Eprints.Qut.Edu.Au

View metadata, citation and similar papers at core.ac.uk brought to you by CORE

provided by Queensland University of Technology ePrints Archive

QUT Digital Repository: http://eprints.qut.edu.au/

This is the author version published as:

This is the accepted version of this article. To be published as : This is the author version published as:

Frost, Ray L. and Palmer, Sara J. and Grand, Laure-Marie (2010) Synthesis and thermal stability of hydrotalcites containing manganese. Journal of

Thermal Analysis and Calorimetry, 100(3). pp. 981-985.

1 Synthesis and thermal stability of hydrotalcites containing manganese 2 3 Laure-Marie Grand, 1, 2 Sara J. Palmer 1 and Ray L. Frost 1 4 5 1 Inorganic Materials Research Program, School of Physical and Chemical Sciences, 6 Queensland University of Technology, GPO Box 2434, Brisbane Queensland 4001, 7 Australia. 8 9 2 ENSICAEN, 6 Boulevard Marechal Juin, 14050 CAEN Cedex 4, France 10 11 ABSTRACT 12 13 The hydrotalcite based upon manganese known as charmarite

14 Mn4Al2(OH)12CO3·3H2O has been synthesised with different Mn/Al ratios from 4:1 to 2:1. 15 Impurities of manganese oxide, rhodochrosite and bayerite at low concentrations were also 16 produced during the synthesis. The thermal stability of charmarite was investigated using 17 thermogravimetry. The manganese hydrotalcite decomposed in stages with mass loss steps at 18 211, 305 and 793°C. The product of the thermal decomposition was amorphous material 19 mixed with manganese oxide. A comparison is made with the thermal decomposition of the 20 Mg/Al hydrotalcite. It is concluded that the synthetic charmarite is slightly less stable than 21 hydrotalcite. 22 23 Keywords: charmarite, rhodochrosite, hydrotalcite, hydrocalumite, synthesis, thermal 24 stability 25 26

 Author to whom correspondence should be addressed ([email protected]) 1

27 Introduction 28 29 Hydrotalcites have been known for an extended period of time. [1-3] Hydrotalcites, 30 or layered double hydroxides (LDH) are fundamentally known as anionic clays [4]. 31 Hydrotalcites containing manganese are known [5-8]. The natural mineral is known as 32 charmarite [9]. The application of hydrotalcites containing manganese rests with their 33 application in catalyst science [7, 10-15]. Some of these types of materials are used for 34 adsorption and chemical storage [8, 16, 17]. However the synthesis and characterization of 35 hydrotalcites containing manganese remains unexplored and not studied. 36 37 Hydrotalcites consist of stacked layers of metal cations (M2+ and M3+) similar to

38 brucite (Mg(OH)2). The structure of hydrotalcite can be derived from a brucite structure 3+ 3+ 2+ 39 (Mg(OH)2) in which e.g. Al or Fe (pyroaurite-sjögrenite) substitutes a part of the Mg [2, 40 18-20]. This substitution creates a positive layer charge on the hydroxide layers, which is 41 compensated by interlayer anions or anionic complexes. In general any divalent cation could 42 substitute for the Mg2+ in the brucite-like layer, including Mn2+. Hydrotalcites consist of 2+ 3+ 43 stacked layers of metal cations (M and M ) similar to brucite (Mg(OH)2). For 44 hydrotalcite-like structures, the substitution of divalent cations for trivalent ones (of 45 similar radii), gives rise to a positive charge on the brucite-like layers. In hydrotalcites a 2+ 3+ 2+ 46 broad range of compositions are possible of the type [M 1-xM x(OH)2] x/n.yH2O, where M 47 and M3+ are the di- and trivalent cations in the octahedral positions within the hydroxide 48 layers with x normally between 0.17 and 0.33. An- is an exchangeable interlayer anion. [21] 49 The positively charged hydroxyl layers are neutralised through the intercalation and 50 adsorption of anionic species, therefore stabilising the structure. Anions that are 51 intercalated between the hydroxyl layers need to meet certain criteria, including having a 52 high charge density and small anionic radius. 53 54 This study is focused upon the synthesis, characterisation of hydrotalcites with 55 manganese substituting for magnesium in the brucite layer of hydrotalcites. 56 57 Experimental 58 59 Synthesis of hydrotalcite samples 60 2

