Bifunctional Characteristics of Al₂O₃ supported Ni in the HI Decomposition of Sulfur-Iodine Process

The Sulfur-Iodine process is in need of catalytic reactor for HI decomposition because the HI decomposition reaction rate is very slow. Nickel as an alternative catalyst for platinum was investigated in this study. Al₂O₃ supported Ni catalysts were prepared by impregnation method. Ni amounts loaded over Al₂O₃ were in the range of 0.1∼20 wt. %. HI decompositions were carried out in the temperature range of 573 ∼ 773 K using the fixed-bed quartz reactor. The difference of catalysts before and after the reaction was analyzed using BET, CO/H₂ chemisorption, XRD, XRF and SEM. It was confirmed by XRD and SEM-EDX analysis that Ni was converted to NiI₂ during the HI decomposition. Catalyst deactivation due to the formation of NiI₂ leads to a reduction of HI conversion. Although Ni of catalyst converted to NiI₂, HI decomposition with low loading (up to 3 wt. %) catalyst showed a little decrease of HI conversion. However, with more than 5 wt. % catalyst, the initial HI conversion was considerably decreased. In the particular case of 20 wt. %, the initial conversion was increased close to 60 %, which is higher than 20 % as an equilibrium conversion at 723 K. These results showed that Ni had not only a catalytic function for HI decomposition, but also function as a sorbent to absorb I₂ produced from HI.