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Decomposition of water over zeolites with possibilities for measuring mass variation of zeolite during irradiation
Renewable Energy 19 (2000) 97±102 www.elsevier.com/locate/renene
Decomposition of water over zeolites with possibilities for measuring mass variation of zeolite during irradiation Magdalena Momirlan* Institute of Physical Chemistry, ``I.G. Murgulescu'', Romanian Academy, Spl. Independentei 202, Bucharest, 77208, Romania
Abstract An experimental device for catalytic decomposition of water over zeolites with possibilities of measuring the mass variation of zeolites during UV radiation was built. By means of an electronic microbalance to which an irradiation system of zeolites was added, mass variation of samples and temperature rise of zeolites during irradiation was measured. Microgravimetric measurements of mass variation of zeolites during irradiation were accomplished at the same time with the study of the temperature increase during irradiation. The decrease in weight of zeolites during irradiation, assigned to the elimination of water molecules from zeolite was noticed. # 1999 Published by Elsevier Science Ltd. All rights reserved.
1. Introduction The dissociation of water using light quanta represents a nonconventional method of hydrogen generation. The use of light energy for water dissociation is possible because water vapor absorbs light (ultraviolet radiation photons of 1949 AÊ). * Tel.: +00-40-1-7255857. E-mail address: mmagdalena@chim®z.icf.ro (M. Momirlan) 0960-1481/00/$ - see front matter # 1999 Published by Elsevier Science Ltd. All rights reserved. PII: S 0 9 6 0 - 1 4 8 1 ( 9 9 ) 0 0 0 2 2 - 1
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M. Momirlan / Renewable Energy 19 (2000) 97±102
Zeolites and zeolite-like materials are based essentially on tetrahedral networks which encompass channels and cavities [1]. Sorbate molecules of various sizes can be accommodated in these intercrystalline voids and undergo chemical reactions subject to stereochemical constraints. According to common views zeolites are based on open and fully crosslinked framework structures of corner-sharing SiO4 and AlO4 tetrahedra [2,3]. Mm=z mAlO2 nSiO2 qH2 O: Mordenite is one of the siliceous zeolites and a typical formula of synthetic mordenite is: Me2/zO[Al2O3 (9±10)SiO2] 6H2O. In our experiments the acid form mordenite was used: H8 Al8 Si40 O96 24H2 O
FeH-mordenite
Fig. 1. Experimental unit for catalytic decomposition of water over zeolites with possibilities for measuring mass variation of the zeolite during irradiation: 1. electrical bath; 2. vacuum valve; 3, 4. thermocouple Pt±Pt Rh; 5. microbalance; 6, 7. quartz tubes; 8, 9. threads for hanging of sample and counterweight; 10, 11. furnaces; 12. irradiation lamp; 13. continuous current ampli®er; 14. hydrogen collecting vessel.
M. Momirlan / Renewable Energy 19 (2000) 97±102
99
obtained from Na form: Na8 Al8 Si40 O96 24H2 O through ionic exchange of Na with H
2. Experimental An experimental device for decomposition of water over zeolites with possibilities for measuring the mass variation of zeolite during UV was built up (Fig. 1). 3. Results Zeolite is active in a vacuum and when it is taken out in the atmosphere is deactivated, gaining the same weight lost in the vacuum. Starting from the performed researches, we can conclude that a zeolite is activated considering when the maximum decrease in weight was registered, proving the complete elimination of water from intercrystalline channels.
Fig. 2. Behaviour of the catalyst to heating with temperature programing to 5508C, in air, after irradiating with UV radiations.
100
M. Momirlan / Renewable Energy 19 (2000) 97±102
Table 1 Hydrogen volumes generated over FeH-mordenites according to the process Activation no.
H2 generating stage
Produced H2 (ml) On stages
Total after activation
I
1 2 3 4 5
0.210 0.165 0.012 0.003 0.001
0.390
II
1 2 3 4 5
0.140 0.126 0.090 0.030 0.002
0.388
III
1 2 3 4 5
0.185 0.102 0.083 0.012 0.005
0.387
IV
1 2 3 4 5
0.163 0.127 0.088 0.021 0.011
0.410
V
1 2 3 4 5
0.209 0.102 0.059 0.013 0.007
0.390
VI
1 2 3 4 5
0.199 0.099 0.046 0.020 0.006
0.370
VII
1 2 3 4 5
0.213 0.101 0.061 0.011 0.004
0.390
VIII
1 2 3 4 5
0.234 0.082 0.073 0.064 0.009
0.462
M. Momirlan / Renewable Energy 19 (2000) 97±102
101
Table 1 (continued ) Activation no.
