Abstract
Niobium-containing materials such as hydrated niobium oxide, niobium phosphate or molecular sieves containing niobium exhibit interesting properties for their application in acid and redox catalytic reactions. But only few microporous niobium silicates have been reported up to now. Mainly, the niobium is incorporated in the tetrahedral framework positions of zeolites (MFI) or mesoporous materials (MCM-41). In 1996, the synthetic analogue of the natural mineral nenadkevichite was reported. This material is the first synthetic example of a molecular sieve formed by tetrahedral Si and Nb in octahedral coordination. The microporous niobium silicate AM-11 was reported in 1998, although its structure is still unknown, characterization studies indicate the presence of octahedral Nb(V) and tetrahedral Si (IV) in the structure. The AM-11 is obtained by the hydrothermal treatment of very dilute synthesis gel at high temperatures (200ºC) for relatively long times (7-15 days). Herein, we report the synthesis of nanorod AM-11 presenting the smallest crystals reported up to now. The presence of fluoride anions in the synthesis gel reduces the synthesis time up to 2 days at 175ºC. Also, we report the catalytic properties of the obtained materials in acid reactions as the cellulose hydrolysis and the conversion of dihydroxyacetone to lactic acid.
