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Solid-solid interaction between manganese carbonate and zinc carbonate and the decomposition of H2O2 over mixed zinc-manganese oxide catalysts
June 1995
ELSEVIER
Materials Letters 24 (1995) 97-101
Solid--solid interaction between manganese carbonate and zinc carbonate and the decomposition of H202 over mixed zinc-manganese oxide catalysts M.K. El-Aiashy, H.S. Mazhar, S.M. Kamal University College for Girls, Ain Shams University, Cairo, Egypt
Received 15 November 1994; in final form 10 March 1995; accepted 4 April 1995
Abstract Pure mixed zinc carbonate and manganese carbonate with molar ratios 3 : 1, 1: 1 and 1: 3 with respect to ZnO : MnOa were prepared. The thermal decomposition of pure salts was studied using DTA. Pure and mixed salts were subjected to thermal treatment at 250,500, ‘150and 1000°C. The decomposition products were characterized by means of X-ray diffraction analysis. The results obtained were used to discuss the different structures of the thermal products of the pure and mixed oxides, at the temperatures under investigation and their catalytic activities were tested in H202 decomposition. The catalytic activity of these solids in hydrogen peroxide decomposition was found to increase with the increase of activation temperature passing through a maximum at 500°C. The increase of calcination temperature above 500°C was accompanied by a decrease of the activity in HzOz decomposition. This may be attributed to sintering and/or formation of the inactive form of ZnMn,O,.
1. Introduction
2. Experimental 2.1. Materials
The decomposition of hydrogen peroxide was studied in many reports [ l-51. This process takes place in homogeneous systems. In catalysis, it is known that the
activity of metal oxide catalysts depends on many factors, such as methods of preparation, calcination conditions and the interaction between components of the catalyst [6,7]. These oxides can be used as catalysts for the production of oxygen from H,Oz instead of the expensive silver oxide or metallic platinum or palladium black [ 81. Numerous investigations have been reported dealing with various aspects of the chemistry of manganese oxides [9-l 11, and of manganese oxides mixed with oxides of other transition elements [ 12,131. Elsevier Science B.V. SSD10167-577x(95)00070-4
The starting materials &Co, - 2ZnO *3Hz0 and MnC03 were obtained from May&Baker Laboratory Chemicals (UK). Three mixtures of molar ratios 3 : 1 (I), 1: 1 (II) and 1: 3 (III) with respect to ZnO:MnO, were prepared by mixing the solids, homogenizing and grinding. The pure zinc carbonate, pure manganese carbonate and their mixtures I, II and III were heated at 250,500,750 and 1000°C each for 4 h.
2.2. Techniques Thermal analysis DTA, TG and DTG of pure zinc carbonate and manganese carbonate were carried out
M.K. El-Aiashy et al. /Materials L&ten 24 (1995) 97-101
98
at about 226°C due to the loss of water and carbon dioxide, and an exotherm around 282”C, which is attributed to the crystallization of zinc oxide. ZnC03 *2ZnO. 3H20 --) 3ZnO + CO2 -t 3H20 . 3.2. Thermal treatment of MnCO, The thermal decomposition of manganese carbonate as indicated by the data obtained by XRD and DTA is in good agreement with the previous studies [911,13,15]. Figs. 2-6 show that the decomposition can be summarized as follows: I
I
200
400
I
t
600
Fig. 1. DTA, TG and DTG plots for pure
620 Zn0.3H20.
t%
ZnCO,.2ZnO. 3&O.
using a Netzsch (West Germany) thermoanalyzer with a different scanning calorimeter cell. The rate of heating was 10°C min-‘. X-ray diffraction patterns were obtained at room temperature using a Philips diffractometer (type ~~1050) employing Ni-filter Cu LYradiation_ The Xray tube was operated at 36 kV and 16 mA. Samples were finely ground and packed in a plastic holder; no adhesive or binder was necessary. The diffraction angle 28 was scanned at a rate of 2 min- ‘. The activity of all samples for the decomposition of H202 was evaluated by the method suggested by Deren et al. [ 141 in which the rate of production of oxygen gas was used as a measure. The reaction was studied at 40°C.
