MEASUREMENT OF THE SURFACE COVERAGE OF V/AL2O3 CATALYSTS BY INFRARED-SPECTROSCOPY, CO2 CHEMISORPTION AND ION-SCATTERING SPECTROSCOPY

Quantitative FTIR studies of alumina hydroxyl groups have been used to measure the surface coverage of V/Al2O3 catalysts. The IR spectra show a preferential consumption of the most basic hydroxyls (3769 cm(-1)) with the initial V uptake. The integrated area of the hydroxyl region was used to calculate the surface coverage of the catalysts. The surface coverage increased to 0.63 as the V loading increased to 6.7 wt%. The surface coverage results obtained from IR were compared to those measured by ion scattering spectroscopy (ISS) and CO2 chemisorption. The surface coverages measured by ISS were comparable to those obtained by IR. In contrast, CO2 chemisorption appears to overestimate the surface coverage of the catalysts. The overestimation of the surface coverage by the CO2 chemisorption method is attributed to the preferential adsorption of the V phase onto the most basic hydroxyls, the same sites which interact with CO2.