61 The hydrotalcites were synthesised by the co-precipitation method using analytical 62 grade chemicals. Two solutions were prepared, solution 1 contained 2M NaOH and 0.2 M 2+ 63 Na2CO3, and solution 2 contained Mn (MnCl2.4H2O) at different concentrations, together 3+ 64 with Al (AlCl3.6H2O). Solution 2 was added at a steady rate to solution 1 drop wise, under 65 vigorous stirring. A separating funnel was used to deliver solution 2 to solution 1. The 66 precipitated minerals were washed at ambient temperatures thoroughly with ultra pure water 67 to remove any residual salts and dried in an oven (85 °C overnight. The following Table 68 shows the masses and concentrations used to synthesise hydrotalcites with a range of Mn/Al 69 ratios. 70 Mn/Al ratio 2:1 2.5:1 3:1 3.5:1 4:1

Concentration of MnCl2.4H2O 0.67M 0.71M 0.75M 0.77M 0.80M

Masses of MnCl2.4H2O 6.63g 7.02g 7.42g 7.62g 7.92g

Concentration of AlCl3.6H2O 0.33M 0.29M 0.25M 0.22M 0.20M

Masses of AlCl3.6H2O 3.98g 3.45g 3.02g 2.68g 2.41g 71 72 73 Characterisation techniques 74 75 Thermal decomposition of approximately 50mg of hydrotalcite was carried out in a 76 TA® Instruments incorporated high-resolution thermogravimetric analyser (series Q500) in a 77 flowing nitrogen atmosphere (80 cm3/min), at a rate of 2.0 °C/min up to 1000 °C. X-Ray 78 diffraction patterns were collected using a Philips X'pert wide angle X-Ray 79 diffractometer, operating in step scan mode, with Cu K radiation (1.54052 Å). For more 80 information on the experimental and analysis techniques used, refer to previous work by 81 the authors [22-27]. 82 83 84

85 Results and discussion 86 87 X-Ray diffraction 88 89 The powdered XRD patterns of the synthesised manganese hydrotalcites together with 90 probable impurities are shown in Figure 1. The natural mineral is known as charmarite

91 Mn4Al2(OH)12CO3·3H2O [9, 28] and the XRD pattern of this mineral is shown in Figure 1. 92 The XRD patterns show that the compound equivalent to the mineral charmarite has been 93 successfully synthesised over a range of concentrations from 4:1 Mn/Al to 2:1. Some 94 impurities are observed in the synthesised manganese hydrotalcite including manganese

95 oxide (Mn3O4), bayerite and rhodochrosite (MnCO3). The formation of Mn/Al hydrotalcites, 96 under these specific synthesis conditions, does not appear to be the most favourable reaction, 97 especially as the concentration of manganese increases in solution. It is proposed that the 98 increase in cation size, compared to magnesium hydrotalcites, restricts the formation of 99 hydrotalcite and allows for other manganese phases to form. It is observed that manganese 100 oxide (predominate phase) and rhodochrosite form predominantly in high manganese 101 concentrations. The d(003) spacing varies from 7.70 to 7.79 Å. It is concluded that the 102 hydrotalcite based upon divalent manganese is successfully synthesised over a wide range of 103 Mn/Al ratios. It should be noted that sodium chloride is not a true precipitate that forms, it is 104 present due to the drying process. 105 106 A comparison may be made with the d-spacings of natural hydrotalcites. There exists 107 in nature a significant number of hydrotalcites which are formed as deposits from ground 108 water containing Ni2+ and Fe3+. [29] These are based upon the dissolution of Ni-Fe sulphides 109 during weathering. Normally the hydrotalcite structure based upon takovite (Ni,Al) and 110 hydrotalcite (Mg,Al) have basal spacings of ~8.0 Å, where the interlayer anion is carbonate. 111 If the carbonate anion is replaced by sulphate, then the mineral carrboydite is obtained. 112 Similarly reevesite is the (Ni,Fe) hydrotalcite with carbonate as the interlayer anion, which 113 when replaced by sulphate the minerals honessite and hydrohonessite are obtained. Among 114 the naturally occurring hydrotalcites are carrboydite and hydrohonessite [30, 31]. These two 115 hydrotalcites are based upon the incorporation of sulphate into the interlayer with expansions 116 of 10.34 to 10.8 Å. 117 118 4

