Copper nanoparticles supported on doped graphenes as catalyst for the dehydrogenative coupling of silanes and alcohols

Single-Walled Cluster Nanotubes for Single-Atom Catalysts with Precise Structures

Spatially confining isolated atomic sites in low-dimensional nanostructures is a promising strategy for preparing high-performance single-atom catalysts (SACs). Herein, fascinating polyoxometalate cluster-based single-walled nanotubes (POM-SWNTs) with atomically precise structures, uniform diameter, and single-cluster wall thickness are constructed by lacunary POM clusters (PW11 and P2W17 clusters). Isolated metal centers are accurately incorporated into the PW11-SWNTs and P2W17-SWNTs supports. The structures of the resulting MPW11-SWNTs and MP2W17-SWNTs are well established (M = Cu, Pt). Molecular dynamics simulations demonstrate the stability of POM-SWNTs. Furthermore, the turnover frequency of PtP2W17-SWNTs is 20 times higher than that of PtP2W17 cluster units and 140 times higher than that of Pt nanoparticles in the alcoholysis of dimethylphenylsilane. Theoretical studies indicate that incorporating a Pt atom into the P2W17 support induces straightforward electron transfer between them, combining the nanoconfined environment to enhance the catalytic activity of PtP2W17-SWNTs. This work shows the feasibility of using subnanometric POM clusters to assemble single-walled cluster nanotubes, highlighting their potential to prepare superior SACs with precise structures.

Carbon supported "core-shell structure" of Fe nanoparticles for enhanced Fenton reaction activity and magnetic separation

Effectively facilitating Fe³⁺/Fe²⁺ cycles and expanding its operating pH range are keys to optimizing the traditional Fenton reaction. In this exploration, we used chitosan and ferrous sulfate as precursors to prepare a multicomponent magnetic Fe/C Fenton-like catalyst, which exhibited extraordinary catalytic properties and excellent stability performance in a pH range of 4~8. Besides, it could be easily separated from the solution by a magnet. The characterization showed that the supported Fe species include troilite-2H (FeS), lepidocrocite (FeOOH), and pyrrhotite-6T (Fe_{1 - x}S) with a unique "core-shell structure." The presence of reductive iron sulfide core in the system can accelerate the reduction of Fe(III). Meanwhile, the graphite-like structure formed after calcination can adsorb and enrich priority pollutants near the active site through π-π coupling and strengthen electron transfer, which endows its high catalytic performance and enables it invulnerable to dissolved organic compounds.

Cyclic metal(oid) clusters control platinum-catalysed hydrosilylation reactions: from soluble to zeolite and MOF catalysts

The Pt-catalysed addition of silanes to functional groups such as alkenes, alkynes, carbonyls and alcohols, i.e. the hydrosilylation reaction, is a fundamental transformation in industrial and academic chemistry, often claimed as the most important application of Pt catalysts in solution. However, the exact nature of the Pt active species and its mechanism of action is not well understood yet, particularly regarding regioselectivity. Here, experimental and computational studies together with an ad hoc graphical method show that the hydroaddition of alkynes proceeds through Pt-Si-H clusters of 3-5 atoms (metal(oid) association) in parts per million amounts (ppm), which decrease the energy of the transition state and direct the regioselectivity of the reaction. Based on these findings, new extremely-active (ppm) microporous solid catalysts for the hydrosilylation of alkynes, alkenes and alcohols have been developed, paving the way for more environmentally-benign industrial applications.

σ-H-H, σ-C-H, and σ-Si-H Bond Activation Catalyzed by Metal Nanoparticles

Activation of H-H, Si-H, and C-H bonds through σ-bond coordination has grown in the past 30 years from a scientific curiosity to an important tool in the functionalization of hydrocarbons. Several mechanisms were discovered via which the initially σ-bonded substrate could be converted: oxidative addition, heterolytic cleavage, σ-bond metathesis, electrophilic attack, etc. The use of metal nanoparticles (NPs) in this area is a more recent development, but obviously nanoparticles offer a much richer basis than classical homogeneous and heterogeneous catalysts for tuning reactivity for such a demanding process as C-H functionalization. Here, we will review the surface chemistry of nanoparticles and catalytic reactions occurring in the liquid phase, catalyzed by either colloidal or supported metal NPs. We consider nanoparticles prepared in solution, which are stabilized and tuned by polymers, ligands, and supports. The question we have addressed concerns the differences and similarities between molecular complexes and metal NPs in their reactivity toward σ-bond activation and functionalization.

