General aspects of zeolite acidity characterization

• Acidity is a relative property.
• The nature of acid sites in zeolites can only be determined through the utilization of adequate probes.
• Thermodesorption results are meaningless unless adequate mathematic models are used.
• Acidity and catalytic performance are not synonyms.

This paper describes the most used techniques in the determination of the acid property in zeolite materials. Two families of techniques, namely spectrometric (IR, NMR) and adsorption–desorption methods (calorimetry, TPD) are considered. Typical experimental conditions, schematics of equipment setup, and rules for molecular probe selection are shown. Selected experiments that make use of these methods are briefly discussed, and their most relevant results are presented. This review shows some of the possibilities that can be used to “measure” acidity in zeolites. It is also shown that the interpretation of such results could be deceiving in certain situations, especially because acidity and catalytic performance are not synonyms and acidity is inherently a relative term.

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