Exploring the Complex Porosity of Transition Aluminas by 129Xe NMR Spectroscopy

Crystalline mesoporous γ-, δ-, and θ-alumina samples with complex porosity and various surface areas (70 to 330 m2/g) were characterized by 129Xe NMR spectroscopy and nitrogen adsorption. Experimental conditions have been optimized to measure 129Xe 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.