119 Thermal analysis –TG and DTG 120 121 The TG and DTG curves for the thermal decomposition of the synthesised charmarite is 122 displayed in Figure 2. The DTG curve of the manganese hydrotalcite resembles those 123 observed for magnesium hydortalcites, Figure 3. The main difference between these different 124 hydrotalcites is the stability of the interlayer water within the hydrotalcite structure. However, 125 the three main decomposition steps observed for magnesium hydrotalcite structures is 126 observed in the manganese hydortalcite: 1) removal of adsorbed water, 2) removal of 127 interlayer water, 3) dehydroxylation and decarbonation of the hydrotalcite structure. 128 129 A series of TG steps are observed with maxima in the DTG curves at 44, 169, 211, 305, 531 130 and 793 °C. The first mass loss at 44 °C is ascribed to the loss of adsorbed water. The 131 theoretical formula based on the molar ratio of Mn2+ and Al3+ in solution is

132 Mn6Al2(OH)16CO3·4H2O. The number of moles of water associated with the structure has 133 been calculated from the theoretical formula and the combined mass loss between 0 and 260 134 °C, appendix 1. The broad mass loss, ranging from 115 to 264 °C, is attributed to the loss of 135 water in the interlayer region. The total mass loss for these two steps is 9.67 % (respectively 136 3.48 and 6.19 %). Compared to the mass losses at higher temperatures, a considerable amount 137 of adsorbed water is associated with this structure. The following thermal decomposition is 138 proposed for the removal of water: 139

140 Mn6Al2(OH)16CO3·4H2O → Mn6Al2(OH)16CO3 + 4H2O 141 142 The decomposition of the hydroxyl layers of the HT structure occurs as a broad peak centred 143 at around 305 °C. The OH units of the brucite-like layers decompose to its corresponding 144 oxides, shown by the decomposition equation below: 145

146 3Mn6Al2(OH)16CO3 → 5Mn3O4 + 3CO2 + 3MnAl2O4 + 16H2O + 3/2O2 147

148 The peak at 531 °C is assigned to the decomposition of MnCO3. A mass loss of 2.41 % is

149 observed, (MnCO3 → MnO +CO2). XRD did not find MnO in the TG residue, however, due 150 to the small concentration of this phase it is proposed XRD is not sensitive enough to detect 151 this phase. 152 5

153 A higher temperature mass loss at around 793 °C of 10.62 % is observed and is assigned to 154 the decomposition of the residual salt. The XRD of the product of the thermal decomposition 155 of charmarite is provided in Figure 4. The product shows a great deal of amorphicity. The 156 main product according to the XRD is manganese oxide. 157 158 Conclusions 159 160 The hydrotalcite mineral charmarite with different Mn/Al ratios have been 161 successfully synthesised. Magnesium hydrotalcite thermally decomposes in stages with mass 162 loss steps at 170 °C attributed to water loss, and at 315 °C assigned to the loss of carbonate

163 and OH units. The impurity MnCO3 is proposed to decompose between 400 and 660 °C to

164 CO2 and manganese oxide. The thermal analysis of the residue showed all compounds 165 decomposed to manganese oxide. The synthesised charmarite also thermally decomposes in 166 steps with principal peaks in the DTG curve at 169, 211, and 305 °C, corresponding well to 167 the decomposition of magnesium hydrotalcites. It is concluded that the thermal stability of 168 charmarite is similar to but slightly less stable than magnesium hydrotalcites. 169 170 Acknowledgements 171 172 The financial and infra-structure support of the Queensland Research and 173 Development Centre (QRDC-RioTintoAlcan) and the Queensland University of 174 Technology Inorganic Materials Research Program of the School of Physical and 175 Chemical Sciences are gratefully acknowledged. One of the authors (LMG) thanks the 176 Queensland University of Technology for a visiting student fellowship. 177 178 179 180

