‐PACN) with a range of pyrolysis temperatures and Ni loadings and correlated their electrochemical activity with extensive physiochemical characterization to rigorously address the origin of activity in these materials. We found that the CO₂R to CO partial current density increased with increased Ni content before plateauing at 2 wt % which suggests a dispersed Ni active site. These dispersed active sites were investigated by hard and soft X‐ray spectroscopy, which revealed that pyrrolic nitrogen ligands selectively bind Ni atoms in a distorted square‐planar geometry that strongly resembles the active sites of molecular metal–porphyrin catalysts.     

Au‐ and Ag‐loaded MnO2 nanostructures supported on nitrogen‐ and nitrogen–sulfur‐doped pyroproteins: Synthesis and catalytic activity in organic transformations

Four novel Au‐ and Ag‐loaded MnO₂ nanostructures supported on nitrogen‐doped pyroprotein of natural silk (Au–MnO₂@PPNS and Ag–MnO₂@PPNS) and nitrogen–sulfur‐doped pyroprotein of natural wool (Au–MnO₂@PPNW and Ag–MnO₂@PPNW) have been synthesized. Nitrogen‐ and nitrogen–sulfur‐doped pyroproteins were prepared by carbonization of natural silk and wool proteins, respectively. The catalysts were investigated for the aerobic oxidation of aromatic hydrocarbons of petroleum naphtha and the aerobic oxidative synthesis of 2‐phenylbenzo[d ]thiazoles, 2‐phenyl‐1H ‐benzo[d ]imidazoles and 2‐phenyl‐4‐quinazolinones in the absence of any co‐promoter and additional oxidizing reagent. The prepared catalytic systems showed higher catalytic activity in comparison to aggregated catalysts.     

Switching on the Metathesis Activity of Re Oxo Alkylidene Surface Sites through a Tailor‐Made Silica–Alumina Support

Re oxo alkylidene surface species are putative active sites in classical heterogeneous Re‐based alkene‐metathesis catalysts. However, the lack of evidence for such species questions their existence and/or relevance as reaction intermediates. Using Re(O)(=CH‐CH=CPh₂)(OtBu_F6)₃(THF), the corresponding well‐defined Re oxo alkylidene surface species can be generated on both silica and silica–alumina supports. While inactive on the silica support, it displays very good activity, even for functionalized olefins, on the silica–alumina support.     

On the Role of Metals in Nitrogen‐Doped Carbon Electrocatalysts for Oxygen Reduction

The notion of metal‐free catalysts is used to refer to carbon materials modified with nonmetallic elements. However, some claimed metal‐free catalysts are prepared using metal‐containing precursors. It is highly contested that metal residues in nitrogen‐doped carbon (NC) catalysts play a crucial role in the oxygen reduction reaction (ORR). In an attempt to reconcile divergent views, a definition for truly metal‐free catalysts is proposed and the differences between NC and M‐N_x/C catalysts are discussed. Metal impurities at levels usually undetectable by techniques such as XPS, XRD, and EDX significantly promote the ORR. Poisoning tests to mask the metal ions reveal the involvement of metal residues as active sites or as modifiers of the electronic structure of the active sites in NC. The unique merits of both M‐N_x/C and NC catalysts are discussed to inspire the development of more advanced nonprecious‐metal catalysts for the ORR.     

Synthesis of N‐Doped Mesoporous Carbon Nanorods through Nano‐Confined Reaction: High‐Performance Catalyst Support for Hydrogenation of Phenol Derivatives

Traditional hard‐template methods for the preparation of mesoporous carbon structures have been well developed, but there are difficulties associated with complete filling of the organic precursors in ordered mesochannels and exact replication of the templates. Herein, mesoporous carbon nanorods (meso‐CNRs) were synthesized through thermal condensation of furfuryl alcohol followed by the nano‐confined decomposition of polyfurfuryl alcohol in silica nanotubes (SiO₂ NTs) with porous shells. Limited and slow release of gaseous water through the porous shells and finite polyfurfuryl precursor inside silica nanotubes are responsible for the formation of the mesoporous structures. Nitrogen can be doped into the meso‐CNRs by adding guanidine hydrochloride to the precursors. The nitrogen dopant not only stabilizes the ultrasmall and active Pd nanocatalyst in the meso‐CNRs but also increases the electron density of Pd and accelerates the dissociation of H₂, both of which increase the catalytic activity of the Pd catalyst in hydrogenation reactions.     