MnCO, - 0.5Hz 0 1oo-3oo”cMnCO, +0.5Hz0, MnCO, 3oo-45o”cMnOz +CO, , 2Mn02
>45o-900 0 Mn,03(cubic) + $C02,
6Mnz 0, -
4Mn3 O,( tetragonal) -t O2 .
(3) (4)
3.3. Interaction between zinc and manganese carbonates
The X-ray diffraction patterns of pure solids and mixtures I, II and III thermally treated at 250,500,750 and 1000°C are presented in Figs. 3-6 respectively. At 25O”C,pure MnC03 was stable, while heating pure zinc
3. Results and discussion To study the solid-solid interaction between the two components at various temperatures, it seems reasonable to characterize the thermal products obtained from each of the components alone. 3. I. Thermal treatment of zinc carbonate Fig. 1 shows the DTA, TG and DTG plots of ZnC03 - 2ZnO. 3H,O. An examination of the TG-curve indicates that the compound begins its decomposition
(1)
Fig. 2. DTA, TG and DTG plots for pure MnC4.
M.K. El-Aiashy et al. /Materials Letters 24 (1995) 97-101
99
At this temperature, ZnO and Mn*Os were found to coexist with ZnMnzOd for mixtures II and III only. This means that the decrease of manganese content in mixtures II and III and the thermal treatment at 750°C for 4 h are not enough for complete combination of the individual oxides to form the monoclinic ZnMn,O,. At lOtWC, pure MnC03 produced tetragonal Mn304 and zinc carbonate gave ZnO crystalline phase. Heating of the mixtures at 1000°C leads to an increase in the formation of the compound ZnMn,O, and in the same time the lines of well crystalline ZnO appeared. 3.4. Catalytic activity of thermally treated mixed oxides
The decompositions of H,O, over the mixed oxides, thermally treated at different temperatures are graphi-
Fig. 3. X-ray diffraction patterns of pure and mixed carbonates heated at 250°C.
carbonate gave crystalline ZnO. X-ray analysis revealed that mixtures I, II and III heated at 250°C produced mainly crystalline ZnO and MnCO,. The increase of the treatment temperature up to 500°C was accompanied by an increase in the crystallization of ZnO and the appearance of cubic Mnp03 crystalline phase. The increase of manganese content showed an increase in the intensity of the lines characteristic of cubic Mnz03 and a decrease of those of ZnO. At 750°C the thermal treatment of mixtures was accompanied by a ‘detectable solid-solid interaction between Zn and Mn-oxides forming monoclinic ZnMn,O,: ZnO + Mnz O3 =z
ZnMnz04 .
Fig. 4. X-my diffraction patterns of pure and mixed carbonates heated at 500°C.
M.K. El-Aiashy et al. /Materials Letters 24 (1995) 97-101
100
-r--
1
MnC03
I L
I IO
3
3
I 50
I 30
Fig. 6. X-ray difiaction patterns of pure and mixed carbonates heated at 1000°C.
Fig. 5. X-ray diffraction patterns of pure and mixed carbonates heated at 750°C.
tally represented in Figs. 7-9. It can be seen that all the samples thermally treated at 250°C were active in H202 decomposition. The activity increased with the increase of manganese oxide content. The calcination of all samples at 500°C produced highly active catalysts compared with those thermally treated at 250°C. The effect of chemical composition on the catalytic activity of 500°C calcined catalysts is the same as for 250°C ones. Further increase of the calcination temperature of the mixed oxide catalysis produced solids with very low activity for H,Oz decomposition. This may be attributed to the sintering of the solid catalysis and/or formation of ZnMn,O,.
V, ml
t, min Fig. 7. The activity of catalyst I, preheated at various temperatures, in the decomposition of hydrogen peroxide.