181 References 182 [1] R. Allmann, Crystal structure of pyroaurite, 183 Acta Crystallographica, Section B: Structural Crystallography and Crystal Chemistry 24 184 (1968) 972-977. 185 [2] L. Ingram, H.F.W. Taylor, Crystal structures of sjoegrenite and pyroaurite, 186 Mineralogical Magazine and Journal of the Mineralogical Society (1876-1968) 36 (1967) 187 465-479. 188 [3] H.F.W. Taylor, Crystal structures of some double hydroxide minerals, 189 Mineralogical Magazine 39 (1973) 377-389. 190 [4] V. Rives, Editor, Layered Double Hydroxides: Present and Future, 2001. 191 [5] J.W. Boclair, P.S. Braterman, Layered Double Hydroxide Stability. 1. Relative 192 Stabilities of Layered Double Hydroxides and Their Simple Counterparts, 193 Chemistry of Materials 11 (1999) 298-302. 194 [6] H.-q. Chen, Z.-k. Zhan, Synthesis, characterization and catalysis of Cu-Mn-Al 195 hydrotalcite like compounds, 196 Huaxue Yanjiu Yu Yingyong 19 (2007) 877-881. 197 [7] J.M. Fernandez, C. Barriga, M.-A. Ulibarri, F.M. Labajos, V. Rives, Preparation and 198 thermal stability of manganese-containing hydrotalcite, 199 [Mg0.75MnII0.04MnIII0.21(OH)2](CO3)0.11Â·nH2O, 200 Journal of Materials Chemistry 4 (1994) 1117-1121. 201 [8] A. Sampieri, G. Fetter, H. Pfeiffer, P. Bosch, Carbonate phobic (Zn,Mn)-Al 202 hydrotalcite-like compounds, 203 Solid State Sciences 9 (2007) 394-403. 204 [9] G.Y. Chao, R.A. Gault, Quintinite-2H, quintinite-3T, charmarite-2H, charmarite-3T 205 and caresite-3T, a new group of carbonate minerals related to the hydrotalcite - manasseite 206 group, 207 Canadian Mineralogist 35 (1997) 1541-1549. 208 [10] A. Chen, H. Xu, Y. Le, W. Hua, W. Shen, Z. Gao, Catalyst using M/Mn/Al 209 hydrotalcite as precursor and its preparation process. (Fudan University, Peop. Rep. China). 210 Application: CN 211 CN, 2004, p. 11 pp. 212 [11] A. Chen, H. Xu, Y. Yue, W. Shen, W. Hua, Z. Gao, M-Mn-Al Hydrotalcite-like 213 Compounds as Precursors for Methyl Benzoate Hydrogenation Catalysts, 214 Industrial & Engineering Chemistry Research 43 (2004) 6409-6415. 215 [12] H. Cheng, W. Ding, X. Lu, Y. Zhang, X. Ai, Hydrotalcite type hydrocracking catalyst 216 and its preparation method. (Shanghai University, Peop. Rep. China). Application: CN 217 CN, 2008, p. 8pp. 218 [13] K. Ebitani, K. Motokura, T. Mizugaki, K. Kaneda, Heterotrimetallic RuMnMn 219 species on a hydrotalcite surface as highly efficient heterogeneous catalysts for liquid-phase 220 oxidation of alcohols with molecular oxygen, 221 Angewandte Chemie, International Edition 44 (2005) 3423-3426. 222 [14] K. Jiratova, P. Cuba, F. Kovanda, L. Hilaire, V. Pitchon, Preparation and 223 characterisation of activated Ni (Mn)/Mg/Al hydrotalcites for combustion catalysis, 224 Catalysis Today 76 (2002) 43-53. 225 [15] K. Pacultova, L. Obalova, F. Kovanda, K. Jiratova, Catalytic reduction of nitrous 226 oxide with carbon monoxide over calcined Co-Mn-Al hydrotalcite, 227 Catalysis Today 137 (2008) 385-389. 228 [16] R. Chitrakar, S. Tezuka, A. Sonoda, K. Sakane, K. Ooi, T. Hirotsu, Adsorption of 229 phosphate from seawater on calcined MgMn-layered double hydroxides, 230 Journal of Colloid and Interface Science 290 (2005) 45-51. 7

