Activity and stability of monometallic and bimetallic catalysts for high-temperature catalytic HI decomposition in the iodine-sulfur hydrogen production cycle

The active carbon-supported monometallic (Pd, Pt, and Ir) and bimetallic (Pd-Pt, Pd-Ir, and Pt-Ir) catalysts were prepared by the impregnation-reduction method, and their catalytic performances for HI decomposition were investigated in a fixed bed reactor at 550 and 600 °C. For stability comparison, fresh and used catalysts were characterized by XRD, TEM, EDX, and XPS. Activity evaluation results indicated that bimetallic Pt-Ir/C exhibited the highest catalytic properties among the monometallic and bimetallic catalysts surveyed. Although structural and morphological characterization results revealed obvious differences between fresh and used Pd-containing catalysts (i.e., Pd/C, Pd-Pt/C, and Pd-Ir/C), used monometallic Ir and bimetallic Pt-Ir catalysts retained virtually the same structure and morphology as fresh catalysts. Synergy between Pt and Ir is believed to strongly improve catalyst structure, morphology, and properties, by promoting stable bimetallic alloys, small metal particles, high metal dispersion, superior activity, and anti-sintering ability.