Integral Intensity of the EPR Signal of NO Molecules Adsorbed on Lewis Acid Sites of Oxide Systems as a Function of Surface Coverage

A simple model is proposed that semi-quantitatively explains the dependence of the EPR signal intensity of adsorbed NO molecules on the adsorption value. It is assumed that there are only two types of NO adsorption sites on each facet of the microcrystal, such that only NO molecules adsorbed on one of them are active in EPR. Within the framework of this model of lattice adsorption, it is assumed that there are Z other adsorption centers from the set under consideration that are available for the adsorption of neighboring NO molecules in the local environment of each EPR-active adsorption center. In this case, the formation of diamagnetic (NO)2 dimers containing an NO molecule adsorbed on a center active in the EPR decreases the integral intensity of the EPR signal. Analytical expressions are obtained for the dependence of the EPR signal intensity on the surface coverage. They were used to analyze experimental data on the adsorption of NO at the Lewis acid sites of sulfated zirconia. The proposed model consistently explains the results of EPR experiments.