Unraveling the Nature of Sites Active toward Hydrogen Peroxide Reduction in Fe‐N‐C Catalysts

Fe‐N‐C catalysts with high O₂ reduction performance are crucial for displacing Pt in low‐temperature fuel cells. However, insufficient understanding of which reaction steps are catalyzed by what sites limits their progress. The nature of sites were investigated that are active toward H₂O₂ reduction, a key intermediate during indirect O₂ reduction and a source of deactivation in fuel cells. Catalysts comprising different relative contents of FeN_x C_y moieties and Fe particles encapsulated in N‐doped carbon layers (0–100 %) show that both types of sites are active, although moderately, toward H₂O₂ reduction. In contrast, N‐doped carbons free of Fe and Fe particles exposed to the electrolyte are inactive. When catalyzing the ORR, FeN_x C_y moieties are more selective than Fe particles encapsulated in N‐doped carbon. These novel insights offer rational approaches for more selective and therefore more durable Fe‐N‐C catalysts.     

Self‐Supporting Metal–Organic Layers as Single‐Site Solid Catalysts

Metal–organic layers (MOLs) represent an emerging class of tunable and functionalizable two‐dimensional materials. In this work, the scalable solvothermal synthesis of self‐supporting MOLs composed of [Hf₆O₄(OH)₄(HCO₂)₆] secondary building units (SBUs) and benzene‐1,3,5‐tribenzoate (BTB) bridging ligands is reported. The MOL structures were directly imaged by TEM and AFM, and doped with 4′‐(4‐benzoate)‐(2,2′,2′′‐terpyridine)‐5,5′′‐dicarboxylate (TPY) before being coordinated with iron centers to afford highly active and reusable single‐site solid catalysts for the hydrosilylation of terminal olefins. MOL‐based heterogeneous catalysts are free from the diffusional constraints placed on all known porous solid catalysts, including metal–organic frameworks. This work uncovers an entirely new strategy for designing single‐site solid catalysts and opens the door to a new class of two‐dimensional coordination materials with molecular functionalities.     

Liquid‐phase α‐Pinene Isomerization over Fe‐doped Sulfated Zirconia Prepared by a Hydrothermal Treatment‐assisted Process

A series of Fe‐doped (0.5%–3%) sulfated zirconia have been prepared by a hydrothermal treatment‐assisted process. Textural and structural characterizations of the as‐synthesized materials were performed by means of N₂ adsorption, X‐ray diffraction, transmission electron microscopy, scanning electron microscopy and thermogravi‐ metric analysis. Temperature‐programmed desorption of ammonia was used to determine the acidity of the samples. The effects of Fe‐doping on the structure, acidity and catalytic activity of sulfated zirconia for liquid‐phase α‐pinene isomerization were investigated. The incorporation of small amounts of Fe into sulfated zirconia results in the increase of sulfate content and the number of acid sites, which is responsible for the enhanced activity of Fe‐doped catalysts in comparison with the undoped one. Meanwhile, hydrothermal treatment helps to improve the activity of the catalyst.     

Linker‐Free,Silica‐Bound Olefin‐Metathesis Catalysts: Applications in Heterogeneous Catalysis

A set of heterogenized olefin‐metathesis catalysts, which consisted of Ru complexes with the H₂ITap ligand (1,3‐bis(2′,6′‐dimethyl‐4′dimethyl aminophenyl)‐4,5‐dihydroimidazol‐2‐ylidene) that had been adsorbed onto a silica support, has been prepared. These complexes showed strong binding to the solid support without the need for tethering groups on the complex or functionalized silica. The catalysts were tested in the ring‐opening–ring‐closing‐metathesis (RO‐RCM) of cyclooctene (COE) and the self‐metathesis of methyl oleate under continuous‐flow conditions. The best complexes showed a TON>4000, which surpasses the previously reported materials that were either based on the Grubbs–Hoveyda II complex on silica or on the classical heterogeneous Re₂O₇/B₂O₃ catalyst.     

The Critical Effect of Niobium Doping on the Formation of Mesostructured TiO2: Single‐Crystalline Ordered Mesoporous Nb‐TiO2 and Plate‐like Nb‐TiO2 with Ordered Mesoscale Dimples

Highly ordered mesoporous niobium‐doped TiO₂ with a single‐crystalline framework was prepared by using silica colloidal crystals with ca. 30 nm in diameter as templates. The preparation of colloidal crystals composed of uniform silica nanoparticles is a key to obtain highly ordered mesoporous Nb‐doped TiO₂. The XPS measurements of Nb‐doped TiO₂ showed the presence of Nb⁵⁺ and correspondingly Ti³⁺. With the increase in the amount of doped Nb, the crystalline phase of the product was converted from rutile into anatase, and the lattice spacings of both rutile and anatase phases increased. Surprisingly, the increase in the amount of Nb led to the formation of plate‐like TiO₂ with dimpled surfaces on one side, which was directly replicated from the surfaces of the colloidal silica crystals.     

