Chromia-Alumina Catalysts: Chromia Area by Excess Oxygen Measurements

Abstract

Chromia-alumina catalysts with chromium concentrations varying from 0.90 to 17.5 wt % were prepared by the impregnation of 77-alumina with chromic acid. Chromia areas were measured by oxygen chemisorption and by excess oxygen determination. The areas by both methods were equal for the 0.90 wt % chromium catalyst. For higher chromium contents the area determined by excess oxygen measurement is higher than that determined by oxygen chemisorption because of subsurface chromium oxidation. At 17.5 wt % chromium the difference between the two measurements is 15% of the area. It is concluded that excess oxygen can be a good measure of chromia area if subsurface oxidation is not too great.