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Synthesis of mullite and Cu / or Fe mullite and their catalytic activity in wet peroxide oxidation of phenol

Introduction Due to their open framework, zeolites are metastable materials, which can be transformed into non-zeolite crystalline aluminosilicates above a certain temperature [1-2]. Since many of the synthetic zeolites have compositions close to those of aluminosilicate-based ceramics, their thermal treatment may result in the formation of ceramic materials, such as mullite. [3]. The need of temperature stable catalysts with selective characteristics induced the synthesis of metal incorporated mullite. The improved new catalysts are designed for the wet oxidation of phenol solutions that are found to be one of the most important representative of organic pollutants and are toxic even at low concentration [4]. Experimental Zeolite A was synthesised by a known synthesis procedure [5]. Ion exchange of the original Na+ ions from the starting zeolite precursor with NH4+ ions was carried out by previously described procedure [6]. The resulting NH4A was then partial exchanged with Cu /Fe from copper nitrate or iron chloride solution, respectively. Post synthesis thermal induced transformations of ammonium, iron and copper form of zeolite A at the appropriate temperature (1273K) and time (3h) in a controlled-temperature chamber furnace yield into a mixture of mullite and amorphous SiO2 in the first case, Fe-mullite and amorphous SiO2 in the second case and to Cu-mullite and SiO2 in the third case. Alkaline treatment of the resulting powder mixtures in 2MNaOH solution resulted to pure mullite, Fe-mullite and Cu-mullite phases after the dissolution of the entire crystal content of amorphous SiO2. The final products were characterized by Fourier Transform Infra Red spectroscopy, X-ray diffraction and Scanning electron microscopy. The evaluation of their catalytic performances for the wet hydrogen peroxide oxidation of phenol was carried out in a stainless steel Parr reactor in batch operation mode under the conditions of the experiments listed in Table 1. Table 1. Experimental conditions for the estimation of catalytic activity Catalyst mCAT=0.1gdm-3 of mullite Fe-mullite Cu-mullite Temperature(K) 353 Pressure(kPa) 100 cphenol(moldm-3) 0.01 cH2O2(moldm-3) 0.1 Results and discussion Figure 1. presents the conversion of phenol as a function of the time over mullite, Cu-mullite and Fe-mullite under the same conditions of the experiment. The highest decrease in phenol concentration showed Fe-mullite catalyst. Figure 1. Phenol oxidation over mullite, Cu-mullite and Fe-mullite Conclusions The present study reports on the catalytic oxidation of phenol on Cu / or Fe exchanged mullite catalyst. Incorporating specific cations (Cu, Fe) into mullite has been found to be a useful technique for improving catalytic properties as it is obtained from the results on the catalytic oxidation of phenol. Acknowledgements The authors thank the Ministry of Science of the Republic of Croatia for financial support. References [1] Subramanian, M.A., Corbin, D.R., Chowdhry, U., Better ceramic substrates through zeolites, Bulletin of Material Science., 16 (1993), 665-678 [2] Dell’Agli, G., Ferone, C., Mascolo, M.C., Pansini, M., Thermal transformation of Ba-exchanged A and X zeolites into monoclinic celsian, Solid State Ionics 127 (2000), 309-317 [3] Kosanović, C., Subotić, B., Invariability of the particulate properties during the thermal treatment of potassium-exchanged zeolite A: evidence for “amorphous crystals”, Microporous Materials, 12 (1997), 261-266 [4] Catrinescu, C., Teodosiu, C., Macoveanu, M., Miehe-Brendl!e, J., Le Dred, R., Catalytic wet peroxide oxidation of phenol over Fe-exchanged pillared beidellite, Water Research, 37 (2003), 1154–1160 [5] Thompson R.W. , Franklin K.C., Verified Syntheses of Zeolitic Materials, H. Robson (ed.) Second Revised Edition, Elsevier Science, Amsterdam (2001), 179-180 [6] Kosanović, C., Čižmek, A., Subotić, B., Šmit, I., Stubičar, M., Tonejc, A., Mechanochemistry of zeolites: Part 4, Influence of cations on the rate of amorphization of zeolite A by ball milling, Zeolites, 15 (1995), 632-636

Cu/or Fe exchanged mullite catalyst; catalytic oxidation; phenol; hydrogen peroxide

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