Monitoring of the Gas Phase Composition: A Prerequisite for Unravelling the Mechanism of Decomposition of Solids. Thermal decomposition of cobalt oxalate dihydrate

The complexity of the processes occurring during cobalt oxalate dihydrate (COD) decomposition indicates that an interpretation of the mechanism based only on the TG curve is of little value. Mass change alone does not allow deeper insight into all of the potential primary and secondary reactions that could occur. The observed mass changes (TG) and thermal effects (DTA/DSC) are a superposition of several phenomena and thus do not necessarily reflect COD decomposition alone. Investigation of the mechanism of decomposition requires the application of different simultaneous techniques that allow the qualitative and quantitative determination of the composition of the gaseous products. Composition of the solid and gaseous products of COD decomposition and heats of dehydration and oxalate decomposition were determined for inert, oxidizing and hydrogen-containing atmospheres. Contrary to previous suggestions about the mechanism of cobalt oxalate decomposition, the solid product formed during decomposition in helium contains not only metallic Co_met, but also a substantial amount of CoO (ca 13 mol%). In all atmospheres, the composition of the primary solid and gaseous products changes as a result of secondary gas-solid and gas-gas reactions, catalyzed by freshly formed Co_met. The course of the following reactions has been investigated under steady-state and transient conditions characteristic for COD decomposition: water gas shift, Fischer-Tropsch, CO disproportionation, CoO reduction by CO and H₂, Co_met oxidation under rich and lean oxygen conditions. This revised version was published online in August 2006 with corrections to the Cover Date.