H2 generating stage
Produced H2 (ml) On stages
Total after activation
IX
1 2 3 4 5
0.201 0.104 0.063 0.016 0.006
0.390
X
1 2 3 4 5
0.203 0.084 0.042 0.009 0.000
0.338
In the case of irradiations with ultraviolet light, the distance between the zeolite and the irradiation source is important. The temperature of the sample was increased from room temperature up to 708C. Microgravimetric measurements of mass variation of the zeolite during irradiation were accomplished at the same time with the study of the temperature increase during irradiation. The decrease in weight of the zeolites during irradiation, due to elimination of water molecules from the zeolite was noted (Fig. 2). Zeolites modi®ed with Ag can be used at water dissociation in hydrogen and oxygen: 1 hg ÿ4 2Ag0 2ZOH O2 2Ag 2ZOÿ ÿ H2 O ÿ 2 zeolite with Ag+ ions. The OH groups are lost after a thermal treatment and H2 is evolved [4]. 1 t0 ÿ4 Ag ZOÿ H2 Ag0 ZOH ÿ 2 The results of hydrogen evolution by decomposition of water in the presence of FeH-mordenites are given in Table 1. After eecting one experiment of successive H2 generation the catalyst undergoes a second process of activation, followed by the reaction. The steps generation stages of H2 are referred to hydrogen volumes collected successively in a reaction cycle. The second and third columns of Table 1 suggest that the hydrogen collected in
102
M. Momirlan / Renewable Energy 19 (2000) 97±102
the last stage of one reaction cycle is much less than in the ®rst, which denotes a deactivation of the catalyst during the reaction. This ®nding imposed the catalyst activation by another cycle. From Table 1 it is noticed that after 10 activations, the catalyst does not present any tendency of weakening its eciency. 4. Conclusion A low degree of water conversion in hydrogen in a cyclic process was developed, use has been made of an experimental device which aords measuring of the mass variation of zeolites during irradiation with UV light. Acknowledgements The author is indebted to Dr G. Pop for the synthesis of zeolites. References [1] Anpo M, Negishi N, Nishiguchi H. Critical Reviews in Surface Chemistry 1993;3 (2):131±69. [2] Murakami Y, Iijina A, Ward JW. In: Proceedings of the 7th International Zeolite Conference, Tokyo, 1986. [3] Meier WM, Olson DH. Atlas of Zeolite Structure Types, 3rd revised ed. Butterworth-Heinemann, 1992. [4] Zamaraev KI, Parmon VN. Catal Rev 1980;22 (2):261±324.
Decomposition of water over zeolites with possibilities for measuring mass variation of zeolite during irradiation Magdalena Momirlan* Institute of Physical Chemistry, ``I.G. Murgulescu'', Romanian Academy, Spl. Independentei 202, Bucharest, 77208, Romania
Abstract An experimental device for catalytic decomposition of water over zeolites with possibilities of measuring the mass variation of zeolites during UV radiation was built. By means of an electronic microbalance to which an irradiation system of zeolites was added, mass variation of samples and temperature rise of zeolites during irradiation was measured. Microgravimetric measurements of mass variation of zeolites during irradiation were accomplished at the same time with the study of the temperature increase during irradiation. The decrease in weight of zeolites during irradiation, assigned to the elimination of water molecules from zeolite was noticed. # 1999 Published by Elsevier Science Ltd. All rights reserved.
1. Introduction The dissociation of water using light quanta represents a nonconventional method of hydrogen generation. The use of light energy for water dissociation is possible because water vapor absorbs light (ultraviolet radiation photons of 1949 AÊ). * Tel.: +00-40-1-7255857. E-mail address: mmagdalena@chim®z.icf.ro (M. Momirlan) 0960-1481/00/$ - see front matter # 1999 Published by Elsevier Science Ltd. All rights reserved. PII: S 0 9 6 0 - 1 4 8 1 ( 9 9 ) 0 0 0 2 2 - 1
98
M. Momirlan / Renewable Energy 19 (2000) 97±102
Zeolites and zeolite-like materials are based essentially on tetrahedral networks which encompass channels and cavities [1]. Sorbate molecules of various sizes can be accommodated in these intercrystalline voids and undergo chemical reactions subject to stereochemical constraints. According to common views zeolites are based on open and fully crosslinked framework structures of corner-sharing SiO4 and AlO4 tetrahedra [2,3]. Mm=z mAlO2 nSiO2 qH2 O: Mordenite is one of the siliceous zeolites and a typical formula of synthetic mordenite is: Me2/zO[Al2O3 (9±10)SiO2] 6H2O. In our experiments the acid form mordenite was used: H8 Al8 Si40 O96 24H2 O
FeH-mordenite
Fig. 1. Experimental unit for catalytic decomposition of water over zeolites with possibilities for measuring mass variation of the zeolite during irradiation: 1. electrical bath; 2. vacuum valve; 3, 4. thermocouple Pt±Pt Rh; 5. microbalance; 6, 7. quartz tubes; 8, 9. threads for hanging of sample and counterweight; 10, 11. furnaces; 12. irradiation lamp; 13. continuous current ampli®er; 14. hydrogen collecting vessel.