231 [17] D.P. Harrison, Sorption-Enhanced Hydrogen Production: A Review, 232 Industrial & Engineering Chemistry Research 47 (2008) 6486-6501. 233 [18] G. Brown, M.C. Van Oosterwyck-Gastuche, Mixed magnesium-aluminum 234 hydroxides. II. Structure and structural chemistry of synthetic hydroxycarbonates and related 235 minerals and compounds, 236 Clay Minerals 7 (1967) 193-201. 237 [19] H.F.W. Taylor, Segregation and cation-ordering in sjogrenite and pyroaurite, 238 Mineralogical Magazine and Journal of the Mineralogical Society (1876-1968) 37 (1969) 239 338-342. 240 [20] R.M. Taylor, Stabilization of color and structure in the pyroaurite-type compounds 241 iron(II) iron(III) aluminum(III) hydroxycarbonates, 242 Clay Minerals 17 (1982) 369-372. 243 [21] J.T. Kloprogge, D. Wharton, L. Hickey, R.L. Frost, Infrared and Raman study of 244 interlayer anions CO2-3, NO-3, SO2-4 and CIO-4 in Mg/Al-hydrotalcite, 245 American Mineralogist 87 (2002) 623-629. 246 [22] R.L. Frost, M.C. Hales, W.N. Martens, Thermogravimetric analysis of selected group 247 (II) carbonate minerals - Implication for the geosequestration of greenhouse gases, 248 Journal of Thermal Analysis and Calorimetry 95 (2009) 999-1005. 249 [23] S.J. Palmer, H.J. Spratt, R.L. Frost, Thermal decomposition of hydrotalcites with 250 variable cationic ratios, 251 Journal of Thermal Analysis and Calorimetry 95 (2009) 123-129. 252 [24] R.L. Frost, A.J. Locke, M.C. Hales, W.N. Martens, Thermal stability of synthetic 253 aurichalcite. Implications for making mixed metal oxides for use as catalysts, 254 Journal of Thermal Analysis and Calorimetry 94 (2008) 203-208. 255 [25] V. Vagvoelgyi, L.M. Daniel, C. Pinto, J. Kristof, R.L. Frost, E. Horvath, Dynamic 256 and controlled rate thermal analysis of attapulgite, 257 Journal of Thermal Analysis and Calorimetry 92 (2008) 589-594. 258 [26] V. Vagvolgyi, R.L. Frost, M. Hales, A. Locke, J. Kristof, E. Horvath, Controlled rate 259 thermal analysis of hydromagnesite, 260 Journal of Thermal Analysis and Calorimetry 92 (2008) 893-897. 261 [27] V. Vagvolgyi, M. Hales, W. Martens, J. Kristof, E. Horvath, R.L. Frost, Dynamic and 262 controlled rate thermal analysis of hydrozincite and smithsonite, 263 Journal of Thermal Analysis and Calorimetry 92 (2008) 911-916. 264 [28] R. Pagano, New minerals. Updates of systematic mineralogy, 265 Rivista Mineralogica Italiana (1999) 62-66. 266 [29] E.H. Nickel, J.E. Wildman, Hydrohonessite - a new hydrated nickel-iron 267 hydroxysulfate mineral; its relationship to honessite, carrboydite, and minerals of the 268 pyroaurite group, 269 Mineralogical Magazine 44 (1981) 333-337. 270 [30] D.L. Bish, A. Livingstone, The crystal chemistry and paragenesis of honessite and 271 hydrohonessite: the sulfate analogs of reevesite, 272 Mineralogical Magazine 44 (1981) 339-343. 273 [31] E.H. Nickel, R.M. Clarke, Carrboydite, a hydrated sulfate of nickel and aluminum: a 274 new mineral from Western Australia, 275 American Mineralogist 61 (1976) 366-372. 276

277 278 279 Figure 1 280 281

282 283 284 Figure 2: TG and DTG curve of the 3:1 Mn2+/Al3+ hydrotalcite. 285 286 287

288 289 290 Figure 3 TG and DTG curve of the 3:1 Mg2+/Al3+ hydrotalcite.

291 292 293 Figure 4 294 295

296 Appendix 1. 297 298 Calculation of water content for Mn2+/Al3+ hydrotalcite 299

300 Proposed composition: Mn6Al2(OH)16CO3·xH2O 301 Total mass of hydrotalcite analysed: 26.852 mg 302 % mass loss of water up to 264°C: 9.67% 303 Mass of water removed up to 264°C: 2.5966 mg –1 304 Molar mass of water: 18.02 g.mol 305 Moles of water removed: 0.144095 mmol 306 Mass of dehydrated mineral: 26.852–2.5966=24.2554 mg –1 307 Molar mass of dehydrated mineral: 715.738 g.mol 308 Moles of dehydrated mineral: 0.033888 mmol 309 Calculation of x:

310 1 mol dehydrated mineral: x mol H2O

311 0.033888mmol dehydrated mineral: 0.144095 mmol H2O 312 x=4.2521~4 mol

313 Formula: Mn6Al2(OH)16CO3·4H2O 314

315 List of Figures 316 317 Figure 1 Powder X-ray diffraction of the synthesised manganese hydrotalcites in the 318 2:1 to 4:1 ratio 319 Figure 2 Thermogravimetric and differential thermogravimetric analysis of the 320 manganese containing hydrotalcite 321 Figure 3 Thermogravimetric and differential thermogravimetric analysis of the 322 magnesium-aluminium containing hydrotalcite 323 Figure 4 XRD of the products of the thermal decomposition of manganese containing 324 hydrotalcite. 325 326