Remotely Bonded Bridging Dioxygen Ligands Enhance Hydrogen Transfer in a Silica-Supported Tetrairidium Cluster Catalyst.

A longstanding challenge in catalysis by noble metals has been to understand the origin of enhancements of rates of hydrogen transfer that result from the bonding of oxygen near metal sites. We investigated structurally well-defined catalysts consisting of supported tetrairidium carbonyl clusters with single-atom (apical iridium) catalytic sites for ethylene hydrogenation. Reaction of the clusters with ethylene and H followed by O led to the onset of catalytic activity as a terminal CO ligand at each apical Ir atom was removed and bridging dioxygen ligands replaced CO ligands at neighboring (basal-plane) sites.

Neural network assisted analysis of bimetallic nanocatalysts using X-ray absorption near edge structure spectroscopy.

X-ray absorption spectroscopy is a common method for probing the local structure of nanocatalysts. One portion of the X-ray absorption spectrum, the X-ray absorption near edge structure (XANES) is a useful alternative to the commonly used extended X-ray absorption fine structure (EXAFS) for probing three-dimensional geometry around each type of atomic species, especially in those cases when the EXAFS data quality is limited by harsh reaction conditions and low metal loading. A methodology for quantitative determination of bimetallic architectures from their XANES spectra is currently lacking.

Enhancing catalytic performance of dilute metal alloy nanomaterials.

Dilute alloys are promising materials for sustainable chemical production; however, their composition and structure affect their performance. Herein, a comprehensive study of the effects of pretreatment conditions on the materials properties of PdAu nanoparticles partially embedded in porous silica is related to the activity for catalytic hydrogenation of 1-hexyne to 1-hexene. A combination of in situ characterization and theoretical calculations provide evidence that changes in palladium surface content are induced by treatment in oxygen, hydrogen and carbon monoxide at various temperatures.

Author Correction: Silica accelerates the selective hydrogenation of CO to methanol on cobalt catalysts.

An amendment to this paper has been published and can be accessed via a link at the top of the paper.

Docking of tetra-methyl zirconium to the surface of silica: a well-defined pre-catalyst for conversion of CO to cyclic carbonates.

The metal complex (Zr(CH3)4(THF)2) has been fully synthesized, characterized and grafted onto partially dehydroxylated silica to give two surface species [([triple bond, length as m-dash]Si-O-)Zr(CH3)3(THF)2] (minor) and [([triple bond, length as m-dash]Si-O-)2Zr(CH3)2(THF)2] (major) which have been characterized by SS NMR, IR, and elemental analysis. These supported pre-catalysts exhibit the best conversion of CO2 to cyclic carbonates, as compared to the previously reported SOMC catalysts.

Silica accelerates the selective hydrogenation of CO to methanol on cobalt catalysts.

The reaction pathways on supported catalysts can be tuned by optimizing the catalyst structures, which helps the development of efficient catalysts. Such design is particularly desired for CO hydrogenation, which is characterized by complex pathways and multiple products. Here, we report an investigation of supported cobalt, which is known for its hydrocarbon production and ability to turn into a selective catalyst for methanol synthesis in CO hydrogenation which exhibits good activity and stability.

Product Selectivity Controlled by Nanoporous Environments in Zeolite Crystals Enveloping Rhodium Nanoparticle Catalysts for CO Hydrogenation.

Supported rhodium nanoparticles (NPs) are well-known for catalyzing methanation in CO hydrogenation. Now we demonstrate that the selectivity in this process can be optimized for CO production by choice of molecular sieve crystals as supports. The NPs are enveloped within the crystals with controlled nanopore environments that allow tuning of the catalytic selectivity to minimize methanation and favor the reverse water-gas shift reaction.

Controlling catalytic activity and selectivity for partial hydrogenation by tuning the environment around active sites in iridium complexes bonded to supports.

