Synthesis and characterization of high hydrothermally stable Cr-MCM-48

Abstract

The hydrothermal stability of Cr-containing MCM-48 in boiling water was found to be higher than that of the pure silica MCM-48, which was first improved with the increasing Cr content at low Si/Cr ratio, then went to the maxima at Si/Cr = 50, and finally instead decreases with the increasing Si/Cr ratio. The Cr-MCM-48 sample synthesized at Si/Cr = 50 maintained their mesoporous structure after refluxing in boiling water for 36 h. The results of diffuse reflectance UV–vis and ESR spectra showed that the calcined Cr-MCM-48 contains Cr(V) and Cr(VI) at low Cr content. Chromium is present as Cr(V), Cr(VI) and Cr(III) species at the rich Cr content. Both of the Cr positioned on the surface of pore walls and in the framework provide the protection against water attack.