Hydrogen trititanate (H 2Ti 3O 7) nanofibers were prepared by a hydrothermal method in 10 M NaOH at 403 K, followed by acidic rinsing and drying at 383 K. Calcining H 2Ti 3O 7 nanofibers at 573 K led to the formation of TiO 2 (B) nanofibers. Calcination at 673 K improved the crystallinity of the TiO 2 (B) nanofibers and did not cause any change in the morphology and dimensions of the nanofibers. TiO 2 (B) and H 2Ti 3O 7 nanofibers are 10-20 nm in diameter and several micrometers long, but FE-SEM reveals that several of these nanofibers tend to bind tightly to each other, forming a fiber bundle. Calcination at 773 K transformed TiO 2 (B) nanofibers into a TiO 2 (B)/anatase bicrystalline mixture with their fibrous morphology remaining intact. Upon increasing the calcination temperature to 873 K, most of the TiO 2 (B) nanofibers were converted into anatase nanofibers and small anatase particles with smoother surfaces. In the photocatalytic dehydrogenation of neat ethanol, 1% Pt/TiO 2 (B) nanofiber calcined at 673 K was the most active catalyst and generated about the same amount of H 2 as did 1% Pt/P-25. TPR indicated that the calcination of 1% Pt/TiO 2 (B) nanofiber at 573 K produced a poor Pt dispersion and poor activity. Calcination at a temperature higher than 773 K (in ambient air) resulted in an SMSI effect similar to that observed over TiO 2 in the reductive atmosphere. As suggested by XPS, such an SMSI effect decreased the surface concentration of Pt metal and created Pt (delta) sites, preventing Pt particles from functioning as a Schottky barrier and leading to a lower activity. Because of the synergetic effect between TiO 2 (B) and anatase phases, the bicrystalline mixture, produced by calcining at 773 K, was able to counter negative effects such as the reduction in surface area and the SMSI effect and maintained its photocatalytic activity.

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Pt nanoparticles of diameter 0.5-1.5 nm were dispersed homogeneously on the inner and outer surfaces of alkali metal titanate nanotubes (M 2 Ti 3 O 7 , M ) Li + , Na + , and K + ) by ion exchange with Pt(NH 3 ) 2 Cl 2 followed by calcination in ambient air at 673 K and reduction in H 2 at 448 K. Both XPS and DRIFTS revealed that these titanate nanotubes donated their electrons to the Pt particles, yielding a negative Pt oxidation state, and that the degree of electron donation increased with the size of the alkali metal cation. The high electron density of the Pt particles promoted the activation of both CdC and CdO functional groups in cinnamaldehyde. Therefore, the order of the catalytic activity in the hydrogenation of cinnamaldehyde was Pt/KTNTs > Pt/ NaTNTs > Pt/LiTNTs. Since the Pt particles were very small, Pt/MTNTs selectively hydrogenated the CdC bond, yielding a hydrocinnamaldehyde with selectivities of 80-87% (at cinnamaldehyde conversions of 27-50%). The alkali metal ions of the titanate nanotubes were able to modify the mode of adsorption of cinnamaldehyde. Therefore, when a KOH promoter was added to the reaction mixture, cinnamyl alcohol became the main product and the cinnamyl alcohol selectivities were 77-83% (at cinnamaldehyde conversions of 49-74%).

Adsorption of L-DOPA and a series of other amino acids and related compounds from aqueous solutions at well-defined Pt(lll) and Pt(100) single-crystal surfaces has been studied: 3-(3,4-dihydroxyphenyl)-Lalanine (DOPA), L-tyrosine (TYR), L-cysteine (CYS), L-phenylalanine (PHE), L-alanine (ALA), dopamine (DA), catechol (CT), and (3,4-dihydroxyphenyl)acetic acid (DOPAC). Packing densities (moles adsorbed per unit area) were measured for each compound by means of quantitative Auger spectroscopy; two independent Auger spectroscopic methods were employed: one based upon measurement of elemental Auger signals from the adsorbed layer and the other upon measurement of the attenuation of the Pt Auger signal by the adsorbed layer. Packing densities of DOPA, TYR, DA, CT, and DOPAC indicate adsorption with the aromatic ring attached parallel to the surface. In contrast, CYS is adsorbed through the sulfur atom, while ALA and PHE are attached to the surface through their amino acid moieties. Vibrational spectra of the adsorbed layer formed from each of these compounds were obtained by means of electron energy-loss spectroscopy (EELS) and were compared with the infrared spectra of the parent compounds in KBr. The EELS (adsorbed layer) and IR (solid compound) spectra are similar except that the hydroxyl hydrogens of DOPA, TYR, DA, CT, and DOPAC as well as the carboxyl hydrogens of PHE and DOPAC are removed as a result of the adsorption process. EELS bands of polar groups such as O-H are not broadened to the same extent as in the IR spectra of the solid compounds, evidently due to less intermolecular bonding among such groups at the surface. LEED experiments indicate that CT forms a (3X3) adlattice at Pt(lll), while each of the other compounds forms an oriented but otherwise structurally disordered layer at Pt(lll) and Pt(100). The packing density of DOPA, CYS, and DOPAC is higher at Pt(100) than at Pt(lll) due to differences in molecular orientation. Single-crystal surface structure, adsorbate orientation, and mode of surface bonding exert a profound influence on the product distribution of electrocatalytic oxidation of these well-characterized adsorbed organic intermediates, on the basis of cyclic voltammetry and potential-step chronocoulometry experiments. This study has also revealed that evacuation does not alter the composition or electrochemical properties of the chemisorbed layer formed from solution.

Sodium titanate nanotubes (NaTNTs) are converted into monoclinic TiO 2 (B) nanotubes by rinsing with 0.10 M HCl followed by drying at 573 K. As calcination temperature is increased to 673 K, these TiO 2 (B) nanotubes start to transform into anatase nanoparticles producing a bi-crystalline mixture consisting of TiO 2 (B) nanotubes and anatase nanoparticles. The primary particle size of the anatase particles was estimated to be around 10 nm using Scherrer equation. After being promoted with 1% Pt, this bi-crystalline material becomes a very active photocatalyst producing 20% more H 2 gas than 1% Pt/Degussa P-25 TiO 2 in the photocatalytic dehydrogenation of neat ethanol after 2 h of UV light irradiation.

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Treatment of 2,4-dien-1-als with allylsilanes and PPh(3)AuSbF(6) (3 mol %) led to formation of 1,4-bis(allyl)cyclopentenyl products; this gold catalyst is superior to commonly used Lewis acids according to catalyst screening. Such gold-catalyzed deoxygenative cyclizations are compatible with various oxygen-, amine-, sulfur-, hydrogen-, and carbon-based nucleophiles. The value of this new catalysis is demonstrated by the diverse annulations of 2,4-dien-1-als with electron-rich alkenes and arenes, providing an easy access to complicated cyclopentenyl frameworks. Structural analysis of annulation products reveals evidence for the participation of Nazarov cyclization. This deoxygenative cyclization is extensible to a tandem intramolecular cyclization/nucleophilic addition cascade, giving polycyclic carbo- or oxacyclic compounds with controlled stereochemistry. This new gold catalysis is applied to a short synthesis of natural compounds of the brazilane family, including brazilane, O-trimethyl-, and O-tetramethyl brazilane.

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