M.K. El-Aiashy et al. /Materials Letters 24 (199s) 97-101
V, ml
101
V, ml
t, min ’ Fig. 8. The activity of catalyst II, preheated at various temperatures in the decomposition of hydrogen peroxide.
References [ 1 ] V. Mucka, Chem. Listy 709 ( 1968). [2] V. Mucka, Thesis Czech. Technical Univ., Praque (1971). [3] M.M. Selim and N.A. Youssef, J. Serb. Chem. Sot. 53 (1988) 157. [4] T. Mimani, P. Ravindranathan and K.C. Path, Proc. Indian Acad. Sci. Chem. Sc:i.99 (1987) 209. [5] K. Kishore and P.N. Moorthy, Radiat. Effects 105 (1988) 257. [6] G.C. Naiti and SK. Ghosh, Indian J. Chem. 24 A (1985) 513. [7] M.F.R. Fouda, R.S. ,4min and M.M. Selim, Thermochim. Acta 141 (1989) 277.
t, min Fig. 9. The activity of catalyst III preheated at various temperatures in the decomposition of hydrogen peroxide. 181 W.Z. Vielstich, Phys. Chem. 15 (1958) 409. [9] A. Muan and W.C. Hahn Jr., J. Phys. Chem. 63 ( 1959) 1826. [ 101 WC. Hahn Jr. and A. Muan, Am. J. Sci. 258 (1960) 66. [ 111 N.V. Sidgwich, Chemical elements and their compounds (Oxford Univ. Press, Oxford, 1951). [ 121 A. Muan and S. Somiya, Am. J. Sci. 260 (1962) 230. [ 131 H.J. Van Hook and M.L. Keith, Am. Mineralogist 43 (1958) 69. [ 141 J. Deren, J. Haber, A. Podgorckaand J. Siechowski, Bull. Acad. Pol. Sci. Ser. Sci. Chem. 10 ( 1966) 8 1. [ 151 M.M. Selim and L.B. Khalil. AFINIDAD 48 (1991) 167.
ELSEVIER
Materials Letters 24 (1995) 97-101
Solid--solid interaction between manganese carbonate and zinc carbonate and the decomposition of H202 over mixed zinc-manganese oxide catalysts M.K. El-Aiashy, H.S. Mazhar, S.M. Kamal University College for Girls, Ain Shams University, Cairo, Egypt
Received 15 November 1994; in final form 10 March 1995; accepted 4 April 1995
Abstract Pure mixed zinc carbonate and manganese carbonate with molar ratios 3 : 1, 1: 1 and 1: 3 with respect to ZnO : MnOa were prepared. The thermal decomposition of pure salts was studied using DTA. Pure and mixed salts were subjected to thermal treatment at 250,500, ‘150and 1000°C. The decomposition products were characterized by means of X-ray diffraction analysis. The results obtained were used to discuss the different structures of the thermal products of the pure and mixed oxides, at the temperatures under investigation and their catalytic activities were tested in H202 decomposition. The catalytic activity of these solids in hydrogen peroxide decomposition was found to increase with the increase of activation temperature passing through a maximum at 500°C. The increase of calcination temperature above 500°C was accompanied by a decrease of the activity in HzOz decomposition. This may be attributed to sintering and/or formation of the inactive form of ZnMn,O,.
1. Introduction
2. Experimental 2.1. Materials
The decomposition of hydrogen peroxide was studied in many reports [ l-51. This process takes place in homogeneous systems. In catalysis, it is known that the
activity of metal oxide catalysts depends on many factors, such as methods of preparation, calcination conditions and the interaction between components of the catalyst [6,7]. These oxides can be used as catalysts for the production of oxygen from H,Oz instead of the expensive silver oxide or metallic platinum or palladium black [ 81. Numerous investigations have been reported dealing with various aspects of the chemistry of manganese oxides [9-l 11, and of manganese oxides mixed with oxides of other transition elements [ 12,131. Elsevier Science B.V. SSD10167-577x(95)00070-4
The starting materials &Co, - 2ZnO *3Hz0 and MnC03 were obtained from May&Baker Laboratory Chemicals (UK). Three mixtures of molar ratios 3 : 1 (I), 1: 1 (II) and 1: 3 (III) with respect to ZnO:MnO, were prepared by mixing the solids, homogenizing and grinding. The pure zinc carbonate, pure manganese carbonate and their mixtures I, II and III were heated at 250,500,750 and 1000°C each for 4 h.