CO2 Overall Splitting by a Bifunctional Metal‐Free Electrocatalyst

Photo/electrochemical CO₂ splitting is impeded by the low cost‐effective catalysts for key reactions: CO₂ reduction (CDRR) and water oxidation. A porous silicon and nitrogen co‐doped carbon (SiNC) nanomaterial by a facile pyrolyzation was developed as a metal‐free bifunctional electrocatalyst. CO₂‐to‐CO and oxygen evolution (OER) partial current density under neutral conditions were enhanced by two orders of magnitude in the Tafel regime on SiNC relative to single‐doped comparisons beyond their specific area gap. The photovoltaic‐driven CO₂ splitting device with SiNC electrodes imitating photosynthesis yielded an overall solar‐to‐chemical efficiency of advanced 12.5 % (by multiplying energy efficiency of CO₂ splitting cell and photovoltaic device) at only 650 mV overpotential. Mechanism studies suggested the elastic electron structure of ?Si(O)?C?N? unit in SiNC as the highly active site for CDRR and OER simultaneously by lowering the free energy of CDRR and OER intermediates adsorption.     

High activity Ziegler–Natta catalysts for the preparation of ethylene copolymers

High activity ethylene polymerization catalysts have been prepared by the interaction of ethylmagnesium chloride in tetrahydrofuran with high surface area silica, followed by reaction with excess titanium tetrachloride in heptane. The catalysts were tested in ethylene—hexene copolymerization reactions in the presence of AlEt₃ at 80°C. For comparison purposes, the copolymerization properties of a similar catalyst prepared without silica were also evaluated. Preparative conditions were identified which provide catalysts that possess high reactivity towards 1-hexane. The silica and the amount of magnesium used in catalyst preparation strongly affect the copolymerization properties of the catalysts. Generally, catalysts prepared with silica showed much higher sensitivity to 1-hexene (effective reactivity ratio r₁ = 25–60) while a similar catalyst prepared without silica exhibited an r₁ value of 125. Fractionation of the copolymer with a series of boiling solvents showed that all the catalysts exhibit a wide distribution of active centers with respect to reactivity ratios, with the r₁ values varying from 5–7 to ca. 200. The width of a the center distribution depends on catalyst composition—it is the narrowest for the catalyst prepared without silica and is the widest for the catalysts with intermediate Ti : Mg ratios.     

Tripod Immobilization of Triphenylphosphane on a Silica‐Gel Surface to Enable Selective Mono‐Ligation to Palladium: Application to Suzuki–Miyaura Cross‐Coupling Reactions with Chloroarenes

A silica‐supported triphenylphosphane (Silica‐3p‐TPP) with a Ph₃P‐type core, immobilized on a silica surface, was synthesized and characterized by nitrogen‐absorption measurements and solid‐state NMR spectroscopy. The tripodal immobilization constrains the mobility of the phosphane molecule and causes the lone pair on the phosphorus atom to face in the direction perpendicular to the support, resulting in the selective formation of a 1:1 metal–phosphane species that is free from unfavorable steric repulsions caused by the silica surface. Heterogeneous Pd catalysts created in this manner enabled room‐temperature Suzuki–Miyaura cross‐coupling reactions with unactivated chloroarenes, despite the moderate electronic and steric nature of the Ph₃P‐based ligands. These catalysts also showed potential in reactions with more challenging substrates under mild conditions. Tripodally immobilized and well‐dispersed phosphanes on the silica surface were crucial for high catalytic activity.     

Rare earth‐doped calcium‐based magnetic catalysts for transesterification of glycerol to glycerol carbonate

Several rare earth‐doped, calcium‐based magnetic catalysts were prepared for the synthesis of glycerol carbonate. The basicity and basic strength analysis of the catalysts showed that the doping of rare earth improved the basicity of the catalysts, and the doping of lanthanum maximized it. In addition, with the doping of lanthanum, the particle size of the catalyst became smaller to promote the organic reactants near the active sites of catalysts, thereby effectively improving the performance. NiFe₂O₄@[CaO‐La₂O₃] shows better catalytic performance with 99.0% yield of glycerol carbonate compared to the other catalysts. The NiFe₂O₄@(CaO‐La₂O₃) could be reused in six cycles without significant loss in activity.     