Active catalyst construction for CO2 recycling via catalytic synthesis of N-doped carbon on supported Cu

Bridging homogeneous and heterogeneous catalysis is a long-term pursuit in the field of catalysis. Herein, we report our results in integration of nano- and molecular catalysis via catalytic synthesis of nitrogen doped carbon layers on AlOx supported nano-Cu which can finely tune the catalytic performance of the supported copper catalyst. This synthetic catalytic material, which can be generated in situ by the reaction of CuAlOx and 1,10-Phen in the presence of hydrogen, could be used for controllable synthesis of N,N-dimethylformamide (DMF) from dimethylamine and CO₂/H₂ via blocking reaction pathways of further catalytic hydrogenation of DMF to N(CH₃)₃. Detailed characterizations and DFT calculations reveal that the presence of N-doped layered carbon on the surface of the nano-Cu particles results in higher activation energy barriers during the conversion of DMF to N(CH₃)₃. Our primary results could promote merging of homogeneous catalysis and heterogeneous catalysis and CO₂ recycling.

Bridging homogeneous and heterogeneous catalysis is a long-term pursuit in the field of catalysis. Here, the authors present results on integration of nano- and molecular catalysis via catalytic synthesis of nitrogen doped carbon layers on AlO_x supported nano-Cu which can finely tune the catalytic performance of the supported copper catalyst.

Creation of Controllable High-Density Defects in Silver Nanowires for Enhanced Catalytic Property

Structural defects have been proven to determine many of the materials' properties. Here, we demonstrate a unique approach to the creation of Ag nanowires with high-density defects through controllable nanoparticles coalescence in one-dimensional pores of mesoporous silica. The density of defects can be easily adjusted by tuning the annealing temperature during synthetic process. The high-density defects promote the adsorption and activation of more reactants on the surface of Ag nanowires during catalytic reactions. As a result, the as-prepared Ag nanowires exhibit enhanced activities in catalyzing dehydrogenative coupling reaction of silane in terms of apparent activation energy and turnover frequency (TOF). We show further that the silane conversion rate can be enhanced by maximizing the defect density and thus the number of active sites on the Ag nanowires, reaching a remarkable TOF of 8288 h(-1), which represents the highest TOF that has been achieved by far on Ag catalysts. This work not only proves the important role of structural defects in catalysis but also provides a new and general strategy for constructing high-density defects in metal catalysts.

Electroresponsive Supramolecular Graphene Oxide Hydrogels for Active Bacteria Adsorption and Removal

Bacteria contamination in drinking water and medical products can cause severe health problems. However, currently available sterilization methods, mainly based on the size-exclusion mechanism, are typically slow and require the entire contaminated water to pass through the filter. Here, we present an electroresponsive hydrogel based approach for bacteria adsorption and removal. We successfully engineered a series of graphene oxide hydrogels using redox-active ruthenium complexes as noncovalent cross-linkers. The resulting hydrogels can reversibly switch their physical properties in response to the applied electric field along with the changes of oxidation states of the ruthenium ions. The hydrogels display strong bacteria adsorbing capability. A hydrogel of 1 cm(3) can adsorb a maximum of 1 × 10(8) E. coli. The adsorbed bacteria in the hydrogels can then be inactivated by a high voltage electric pulse and removed from the hydrogels subsequently. Owing to the high bacteria removal rate, reusability, and low production cost, these hydrogels represent promising candidates for the emergent sterilization of medical products or large-scale purification of drinking water.

High catalytic activity of oriented 2.0.0 copper(I) oxide grown on graphene film

Metal oxide nanoparticles supported on graphene exhibit high catalytic activity for oxidation, reduction and coupling reactions. Here we show that pyrolysis at 900 °C under inert atmosphere of copper(II) nitrate embedded in chitosan films affords 1.1.1 facet-oriented copper nanoplatelets supported on few-layered graphene. Oriented (1.1.1) copper nanoplatelets on graphene undergo spontaneous oxidation to render oriented (2.0.0) copper(I) oxide nanoplatelets on few-layered graphene. These films containing oriented copper(I) oxide exhibit as catalyst turnover numbers that can be three orders of magnitude higher for the Ullmann-type coupling, dehydrogenative coupling of dimethylphenylsilane with n-butanol and C–N cross-coupling than those of analogous unoriented graphene-supported copper(I) oxide nanoplatelets.

Supported metal nanoparticles have been widely used as heterogeneous catalysts. Here, the authors report the synthesis of (1.1.1) copper on few layer graphene which oxidize to orientated (2.0.0) copper(I) oxide nanoplatelets which display high catalytic activity for a number of organic coupling reactions.