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High‐Surface‐Area Alumina–Silica Nanocatalysts Prepared by a Hybrid Sol–Gel Route Using a Boehmite Precursor
Author(s) -
Nampi Padmaja Parameswaran,
Moothetty Padmanabhan,
Wunderlich Wilfried,
Berry Frank John,
Mortimer Michael,
Creamer Neil John,
Warrier Krishna Gopakumar
Publication year - 2010
Publication title -
journal of the american ceramic society
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.9
H-Index - 196
eISSN - 1551-2916
pISSN - 0002-7820
DOI - 10.1111/j.1551-2916.2010.03997.x
Subject(s) - boehmite , tetraethyl orthosilicate , calcination , materials science , sol gel , specific surface area , aluminosilicate , chemical engineering , aluminium nitrate , aluminium oxide , mineralogy , adsorption , analytical chemistry (journal) , aluminium , nanotechnology , catalysis , chemistry , composite material , chromatography , organic chemistry , engineering
High‐surface‐area alumina–silica mixed oxide (Al 2 O 3 :SiO 2 ) nanocatalysts have been prepared by a hybrid sol–gel method using boehmite (synthesized from aluminum nitrate) as the source of alumina and tetraethyl orthosilicate as the source of silica. The gels, after calcination at 400°C, result in mixed oxides with specific surface areas of 287 m 2 /g (Al 2 O 3 :SiO 2 =3:1) and 262 m 2 /g (Al 2 O 3 :SiO 2 =3:4). Further heating to 600°C produces materials with specific surface areas of 237 and 205 m 2 /g, respectively. The larger specific surface areas characteristic of the 3Al 2 O 3 :SiO 2 samples are attributed, via transmission electron micrograph investigations, to the presence of ∼10 nm size, needle‐like particles having an aspect ratio of 1:50. Further addition of silica leads to the formation of larger needles of 20–75 nm size. Calcination at 600°C induced an approximately 5% decrease in the total pore volume for the 3Al 2 O 3 :SiO 2 sample. In contrast, the material with Al 2 O 3 :SiO 2 =3:4 showed an approximately 12% increase in pore volume when heated at 600°C. The pore‐size distribution was in the range 1–3.5 nm with r max at ∼2 and ∼2.5 nm at 600° and 800°C, respectively. Adsorption isotherms and pore‐size distribution analyses are discussed in some detail for the aluminosilicates at different calcination temperatures. This discussion is supported by structural information determined from FTIR and 27 Al MAS NMR studies. Relatively high acidity values (0.234 mmol/g for Al 2 O 3 : SiO 2 =3:4) are observed for silica‐rich compositions consistent with their application as efficient acid catalysts.