Tungsten‐Doped L10‐PtCo Ultrasmall Nanoparticles as a High‐Performance Fuel Cell Cathode

The commercialization of proton exchange membrane fuel cells (PEMFCs) relies on highly active and stable electrocatalysts for oxygen reduction reaction (ORR) in acid media. The most successful catalysts for this reaction are nanostructured Pt‐alloy with a Pt‐skin. The synthesis of ultrasmall and ordered L1₀‐PtCo nanoparticle ORR catalysts further doped with a few percent of metals (W, Ga, Zn) is reported. Compared to commercial Pt/C catalyst, the L1₀‐W‐PtCo/C catalyst shows significant improvement in both initial activity and high‐temperature stability. The L1₀‐W‐PtCo/C catalyst achieves high activity and stability in the PEMFC after 50 000 voltage cycles at 80 °C, which is superior to the DOE 2020 targets. EXAFS analysis and density functional theory calculations reveal that W doping not only stabilizes the ordered intermetallic structure, but also tunes the Pt‐Pt distances in such a way to optimize the binding energy between Pt and O intermediates on the surface.     

Ordered Porous Nitrogen‐Doped Carbon Matrix with Atomically Dispersed Cobalt Sites as an Efficient Catalyst for Dehydrogenation and Transfer Hydrogenation of N‐Heterocycles

Single‐atom catalysts (SACs) have been explored widely as potential substitutes for homogeneous catalysts. Isolated cobalt single‐atom sites were stabilized on an ordered porous nitrogen‐doped carbon matrix (ISAS‐Co/OPNC). ISAS‐Co/OPNC is a highly efficient catalyst for acceptorless dehydrogenation of N‐heterocycles to release H₂. ISAS‐Co/OPNC also exhibits excellent catalytic activity for the reverse transfer hydrogenation (or hydrogenation) of N‐heterocycles to store H₂, using formic acid or external hydrogen as a hydrogen source. The catalytic performance of ISAS‐Co/OPNC in both reactions surpasses previously reported homogeneous and heterogeneous precious‐metal catalysts. The reaction mechanisms are systematically investigated using first‐principles calculations and it is suggested that the Eley–Rideal mechanism is dominant.     

Hierarchically Ordered Porous Carbon with Atomically Dispersed FeN4 for Ultraefficient Oxygen Reduction Reaction in Proton‐Exchange Membrane Fuel Cells

The low catalytic activity and poor mass transport capacity of platinum group metal free (PGM‐free) catalysts seriously restrict the application of proton‐exchange membrane fuel cells (PEMFCs). Catalysts derived from Fe‐doped ZIF‐8 could in theory be as active as Pt/C thanks to the high intrinsic activity of FeN₄; however, the micropores fail to meet rapid mass transfer. Herein, an ordered hierarchical porous structure is introduced into Fe‐doped ZIF‐8 single crystals, which were subsequently carbonized to obtain an FeN₄‐doped hierarchical ordered porous carbon (FeN₄/HOPC) skeleton. The optimal catalyst FeN₄/HOPC‐c‐1000 shows excellent performance with a half‐wave potential of 0.80 V in 0.5 m H₂SO₄ solution, only 20 mV lower than that of commercial Pt/C (0.82 V). In a real PEMFC, FeN₄/HOPC‐c‐1000 exhibits significantly enhanced current density and power density relative to FeN₄/C, which does not have an optimized pore structure, implying an efficient utilization of the active sites and enhanced mass transfer to promote the oxygen reduction reaction (ORR).     

Synergistic Effects between Atomically Dispersed Fe−N−C and C−S−C for the Oxygen Reduction Reaction in Acidic Media

Various advanced catalysts based on sulfur‐doped Fe/N/C materials have recently been designed for the oxygen reduction reaction (ORR); however, the enhanced activity is still controversial and usually attributed to differences in the surface area, improved conductivity, or uncertain synergistic effects. Herein, a sulfur‐doped Fe/N/C catalyst (denoted as Fe/SNC) was obtained by a template‐sacrificing method. The incorporated sulfur gives a thiophene‐like structure (C−S−C), reduces the electron localization around the Fe centers, improves the interaction with oxygenated species, and therefore facilitates the complete 4 e⁻ ORR in acidic solution. Owing to these synergistic effects, the Fe/SNC catalyst exhibits much better ORR activity than the sulfur‐free variant (Fe/NC) in 0.5 m H₂SO₄.     

Fluorine‐Doped Porous Single‐Crystal Rutile TiO2 Nanorods for Enhancing Photoelectrochemical Water Splitting

Fluorine‐doped hierarchical porous single‐crystal rutile TiO₂ nanorods have been synthesized through a silica template method, in which F^? ions acts as both n‐type dopants and capping agents to make the isotropic growth of the nanorods. The combination of high crystallinity, abundant surface reactive sites, large porosity, and improved electronic conductivity leads to an excellent photoelectrochemical activity. The photoanode made of F‐doped porous single crystals displays a remarkably enhanced solar‐to‐hydrogen conversion efficiency (≈0.35 % at ?0.33 V vs. Ag/AgCl) under 100 mW cm^?2 of AM=1.5 solar simulator illumination that is ten times of the pristine solid TiO₂ single crystals.