Exploring the Complex Porosity of Transition Aluminas by Xe-129 NMR Spectroscopy
Résumé
Crystalline mesoporous gamma-, delta-, and theta-alumina samples with complex porosity and various surface areas (70 to 330 m(2)/g) were characterized by Xe-129 NMR spectroscopy and nitrogen adsorption. Experimental conditions have been optimized to measure Xe-129 NMR chemical shifts independent of the nature of the surface and solely dependent on the pore size. Xenon adsorption constants have been determined from xenon adsorption isotherms and from the fit of the chemical shift versus volume to surface ratio (V/S) curves with a simple exchange model. The discrepancy observed between those values has been attributed to the rugosity of the alumina pore surface. A direct correlation between the observed chemical shift and the alumina pore diameter was obtained for the whole series of alumina samples.