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

Abstract

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.