The activities of some metal oxides in promoting the thermal decomposition of potassium oxalate

Transition metal oxalates undergo anion breakdown in the solid state, many between 200 and 400 °C, at much lower temperatures than the decomposition of potassium oxalate (at around 600 °C) which melts at about 400 °C. The present article reports studies of the chemical changes that occurred on heating equimolar crushed mixtures of potassium oxalate with each of a range of (mainly transition metal) oxides, ZnO, PbO, NiO, CuO, Cu2O, Fe2O3, Co3O4 and Cr2O3, in flowing air or hydrogen. The objective was to determine the abilities of these added oxides to promote oxalate ion breakdown. Possible mechanisms of catalysis appeared to include the intervention of the relatively less stable metal oxalates and/or a heterogeneous, catalytic reaction on the surfaces of the oxide or, under reducing conditions, on some of these metals. Melting might also be expected to increase reactivity. The results showed that the activities of these selected oxides in promoting oxalate anion breakdown were unexpectedly small. While these additives resulted in some reaction, there was evidence of the occurrence of some unpromoted decomposition of potassium oxalate during the final stages of heating (about 590–650 °C) of all the mixtures studied. Under reducing conditions, in hydrogen, the limited catalytic activities of most oxides were further diminished, evidence that the metal formed was inactive. This contrasts with the autocatalytic reactions, envisaged as proceeding on the surfaces of metal product, in some solid state decompositions, such as nickel oxalate. Potassium oxalate melting was not associated with any increase in reactivity. It is concluded that these oxides do not interact appreciably with the ionic salt and potential oxalate intermediates do not form under these conditions. Surfaces of oxides and of metals similarly do not exhibit catalytic activity for the breakdown of ionic oxalate.