M. Momirlan / Renewable Energy 19 (2000) 97±102
99
obtained from Na form: Na8 Al8 Si40 O96 24H2 O through ionic exchange of Na with H
2. Experimental An experimental device for decomposition of water over zeolites with possibilities for measuring the mass variation of zeolite during UV was built up (Fig. 1). 3. Results Zeolite is active in a vacuum and when it is taken out in the atmosphere is deactivated, gaining the same weight lost in the vacuum. Starting from the performed researches, we can conclude that a zeolite is activated considering when the maximum decrease in weight was registered, proving the complete elimination of water from intercrystalline channels.
Fig. 2. Behaviour of the catalyst to heating with temperature programing to 5508C, in air, after irradiating with UV radiations.
100
M. Momirlan / Renewable Energy 19 (2000) 97±102
Table 1 Hydrogen volumes generated over FeH-mordenites according to the process Activation no.
H2 generating stage
Produced H2 (ml) On stages
Total after activation
I
1 2 3 4 5
0.210 0.165 0.012 0.003 0.001
0.390
II
1 2 3 4 5
0.140 0.126 0.090 0.030 0.002
0.388
III
1 2 3 4 5
0.185 0.102 0.083 0.012 0.005
0.387
IV
1 2 3 4 5
0.163 0.127 0.088 0.021 0.011
0.410
V
1 2 3 4 5
0.209 0.102 0.059 0.013 0.007
0.390
VI
1 2 3 4 5
0.199 0.099 0.046 0.020 0.006
0.370
VII
1 2 3 4 5
0.213 0.101 0.061 0.011 0.004
0.390
VIII
1 2 3 4 5
0.234 0.082 0.073 0.064 0.009
0.462
M. Momirlan / Renewable Energy 19 (2000) 97±102
101
Table 1 (continued ) Activation no.
H2 generating stage
Produced H2 (ml) On stages
Total after activation
IX
1 2 3 4 5
0.201 0.104 0.063 0.016 0.006
0.390
X
1 2 3 4 5
0.203 0.084 0.042 0.009 0.000
0.338
In the case of irradiations with ultraviolet light, the distance between the zeolite and the irradiation source is important. The temperature of the sample was increased from room temperature up to 708C. Microgravimetric measurements of mass variation of the zeolite during irradiation were accomplished at the same time with the study of the temperature increase during irradiation. The decrease in weight of the zeolites during irradiation, due to elimination of water molecules from the zeolite was noted (Fig. 2). Zeolites modi®ed with Ag can be used at water dissociation in hydrogen and oxygen: 1 hg ÿ4 2Ag0 2ZOH O2 2Ag 2ZOÿ ÿ H2 O ÿ 2 zeolite with Ag+ ions. The OH groups are lost after a thermal treatment and H2 is evolved [4]. 1 t0 ÿ4 Ag ZOÿ H2 Ag0 ZOH ÿ 2 The results of hydrogen evolution by decomposition of water in the presence of FeH-mordenites are given in Table 1. After eecting one experiment of successive H2 generation the catalyst undergoes a second process of activation, followed by the reaction. The steps generation stages of H2 are referred to hydrogen volumes collected successively in a reaction cycle. The second and third columns of Table 1 suggest that the hydrogen collected in
102
M. Momirlan / Renewable Energy 19 (2000) 97±102
the last stage of one reaction cycle is much less than in the ®rst, which denotes a deactivation of the catalyst during the reaction. This ®nding imposed the catalyst activation by another cycle. From Table 1 it is noticed that after 10 activations, the catalyst does not present any tendency of weakening its eciency. 4. Conclusion A low degree of water conversion in hydrogen in a cyclic process was developed, use has been made of an experimental device which aords measuring of the mass variation of zeolites during irradiation with UV light. Acknowledgements The author is indebted to Dr G. Pop for the synthesis of zeolites. References [1] Anpo M, Negishi N, Nishiguchi H. Critical Reviews in Surface Chemistry 1993;3 (2):131±69. [2] Murakami Y, Iijina A, Ward JW. In: Proceedings of the 7th International Zeolite Conference, Tokyo, 1986. [3] Meier WM, Olson DH. Atlas of Zeolite Structure Types, 3rd revised ed. Butterworth-Heinemann, 1992. [4] Zamaraev KI, Parmon VN. Catal Rev 1980;22 (2):261±324.