2.2. Techniques Thermal analysis DTA, TG and DTG of pure zinc carbonate and manganese carbonate were carried out
M.K. El-Aiashy et al. /Materials L&ten 24 (1995) 97-101
98
at about 226°C due to the loss of water and carbon dioxide, and an exotherm around 282”C, which is attributed to the crystallization of zinc oxide. ZnC03 *2ZnO. 3H20 --) 3ZnO + CO2 -t 3H20 . 3.2. Thermal treatment of MnCO, The thermal decomposition of manganese carbonate as indicated by the data obtained by XRD and DTA is in good agreement with the previous studies [911,13,15]. Figs. 2-6 show that the decomposition can be summarized as follows: I
I
200
400
I
t
600
Fig. 1. DTA, TG and DTG plots for pure
620 Zn0.3H20.
t%
ZnCO,.2ZnO. 3&O.
using a Netzsch (West Germany) thermoanalyzer with a different scanning calorimeter cell. The rate of heating was 10°C min-‘. X-ray diffraction patterns were obtained at room temperature using a Philips diffractometer (type ~~1050) employing Ni-filter Cu LYradiation_ The Xray tube was operated at 36 kV and 16 mA. Samples were finely ground and packed in a plastic holder; no adhesive or binder was necessary. The diffraction angle 28 was scanned at a rate of 2 min- ‘. The activity of all samples for the decomposition of H202 was evaluated by the method suggested by Deren et al. [ 141 in which the rate of production of oxygen gas was used as a measure. The reaction was studied at 40°C.
MnCO, - 0.5Hz 0 1oo-3oo”cMnCO, +0.5Hz0, MnCO, 3oo-45o”cMnOz +CO, , 2Mn02
>45o-900 0 Mn,03(cubic) + $C02,
6Mnz 0, -
4Mn3 O,( tetragonal) -t O2 .
(3) (4)
3.3. Interaction between zinc and manganese carbonates
The X-ray diffraction patterns of pure solids and mixtures I, II and III thermally treated at 250,500,750 and 1000°C are presented in Figs. 3-6 respectively. At 25O”C,pure MnC03 was stable, while heating pure zinc
3. Results and discussion To study the solid-solid interaction between the two components at various temperatures, it seems reasonable to characterize the thermal products obtained from each of the components alone. 3. I. Thermal treatment of zinc carbonate Fig. 1 shows the DTA, TG and DTG plots of ZnC03 - 2ZnO. 3H,O. An examination of the TG-curve indicates that the compound begins its decomposition
(1)
Fig. 2. DTA, TG and DTG plots for pure MnC4.
M.K. El-Aiashy et al. /Materials Letters 24 (1995) 97-101
99
At this temperature, ZnO and Mn*Os were found to coexist with ZnMnzOd for mixtures II and III only. This means that the decrease of manganese content in mixtures II and III and the thermal treatment at 750°C for 4 h are not enough for complete combination of the individual oxides to form the monoclinic ZnMn,O,. At lOtWC, pure MnC03 produced tetragonal Mn304 and zinc carbonate gave ZnO crystalline phase. Heating of the mixtures at 1000°C leads to an increase in the formation of the compound ZnMn,O, and in the same time the lines of well crystalline ZnO appeared. 3.4. Catalytic activity of thermally treated mixed oxides
The decompositions of H,O, over the mixed oxides, thermally treated at different temperatures are graphi-
Fig. 3. X-ray diffraction patterns of pure and mixed carbonates heated at 250°C.
