Thermal spreading of MoO3 in H-ZY

This work provides a structural, optical and kinetics approach to the molybdenum oxo-species formed during thermally driven migration on H-ZY starting from mechanical mixtures with MoO3. The samples were characterized as a function of time of treatment by UV-vis diffuse reflectance, X-ray diffraction, N-2 adsorption and scanning transmission electron microscopy (STEM). Local analysis of elemental compositions obtained from linear scan of characteristic X-ray signal show a direct evidence of molybdenum presence into the zeolite crystals. Ultraviolet absorption spectra were used to determine both the kinetics of the spreading and the speciation of MoOx in the H-ZY. Besides MoO3, three surface molybdenum oxo-species were identified according to the edge energy (E-g) values of bulk molybdenum oxide reference compounds. This study shows that the tetrahedral species prevailed on H-ZY. This is consistent with limitations in the migration and growth of MoOx in the channel structure of the zeolite. Kinetic study suggest that migration of MoOx in the H-ZY at low temperature (ca. 723 K) occurs across the formation and diffusion of hydrated species such as MoO2(OH)(2), which interact with the zeolite and form monomeric and dimeric structures (like (MoO4)(2-) and (Mo2O7)(2-)). Migration of MoOx species in the H-ZY studied is significant even at 723 K and after very short periods of treatment (< 5 min). (c) 2010 Elsevier BM. All rights reserved.