Single-site Ir(CO) complexes bonded to high-surface-area metal oxide supports, SiO, TiO, FeO, CeO, MgO, and LaO, were synthesized by chemisorption of Ir(CO)(acac) (acac = acetylacetonate) followed by coating with each of the following ionic liquids (ILs): 1--butyl-3-methylimidazolium tetrafluoroborate, [BMIM][BF], 1--butyl-3-methylimidazolium acetate, [BMIM][Ac], and 1-(3-cyanopropyl)-3-methylimidazolium dicyanamide, [CPMIM][DCA]. Extended X-ray absorption fine structure spectroscopy showed that site-isolated iridium was bonded to oxygen atoms of the support. Electron densities on the iridium enveloped by each IL sheath/support combination were characterized by carbonyl infrared spectroscopy of the iridium -dicarbonyls and by X-ray absorption near-edge structure data.

Bulky Calixarene Ligands Stabilize Supported Iridium Pair-Site Catalysts.

Although essentially molecular noble metal species provide active sites and highly tunable platforms for the design of supported catalysts, the susceptibility of the metals to reduction and aggregation and the consequent loss of catalytic activity and selectivity limit opportunities for their application. Here, we demonstrate a new construct to stabilize supported molecular noble-metal catalysts, taking advantage of sterically bulky ligands on the metal that serve as surrogate supports and isolate the active sites under conditions involving steady-state catalytic turnover in a reducing environment. The result is demonstrated with an iridium pair-site catalyst incorporating P-bridging calix[4]arene ligands dispersed on siliceous supports, chosen as prototypes because they offer weakly interacting surfaces on which metal aggregation is prone to occur.

Supported cluster catalysts synthesized to be small, simple, selective, and stable.

Molecular metal complexes on supports have drawn wide attention as catalysts offering new properties and opportunities for precise synthesis to make uniform catalytic species that can be understood in depth. Here we highlight advances in research with catalysts that are a step more complex than those incorporating single, isolated metal atoms on supports. These more complex catalysts consist of supported noble metal clusters and supported metal oxide clusters, and our emphasis is placed on some of the simplest and best-defined of these catalysts, made by precise synthesis, usually with organometallic precursors.

Single-site catalyst promoters accelerate metal-catalyzed nitroarene hydrogenation.

Atomically dispersed supported metal catalysts are drawing wide attention because of the opportunities they offer for new catalytic properties combined with efficient use of the metals. We extend this class of materials to catalysts that incorporate atomically dispersed metal atoms as promoters. The catalysts are used for the challenging nitroarene hydrogenation and found to have both high activity and selectivity.

Modulating the nanorods protrusion from poly(allylamine hydrochloride)-g-pyrene microcapsules by 1-pyrenesulfonic acid sodium salt.

It was found previously that the Schiff base bonds in poly(allylamine hydrochloride)-g-pyrene (PAH-Py) microcapsules (MCs) are hydrolyzed at pH 2 within 1 h, leading to disassembly of the MCs and protrusion of pyrene aldehyde (Py) nanorods (NRs) on the capsule surface. Herein, we found a new way to modulate the protrusion of NRs by addition of 1-pyrenesulfonic acid sodium salt (PySO3Na). Along with the increase in PySO3Na to Py molar ratio in the MCs solution, the protrusion of NRs was progressively blocked and even inhibited at a ratio of 2.

A pyridinyl-functionalized tetraphenylethylene fluorogen for specific sensing of trivalent cations.

A pyridinyl-functionalized tetraphenylethene (Py-TPE) was synthesized and it demonstrated colorimetric and ratiometric fluorescent responses to trivalent metal cations (M(3+), M = Cr, Fe, Al) over a variety of mono- and divalent metal cations.

Decomposition-assembly of tetraphenylethylene nanoparticles with uniform size and aggregation-induced emission property.

Tetraphenylethylene (TPE)-substituted poly(allylamine hydrochloride) (PAH-g-TPE) is synthesized by a Schiff base reaction between PAH and TPE-CHO. The PAH-g-TPE forms micelles in water at pH 6, which are further transformed into pure TPE-CHO nanoparticles (NPs) with a diameter of ≈300 nm after incubation in a solution of low pH value. In contrast, only amorphous precipitates are obtained when TPE-CHO methanol solution is incubated in water.