(575b) Supported Catalysts in Heterogeneous Gas Phase Hydrogen Iodide Decomposition Reaction: a Screening Study

The hydrogen iodide decomposition reaction represents the hydrogen-evolution step in the sulphur- iodine (S-I) water splitting thermochemical cycle, according to the equilibrium HI↔ H2+I2. In terms of the whole cycle thermal efficiency and regarding the corrosivity problems associated with the use of HI-I2 mixtures in process equipment, the operating temperature of this step is a severe controlling factor: it is favourable to carry out the reaction around or below 700 K. Performing the decomposition reaction in the form of a homogeneous gas phase reaction leads to a low rate of the reaction, on the contrary, the heterogeneous gas-phase catalyzed reaction allows a substantial reduction in temperature to achieve the same rate with the added possibility of going to enhanced conversion schemes. Many studies were reported in literature [O'Keefe et al., Catalysis research in thermochemical water-splitting processes. Catal Rev?Sci,Eng 1980;22(3):325?69.; Oosawa Yet al. Kinetics of the catalytic decomposition of hydrogen iodide in the magnesium?iodine thermochemical cycle. Bull Chem Soc Japan 1981;54:742] in which different kinds of catalysts were employed to decompose HI and catalytic decomposition mechanisms were also investigated. Some studies have been conducted on the first series of transition metals other than nickel and on molybdenum, tungsten and silver supported on γ-alumina and on activated carbon.The current focus of this work is to carry out a screening test of various catalysts prepared from different methods and from two different catalyst supports, such as γ-alumina and activated carbon.Catalysts were produced and characterized by BET, XRD and SEM analysis, then tested in terms of catalytic activity and stability by means of a tubular quartz reactor. In particular the relationships between catalytic activity and preparation procedure was investigated. Keywords: nickel and platinum supported catalysts, thermochemical water splitting cycle, catalytic hydrogen iodide decomposition,