Secondary catalytic reactions during thermal decomposition of oxalates of zinc, nickel and iron(II)

Thermal decomposition of the oxalates of zinc, nickel and iron(II) have bee n reexamined from a fresh experimental approach. Differential thermal analy sis (DTA) and thermogravimetry (TG) of the individual oxalates and of mixtu res of zinc oxalate with either nickel/iron oxalate or products of decompos ition of the latter two, were carried out in air in sample cells made of di fferent materials (Pt, Al, Al2O3, Ni). The information gathered from thermo analytical experiments, together with information derived from specific che mical tests for the evolution of carbon monoxide during decomposition, chem ical analyses, XRD and stoichiometric and thermochemical considerations hel ped to specify some of the inadequately explained features of the courses a nd kinetics of decomposition of the metal oxalates. Demonstrative evidence strongly indicates that secondary exothermic oxidation of carbon monoxide l iberated in situ, takes place at relatively low temperatures in the presenc e of Pt (sample cell material), NiO and Fe3O4 (decomposition products) whic h act as catalysts and are reflected in overall exothermic DTA responses th at are endothermic in air/oxygen in the absence of catalyst surfaces. (C) 1 999 Elsevier Science B.V. All rights reserved.