Catalytic Decomposition of Hydrogen-Iodide Over Nanocrystalline Ceria Promoted by Transition Metal Oxides for Hydrogen Production in Sulfur-Iodine Thermo-Chemical Cycle

In this study, CeO2, and CeO2-M (M=Fe, Co, and Ni) catalysts were prepared by sol-gel method for catalytic decomposition of hydrogen-iodide in sulfur-iodine (SI) cycle. These catalysts sample were characterized by Brunauer-Emmett-Teller (BET), X-ray diffraction (XRD), inductively coupled plasma-atomic emission spectroscopy (ICP-AES), transmission electron microscopy (TEM), and Raman spectroscopy. The powder XRD, and TEM results gave 4-5 nm average size particles of CeO2-Ni-300 sample. BET and Raman results showed a high specific surface area, and large number of oxygen vacancy in the Ni sample. The hydrogen-iodide decomposition experiments were carried out in the temperature range of 400-550 A degrees C in a quartz-tube vertical fixed-bed reactor with 55 wt% HI feed over prepared CeO2-M catalysts using nitrogen as a carrier gas at atmospheric pressure. The experimental hydrogen-iodide decomposition results showed high catalytic activity of Ni sample as compared to Co and Fe samples. They followed the catalytic order: CeO2-Ni-300 > CeO2-Co-300 > CeO2-Fe-300 > CeO2-300. The effect of calcination temperatures (300, 500, and 700 A degrees C) of CeO2-Ni sample (during sol-gel method) on hydrogen-iodide conversion was also studied and showed that the following catalytic order: CeO2-Ni-300 > CeO2-Ni-500 > CeO2-Ni-700. With increase in calcination temperatures the conversion decreased. CeO2-Ni-300 sample also gave a reasonable stability for time-on-stream of about 5 h. So, based on these results, CeO2-Ni-300 is an attractive candidate which has potential for producing large quantity of hydrogen in SI cycle. [GRAPHICS] .