Thermodynamics and Kinetic Modeling of the ZnSO4.H2O Thermal Decomposition in the Presence of a Pd/Al2O3 Catalyst

The sulfur–iodine thermochemical water-splitting cycle is a promising route proposed for hydrogen production. The decomposition temperature remains a challenge in the process. Catalysts, such as Pd supported on Al2O3, are being considered to decrease reaction temperatures. However, little is known regarding the kinetic behavior of such systems. In this work, zinc sulfate thermal decomposition was studied through non-isothermal thermogravimetric analysis to understand the effect of a catalyst within the sulfur–iodine reaction system context. The findings of this analysis were also related to a thermodynamic assessment. It was observed that the presence of Pd/Al2O3 modified the reaction mechanism, possibly with some intermediate reactions that were suppressed or remarkably accelerated. The proposed model suggests that zinc sulfate transformation occurred in two sequential stages without the Pd-based material. Activation energy values of 238 and 368 kJ.mol−1 were calculated. In the presence of Pd/Al2O3, an activation energy value of 204 kJ.mol−1 was calculated, which is lower than observed previously.

CALCULATION OF THE TEMPERATURES OF THE CHEMICAL REACTIONS OF THE IRON STEPPED RECOVERY FROM HEMATITE WITH CO GAS AND GASIFICATION OF SOLID CARBON ACCORDING EXISTING FORMULAS AND BY STANDARD VALUES OF ENTHALPY AND ENTROPY OF SUBSTANCES

The article presents the results of a thermodynamic assessment of the possibility of chemical reactions of the stepped recovery of iron from hematite with a recovering gas CO, as well as the Bell-Boudoir chemical reaction. It has been established that for each of the indicated chemical reactions there is a certain temperature (called by the author as "boundary temperature"), up to or above which CO gas cannot be a recovering agent for lower iron oxide from higher or the metallic iron itself from wustite, as well as gasification of solid carbon; while the recovery of Fe3O4 from Fe2O3 is theoretically possible at any temperatures above 0 ° C, the recovery of FeO from Fe3O4 and the gasification of solid carbon are theoretically possible above certain temperatures (i.e. at elevated and high temperatures), and the recovery of iron from FeO is below a certain temperature (i.e. at low temperatures). The numerical values of the boundary temperatures for the reactions of iron recovery and its lower oxides, as well as the reaction of gasification of solid carbon are given; graphical dependences of the Gibbs free energy of the indicated chemical reactions on temperature are made according to the equations available in metallurgical literary sources, and according to the expressions derived in the article by the author.