Amorphous Metal Fluorides with Extraordinary High Surface Areas

摘要

Inorganic materials having high surface areas are of interest, for example, in heterogeneous catalysis where the activity of a catalyst depends largely on its surface. Metal oxides with very high surface areas can be prepared by sol-gel routes, by freeze-drying, or under supercritical conditions as xrogels or aerogels. However, no such synthetic routes exist to date for metal fluordies, which because of their high lattice energy tend to form regular crystalline structures. Thus, aluminum trifluoride prepared conventionally by precipitation in aqueous media exhibits surface areas in the range from 10 to 60 m~2 g~(-1) only. In spite of this, AIF_3 is widely used as catalyst, and other metal fluorides, such as magnesium fluoride, are used as supports for catalytically active materials. By a sophisticated NF_3 plasma-etching treatment of aluminum-rich zeolites it could be shown that AlF_3 with surface areas of up to 190 m~2 g~(-1) is in principal accessible.