Surfaces acidic properties

Lucio Forni (J ), while discussing catalysis research, commented that "Each technique, in fact, taken by itself, allows some useful information to be collected, but can give rise to criticisms. The combination of information obtainable by two or more of them can often be the only way to give a complete picture of the surface acid properties of the solid."... 

Data reported in the present work demonstrate that the degree of crystallinity and the acid properties are related the amount of present at the surface of VPP. When the VPP is not fully equilibrated, and hence may contain discrete amounts of it is more selective to MA and less to PA. The reason is that in oxidized catalysts, the olefmic intermediate is preferentially oxidized to MA, rather then being subjected to the acid-catalyzed condensation with a second unsaturated molecule, to yield the precursor of PA. When instead the catalyst is more crystalline, and hence it does contain less oxidized V sites, its surface acid properties predominate over O-insertion properties, and the catalyst becomes more effective in PA formation. In this case, the selectivity to PA at 50% n-pentane conversion becomes comparable to that one of MA. 

The effect of Ca loading on the acid-base and redox properties of chromia catalysts supported on alumina has been investigated by microcalorimetry of NH3 adsorption and TPR. This alkaline promoter strongly decreases the acidity of the chromia catalyst, particularly suppressing the medium and strong acid sites. No clear correlations were found between the surface acidic properties and the catalytic behavior of the investigated samples in the oxidative dehydrogenation of isobutene, while clear trends were observed between reducibihty and catalytic activity [52]. 

Finck, N. et al., Temperature effect on the surface acidity properties of zirconium diphosphate, J. Colloid Interf. Sci., 312, 230, 2007. 

Adsorption of pyridine bases is generally applied to test the surface acid properties of zeolites. Adsorbed pyridine base molecules interact with the surface acid site and the strength of the interaction can be monitored by spectroscopic methods. Komiyama et al. [47] obtained in situ molecular AFM images of well ordered arrays of pyridine and P-picoline on the (010)... 

Solid-state NMR techniques have been employed to investigate the surface acidic properties of Ti02 and sulfated Ti02, toward 2-propanol. The multinuclear MAS NMR experiments clearly revealed that three different types of Bronsted acid sites with much stronger acid strength were generated after the sulfation of Ti02. ... 

Ammonia is among the smallest strongly basic molecules and its diffusion is little affected by the porous structure, if at all. Because of this, it is the most commonly used probe molecule for testing surface acid properties. It is adsorbed as an ammonium ion, and the corresponding heat of adsorption depends both on the proton mobility and on the affinity of ammonia for the proton. 

The intrinsic (measured in cyclohexane, apolar and aprotic solvent) and effective (measured in water or other liquids) acidity of series of mixed silica-niobia oxides have been determined by this method with the principal aim of disclosing relationships between the surface acid properties and catalytic activity [9]. Dispersed niobia... 

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