The interaction of size-selected Ru3 clusters with TiO2: depth-profiling of encapsulated clusters.

Ru is a metal of interest in catalysis. Monodisperse Ru3 clusters as catalytic sites are relevant for the development of catalysts because clusters use significantly lower amounts of precious materials for forming active sites due to the small size of the cluster. However, retaining the mono-dispersity of the cluster size after deposition is a challenge because surface energy could drive both agglomeration and encapsulation of the clusters. In the present work Ru3 clusters are deposited by chemical vapor deposition (CVD) of Ru3(CO)12 and cluster source depositions of bare Ru3 onto radio frequency sputter-deposited TiO2 (RF-TiO2) substrates, TiO2(100), and SiO2. When supported on RF-TiO2, bare Ru3 is encapsulated by a layer of titania substrate material during deposition with a cluster source. Ligated Ru3(CO)12 is also encapsulated by a layer of titania when deposited onto sputter-treated RF-TiO2, but only through heat treatment which is required to remove most of the ligands. The titania overlayer thickness was determined to be 1-2 monolayers for Ru3(CO)12 clusters on RF-TiO2, which is thin enough for catalytic or photocatalytic reactions to potentially occur even without clusters being part of the very outermost layer. The implication for catalysis of the encapsulation of Ru3 into the RF-TiO2 is discussed. Temperature-dependent X-ray photoelectron spectroscopy (XPS), angle-resolved XPS, and temperature-dependent low energy ion scattering (TD-LEIS) are used to probe how the cluster-surface interaction changes due to heat treatment and scanning transmission electron microscopy (STEM) was used to image the depth of the surface from side-on.

Carbon Nitride Loaded with an Ultrafine, Monodisperse, Metallic Platinum-Cluster Cocatalyst for the Photocatalytic Hydrogen-Evolution Reaction.

For the realization of a next-generation energy society, further improvement in the activity of water-splitting photocatalysts is essential. Platinum (Pt) is predicted to be the most effective cocatalyst for hydrogen evolution from water. However, when the number of active sites is increased by decreasing the particle size, the Pt cocatalyst is easily oxidized and thereby loses its activity. In this study, a method to load ultrafine, monodisperse, metallic Pt nanoclusters (NCs) on graphitic carbon nitride is developed, which is a promising visible-light-driven photocatalyst. In this photocatalyst, a part of the surface of the Pt NCs is protected by sulfur atoms, preventing oxidation. Consequently, the hydrogen-evolution activity per loading weight of Pt cocatalyst is significantly improved, 53 times, compared with that of a Pt-cocatalyst loaded photocatalyst by the conventional method. The developed method is also effective to enhance the overall water-splitting activity of other advanced photocatalysts such as SrTiO3 and BaLa4 Ti4 O15 .

Creation of High-Performance Heterogeneous Photocatalysts by Controlling Ligand Desorption and Particle Size of Gold Nanocluster.

Recently, the creation of new heterogeneous catalysts using the unique electronic/geometric structures of small metal nanoclusters (NCs) has received considerable attention. However, to achieve this, it is extremely important to establish methods to remove the ligands from ligand-protected metal NCs while preventing the aggregation of metal NCs. In this study, the ligand-desorption process during calcination was followed for metal-oxide-supported 2-phenylethanethiolate-protected gold (Au) 25-atom metal NCs using five experimental techniques. The results clearly demonstrate that the ligand-desorption process consists of ligand dissociation on the surface of the metal NCs, adsorption of the generated compounds on the support and desorption of the compounds from the support, and the temperatures at which these processes occurred were elucidated. Based on the obtained knowledge, we established a method to form a metal-oxide layer on the surface of Au NCs while preventing their aggregation, thereby succeeding in creating a water-splitting photocatalyst with high activity and stability.

Reduction and Diffusion of Cr-Oxide Layers into P25, BaLa4Ti4O15, and Al:SrTiO3 Particles upon High-Temperature Annealing.

