Surface coverage of rhenium-alumina catalysts

The surface coverage of a series of rhenium-alumina catalysts prepared by equilibrium adsorption was determined by ion scattering spectroscopy (ISS) and infrared spectroscopy (IR), The coverage results were compared with those determined from previously published CO2 chemisorption data. The ISS results show an almost linear increase in Re coverage with increasing Re loading, reaching similar to 30% coverage for a loading of similar to 6.5 wt.% Re, The near-linearity of the coverage with increasing Re content indicates a uniform build-up of the surface species, The Re cross-sections calculated from the corresponding surface coverages (24.8-30.5 Angstrom(2)/Re) were comparable with those previously reported for the Re/Al2O3 system. The surface coverage determined from IR was shown to depend on the extent of dehydroxylation of the samples, Following pretreatment at 500 degrees C, the coverage values for high loading catalysts were comparable with those obtained from ISS. However, the IR method yielded increasingly higher coverage values with decreasing Re loading, The Re cross-section values estimated from the corresponding surface coverages indicate an increased overestimation of the coverage with decreasing loading, As expected, the CO2 chemisorption method consistently leads to an overestimation of the Re surface coverage.