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Characterization of Thermally Stable Brønsted Acid Sites on Alumina‐Supported Niobium Oxide after Calcination at High Temperatures
Author(s) -
Kitano Tomoyuki,
Shishido Tetsuya,
Teramura Kentaro,
Tanaka Tsunehiro
Publication year - 2013
Publication title -
chemphyschem
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.016
H-Index - 140
eISSN - 1439-7641
pISSN - 1439-4235
DOI - 10.1002/cphc.201300189
Subject(s) - calcination , niobium , niobium oxide , brønsted–lowry acid–base theory , fourier transform infrared spectroscopy , monolayer , oxide , materials science , transmission electron microscopy , infrared spectroscopy , inorganic chemistry , catalysis , chemistry , chemical engineering , nanotechnology , organic chemistry , metallurgy , engineering
Thermally stable Brønsted acid sites were generated on alumina‐supported niobium oxide (Nb 2 O 5 /Al 2 O 3 ) by calcination at high temperatures, such as 1123 K. The results of structural characterization by using Fourier‐transform infrared (FTIR) spectroscopy, TEM, scanning transmission electron microscopy (STEM), and energy‐dispersive X‐ray (EDX) analysis indicated that the Nb 2 O 5 monolayer domains were highly dispersed over alumina at low Nb 2 O 5 loadings, such as 5 wt %, and no Brønsted acid sites were presents. The coverage of Nb 2 O 5 monolayer domains over Al 2 O 3 increased with increasing Nb 2 O 5 loading and almost‐full coverage was obtained at a loading of 16 wt %. A sharp increase in the number of hydroxy groups, which acted as Brønsted acid sites, was observed at this loading level. The relationship between the acidic properties and the structure of the material suggested that the bridging hydroxy groups (NbO(H)Nb), which were formed at the boundaries between the domains of the Nb 2 O 5 monolayer, acted as thermally stable Brønsted acid sites.