Thermal decomposition of CuProp2: In-situ analysis of film and powder pyrolysis

Abstract

The thermal decomposition of CuProp2 in the form of film and powder was studied in different atmospheres by means of thermal analysis techniques (TG-MS, TG-IR, EGA), chemical-structural methods (FTIR, XRD, EA) and computational thermochemistry (VASP/PBE). The decomposition mechanism in terms of volatiles evolved was disclosed with the aid of ab-initio modeling; it was found to be dependent on the gas diffusion in and out of the sample and accelerated by a humid atmosphere. In films, the copper redox behavior showed sensitivity to the residual atmosphere. Finally, the role of the metal center is discussed in the frame of a general decomposition mechanism for metal propionates. Volatile species evolved during decomposition can be detected by means of thermogravimetry (TG) coupled with Evolved Gas Analysis (EGA), which mainly works by infrared (EGA-FTIR or TG-FTIR) or by mass spectrometry (EGA-MS or TG-MS) detection. In fact, by EGA-FTIR and EGA-MS, it was shown that the decomposition of propionates in inert atmospheres involves formation of radicals C2H5• and C2H5CO• (along with CO2) and their recombination to form a symmetrical ketone [20-22]. For longer chain salts such as Ca(II)decanoate, techniques like pyrolysis coupled to gas chromatography (GC) revealed a more complicated scenario where normal alkanes were found along with several symmetrical ketones [23]. For odd chain length of Cu(II)carboxylates like Cu(II)propionate, only MS has been used for the in-situ EGA analysis and 2-pentanone (asymmetrical ketone) was reported to be the main decomposition product [11]. Formation of this asymmetrical ke-tone implies cleavage of a CeC(C]O) bond, instead of the expected CeC(]O) and C(]O)eO bonds. Conversely, no ketones at all were observed for even chain carboxylates of copper(II) [24], mercury(II) [25] and silver(I) [26]. In fact, references [24,25] report on the

Effect of triethanolamine on the pyrolysis of metal-propionate-based solutions

“…The FTIR analysis of the dry film from solution C, Fig. 3a, shows the appearance of the TEA IR bands and of CuProp 2 vibrations [20,25,38], in agreement with the expected replacement of acetate groups by propionates of the solvent when this is in excess [37] (details in Fig. S2).…”

“…In particular, the first stage, between 100-230°C, matches with CuProp 2 decomposition and TEA removal: the FTIR (Fig.3a) of the solid residues quenched at 185°C shows that the main TEA vibrational band at 1082 cm -1 is decreasing; simultaneously the CuProp 2 reflections are detected by XRD ( Fig.3b) [25,39] decreasing while it decomposes to propionic acid and CO 2 (TG-FTIR analysis in Fig. 4) according to the expected hydrolysis and degradative oxidation path [25]. Between 95 and 185°C, an IR band at 1735 cm -1 appears in the solid residue, Fig.…”

“…S2). But the XRD pattern is significantly different from that of CuProp 2 [25] (see Fig. S2), suggesting a possible coordination of TEA with CuProp 2 .…”

“…Finally, metal propionate salts have been shown to decompose following a radical path in inert atmosphere and high temperatures, releasing a symmetrical ketone (3-pentanone) and CO 2 [18][19][20][21][22][23] and forming the corresponding oxides (for YProp 3 ) or carbonates (for BaProp 2 ) by 500°C. In O 2 , oxidative degradation of the ligand is expected to occur at low temperature releasing propionic acid, acetaldehyde, CO 2 and water, but without changing the final phases [24][25][26]. Conversely, for CuProp 2 , propionic acid is expected to be the main volatile independently of the atmosphere [25], followed by acetaldehyde and CO 2 to give the corresponding oxide in film, and metallic copper as powder.…”

“…In O 2 , oxidative degradation of the ligand is expected to occur at low temperature releasing propionic acid, acetaldehyde, CO 2 and water, but without changing the final phases [24][25][26]. Conversely, for CuProp 2 , propionic acid is expected to be the main volatile independently of the atmosphere [25], followed by acetaldehyde and CO 2 to give the corresponding oxide in film, and metallic copper as powder.…”