Effect of hydrothermal treatment on Cr-SiO2 mesoporous materials

Amorphous Cr/SiO2 Materials Hydrothermally Treated: Liquid Phase Cyclohexanol Oxidation

“…From the above results and those reported in previous papers [25][26][27], we can conclude that Cr 3+ species were the . The spectra were determined after evacuation for 30 min at room temperature only one into the catalyst samples dried at 110 °C, whereas in samples treated at temperatures higher than 110 °C, both Cr 3+ and Cr 6+ species were present.…”

“…The spectra were determined after evacuation for 30 min at room temperature only one into the catalyst samples dried at 110 °C, whereas in samples treated at temperatures higher than 110 °C, both Cr 3+ and Cr 6+ species were present. Similar results were obtained over Cr-MCM-41 materials on which the relative amount of both species was quantified by XPS [25,26].…”

“…All the above characterization results let to conclude that hydrothermal treatment enhances the incorporation of Cr 3+ into the silica structure, through the Si-O-Cr bonds formation, avoiding the leaching and also the formation of either dichromate or polychromate polymeric species [25][26][27]. The X-ray diffraction profiles of 5SG materials (not shown) established the absence of crystalline species, even after calcination in air up to 450 °C.…”

“…For comparison, and considering that the leaching and reusability of the 5SG 150 110 catalyst were determined previously (Fig. 8), the catalyst with no hydrothermal treatment was chosen since it presents the weakest metal-support interaction and consequently it is the most susceptible to leaching [25][26][27].…”

“…However, the stability of these metal ions is not enough to avoid leaching into the liquid phase [6,16,20]. Recently, our research group has reported the synthesis of Cr-SiO 2 catalysts by sol-gel technique followed by hydrothermal treatment [25][26][27] up to 220 °C. It was observed a progressive incorporation of Cr 3+ ions in the silica network as the hydrothermal temperature increases from 120 to 220 °C.…”