No abstract

No abstract

A highly active and stable catalyst for hydrogen-iodide decomposition reaction in sulfur-iodine (SI) cycle has been prepared in the form of Pd-CeO 2 nanocatalyst by sol-gel method with different calcination temperatures (300°C, 500°C, and 700°C). XRD and TEM confirmed a size around 6-8 nm for Pd-CeO 2 particles calcined at 300°C. Raman study revealed large number oxygen vacancies in Pd-CeO 2-300 when compared to Pd-CeO 2-500 and Pd-CeO 2-700. With increase in calcination temperature, the average particle size increased whereas the specific surface area and number of oxygen vacancies decreased. Hydrogen-iodide catalytic-decomposition was carried out in the temperature range of 400°C-550°C in a quartz-tube, vertical, fixed-bed reactor with 55 wt % aqueous hydrogen-iodide feed over Pd-CeO 2 catalyst using nitrogen as a carrier gas. Pd-CeO 2-300 showed hydrogen-iodide conversion of 23.3 %, which is close to the theoretical equilibrium conversion of 24 %, at 550°C. It also showed a reasonable stability with a time-on-stream of 5 h.

Bimetallic Ni-Pt nanoparticles supported on four different supports (activated carbon (AC)) 1 , γ-alumina, zirconia, and ceria) were prepared by modified impregnation-reduction technique for decomposition of hydrogen iodide to hydrogen and iodine, in the thermochemical water-splitting sulfur-iodine (SI) cycle. The catalysts were characterized by powder X-ray diffraction (XRD), transmission electron microscopy (TEM), and Brunauer-Emmett-Teller (BET) method to find their structure, morphology, and surface area, respectively. High metal dispersions (Ni-Pt) were obtained with particle sizes of the order of 10 nm or lesser, in the high-surface-area supports. The hydrogen iodide-decomposition results showed the following catalytic activity order of Ni-Pt nanoparticles on different supports: Ni(2.5%)-Pt(2.5%)/AC > Ni(2.5%)-Pt(2.5%)/γ-alumina > Ni(2.5%)-Pt(2.5%)/Zirconia > Ni(2.5%)-Pt(2.5%)/Ceria. Bimetallic Ni(2.5%)-Pt(2.5%)/AC also showed excellent stability for 100 h in the hydrogen iodide-decomposition reaction, and with a higher performance relative to the corresponding Pt supported catalyst under the same operating conditions.

NiO/ZrO2 prepared by solution-combustion (SC) showed near equilibrium conversions of HI to H2 and I2, at 500-550 o C, at space velocities of 12 hr-1 , without any performance degradation over 50 hours., , XRD data of the catalyst after 10 h of reaction were compared with the same after a TPR step in H2/Ar on another catalyst sample, to verify Ni ex-solution. Ni is clearly visible in the XRD after TPR, although it is not observed under reaction conditions (HI/H2O/N2), even after 10 hrs. Instead, onset of monoclinic ZrO2 is observed after reaction, which was not visible after TPR.