Acidic sites on silica-alumina catalysts with reduced aluminium content. Infra-red and thermogravimetric studies

Abstract

Infra-red and thermogravimetric studies of the chemisorption of pyridine at different temperatures have been carried out on an amorphous silica-alumina containing 14% alumina and on 3 other catalysts (9.4, 2.4 and 0.1 % alumina) prepared using HCl solutions to remove aluminium. Like silica, the sample with 0.1 % of alumina does not have Lewis or Bronsted acid sites capable of chemisorbing pyridine. The two other catalysts have less acidic sites than the starting material, but the aluminium extraction eliminates predominantly the non-acid aluminium atoms. Lewis and Bronsted sites of weak or medium acid strength are partly eliminated. The strongest acid sites remain, particularly the upper stability limit of the pyridinium ions is the same.