carbonate gave crystalline ZnO. X-ray analysis revealed that mixtures I, II and III heated at 250°C produced mainly crystalline ZnO and MnCO,. The increase of the treatment temperature up to 500°C was accompanied by an increase in the crystallization of ZnO and the appearance of cubic Mnp03 crystalline phase. The increase of manganese content showed an increase in the intensity of the lines characteristic of cubic Mnz03 and a decrease of those of ZnO. At 750°C the thermal treatment of mixtures was accompanied by a ‘detectable solid-solid interaction between Zn and Mn-oxides forming monoclinic ZnMn,O,: ZnO + Mnz O3 =z
ZnMnz04 .
Fig. 4. X-my diffraction patterns of pure and mixed carbonates heated at 500°C.
M.K. El-Aiashy et al. /Materials Letters 24 (1995) 97-101
100
-r--
1
MnC03
I L
I IO
3
3
I 50
I 30
Fig. 6. X-ray difiaction patterns of pure and mixed carbonates heated at 1000°C.
Fig. 5. X-ray diffraction patterns of pure and mixed carbonates heated at 750°C.
tally represented in Figs. 7-9. It can be seen that all the samples thermally treated at 250°C were active in H202 decomposition. The activity increased with the increase of manganese oxide content. The calcination of all samples at 500°C produced highly active catalysts compared with those thermally treated at 250°C. The effect of chemical composition on the catalytic activity of 500°C calcined catalysts is the same as for 250°C ones. Further increase of the calcination temperature of the mixed oxide catalysis produced solids with very low activity for H,Oz decomposition. This may be attributed to the sintering of the solid catalysis and/or formation of ZnMn,O,.
V, ml
t, min Fig. 7. The activity of catalyst I, preheated at various temperatures, in the decomposition of hydrogen peroxide.
M.K. El-Aiashy et al. /Materials Letters 24 (199s) 97-101
V, ml
101
V, ml
t, min ’ Fig. 8. The activity of catalyst II, preheated at various temperatures in the decomposition of hydrogen peroxide.
References [ 1 ] V. Mucka, Chem. Listy 709 ( 1968). [2] V. Mucka, Thesis Czech. Technical Univ., Praque (1971). [3] M.M. Selim and N.A. Youssef, J. Serb. Chem. Sot. 53 (1988) 157. [4] T. Mimani, P. Ravindranathan and K.C. Path, Proc. Indian Acad. Sci. Chem. Sc:i.99 (1987) 209. [5] K. Kishore and P.N. Moorthy, Radiat. Effects 105 (1988) 257. [6] G.C. Naiti and SK. Ghosh, Indian J. Chem. 24 A (1985) 513. [7] M.F.R. Fouda, R.S. ,4min and M.M. Selim, Thermochim. Acta 141 (1989) 277.
t, min Fig. 9. The activity of catalyst III preheated at various temperatures in the decomposition of hydrogen peroxide. 181 W.Z. Vielstich, Phys. Chem. 15 (1958) 409. [9] A. Muan and W.C. Hahn Jr., J. Phys. Chem. 63 ( 1959) 1826. [ 101 WC. Hahn Jr. and A. Muan, Am. J. Sci. 258 (1960) 66. [ 111 N.V. Sidgwich, Chemical elements and their compounds (Oxford Univ. Press, Oxford, 1951). [ 121 A. Muan and S. Somiya, Am. J. Sci. 260 (1962) 230. [ 131 H.J. Van Hook and M.L. Keith, Am. Mineralogist 43 (1958) 69. [ 141 J. Deren, J. Haber, A. Podgorckaand J. Siechowski, Bull. Acad. Pol. Sci. Ser. Sci. Chem. 10 ( 1966) 8 1. [ 151 M.M. Selim and L.B. Khalil. AFINIDAD 48 (1991) 167.