Acidity evolution on highly dispersed chromium supported on mesostructured silica: The effect of hydrothermal treatment and calcination temperature

Abstract

Mesoporous Cr-MCM-41 catalysts were synthesized, under different hydrothermal temperatures, by the sol-gel procedure using tetraethylorthosilicate (TEOS) as silica precursor and cetyltrimethylammonium bromide (CTAB) as a structure-directing agent. Materials were characterized by several techniques (XRD, XPS, TG-DTA, FTIR, UV–Vis, AA and N2 sorptometry). The amount and accessibility of different hydroxyl groups were analyzed by FTIR spectroscopy after heat treatment in vacuum (10 5 mmHg) and subsequent exchange of hydrogen by deuterium using D2O. TG-DTA, FTIR of adsorbed pyridine and 2,6-dimethylpyridine and TPD of pyridine, let to determine the strength, thermal evolution, and amount of the different acid sites present at the surface. Results correlate with catalytic activity against 2-propanol in the gas phase, and let to propose mechanisms for dehydration and dehydrogenation reactions