Interface excess on Li2O-doped γ-Al2O3 nanoparticles

Abstract

One of the attempts to improve γ-alumina catalytic performance lies in the use of additives that prone to segregate on its interfaces. The catalytic activity depends on the acidity or basicity of the doping oxides. Li2O is one of these oxides that when is loaded on γ-alumina surface decreases the number of Lewis acid sites. However, little is known about the Li2O distribution in the γ-alumina structure and interfaces. Thus, a detailed study of the lithium oxide distribution in the nanostructure of γ-alumina is the aim of this study. Nanometric powders were synthesized by the polymeric precursor method. The nanopowders were doped with Li+ ions (0.1, 0.5, 1, 3, 5, and 10 mol%) followed by calcination at 650 °C and 750 °C for 15 h. The powders were characterized by XRD, XRF, FTIR-DRIFT, BET specific surface area (SSA) and helium pycnometry. The surface excess due to the lithium oxide segregation was determined by the selective lixiviation method which has proved to be effective in quantifying surface excess of segregated ions at oxide interfaces. The crystallite sizes of the nanopowders varied from 3.3 nm to 9.2 nm, while their SSA were between 82.0 m2/g to 119.9 m2/g. The chemical analyses suggest that the lithium segregates in the γ-alumina interfaces at 650 °C, but it volatilizes from the surface after calcination at 750 °C.