The role of zeolite Fe-ZSM-5 porous structure for heterogeneous Fenton catalyst activity and stability

• Activity of 330-nm Fe-ZSM-5 crystals in H2O2 decomposition is 1.4 times higher compared with large crystals.
• Catalytic activity of ferric species consisting amorphous silica phase is significantly lower.
• Ferric sites composed of zeolite are stable due to limited diffusion of complexing agents in microporous structure.
• Ferric species supported on amorphous silica are extremely unstable.

Four types of iron containing materials have been synthesized: conventional zeolite Fe-ZSM-5 (conv), hierarchical zeolite Fe-ZSM-5 (hier), small crystals (d = 330 nm) of zeolite Fe-ZSM-5 (nano) and ferric oxide species supported on the amorphous silica Fe/SiO2. Samples were prepared by hydrothermal treatment, polystyrene spheres were used as a template for Fe-ZSM-5 (hier) and Fe/SiO2. The materials were characterized by different techniques. Nature of iron-containing particles in the samples and stability of iron species in the reaction media were suggested by using thermodynamic considerations. All solid-phase Fe-containing samples as well as dissolved Fe(NO3)3 were tested in H2O2 decomposition reactions in absence or presence of iron-complexing agent Na2EDTA, which has been used to test the catalyst stability. Catalytic activity of ferric species in hydrogen peroxide decomposition for small 330-nm crystals of Fe-ZSM-5 was 1.4 times higher than for large zeolite crystals, and significant decrease of the activity was observed for samples containing amorphous silica phase. Experimental results showed that ferric sites in zeolite were stable due to the limited diffusion of Na2EDTA in zeolite phase. Wet hydrogen peroxide oxidation of organic complexing agents by H2O2 using Fe-containing zeolites has a good potential for purification of nuclear waste water.

Figure optionsDownload as PowerPoint slide