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COMO, III. Workshop on Oxide Based Materials, 13-16. October 2004.
CATALYTIC WET PEROXIDE OXIDATION OF PHENOL OVER
ZEOLITES CONTAINING COPPER
K. Maduna1, T. Granato2, A. Katovic2, G. Giordano2
1
Faculty of Chemical Engineering and Technology, University of Zagreb, Croatia
2
Dip. Ing. Chim. & Mat., Università della Calabria, I-87036 Rende (CS), Italy
Introduction
One of the new emerging oxidation processes - catalytic wet peroxide oxidation (CWPO) is
being studied for the use in the treatment of industrial wastewater. This method of waste treatment
is specially appealing from the ecological standpoint due to its ability to eliminate pollutants as
oppose to classical oxidation that results in turning the pollution from one form into another. The
process is operated at mild conditions (0.1-0.5 MPa, T≤100 ºC), and therefore with low energy
requirements, with the addition of different types of catalysts. In the recent years, only a few
studies dealing with the use of zeolites containing copper were reported, making this aspect of the
process open for further investigations.1,2
It has been reported that metal bearing zeolites prepared using classical procedures show severe
metal leaching, leading to side reactions catalyzed in homogeneous phase.3 The aim of the present
work is to study heterogeneous catalytic wet peroxide oxidation of phenol using copper bearing
FAU and MFI zeolites prepared by direct hydrothermal synthesis. The effect of the presence of the
inorganic cation in the zeolite structure, as well as leaching of the active metal component were
also studied.
Experimental
The starting synthesis systems for the preparation of copper bearing zeolite catalysts
Cu-FAU (I) and Cu-MFI (II) were:
(II)
(I)
6 Na2O – 0.35 Al2O3 – 0.3 Cu(NO3)2/0.9 H3PO4 – 1 SiO2 – 240 H2O
0.16Na2O – 0.08TPABr – 0.0075Al2O3 – 0.015Cu(NO3)2/0.03H3PO4 – 1SiO2 – 20H2O
The sources of materials used were: precipitated or colloidal silica, sodium aluminate, copper
nitrate, phosphoric acid, organic compound and distilled water. In the (II) synthesis system TPABr
stays for tetrapropylammonium bromide. The samples were characterized by: powder X-ray
diffraction (XRD), scanning electron microscopy (SEM), atomic absorption spectroscopy (AAS),
while the adsorption techniques were used for the measurement of the specific surface area.
Cu-Na-FAU and Cu-Na-MFI samples were treated with 1M solution of NH4Cl at 80 °C for 2 hours
in order to exchange the metal cation and to prepare the zeolites in the protonic form: Cu-H-FAU
and Cu-H-MFI, respectively.
The post synthesis thermal treatment consisted in the calcination of the samples at 550°C for 5
hours.
The catalytic tests were carried out in a 500 cm3 thermostated stirred batch reactor. The catalyst
was introduced in the phenol aqueous solution (1 g/L) at 70 °C followed by the addition of the
required amount of the hydrogen peroxide solution. The change of phenol concentration during the
reaction was monitored with an UV-VIS spectrophotometer, while the concentration of the
remaining H2O2 was determined by a modified iodometric titration method. The leaching of copper
during the oxidation process was determined by AAS.
Results and Discussion
The screening tests were performed in order to optimize the following reaction parameters:
catalyst amount, H2O2 concentration and reaction temperature.
The obtained results put in evidence that the samples prepared by direct hydrothermal synthesis
show promising catalytic performances. Furthermore, it was observed that the H- form of the
Cu-MFI catalyst showed no catalytic activity (Fig.1) as opposed to the H- form of the Cu-FAU
catalyst that exhibited higher phenol conversions (Fig.2).
100
100
95.2
98.8
99.4
99.5
97.7
Cu-H-MFI
50
Cu-Na-MFI
73.8
60
Cu-Na-FAU
Cu-H-FAU
50
35.2
52.4
0
0
0
5.04
0
6.56
8.96
0
30
t, min
0
0
6.5
7.9
0
60
5
120
30
60
t, min
Figure 1. Catalytic activity of MFI samples
120
Figure 2. Catalytic activity of FAU samples
The copper bearing zeolites prepared following the metal complex method allows preparation of
materials with controlled metal loading and stable active copper species.
References:
1. H. Debellefontaine, M. Chakchouk, J.N. Foussard, D. Tissot, P. Stirolo, Environmental
Pollution 92 (1996) 155-164
2. G. Ovejero, J.L. Sotelo, F. Martinez, L. Gordo, Water Science and Technology, 44 (2001)
153-160