Spatiotemporal Spectroscopy of Molecular Sieves : Interplay between Hydrothermal Treatments and the Methanol-To-Hydrocarbons reaction

Abstract

Unraveling the influence that heterogeneities within a catalytic material may have on its overall performance is far from trivial and still represents a scientific challenge. It requires the development and use of advanced in-situ characterization techniques, capable of bridging the different length scales, ranging from the level of the reactor down to the catalytically active phase. Moreover, such a selection of techniques should be applied under relevant reaction conditions, being able to characterize the inorganic as well as the organic phases present in the catalyst material and desirably causing the least possible interference with its working principles. Within this context, an array of bulk and micro-spectroscopic characterization techniques has been used in this PhD thesis to increase our understanding of the effect of a hydrothermal treatment on the physicochemical properties and related reactivity of the archetypal molecular sieves, namely ZSM-5 and SAPO-34, for the Methanol-to-Hydrocarbons (MTH) reaction. For this purpose, two different catalyst systems have been investigated, namely large zeolite ZSM-5 crystals and commercially available ZSM-5 and SAPO-34 catalyst powders. The former materials have been used as model systems to elucidate the effect of steaming on the porosity, pore accessibility, acidity and MTH reactivity of these catalytic solids. On the other hand, commercially available ZSM-5 and SAPO-34 powders have been used as practical catalyst systems to elucidate the effect of a hydrothermal treatment on both the physicochemical properties and reactivity at the level of a single catalyst particle. In this manner, new insights in the origin and impact of spatiotemporal heterogeneities on MTH catalysis have been obtained.