Catalytic Properties Of The Chloroorganic Deposits On Zeolite Supports
CATALYTIC PROPERTIES of THE CHLORoorganic DEPOSITS ON ZEOLITE SUPPORTS
M. Gasior1, J.J. Oszczudlowski2
1Institute of Catalysis and Surface Chemistry, Polish Academy of Sciences,
ul. Niezapominajek 8, 30-239 Cracow, Poland,
e-mail: ncgasior@cyf-kr.edu.pl
2Institute of Chemistry, Pedagogical University,
ul. Checinska 5, 25-020 Kielce, Poland, e-mail: josz@pu.kielce.pl
Products of monomolecular elimination of hydrogen chloride with formation of chloroolefines and olefins, C-C bond disintegration with generation of free radicals and formation of carbonaceous and chloroorganic deposits on the catalysts surface, result from catalytic transformation of chloroorganic derivatives of hydrocarbons with two carbon atoms (i.e. 1,2-dichloroethane, trichloroethane, trichloroethene, or tetrachloroethene) [1].
Catalytic decomposition of chlorine-derivatives in the atmosphere of neutral gas leads to formation of polychlorinated deposits from chloroolefines and quick catalysts inactivation. Carbon deposits on the catalysts surfaces may be precursors for other catalytic processes, or may be active centers, such as in dehydrogenation of ethylobenzene to styrene [2].
Investigations were performed to observe the catalytic properties of zeolite samples with carbonaceous and chloroorganic deposits for oxidation of toluene and xylenes in the liquid phase, in the presence of hydrogen peroxide solution. The application of such catalysts was connected with hydrophobic properties of so called "coked" catalysts. High hydrophobic properties of chloroorganic deposits simplify catalytic oxidation of organic compounds in the liquid phases.
Chloroorganic deposits were obtained in transformation of 1,1,1-trichloroethane, in the gaseous phase, at temperature 623 K. The following catalysts were used in this reaction: Al2O3, zeolites: NaY and ZSM-5, modified by lanthanum (III) ions.
In the presence of zeolite catalysts, the oxidation of toluene leads to generation of benzoaldehyde, cresol and metyloquinone. Toluene conversion
is more effective in the presence of catalysts with deposit. Thus, chloroorganic deposit is active during oxidation of selected hydrocarbons.
The experimental results show that "coked" zeolite samples posses significant activity for both the oxidation of methyl groups and the hydroxylation of aromatic ring.
After catalytic oxidation in the liquid phase, the analysis of aqueous solutions for the presence of lanthanum and chlorine was performed, using the XRF method with molybdenum tube. After oxidation of selected aromatic hydrocarbons in the presence of zeolites without deposit, the lanthanum ions are detected in solutions. Deposits on the surface of catalysts stop the process of lanthanum ions releasing, during the oxidation of toluene and xylenes in the liquid phase, in the presence of hydrogen peroxide solution.
Conclusions:
1. Zeolite catalysts with deposit were more active in the oxidation of selected aromatic hydrocarbons.
2. Deposits on the surface of catalyst stop releasing lanthanum ions during oxidation.
3. The composition of oxidation products is an evidence for relatively low selectivity of catalysts.
References
1. J. Oszczudłowski, Works & Studies of the Institute of Environmental Engineering of the Polish Academy of Sciences, Zabrze, 2000, vol. 53, p. 129.
2. T. G. Alkhazov, A. E. Lisovskii, M. G. Safarov, A. M Dadasheva, Kinet. Katal., 1972, vol. 13, p. 509.
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