The assumption that oxidative addition is the key step during the cross-coupling reaction of aryl halides has led to the development of a plethora of increasingly complex metal catalysts, thereby ...obviating in many cases the exact influence of the base, which is a simple, inexpensive, and necessary reagent for this paramount transformation. Here, a combined experimental and computational study shows that the oxidative addition is not the single kinetically relevant step in different cross-coupling reactions catalyzed by sub-nanometer Pt or Pd species, since the reactivity control is shifted toward subtle changes in the base. The exposed metal atoms in the cluster cooperate to enable an extremely easy oxidative addition of the aryl halide, even chlorides, and allow the base to bifurcate the coupling. With sub-nanometer Pd species, amines drive to the Heck reaction, carbonate drives to the Sonogahira reaction, and phosphate drives to the Suzuki reaction, while for Pt clusters and single atoms, good conversion is only achieved using acetate as a base. This base-controlled orthogonal reactivity with ligand-free catalysts opens new avenues in the design of cross-coupling reactions in organic synthesis.
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This work shows an easy and eco-friendly methodology to obtain almost pristine anatase phase of TiO2 by using furfural, a biomass-derived molecule, as a bio-template. The ...photocatalytic activity was studied following the degradation of methylene blue and phenol under artificial solar irradiation. Results were compared against those obtained on a commercial pristine anatase TiO2. The pseudo first-order, the second-order and the intraparticle diffusion kinetic models were verified. The textural and surface chemistry properties of the materials were correlated with the surface density of molecules adsorbed in equilibrium. The reaction-rate showed an almost perfect quadratic regression as a function of the surface density. Theoretical estimations of the density of states by DFT + U were performed showing that the total electron charge in the oxygen bonded to anatase TiO2 increased due to carbon doping in agreement with the prediction of appearance of atomic orbitals 2p from carbon atom in the hybrid material. C-doping is responsible of the red-shift from 3.14 to 2.94 eV observed for a Ti15O32C super-cell than pristine anatase Ti16O32. The increase in the activity of the C-doped TiO2 photocatalyst was due to the decrease in the energy band-gap promoting a higher absorption of photons from the visible light.
A lot of interesting and sophisticated examples of nanoparticle (NP) self-assembly (SA) are known. From both fundamental and technological standpoints, this field requires advancements in three ...principle directions: (a) understanding the mechanism and driving forces of three-dimensional (3D) SA with both nano- and microlevels of organization; (b) understanding disassembly/deconstruction processes; and (c) finding synthetic methods of assembly into continuous superstructures without insulating barriers. From this perspective, we investigated the formation of well-known star-like PbS superstructures and found a number of previously unknown or overlooked aspects that can advance the knowledge of NP self-assembly in these three directions. The primary one is that the formation of large seemingly monocrystalline PbS superstructures with multiple levels of octahedral symmetry can be explained only by SA of small octahedral NPs. We found five distinct periods in the formation PbS hyperbranched stars: (1) nucleation of early PbS NPs with an average diameter of 31 nm; (2) assembly into 100–500 nm octahedral mesocrystals; (3) assembly into 1000–2500 nm hyperbranched stars; (4) assembly and ionic recrystallization into six-arm rods accompanied by disappearance of fine nanoscale structure; (5) deconstruction into rods and cuboctahedral NPs. The switches in assembly patterns between the periods occur due to variable dominance of pattern-determining forces that include van der Waals and electrostatic (charge–charge, dipole–dipole, and polarization) interactions. The superstructure deconstruction is triggered by chemical changes in the deep eutectic solvent (DES) used as the media. PbS superstructures can be excellent models for fundamental studies of nanoscale organization and SA manufacturing of (opto)electronics and energy-harvesting devices which require organization of PbS components at multiple scales.
Stainless-steel honeycomb monoliths (square cell-shape/230 cpsi cylinders) were 3D-printed and used as support of a Ni/CeO2-ZrO2 powder deposited by washcoating. The resulting catalysts were ...characterized by XRF, SEM-EDX and H2-TPR, and tested in the dry reforming of methane reaction. In the 750–900 °C range, they showed competitive conversions (45–95%) and H2/CO ratio (0.84–0.94) compared to cordierite honeycombs with same catalyst loading and geometric characteristics, but did not require activation time thanks to better heat transfer. Both structured catalysts were stable in prolonged TOS experiments. The bare metallic monoliths exhibited significant activity at 900 °C due to their intrinsic nickel content.
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•Nickel catalyst onto 3D-printed stainless-steel honeycomb for methane dry reforming•3D-printed metal honeycomb overcomes cordierite for similar washcoat loading•Bare 3D-printed metal honeycomb is active at 900 °C due to its intrinsic Ni content•Surface roughness inherent in 3D-printing sums to the heat transfer assistance•Room for improvement via channel geometry control and adequate raw powder selection
Low atomicity clusters present properties dependent on the size, due to the quantum confinement, with well‐defined electronic structures and high stability. Here it is shown that Ag5 clusters ...catalyze the complete oxidation of sulfur to S+6. Ag5 catalytic activity increases with different oxidant species in the order O2 ≪ H2O2 < OH•. Selective oxidation of thiols on the cysteine residues of glutathione and thioredoxin is the primary mechanism human cells have to maintain redox homeostasis. Contingent upon oxidant concentration, Ag5 catalyzes the irreversible oxidation of glutathione and thioredoxin, triggering apoptosis. Modification of the intracellular environment to a more oxidized state to mimic conditions within cancer cells through the expression of an activated oncogene (HRASG12V) or through ARID1A mutation, sensitizes cells to Ag5 mediated apoptosis. While cancers evolve to evade treatments designed to target pathways or genetic mutations that drive them, they cannot evade a treatment that takes advantage of aberrant redox homeostasis, which is essential for tumor progression and metastasis. Ag5 has antitumor activity in mice with orthotopic lung tumors reducing primary tumor size, and the burden of affected lymphatic nodes. The findings suggest the unique intracellular redox chemistry of Ag5 may lead to new redox‐based approaches to cancer therapy.
