XPS as a probe of the chemical state of Cu during thermal decomposition of copper oxalate in hydrogen

• XPS study of the thermal decomposition of CuC 2 O 4 ·0.31H 2 O under H 2 environment. • In the range of 230–260 °C, the sample consists of defective oxalate (Cu 2+ ) and Cu 2 O (Cu 1+ ) and Cu 0 nuclei. • The physicochemical state of CuC 2 O 4 under thermal exposure differs from that under prolonged X-ray irradiation. • A variety of oxygenated carbon functionalities detected on Cu indicates the occurrence of catalytic reactions. X-ray photoelectron spectroscopy was employed to study the thermal decomposition of Cu oxalate hydrate, CuC 2 O 4 ·0.31H 2 O, under hydrogen environmental conditions. Analysis of the parameters of Cu 2p, Cu L 3 VV, C 1 s, O 1 s and valence band high-resolution XP spectra showed that the structure, composition and chemical state of copper atoms continuously change with increasing temperature. After dehydration of the sample, the nucleation and accumulation of Cu 2 O and Cu phases along with the deterioration of the residuary oxalate structure was revealed to occur in the temperature range of ∼230–260 °C. The simultaneous existence of all three chemical states, Cu 2+ , Cu 1+ and Cu 0 , in the decomposing material indicated two reaction pathways for the decomposition of oxalate to be in operation. In this range of temperatures, the amount of Cu 2 O increased slowly and non– monotonically, peaking at 250 °C, whereas the amount of Cu increased monotonically, remaining below that of Cu 2 O up to 250 °C, before snowballing due to the rapid disintegration of the oxalate structure to form metallic Cu at 280 °C. The surface of the final product was found to be covered with various adsorbed oxygen-containing carbon functional groups formed because of various reactions, including hydrogenation of the evolving CO 2 catalyzed by active Cu nanoparticles. A comparison of the changes in the Cu oxalate state under heating and prolonged X-ray irradiation was performed. The XPS studies were complemented by XRD, TG, and TPDec coupled with quadrupole mass spectrometry.