Weakly acidic zeolites: A review on uses and relationship between nature of the active sites and catalytic behaviour

Weakly acidic zeolites play a role in catalytic reactions, especially for transformation of biomass-derived products, where the control of the selectivity plays a crucial role. This review discusses this topic, having received limited attention in literature, to remark how represent both a scientific and applicative valuable area. The review offers clues for understanding how weak acid sites in zeolites could be an opportunity in some specific cases, but the aim is not to provide a systematic state-of-the-art. Rather, after introducing considerable examples and cases where mild acidity could be important (etherification, esterification, epoxidation and Beckmann rearrangement) and a discussion of the nature of weak acid sites, related to defects, present in Silicalite and how to control their nature/amount, the discussion is centred on a more in-depth analysis of three case examples: i) the effect of introduction of T3+ atoms in Silicalite-1, ii) the creation of mesoporosity in Fe-MFI and iii) catalysis by ammonium zeolite forms. HMF (5-hydroxymethyl furfural) etherification reaction is a main reaction discussed.