jp7b02498_si_001.pdf (1.54 MB)
Thermodynamic Characterization of the Hydroxyl Group on the γ‑Alumina Surface by the Energy Distribution Function
journal contribution
posted on 2017-07-07, 00:00 authored by Matthieu Lagauche, Kim Larmier, Elsa Jolimaitre, Karin Barthelet, Céline Chizallet, Loïc Favergeon, Michèle PijolatControlling
water adsorption on γ-alumina, i.e., the quantity
and nature of the surface hydroxyl groups, is essential for adjusting
the acidic/basic properties of the surface. IR and DFT studies have
shown that different OH groups, each of them characterized by its
own chemical environment and adsorption properties, can be present
on the surface of γ-alumina. However, quantifying this surface
heterogeneity and predicting the influence of the synthesis and activation
conditions is still a challenging problem. In this paper, a detailed
experimental study is conducted on a γ-alumina sample obtained
by thermal decomposition of a commercial boehmite. Using a thermogravimetric
setup, both water-adsorption equilibrium and desorption kinetics were
acquired in a large range of controlled experimental conditions (1
Pa < partial pressure of water <1400 Pa ; 100 °C < temperatures
<600 °C). The energy distribution function (EDF) of water-adsorption
enthalpy is evaluated on the basis of the theories developed for strongly
heterogeneous surfaces but so far never applied to the water vapor
interactions with γ-alumina. The OH adsorption enthalpy range
of the EDF, and the experimental OH contents, are in good agreement
with density functional theory simulations, making a bridge between
macroscopic and atomistic features. It is also shown that the EDF
of the γ-alumina surface is a very powerful tool to predict
the hydroxyl coverage as a function of the pretreatment history of
the sample.