The interaction between V2O5 and TiO2 under milling in a ball mill (an alternative procedure of catalyst preparation) was characterized by 1H, 51V MAS, and 51V static (wide line) NMR spectroscopy supplemented by simulations of 51V NMR spectra. Additionally, ESR and magnetic susceptibility measurements were carried out for the characterization of the paramagnetic V4+ and V3+ sites. It has been shown that after milling, two different types of octahedrally coordinated vanadium (V5+) species (V5+(I) and V5+(II)) strongly bonded to TiO2 are formed. At the same time, the appearance of V3+ ions and an increase of their concentration is observed during milling−calcination processes, along with the formation of at least three different types of paramagnetic V4+ species corresponding to (i) V4+ centers in O-deficient V2O5 - x ; (ii) VO2+ vanadyl species (V4+(I)) with the vanadium centers in octahedral symmetry with axial distortion; (iii) V4+(II) species with vanadium centers also in octahedral symmetry, but with different bond lengths and strengths as compared to V4+(I). Relative amounts of different V4+ and V5+ species depend on the milling time, the presence of H2O in the system, and the subsequent calcination procedure (temperature and calcination time). Thus, V5+(I) species formed predominantly during milling, whereas V5+(II) species formed after thermal treatment. For the structural characterization of these species, complete sets of the quadrupole and chemical shielding tensor parameters, including relative tensor orientations, have been estimated. This allows us to conclude that the octahedral environment of vanadium in V5+(II) species is less distorted than in V5+(I) and in both cases the distortion is less axial than in V2O5. Combined NMR, ESR, and magnetic susceptibility measurements indicate that all vanadium species (V3+, V4+, and V5+) are isolated from each other on the TiO2 support.

1999 magnetic resonance, nuclear quadrupole resonance magnetic resonance, nuclear quadrupole resonance (solids and liquids) D 6560 50 -017 Characterization of V 2 O 5 -TiO 2 Catalysts by Milling by ESR and Solid State 1 H and 51 V NMR. -Milling of V 2 O 5 /TiO 2 mixtures induces spreading of vanadia across the titania surface, whereby two types of V 5+ species strongly bonded to titania are formed. In addition, V 3+ centers and at least three structurally different V 4+ centers are detected. -(LAPINA, OLGA B.; SHUBIN, ALEXANDER A.; NOSOV, ANDREI V.; BOSCH, ERIC; SPENGLER, JOERG; KNOEZINGER, HELMUT; J. Phys. Chem. B 103 (1999) 36, 7599-7606; Inst. Phys. Chem.,

The NMR spectroscopy of xenon sorbed in beds of ZSM-5 zeolite is used to study the rate of adsorption of benzene molecules from the gas phase, as well as the rate of the combined process of adsorption and desorption in a bed consisting of two types of crystallites, some being initially benzene-loaded, some not. The exchange rate is shown to depend dramatically on the crystallite arrangement. The magnitudes of the observed rate constants and line shifts are confirmed by calculations based on simple models.