A study of surface interactions on γ-alumina, silica-alumina, and silica-magnesia using the EPR spectra of adsorbed nitric oxide

Abstract

The EPR spectrum of the adsorbed NO molecule was used to determine crystal and magnetic field interactions on the surface of γ-alumina, silica-alumina, and silica-magnesia. The crystal-field splitting, Δ, of the 2pπ ∗ levels of NO was found to be 0.75 eV on dehydrated γ-alumina and 0.60 eV on dehydrated silica-alumina. The spectrum on silica-magnesia indicated two adsorption sites with Δ equal to 0.60 and 0.33 eV. Spectra of NO on γ-alumina and silica-alumina show considerable hyperfine coupling with an 27Al atom at the adsorption site. The spectra were very similar to the spectrum of NO on a decationated Y zeolite. The maximum number of adsorption sites (as indicated by the spin concentration) was found to be 4(± 1) × 10 12 sites/cm 2 for 7-alumina and two types of silica-alumina. Silica-magnesia had 1.1(± 0.3) × 10 12 sites/cm 2. The number of sites and the shape of the spectra were a function of the degree of dehydration. Water added back to dehydrated γ-alumina and silica-alumina also affected the spectra. It appears that these adsorption sites are the α sites which Peri has studied using the IR spectra of adsorbed CO 2.