Surface Acidity of Molybdena-Alumina Catalysts
1976 Volume 1976 Issue 2 Pages 227-231
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1976 Volume 1976 Issue 2 Pages 227-231
The surface acidity of MoO3-Al2O3 catalysts containing 1-63 wt% MoO3. was measured by butylamine titration using H0 indicators and by adsorption of NH3, pyridine and quinoline.
The acid strength of the catalysts containing more than 27% MoO3 was distribut ed from H, 6.8 to 3.3, while stronger acid sites (H0<-3.3) were observed on the catalysts containin g less than 12.5% MoO3. The amounts of NH3 adsorbed at 200° and 300°C on the catalysts containing more than 27% MoO3 agreed with the numbers of acid sites at H0 3.3 and 1.5determined by amine titration.
Two types of adsorb ed basic molecules were found on the catalysts at 200°C; ( I ) the one was reversibly adsorbed molecule which was easily removed by evacuation at 10-5 mmHg, and 00 the other was irreversibly adsorbed molecule which was retained on the evacuation. When the catalysis were pretreated with H2 or H2S, the amount of irreversibly adsorbed basic molecules increased.
The surf ace structure of the catalysts for these two acidic sites are discussed.
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