Cr/SiO2mesoporous catalysts: Effect of hydrothermal treatment andcalcination temperature on the structure and catalytic activity in thegas phase dehydration and dehydrogenation of cyclohexanol

PABLO M.CUESTA ZAPATA; MARCELO S. NAZZARRO; ELIO E.GONZO; MÓNICA L. PARENTIS; NORBERTO A.BONINI

CATALYSIS TODAY

ELSEVIER SCIENCE BV

Lugar: Amsterdam; Año: 2015 vol. 259 p. 39 - 49

0920-5861

tCr/SiO2mesoporous materials (Cr-MCM-41) were obtained by hydrothermal synthesis. The effect ofhydrothermal treatment and calcination temperature on the structure and catalytic behavior of syn-thesized materials were analyzed. The materials were characterized by XRD, N2adsorption?desorption,TEM-SEM, TG-DTA, FTIR-HATR, DRUV?vis and XPS. The hydrothermal treatment promoted the incor-poration of Cr3+into the silica network, improving their resistance to oxidation. The calcination in airproduces the simultaneous presence of Cr3+and Cr6+ions, and their relative amounts depend both onthe hydrothermal pretreatment and the calcination temperatures. The Cr3+ions constituted coordinativeunsaturated acid centers responsible of the cyclohexanol to cyclohexene dehydration reaction. More-over, the Cr6+ions correspond to either isolated monochromate species linked to the silica structure orto polychromate aggregates, which produce crystalline -Cr2O3clusters after calcination in air to 450◦C.The monochromate centers were active for the dehydrogenation reaction. So, although dehydration wasthe main reaction, the dehydrogenation reaction to cyclohexanone also was observed after calcinationin air to 450◦C.