Multiscale Visualization and Quantification of the Effect of Binders on the Acidity of Shaped Zeolites

Shaping is a crucial step in the preparation of catalysts at the industrial scale, but a rationalized understanding of how binders impact the catalyst's performance is still far from apparent. In this work, the effect of shaping with common binders (boehmite, γ-Al2O3, and silica) on the acidity and catalytic properties of an acid zeolite catalyst, H-ZSM-5, is probed. The zeolite–binder samples (1:1 ratio) are shaped following commonly employed procedures and analyzed using both conventional characterizations of the acidity and porosity as well as using advanced fluorescence microspectroscopic characterization. In the latter approach, the fluorescence intensity stemming from the Brønsted acid-catalyzed furfuryl alcohol oligomerization is used to determine in detail the effect of shaping on acid zeolite's catalytic activity. Through density functional theory calculations, the observed changes in catalytic performance are assigned to atomic-scale processes such as the interaction of acid sites with binder-related molecular species and the migration of ions. The most detrimental effects related to shaping are migration of cations, here Na+, from the binder to the zeolite, which is an important mechanism for silica binders, as well as pore blockage by alumina and silica species. Strong acid sites are also likely to be converted into weak ones upon interaction with binders. A counterbalancing effect is the genesis of some additional bridging OH groups upon filling of local defects with alumina species from alumina binders. With such knowledge in hand, it becomes possible to balance these effects to get the desired properties.