Materials Chemistry and Physics 132 (2012) 375–386 Contents lists available at SciVerse ScienceDirect Materials Chemistry and Physics j ourna l ho me pag e: www.elsevier.com/locate/matchemphys Influence of divalent metal on the decomposition products of hydrotalcite-like ternary systems M II –Al–Cr (M II = Zn, Cd) M.R. Pérez a , I. Crespo a , M.A. Ulibarri a , C. Barriga a , V. Rives b , J.M. Fernández a,∗ a Departamento de Química Inorgánica e Ingeniería Química, Campus de Rabanales, Universidad de Córdoba, Córdoba, Spain b GIR-QUESCAT, Departamento de Química Inorgánica, Universidad de Salamanca, Salamanca, Spain a r t i c l e i n f o Article history: Received 7 April 2011 Received in revised form 11 October 2011 Accepted 17 November 2011 Keywords: Hydrotalcite Double oxides Spinels Heat treatment a b s t r a c t Layered double hydroxides (LDHs) containing M II , Al III , and Cr III in the brucite-like layers (M = Cd, Zn) with different starting Al/Cr molar ratios and nitrate/carbonate as the interlayer anion have been pre- pared following the coprecipitation method at a constant pH: Zn II –Al III –Cr III –CO 3 2- at pH = 10, and Cd II –Al III –Cr III –NO 3 - at pH = 8. Two additional M II ,Al III –LDH samples (M = Cd, Zn) with chromate ions (CrO 4 2- ) in the interlayer have been prepared by ionic exchange at pH = 9 and 8, respectively, starting from M II –Al III –NO 3 - . The samples have been characterised by absorption atomic spectrometry, powder X-ray diffraction (PXRD), FT-IR spectroscopy and transmission electron microscopy (TEM). Their thermal stability has been assessed by DTA-TG and mass spectrometric analysis of the evolved gases. The PXRD patterns of the solids calcined at 800 ◦ C show diffraction lines corresponding to ZnO and ZnAl 2-x Cr x O 4 for the Zn-containing samples, and diffraction lines attributed to CdO and CdCr 2 O 4 and (Al,Cr) 2 O 3 for the Cd-containing ones. Additionally a minority oxide, Cd 2 CrO 5 , is observed to Cd II –Al III –LDH samples with chromate ions in the interlayer. © 2011 Elsevier B.V. All rights reserved. 1. Introduction Layered double hydroxides (LDH), a wide group of compounds also known as hydrotalcite-like compounds, are inexpensive and easy to synthesize. In spite of some similarities with clay miner- als, and the existence of some of them in Nature, they constitute another class of layered materials, as it has been stated by Bergaya and Lagaly [1], owing to the synthetic origin of most of them. The partial isomorphic substitution of M II cations in octahedral coordination by M III cations in the brucite layer, M(OH) 2 , gives rise to positive charges in the layers which are electrically bal- anced by anions in the interlayer space. The general formula [M II 1-x M III x (OH) 2 ] x+ A m- x/m ·nH 2 O is used to represent these com- pounds, where the identities of the divalent and trivalent cations (M II and M III , respectively), the interlayer anion (A n- ) and the stoichiometric coefficient (x) may be assorted over a wide range. Control of the precipitation conditions enables to prepare a large number of layered double hydroxides with different interlayer anions and metal cations in the brucite layers. The metal cations are homogeneously distributed in the layers when the coprecip- itation method is used [2]. In this sense, it is possible to prepare tailored LDHs. The incorporation of different metals in the layer and/or interlayer makes these compounds suitable as catalysts or ∗ Corresponding author. Tel.: +34 957 218648; fax: +34 957 218621. E-mail address: um1feroj@uco.es (J.M. Fernández). catalyst precursors. LDH with M II = Zn, M III = Al and A m- = CO 3 2- , NO 3 - can be used to incorporate one or more transition metal cations in the layer, when Zn 2+ and/or Al 3+ cations are totally or partially replaced. The transition metal induces a certain degree of acidity [3] so it is possible to tune the basic strength of a series of ternary LDHs according to their pursued application or use [4]. Broadly speaking, the thermal decomposition of LDHs is well known; calcination at intermediate temperatures (450–600 ◦ C) yields an amorphous phase M II 1-x M III x O 1+x/2 which is turned into crystalline phases, the divalent oxide MO and a mixed oxide (usually M II M III 2 O 4 spinel), at higher temperatures; the LDHs are potential precursors to such spinels. Meng et al. [5] have reported that when the divalent cation is Zn the zincite phase obtained can be eliminated by dissolution in aqueous NaOH resulting in the forma- tion of the pure spinel phase. Furthermore, the products obtained from LDHs show several advantages if compared to those prepared by the ceramic process: an increase in surface area and pore vol- ume, formation of a homogenous spinel phase, the ferrite spinel enhances their saturation magnetization [6], etc. On the other hand, the final calcination products from ternary systems depend on the nature of the cations and their location (layer or interlayer space) [7,8,10]. Consequently different mixed oxides could be obtained to be used as catalysts or catalyst precur- sors, ZnO and CdO and mixtures as photocatalyst [11–13]. Although few data have been reported regarding ternary systems in compari- son with binary ones [14–16] the research in this area has increased in the last ten years due to their interest in catalysis [17,18]. 0254-0584/$ – see front matter © 2011 Elsevier B.V. All rights reserved. doi:10.1016/j.matchemphys.2011.11.040