TiO2 as a catalyst for hydrogen production from hydrogen-iodide in thermo-chemical water-splitting sulfur-iodine cycle

Abstract

In this work, TiO2 nanoparticles have been prepared by the sol–gel (at different calcination temperatures) and solution-combustion method for hydrogen-iodide decomposition in thermo-chemical water-splitting sulfur-iodine (SI) cycle for hydrogen production. The sol-gel method derived TiO2 (TiO2-SGM-300 and TiO2-SGM-500) provide smaller nanoparticles as compared to the solution-combustion (TiO2-SCM). TEM revealed a particle size of around 4–5 nm of TiO2-SGM-300. XRD and Raman confirmed that TiO2-SGM-300 and TiO2-SGM-500 exhibited pure anatase phase, whereas a small amount of rutile phase was observed in TiO2-SGM-700 and TiO2-SCM samples. It is found that with increase in calcination temperatures during sol-gel method, the average particle size of TiO2 increases and specific surface area decreases. Commercial TiO2 (Degussa P-25) was used for the comparison purpose. As far as the author knows, TiO2 has been used here for the first time for hydrogen-iodide decomposition. The hydrogen-iodide decomposition experiments were carried out in a vertical-fixed bed quartz reactor at a WHSV of 12.9 h−1 under atmospheric pressure. The order of catalytic activity was as follows: TiO2-SGM-300 > TiO2-SCM > TiO2-COMM (commercial). Also, it was observed that the hydrogen-iodide conversion decreases with increase in calcination temperatures of TiO2 during sol–gel method. Their activity was as follows: TiO2-SGM-300 > TiO2-SGM-500 > TiO2-SGM-700. TiO2-SGM-300 catalyst also showed a reasonable time-on-stream stability of 6 h for hydrogen-iodide decomposition. The apparent activation energy of TiO2-SGM-300 is found to be 72.29 kJ mol−1. This shows that the TiO2 has a potential of generating hydrogen from hydrogen iodide in SI cycle. This can further be explored as a catalyst support using some non-precious and precious metal catalysts for hydrogen-iodide decomposition.