On the Interaction of CrO2Cl2 Vapor with the Surface of γ-Al2O3 and the Formation of a Chromium Oxide Covering

Abstract

Samples of γ-Al2O3 containing different amounts of residual hydroxyl groups were obtained by thermal treatment. The possibility of interaction of the surface hydroxyl groups of γ-Al2O3 with chromyl chloride vapor was studied by IR spectroscopy. The hydrogen chloride evolved as a result of the reaction interacts with both strained Al–O–Al bridges and the surface OH groups. Different types of OH groups show different reactivities with respect to the interaction with CrO2Cl2. Bands at 3780 and 3700 cm−1 are due to OH groups which have a much higher reactivity than the OH groups responsible for bands at 3744 and 3733 cm−1. Not all of the OH groups participate in the surface reaction. Decrease in their surface density results in increase in the reactivity. Modification of the γ-Al2O3 surface is achieved by reaction cycles consisting of treatment with CrO2Cl2 vapor and hydrolysis of the compounds obtained by water vapor. As a result, an increase in the chromium oxide amount on the surface of γ-Al2O3 is observed. This is ascribed to the “secondary” OH groups formed after the hydrolysis.

Controlled Formation of ZrO2 in the Reaction of ZrCl4 Vapor with Porous Silica and γ-Alumina Surfaces

“…It is clear, however, that at least some of the original OH groups of alumina must have been left intact. The band of isolated OH groups at 3700−3720 cm -1 still appeared in the IR spectra, and these groups could not have been formed in the dissociation of HCl because groups so formed would appear in the lower wavenumber area as a result of OH···Cl interaction . The decreasing amount of OH groups left on the surface after reaction at increasing temperature could have been an indication of the increasing reactivity of OH groups (Table ).…”

“…Thus, according to their review, the possible five reaction routes are the following: On alumina, possible adsorption sites are provided not only by OH groups but also by coordinatively unsaturated aluminum and oxygen sites. It has namely been suggested that metal oxychlorides can dissociate to (Al−O) sites and that ZrCl 4 can react with exposed oxygen , These reactions of HCl can be presented as follows: Furthermore, Hochman and Setinek concluded in their study on reactions of TiCl 4 and other chlorides with alumina that reactions with OH groups and direct chlorination of the surface are both possible.…”

“…It has namely been suggested that metal oxychlorides can dissociate to (Al−O) sites and that ZrCl 4 can react with exposed oxygen , These reactions of HCl can be presented as follows: Furthermore, Hochman and Setinek concluded in their study on reactions of TiCl 4 and other chlorides with alumina that reactions with OH groups and direct chlorination of the surface are both possible. Direct chlorination leads to bonding of only the halogen of the metal chloride, and the remaining part of the molecule with a reduced number of halogen atoms is proposed to volatilize and be removed by the carrier gas used in the preparation.…”

Chromyl Chloride Chemistry on the TiO2(110) Surface

“…Removal of the Cr typically required a total 3 kV Ar + exposure of about 10 mC/cm 2 (about 120 ML of Ar + ), whereas the chlorine was removed by annealing at 820 K prior to sputtering. After 3 kV sputtering the surface was smoothed by sputtering with 500 V Ar + , then oxidized in 1 × 10 -7 Torr O 2 at 820 K for 10 min followed by cooling in O 2 to below 400 K. By use of 18 O 2 instead of 16 O 2 , the surface could be converted to Ti 18 O 2 (110). The natural isotopic abundance of oxygen was restored easily by sputtering off the thin 18 O-containing layer.…”

“…Surface chemistry was then studied using temperature-programmed desorption (TPD), Auger electron spectroscopy (AES), static secondary ion mass spectrometry (SSIMS), work function change measurement (ΔΦ), and X-ray photoelectron spectroscopy (XPS). To the authors' knowledge, no information regarding the interactions of Cr(VI)-containing inorganic molecules such as chromyl chloride with polycrystalline or single-crystal TiO 2 is available in the published literature, although there are published accounts dealing with chromyl chloride adsorption on other oxide materials. − This paper deals with the thermal induced chemistry of chromyl chloride at the TiO 2 (110) surface in the absence of coadsorbed water. More specifically, the objectives of the study are to understand the binding of chromyl chloride with the TiO 2 (110) surface, to quantify the partitioning between the desorbed and the decomposed chromyl chloride, and to determine the chromyl chloride decomposition pathways.…”