Characterization of Catalytically Active Sites on Aluminum Oxides, Hydroxyfluorides, and Fluorides in Correlation with Their Catalytic Behavior

Amorphous Metal Fluorides with Extraordinary High Surface Areas

“…This difference in reactivity is clearly founded in the presence of substantially more acidic sites in HS-AlF 3 , as demonstrated by the NH 3 -TPD curves shown in Figure 5. Although their profile is rather similar, the NH 3 desorption from the amorphous AlF 3 is completed at around 500 8C, as found for b-AlF 3 (see above) [9] whereas with HS-AlF 3 completion is around 600 8C. The heterogeneity of the acidic strength of the surface sites is the reason for the different temperature dependencies of this reaction in which the energy of activation for HS-AlF 3 is apparently higher than for amorphous AlF 3 .…”

Reactivity of the β-AlF3(100) surface: defects, fluorine mobility and catalysis of the CCl2F2 dismutation reaction

“…The surfaces of α-AlF 3 are known to be less catalytically active than the surfaces of the β phase, which show moderate catalytic activity, and the amorphous HS materials, which show high catalytic activity 10 . Many experimental studies have been performed to investigate the structure and chemical properties of AlF 3 , including solid state NMR [11][12][13] , powder X-ray diffraction 11,12,[14][15][16][17][18] , infrared spectroscopy [17][18][19] , X-ray photoelectron spectroscopy 11,19,20 and temperature programmed desorption 21 . The majority of traditional surface science techniques for determining surface structure require large, pure, crystalline samples.…”

Characterization of Lewis acid sites on the (100) surface of β-AlF3: Ab initio calculations of NH3 adsorption

“…The surface of β-AlF 3 is known to catalyse many fluorine and chlorine exchange reactions 5,6,7 . Experimental studies, including X-ray absorption near-edge structure at the F K-edge 8 , temperature programmed desorption of NH 3 9 and the temperature programmed dismutation reaction of CCl 2 F 2 10 , suggest that amorphous HS-AlF 3 has a structure closely related to β-AlF 3 .…”