Ag5 clusters show unique catalytic activities to oxidize thiols. They catalyze the complete oxidation of thiols present in cysteine, glutathione, and thioredoxin. This oxidation is tunable by relevant biological oxidants species (hydrogen peroxide and hydroxyl radical), allowing Ag5 to inhibit the thiol‐based antioxidants leading to the selective death of tumor proliferating cells.
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•SiO2-TiO2-C photocatalysts prepared by solvothermal treatment.•Rice husk as biogenic precursor of mesoporous photocatalysts.•SiO2-TiO2-C showed photocatalytic activity under solar ...light.•Si-based catalysts presented similar activity than commercial TiO2.•The mechanism of RhB degradation depends on the surface pH of the photocatalyst.
Carbon-containing SiO2-based photocatalysts were prepared by the solvothermal treatment of rice husk as biogenic precursor in the presence and absence of TiO2 and used for the photocatalytic degradation of rhodamine-B under simulated solar light. Data showed that the prepared catalysts are mainly composed of biogenic silica and displayed mesoporous character with surface areas ranging from 65 to 174 m2 g-1. The obtained materials showed photocatalytic activity comparable to that of commercial TiO2-P25 powders for the degradation of rhodamine-B under sunlight. The calcination at 350 °C improved the photocatalytic activity of the biogenic precursor by three times in the absence of TiO2. At converse, calcination of sample SiO2-TiO2 decreased the photoactivity due to the appearance of non-photoactive TiSiO4 crystalline phases in the catalyst, as inferred by XRD and XPS. A reaction mechanism for rhodamine-B degradation excluding the deethylation pathway has been proposed, based on the evolution of the absorbance spectra of rhodamine-B upon the photocatalytic tests.
Nature uses enzymes to dissociate and transfer H2 by combining Fe2+ and H+ acceptor/donor catalytic active sites. Following a biomimetic approach, it is reported here that very small planar Fe2,3+ ...oxide nanoparticles (2.0 ± 0.5 nm) supported on slightly acidic inorganic oxides (nanocrystalline TiO2, ZrO2, ZnO) act as bifunctional catalysts to dissociate and transfer H2 to alkynes chemo- and stereoselectively. This catalyst is synthesized by oxidative dispersion of Fe0 nanoparticles at the isoelectronic point of the support. The resulting Fe2+,3+ solid catalyzes not only, in batch, the semihydrogenation of different alkynes with good yields but also the removal of acetylene from ethylene streams with >99.9% conversion and selectivity. These efficient and robust non-noble-metal catalysts, alternative to existing industrial technologies based on Pd, constitute a step forward toward the design of fully sustainable and nontoxic selective hydrogenation solid catalysts.
This work shows an easy and eco-friendly methodology to obtain almost pristine anatase phase of TiO
by using furfural, a biomass-derived molecule, as a bio-template. The photocatalytic activity was ...studied following the degradation of methylene blue and phenol under artificial solar irradiation. Results were compared against those obtained on a commercial pristine anatase TiO
. The pseudo first-order, the second-order and the intraparticle diffusion kinetic models were verified. The textural and surface chemistry properties of the materials were correlated with the surface density of molecules adsorbed in equilibrium. The reaction-rate showed an almost perfect quadratic regression as a function of the surface density. Theoretical estimations of the density of states by DFT + U were performed showing that the total electron charge in the oxygen bonded to anatase TiO
increased due to carbon doping in agreement with the prediction of appearance of atomic orbitals 2p from carbon atom in the hybrid material. C-doping is responsible of the red-shift from 3.14 to 2.94 eV observed for a Ti
O
C super-cell than pristine anatase Ti
O
The increase in the activity of the C-doped TiO
photocatalyst was due to the decrease in the energy band-gap promoting a higher absorption of photons from the visible light.
Nanocrystalline C-doped TiO2 hybrid hollow spheres were prepared by solvothermal synthesis by controlling calcinations of mixtures of furfural, chitosan or saccharose with titanium isopropoxide. The ...origin of the carbon influences the texture, the crystalline framework, and the optical and photoelectrochemistry properties of the TiO2. The results indicate that the carbon–TiO2 hybrid hollow spheres may be used as TiO2-based film electrodes for use in solar cells.
The gram‐scale synthesis, stabilization, and characterization of well‐defined ultrasmall subnanometric catalytic clusters on solids is a challenge. The chemical synthesis and X‐ray snapshots of Pt02 ...clusters, homogenously distributed and densely packaged within the channels of a metal–organic framework, is presented. This hybrid material catalyzes efficiently, and even more importantly from an economic and environmental viewpoint, at low temperature (25 to 140 °C), energetically costly industrial reactions in the gas phase such as HCN production, CO2 methanation, and alkene hydrogenations. These results open the way for the design of precisely defined catalytically active ultrasmall metal clusters in solids for technically easier, cheaper, and dramatically less‐dangerous industrial reactions.
The multigram synthesis of Pt02 clusters within a metal–organic framework (MOF) is presented. The high stability and crystallinity of the selected MOF offers an unprecedented characterization of such ultrasmall entities. This hybrid material catalyzes important industrial reactions efficiently and at low temperature, such as HCN production, CO2 methanation, and alkene hydrogenations.
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