On the nature of strong acidic Bronsted sites of amorphous silica-aluminas

Journal Article · Fri Apr 01 04:00:00 EST 1983 · J. Catal.; (United States)

OSTI ID:5556504

Borovkov, V Y; Alexeev, A A; Kazansky, V B

The problem concerning the nature of Bronsted acidity of amorphous silica-aluminas has been discussed for years but still is not completely solved. Therefore, highly dehydroxylated powdered samples of amorphous silica-alumina M-46 ''Houdry'' with Al/sub 2/O/sub 3/ content of 12 wt% were used. The samples were heated under vacuum at 1070 K and pressure of 10/sup -2/ N m/sup -2/ for 2 h. Acidic hydroxyls were regenerated by adsorption of small amounts of H/sub 2/O (D/sub 2/O) at room temperature. Infrared spectra of OH (OD) groups were measured in diffuse scattered light in the range 2000-4000 cm/sup -1/ using a double-beam ratio recording Perkin-Elmer 580B spectrophotometer and special ir cells supplied with CaF/sub 2/ windows. Results show an obvious similarity between acidic OH groups of amorphous silica-alumina and zeolites. Their amount in silica-alumina is however much lower. For M-46 it is of the order of 5 x 10/sup 19/ OH/g or only about 1% of the total amount of surface silanol groups. In conclusion, it should be noted that after adsorption of D/sub 2/O the acidic OH groups also can be detected by ir spectroscopy for samples pretreated at lower temperatures, for instance at 770 K. For these samples, however, the corresponding bands are not so pronounced because the major part of acidic groups likely interacts with neighboring silanol groups via H bonding.

• Research Organization: Academy of Sciences of USSR, Moscow
• OSTI ID: 5556504
• Journal Information: J. Catal.; (United States), Journal Name: J. Catal.; (United States) Vol. 80:2; ISSN JCTLA
• Country of Publication: United States
• Language: English

Related Subjects

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CHEMISTRY
400201* -- Chemical & Physicochemical Properties
ADSORPTION
ALKALINE EARTH METAL COMPOUNDS
ALUMINIUM COMPOUNDS
ALUMINIUM OXIDES
CALCIUM COMPOUNDS
CALCIUM FLUORIDES
CALCIUM HALIDES
CHALCOGENIDES
CHEMICAL BONDS
DEUTERIUM
FLUORIDES
FLUORINE COMPOUNDS
HALIDES
HALOGEN COMPOUNDS
HEAVY WATER
HYDROGEN COMPOUNDS
HYDROGEN ISOTOPES
HYDROXYL RADICALS
INFRARED SPECTRA
INORGANIC ION EXCHANGERS
ION EXCHANGE MATERIALS
ISOTOPES
LIGHT NUCLEI
MATERIALS
MINERALS
NUCLEI
ODD-ODD NUCLEI
OXIDE MINERALS
OXIDES
OXYGEN COMPOUNDS
RADICALS
SILICA
SILICON COMPOUNDS
SILICON OXIDES
SORPTION
SPECTRA
STABLE ISOTOPES
STRUCTURAL CHEMICAL ANALYSIS
VERY HIGH TEMPERATURE
WATER
ZEOLITES