Direct synthesis of Cr-MCM-48-like large pore mesoporous silica<br /> and its catalytic properties<br />
Journal Title: Science Paper Online - Year 2009, Vol 4, Issue 3
Abstract
Chromium substituted MCM-48-like large pore mesoporous silica with average pore size up to 10 nm was directly synthesized by using P123 (EO20PO70EO20) as template, n-butanol as assistant and chromium nitrate as chromium source. The Cr species were doped by simply adjusting the pH value of the synthesis system with ammonia from strong acid to nearly neutral after crystallization for 24 h. The Si/Cr ratios in the initial gel ranged from 10 to 80 and the actual weight percentage of Cr content was analyzed by ICP. X-ray diffraction pattern (XRD), transmission electron microscopy (TEM) and N2 adsorption-desorption isotherm were employed to investigate the pore structure properties of these materials. The results indicate the pH adjusting method is an efficient way to incorporate large amount of chromium into the large pore Ia3d mesostructure. UV-vis and ESR spectra reveal that at lower Cr content (Si/Cr>30), only Cr (VI) and Cr(V) species exist in the mesoporous framework, and at higher Cr content, the Cr (III) species appeares. The catalysis ability of Cr-doped MCM-48-like large mesoporous silica for the oxidation of cyclohexane by hydroperoxide (H2O2) was also investigated and the conversion percent was high to 53%. The experiment using tert-butylhydroperoxide (TBHP) as oxidatnt got 86% cyclohexnone selectivity.
Authors and Affiliations
Lei WANG , Lingzhi WANG , Guodong CHEN , Jinlong ZHANG
Keywords
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