Modification Of Ukrainian Natural Zeolite Rocks Towards The Catalysts
MODIFICATION OF UKRAINIAN NATURAL ZEOLITE ROCKS TOWARDS THE CATALYSTS
K. Patrylak1, F. Bobonych2, Yu. Voloshyna2, L. Patrylak1
1Institute of Bioorganic Chemistry and Petrochemistry of National Academy of Sciences of Ukraine, Kyiv, Ukraine
2L.V. Pisarzhevskij Institute of Physical Chemistry of National Academy of Sciences of Ukraine, Kyiv, Ukraine
The acid treatment of preliminary decationized mordenite-clinoptilolite rocks (Lypcha deposit, Ukraine), unlike the treatment of the starting ones, is more effective way for the preparation of linear hexane isomerization catalyst on the basis of natural zeolites [1,2]. In the present work some peculiarities of the decationization procedure as such one, which influences the dealumination results and, respectively, the catalytic activity of Pd-containing (0.5 wt %) catalysts based on dealuminated decationized rocks, are studied.
The rocks of 3:1 and 1:1 mordenite/clinoptilolite ratios (rocks A and B respectively) as well as the pure natural clinoptilolite [2] were investigated. It was determined that previous decationization of the rocks essentially increases their acid stability (Table), manly due to the sharp increase of clinoptilolite phase acid resistance.
Table. Influence of Acid Treatment on Chemical Composition (Si/Al), Characteristic Water Adsorption Energy (E, kJ/mol) and Micropore Volumes with Respect to n-Hexane (W, cm3/g) of Mordenite-Clinoptilolite Rocks
HCl mo-larity
Rock B
H-form of rock B
H-form of rock A
Si/Al
E
W
Si/Al
E
W
Si/Al
E
W
0
4.5
25.2
0.031
4.5
19.2
0.043
4.7
18.9
0.047
0.5
5.7
20.3
0.069
5.1
19.9
0.071
-
-
-
1
6.8
17.1
0.080
5.2
20.0
0.071
6.2
15.5
0.077
3
9.2
14.1
0.077
5.4
19.4
0.079
7.0
15.8
0.081
5
13.0
11.4
0.070
5.8
18.7
0.082
7.8
15.9
0.084
To a certain extent, the increase of above acid stability, as a result of previous decationization, is due to the loss of a part of aluminium atoms by zeolite framework during high-temperature (875 K) treatment of NH4 forms of the rocks. The decrease of the characteristic water adsorption energy from 27.1 [3] and 25.2 kJ/mol to 18.9 and 19.2 kJ/mol (Table) for starting and decationized forms of rock A and B, respectively, testifies to such a loss of aluminium. The part (about 25 %) of aluminium atoms was estimated to be located in the extraframework positions. Such a localization results in some locking of micropores, to what the W values decrease from 0.073 [3] to 0.047 cm3/g (Table) for NH4 and decationized rock A forms, testifies. Micropores become accessible to linear hexane after acid treatment by weak HCl solutions.
Judging from E values and Si/Al ratios (Table), aluminium passes into solution on the acid dealumination of the rock H-forms either mainly (rock B) or preferentially (rock A) as extraframework one. It was stated by the experiments on displacement of extraframework aluminium into NH4Cl solution that such an aluminium partially is in ion exchangeable state.
Extraframework aluminium in acid treated samples of predecationized rocks it was shown to influence their catalytic properties.
It is supposed that transition of a part of aluminium to extraframework state, the acid stability of mordenite and clinoptilolite phases as a result of the previous rock decationization being leveled, leads to the more uniform distribution of aluminium atoms in acid treated crystals of mordenite and clinoptilolite in comparison with such one for acid treated starting rocks. The increase of distribution uniformity of aluminium atoms along the radius zeolitic crystals promotes an efficiency increase of catalysts based on mordenite-clinoptilolite rocks.
References
1. Patrylak K.I., Bobonych F.M., Voloshyna Yu.G., Levchuk M.M. et al. // Appl. Catal. A: General.-1998.-174,№1-2.-P.187-198.
2. Patrylak K.I., Bobonych F.M., Voloshyna Yu.G., Levchuk N.N. et al. // Zhurn. Prikl. Khimii.-1999.- 72,№11.-P.1836-1841.
3. Bobonych F.M. // Teor. Eksperim. Khimiya.-1994.-30,№1.-P.12-24.
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