Multiscale Visualization and Quantification of the Effect of Binderson the Acidity of Shaped Zeolites

Shaping is a crucial step in the preparation of catalysts at theindustrial scale, but a rationalized understanding of how binders impact thecatalyst's performance is still far from apparent. In this work, the effect of shapingwith common binders (boehmite,gamma-Al2O3, and silica) on the acidity and catalyticproperties of an acid zeolite catalyst, H-ZSM-5, is probed. The zeolite-bindersamples (1:1 ratio) are shaped following commonly employed procedures andanalyzed using both conventional characterizations of the acidity and porosity aswell as using advancedfluorescence microspectroscopic characterization. In thelatter approach, thefluorescence intensity stemming from the Bronsted acid-catalyzed furfuryl alcohol oligomerization is used to determine in detail the effectof shaping on acid zeolite's catalytic activity. Through density functional theorycalculations, the observed changes in catalytic performance are assigned to atomic-scale processes such as the interaction of acid siteswith binder-related molecular species and the migration of ions. The most detrimental effects related to shaping are migration ofcations, here Na+, from the binder to the zeolite, which is an important mechanism for silica binders, as well as pore blockage byalumina and silica species. Strong acid sites are also likely to be converted into weak ones upon interaction with binders. Acounterbalancing effect is the genesis of some additional bridging OH groups uponfilling of local defects with alumina species fromalumina binders. With such knowledge in hand, it becomes possible to balance these effects to get the desired properties