Thermal behavior and decomposition of cerium(III) butanoate, pentanoate and hexanoate salts upon heating in argon

doi:10.1016/j.jaap.2017.06.022

Journal of Analytical and Applied Pyrolysis

Volume 126, July 2017, Pages 77-87

https://doi.org/10.1016/j.jaap.2017.06.022 Get rights and content

Highlights

•
The thermal decomposition of cerium butanoate, pentanoate and hexanoate has been studied in Ar.
•
All compounds present transitions including melting prior to decomposition.
•
Gas release in the molten state results in irregular mass loss.
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CO₂ and symmetrical ketones are the main evolving gas species.
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Ce₂O(C_nH_2n+1CO₂)₄ and Ce₂O₂CO₃ intermediate are detected before CeO₂ formation.

Abstract

The thermal behavior and decomposition of Ce-butanoate monohydrate (Ce(C₃H₇CO₂)₃·H₂O), Ce-pentanoate (Ce(C₄H₉CO₂)₃) and Ce-hexanoate (Ce(C₅H₁₁CO₂)₃) were studied in a flow of argon while heating at 5 °C/min. By means of several techniques such as simultaneous TG-DTA, FTIR evolved gas analysis, in-situ x-ray diffraction using a synchrotron source and hot-stage microscopy, it was found that all three compounds undergo melting transitions prior to decomposition and that decomposition involves intermediate stages including at least a Ce₂O(C_nH_2n+1CO₂)₄ intermediate (n = 3, 4 or 5 for Ce-butanoate, pentanoate or hexanoate respectively). The final decomposition product consists of CeO₂, which is formed through a Ce-oxycarbonate. The Ce³⁺ → Ce⁴⁺ oxidation seems to proceed via Ce₂O₃ that first results from the decomposition of the oxycarbonate phase. During the whole decomposition process, the evolved gas species consist of CO₂ and symmetrical ketones.

Introduction

Due to its outstanding properties, CeO₂ has tremendous potential for exploitation in various fields including biomedical applications (biosensing, immunoassay, drug delivery, radiation protection, tissue engineering, ophthalmology, implant coatings and antioxidant usage) [1], [2], [3], [4], [5], [6], photocatalysis [7], steam reforming [8], preferential oxidation of impurities and pollutants (CO [9], SO₂, NO_x [10]), fuel cells and automotive applications [11], buffer layer coatings for superconducting tapes [12], [13], etc.

The synthesis of CeO₂ nanoparticles and/or coatings can be achieved via different routes such as solvothermal [14], hydrothermal [15], precipitation [16], [17], [18] or thermal decomposition of complex precursors [19], [20], [21]. For the application of the latter technique, a good knowledge of the decomposition process is highly advantageous in order to control the morphology of the coating or nanoparticles as well as for ensuring safety during large scale handling due to the evolution of potentially toxic gases. Numerous studies have been published on the thermal decomposition of various cerium carboxylate salts as will be discussed in Section 3.4. Among this class of metalorganic compounds, the linear chain alkanoates have received limited attention. Besides cerium formate [22], [23] and cerium acetate [24], [25], the thermal decomposition of longer chain cerium alkanoates is limited to a few studies on cerium propionate [26], [27], butanoate [28], pentanoate [29], hexanoate [30] and octanoate [30] performed under various conditions that do not allow systematic comparisons. Besides, there are some older works on Ce-laurate, palmitate and stearate [31] as well as hexanoate [28] that are based solely on thermogravimetric data with poor resolution (one point every 20 °C), from which limited information can be obtained. The aim of the present work was to systematically study the thermal decomposition of cerium butanoate, pentanoate and hexanoate under fixed conditions to study their thermal behavior, find similarities as well as differences between them and compare the results with those previously published on other cerium carboxylates and rare-earth butanoates, pentanoates and hexanoates.

Section snippets

Experimental

200 mg aliquots of Ce₂(CO₃)₃·xH₂O (x ≈ 4) from Alfa Aesar (99.9% purity (rare earth basis)) were dissolved separately in excess (4 ml) butanoic acid (Alfa Aesar, 99 +%, common name: butyric acid), pentanoic acid (Alfa Aesar, 99%, common name: valeric acid) or hexanoic acid (Alfa Aesar, 98+ %, common name: caproic acid). After slow evaporation at room temperature for the solution in butanoic acid or 60 °C for the other two solutions during several weeks without stirring, a hard, yellow, transparent

Ce-hexanoate

The FTIR spectrum of the dried powder is shown in Fig. 1. It includes all the absorption bands previously observed in Ce-hexanoate [34], Y-hexanoate [35] and La-hexanoate [36], while the characteristic strong absorption bands for Ce-acetate at 1017 cm⁻¹ and 1054 cm⁻¹ [37] are not apparent, which allows concluding that the obtained compound consists of Ce-hexanoate. This is further supported by the similarity of the XRD pattern features (31 °C in Fig. 2) with those of La-hexanoate [36] as well as

Conclusions

The thermal behavior and decomposition of Ce-butanoate monohydrate (Ce(C₃H₇CO₂)₃·H₂O), Ce-pentanoate (Ce(C₄H₉CO₂)₃) and Ce-hexanoate (Ce(C₅H₁₁CO₂)₃) in argon atmosphere is a complex process, which seems to become more complicated as the ligand chain length decreases.

Dehydration of Ce(C₃H₇CO₂)₃·H₂O starts around 60 °C. The fact that the other two compounds were obtained in an anhydrous state is probably only due to the temperature (60 °C) used for evaporating the solvent during sample synthesis.

Acknowledgements

This work was supported by the Danish Agency for Science, Technology and Innovation under contract nr. 09-062997 and by DTU project nr. 49605-E5. The authors also acknowledge financial support from DANSCATT as well as DESY/HASYLAB (project I-20110113 EC). These funding sources have no role in study design; in the collection, analysis and interpretation of data; in the writing of the report; and in the decision to submit the article for publication.

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Thermal behavior and decomposition of cerium(III) butanoate, pentanoate and hexanoate salts upon heating in argon

Highlights

Abstract

Introduction

Section snippets

Experimental

Ce-hexanoate

Conclusions

Acknowledgements

J. Photochem. Photobiol. C: Photochem. Rev.

Chem. Eng. J.

Phys. C

J. Alloys Compd.

Appl. Surf. Sci.

Mater. Chem. Phys.

Thermochim. Acta

J. Eur. Ceram. Soc.

J. Inorg. Nucl. Chem.

J. Anal. Appl. Pyrolysis

Thermochim. Acta

Mater. Sci. Eng. C

Coord. Chem. Rev.

J. Anal. Appl. Pyrolysis

Spectrochim. Acta A

J. Anal. Appl. Pyrolysis

Thermochim. Acta

J. Anal. Appl. Pyrolysis

J. Inorg. Nucl. Chem.

Inorg. Chim. Acta

Thermochim. Acta

Thermochim. Acta

Thermochim. Acta

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Antioxidants

Cerium oxide nanoparticles and its cytotoxicity human cancer cells

Rom. Biotech. Lett.

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Structuring CuO/CeO2 catalyst as option to improve performance towards CO-PROX

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Fundamental understanding of the interaction of acid gases with CeO2: from surface science to practical catalysis

Ind. Eng. Chem. Res.

Structuring CuO/CeO₂ catalyst as option to improve performance towards CO-PROX

Fundamental understanding of the interaction of acid gases with CeO₂: from surface science to practical catalysis