Surface and bulk reduction of bismuth/molybdenum oxides studied by electron spin resonance spectroscopy

Abstract

E.s.r. spectra due to Mo^V ions in Bi/Mo mixed oxides reduced under vacuum and by propene show bulk and surface reduction governed by the oxygen diffusion. The equilibrium between the two types of reduction depends on the temperature and the catalyst composition and is independent of the actual reduction process. The e.s.r. spectrum due to surface Mo^V ions is broadened by dipolar interactions with adsorbed oxygen. The residual spectrum is attributed to sites in which Mo^V ions are probably associated with lattice defects.