Consequences on Acidity and Reactivity of Inhomogeneous Sodium Exchange in the Shaping of ZSM‐5 with Silica Binders

Abstract Proton‐exchanged zeolite catalysts are used industrially in the form of objects shaped with binders, while their properties are optimized on powders at the research scale. Herein, the impact on the Brønsted acidity (probed by pyridine adsorption and thermodesorption) and on the catalytic properties (in meta‐xylene isomerization) of ZSM‐5 zeolites shaped with silica binders is quantified. The effect of sodium was assessed by using two binders exhibiting different sodium contents. Operando infrared monitoring of the reaction shows that only a portion of the zeolite crystallites is active at short time on stream, which suggests that the inner part of the crystallites does not take part in the catalytic test reaction. The evolution of acidity and activity upon shaping by extrusion is compatible with a model where sodium from the binder heterogeneously poisons the zeolites dominantly at the outer shell of the crystallites. The quantitative impact of shaping zeolites thus depends strongly on the silica source, the crystallite size and shape, the Si/Al ratio of the zeolite, and on the catalytic reaction of interest.