Reference LPI-ARTICLE-1999-017View record in Web of Science Record created on 2006-02-21, modified on 2017-05-12

/pdf/metal-oxide-surfaces-and-their-interactions-with-aqueous-22jt31pax0.pdf

Metal Oxide Surfaces and Their Interactions with Aqueous Solutions and Microbial Organisms.

The surfaces of hydrophilic (P25) and hydrophobic (T805) TiO2 particles were characterized by X-ray photoelectron spectroscopy (XPS) and Fourier transform infrared spectroscopy (FTIR) to gain a better understanding of the adsorption mechanism of OLOA 370 (polybutene-succinimide pentamine) on TiO2 particles dispersed in styrene monomer prior to miniemulsion encapsulation polymerizations. XPS analysis revealed that both the P25 and T805 TiO2 particles had significant amounts of hydroxyl groups on their surfaces. The XPS results showed that the surface hydroxyl concentration on the hydrophilic (P25) particles was 3.3 OH/nm2, whereas the trimethoxy octyl silane (TMOS)-surface-modified hydrophobic (T805) particles unexpectedly contained 6.6 OH/nm2. This apparent increase in the hydroxyls was attributed to hydrolysis of −OCH3 on the TMOS. The majority of these groups, however, were apparently either not acidic or not accessible to the OLOA 370 in adsorption studies, where the concentration of reactive hydroxyls...

XPS and FTIR Surface Characterization of TiO2 Particles Used in Polymer Encapsulation

Hydrogen Spillover. Facts and Fiction

Infrared spectroscopic identification of species arising from reactive adsorption of carbon oxides on metal oxide surfaces

A visible-light (vis)-active titanium oxide photocatalyst was prepared by a simple wet process: the calcination of the hydrolysis product of Ti(SO 4 ) 2 with ammonia using an ordinary electric furnace in dry air at 400 °C. The color of this photocatalyst was vivid yellow and absorbed light in the blue (400 nm) to bluish-green (550 nm) region exclusively. Its structure was characterized to anatase with oxygen-deficient stoichiometry by XRD and X-ray photoelectron spectroscopy. Nitrogen was also detected, but only in trace amounts. Using blue-light-emitting diodes as a light source, 540 ppm of acetone was decomposed within 36 h and a stoichiometric yield of CO 2 was obtained. From the results of the crystalline size D , it was found that vis-activity could be realized on polycrystalline particles and the grain-boundaries (GBs) are thought to be important, since oxygen vacancies are easily created in GBs, which could form a GB state. Finally, we concluded that oxygen-deficient sites formed in GBs are important to emerge vis-activity, and nitrogen doped in the part of oxygen-deficient sites are important as a blocker for reoxidation.

Visible-light-active titanium oxide photocatalyst realized by an oxygen-deficient structure and by nitrogen doping

Infrared study of the surface of titanium dioxides. I. Hydroxyl groups

Infrared study of the surface of titanium dioxides. II. Acidic and basic properties

U.v. diffuse reflectance and i.r. spectroscopies have been used to study the benzene adsorption on silica, alumina, silica—alumina and Y zeolites containing cations or protons. C6H6 is strongly adsorbed on the zeolite support especially in the case of cation-exchanged zeolites.U.v. measurements show that benzene molecules are perturbed by the zeolite surface and that the aromatic ring is no longer planar. I.r. spectra confirm this observation and also show the presence of two types of adsorbed benzene. The first type, more or less strongly held, is directly bonded to the cation by formation of a π-complex and the second type corresponds to benzene molecules in interaction with the cation–C6H6 complex. This latter type might explain the new extra u.v. band observed at 215 nm which is assigned to a charge-transfer complex. In both cases, adsorption leads to a decrease in the aromatic character.

Spectroscopic studies of benzene hydrogenation on platinum-loaded zeolites. Part 1.—Benzene adsorption on supports

Alumina-supported platinum catalysts with various metal contents have been prepared and chlorinated by CCl4 at 473 and 573 K. Their acidity has been measured by pyridine adsorption and catalytic activity in n-butane isomerization. The state of platinum has been followed by infrared spectroscopy, whereas the modifications of the dispersion were measured by electron microscopy and by H2–O2 titrations.The presence of metal in chlorinated alumina produces only small changes in acidity but a great enhancement in isomerization activity for samples chlorinated at 573 K. After chlorination, platinum is oxidized to platinum chloride, which reacts with AlCl3 to produce the PtCl2·2AlCl3 complex. This complex is mobile on the support and agglomerates in large particles. During the isomerization of n-butane, platinum is reduced in the metallic state leading to very low metal dispersion. Very small platinum clusters are also present, they are able to perform the hydrogenation of butenes and to decrease the coke formation. Thus ageing is limited in comparison with pure alumina. The possible role of HCl leading to superacid species is also discussed.

Physicochemical properties and isomerization activity of chlorinated Pt/Al2O3 catalysts

The hydrogenation of benzene adsorbed on Y zeolites containing various low platinum contents has been followed by u.v. and i.r. spectroscopies. Hydrogenation involves benzene which is irreversibly adsorbed at room temperature on PtNaY, PtHY or PtCaY samples. The reaction was performed in a static system with a constant and known hydrogen pressure. The concentration of benzene adsorbed on the zeolite decreases linearly as a function of the time of contact under hydrogen. Experiments using CO as a test molecule suggest that the platinum particles are covered by C6H6 during the hydrogenation process. By varying the hydrogen pressure, the rate of the reaction was found to be proportional to H2 pressure. It was concluded that the hydrogenation reaction takes place on the metal: hydrogen is dissociated on the platinum particles and C6H6 weakly adsorbed on the support can migrate towards the metallic phase to be hydrogenated. Determination of turnover number, N, shows an increase of N with platinum content suggesting either the presence of thermal effects or changes of catalytic activity with the metal particle size.

Michel V. Mathieu

Papers

Infrared study of the surface of titanium dioxides. I. Hydroxyl groups

Infrared study of the surface of titanium dioxides. II. Acidic and basic properties

Spectroscopic studies of benzene hydrogenation on platinum-loaded zeolites. Part 1.—Benzene adsorption on supports

Physicochemical properties and isomerization activity of chlorinated Pt/Al2O3 catalysts

Spectroscopic studies of benzene hydrogenation on platinum-loaded zeolites. Part 2.—Hydrogenation of adsorbed species