Probe molecules acid-base surface investigation using

Probe molecules such as, pyridine, ammonia, carbon monoxide, piperidine, and -butylamine are used to investigate acid-base surface properties due to their capability to distinguish between surface Lewis and Brpnsted acid sites of oxide materials. These molecules possess the ability to interact as distinct adsorbed surface species according to the nature of the acid site. 

The snrface acid-base properties of supported oxides can be conveniently investigated by studying the adsorption of suitably chosen basic-acidic probe molecules on the solid. As shown, acidic and basic sites are often present simultaneously on solid surfaces. The knowledge of the detailed amphoteric character of supported metal oxides is of extreme interest due to the possibility of using them as catalysts in different reactions in which acidity governs the reaction mechanism. 

In the present work the behaviour of zirconia samples doped with oxides of alkali metals and alkaline-earth metals was investigated, in order to better understand the role of both the nature and the amount of the doping cation. Li-, K-, Ca-, and Ba-doped zirconia samples were prepared. Their surface acid-base properties were assessed by means of adsorption microcalorimetry, using ammonia and carbon dioxide as probe molecules. Their catalytic activity for the 4-methylpentan-2-ol dehydration was tested in a flow microreactor. 

One typical TPD experiment is designed in a way to enable the pre-treatment of the sample, in situ the admission of specific adsorbate (probe) up to some specific surface coverage or up to the saturation and subsequently, desorption which is performed in a temperature-controlled regime. Many different chemical species can be used as probes if a chosen probe can titrate acid or basic sites at the surface, TPD can be used for the characterization of acidity/basicity of some adsorbent. In fact, temperature-programmed desorption and adsorption calorimetry are most commonly used for the study of acid/base properties of solid materials [20, 35, 36]. The same probe molecules that are used for adsorption calorimetry experiments are applicable in the case of TPD while the investigation of acidic/basic character of solids is perhaps... 

The organic molecules or "probes used to investigate the dispersive surface energies of the fiber surfaces were a series of n-alkanes. The probes used to study the non dispersive forces were chosen based on their acidic or basic character as determined by Gutmann (8). Gutmann has practically defined basicity as the donor number, DN, or electron-donor capability in the Lewis sense. The donor scale is based on the value of the molar enthalpy for the reaction of the electron donor with a reference acceptor, SbCl. ... 

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