FeAl12-Keggin type cation as an active site source for Fe,Al-silica mesoporous catalysts

Iron-containing mesoporous mesophase materials Fe,Al-MMM-2 have been synthesized according to a sol-mesophase route under mild acidic conditions (pH 2.3–4.4) using Keggin type cation [FeAl12O4(OH)24(H2O)12]7+ (FeAl127+) as Al and Fe sources. Effect of pH of the synthetic solution on structural and physicochemical properties of Fe,Al-MMM-2 has been evaluated by means of small- and wide-angle XRD, FTIR, DR-UV–vis, and N2-adsorption/desorption analysis. It has been established that deviation of stability of FeAl127+ cation at various pH determines Al/Fe ratio in the resulting material as 12/1 (material synthesized at pH 4.4), and 6/1 (pH 2.4 and 3.3). Correlation between incorporation of Al and Fe in different forms and resulting materials texture is discussed. Fe,Al-MMM-2 materials have been tested as catalysts for wet phenol oxidation with H2O2. Insertion of Al species into the framework of the silicate matrix increases the activity comparing to a reference Fe,Al-pillared clay due to both higher surface acidity and lower diffusion limitations that correspond to Fe,Al-MMM-2.