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Influence of Postsynthesis Thermal Treatment on Properties of Cu/13X Catalyst in Catalytic Wet Peroxide Oxidation of Phenol

Introduction To this day numerous scientific investigations are conducted in order to develop new technologies for most effective purification of wastewaters polluted with organic compounds such as phenol and its derivatives. Therefore, it is of the most importance to constantly develop new and improve existing technologies in order to enhance wastewater treatment processes. Low-temperature, aqueous-phase heterogeneous catalytic oxidation of dissolved organic compounds is a potential means for remediation of contaminated industrial effluents and other wastewater streams. Catalytic wet peroxide oxidation, known as CWPO process is one of the methods that can be used for the minimization of organic pollution in practice. With the use of catalyst (homogeneous or heterogeneous) the process can be successfully operated under mild conditions with low energy consumption - atmospheric pressure and temperatures bellow 353 K Commercial zeolite type 13X was selected as catalyst support for copper cations. Activity and stability of such prepared catalyst was tested in catalytic wet peroxide oxidation of phenol in aqueous medium. Influence of postsynthesis thermal treatment on activity and stability of prepared catalysts in the catalytic wet oxidation process with hydrogen peroxide as oxidant was investigated. Special attention was directed towards evaluation of catalysts' stability in terms of copper leeching into reaction mixture. Experimental Copper bearing 13X zeolite was prepared from commercial 13X zeolite via ion-exchange with copper acetate solutions. After the incorporation of copper Cu/13X catalyst was exposed to post synthesis thermal treatment at three different temperatures (773, 1023 and 1273 K). The prepared catalysts were characterized by XRD and FTIR, while the adsorption techniques were used for the measurement of the specific surface area and pore volume. The catalytic tests were carried out in a stainless steel Parr reactor in batch operation mode at atmospheric pressure at 353 K. Results The incorporation of copper on 13X zeolite did not have a significant effect on the measured surface area and pore volume since the values obtained for 13X and Cu/13X are in good accordance. On the other hand, the thermal treatment caused the decrease of both BET surface area and pore volume. Copper content of all samples was around 3.5 wt. % and wasn't affected by thermal treatment. Copper bearing zeolite calcined at 773 K retains the crystal structure of FAU zeolite, while the catalysts that were thermally treated at 1023 and 1273 K exhibit a change in number, intensity and position of peaks. By heating above 773 K Cu/13X catalyst undergoes phase transformations: amorphization (1023 K) and recrystallization of new phase (1273 K) that was identified as nepheline. The experimental results showed that total degradation of phenol can be achieved under mild operating conditions. The postsynthesis thermal treatment resulted in more stable catalyst in respect to stability of both catalysts' active metal component (copper) and support while the activity of catalysts in terms of TOC conversion remained unaltered.

Zeolites; postsynthesis thermal treatment; hydrogen peroxide; CWPO

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