Chromium oxide (Cr2O3) is a beneficial metal oxide used to prevent the backward reaction in photocatalytic water splitting. The present work investigates the stability, oxidation state, and the bulk and surface electronic structure of Cr-oxide photodeposited onto P25, BaLa4Ti4O15, and Al:SrTiO3 particles as a function of the annealing process. The oxidation state of the Cr-oxide layer as deposited is found to be Cr2O3 on the surface of P25 and Al:SrTiO3 particles and Cr(OH)3 on BaLa4Ti4O15. After annealing at 600 °C, for P25 (a mixture of rutile and anatase TiO2), the Cr2O3 layer diffuses into the anatase phase but remains at the surface of the rutile phase. For BaLa4Ti4O15, Cr(OH)3 converts to Cr2O3 upon annealing and diffuses slightly into the particles. However, for Al:SrTiO3, the Cr2O3 remains stable at the surface of the particles. The diffusion here is due to the strong metal-support interaction effect. In addition, some of the Cr2O3 on the P25, BaLa4Ti4O15, and Al:SrTiO3 particles is reduced to metallic Cr after annealing. The effect of Cr2O3 formation and diffusion into the bulk on the surface and bulk band gaps is investigated with electronic spectroscopy, electron diffraction, DRS, and high-resolution imaging. The implications of the stability and diffusion of Cr2O3 for photocatalytic water splitting are discussed.

Pt17 nanocluster electrocatalysts: preparation and origin of high oxygen reduction reaction activity.

We recently found that [Pt17(CO)12(PPh3)8]z (Pt = platinum; CO = carbon monoxide; PPh3 = triphenylphosphine; z = 1+ or 2+) is a Pt nanocluster (Pt NC) that can be synthesized with atomic precision in air. The present study demonstrates that it is possible to prepare a Pt17-supported carbon black (CB) catalyst (Pt17/CB) with 2.1 times higher oxygen reduction reaction (ORR) activity than commercial Pt nanoparticles/CB by the adsorption of [Pt17(CO)12(PPh3)8]z onto CB and subsequent calcination of the catalyst. Density functional theory calculation strongly suggests that the high ORR activity of Pt17/CB originates from the surface Pt atoms that have an electronic structure appropriate for the progress of ORR. These results are expected to provide design guidelines for the fabrication of highly active ORR catalysts using Pt NCs with a diameter of about 1 nm and thereby enabling the use of reduced amounts of Pt in polymer electrolyte fuel cells.

Simple and high-yield preparation of carbon-black-supported ∼1 nm platinum nanoclusters and their oxygen reduction reactivity.

The improvement of oxygen reduction reaction (ORR) catalysts is essential before polymer electrolyte fuel cells can be used widely. To this end, we established a simple method for the size-selective synthesis of a series of ligand-protected platinum nanoclusters with ∼1 nm particle size (Ptn NCs; n = ∼35, ∼51, and ∼66) and narrow size distribution (±âˆ¼4 Pt atoms) under atmospheric conditions. Using this method, each ligand-protected ∼1 nm Pt NC was obtained in a relatively high yield (nearly 80% for Pt∼66). We succeeded in adsorbing each ligand-protected ∼1 nm Pt NC on carbon black (CB) and then removing most of the ligands from the surface of the Pt NCs via calcination while maintaining the original size. The obtained Pt∼35/CB, Pt∼51/CB, and Pt∼66/CB exhibited ORR mass activities that were 1.6, 2.1, and 1.6 times higher, respectively, than that of commercial CB supported-Pt nanoparticles, and also display high durability.

Synthesis of twist-twist pi-conjugated di-sec-alkylstilbenes and stilbene polymers.

Twist-twist pi-conjugated (TTPC) pi systems promise unique properties with their 90 degrees twist angles. Di-sec-alkyl substituted stilbenes, 5, were prepared by low-valent titanium coupling of phenyl ketones, 4. Long alkyl chains stopped the coupling reaction. Stilbenes 5 were shown to be approximately 90% TTPC. Inserting TTPC units into poly(p-phenylene) polymers created highly fluorescent, soluble, TTPC pi systems with weak electronic segmentation for organic light emitting diode (OLED) studies.