H2SO4 poisoning of Ru-based and Ni-based catalysts for HI decomposition in SulfurIodine cycle for hydrogen production

The sulfur–iodine (SI) cycle is deemed to be one of the most promising alternative methods for large-scale hydrogen production by water splitting, free of CO 2 emissions. Decomposition of hydrogen iodide is a pivotal reaction that produces hydrogen . The homogeneous conversion of hydrogen iodide is only 2.2% even at 773 K [1]. A suitable catalyst should be selected to reduce the decomposition temperature of HI and attain reaction yields approaching to the thermodynamic equilibrium conversion. However, residual H 2 SO 4 could not be avoided in the SI cycle because of incomplete purification. The H 2 SO 4 present in the HI feeding stream may lead to the poisoning of HI decomposition catalysts. In this study, the activity and sulfur poisoning of Ru and Ni catalysts loaded on carbon and alumina , respectively, were investigated at 773 K. HI conversion efficiency markedly decreased from 21% to 10% with H 2 SO 4 (3000 ppm) present, which was reversible when H 2 SO 4 was withdrawn in the case of Ru/C. In the case of Ru/C and Ni/Al 2 O 3 , catalyst deactivation depends on the concentration of H 2 SO 4 ; the higher the concentration of H 2 SO 4, the greater the severity of deactivation. Catalysts before and after sulfur poisoning were characterized by transmission electron microscopy (TEM), energy-dispersive X-Ray spectroscopy (EDX), X-ray photoelectron spectroscopy (XPS), and X-ray diffraction (XRD). Experimental results and characterization of poisoned and fresh catalysts indicate that the catalyst deactivation could be ascribed to the competitive adsorption of sulfur species and change in its surface properties.