Effect of rare earth (RE - La, Pr, Nd) metal-doped ceria nanoparticles on catalytic hydrogen iodide decomposition for hydrogen production

In this work, high surface area rare earth (RE = La, Pr, and Nd) metal-doped ceria (CeO2) nanocatalysts have been synthesized by the citric-aided sol-gel method for hydrogen iodide decomposition in thermochemical water-splitting sulfur-iodine (SI) cycle for hydrogen production. This sol-gel method allows the insertion of rare earth metal M3+ ions into the CeO2 material. Incorporation of rare earth metals created a different synergistic effect between RE and Ce components such as increase of oxygen mobility, oxygen vacancy, and thermal stability of the CeO2 material. These doped-CeO2 materials were characterized by various physicochemical techniques, namely, XRD, BET, ICP-AES, TEM, TGA, and RAMAN spectroscopy. XRD and TEM studies revealed 5-10 nm particles of the RE-CeO2 material. Shifting of peaks and increase in lattice parameter values confirmed the formation of Ce-RE solid solutions (XRD and Raman). Incorporation of dopants resulted in an increase in the specific surface area (BET), thermal stability (TGA), and oxygen vacancy concentration (Raman). Among different dopants, CeO2-L (La-doped CeO2) material exhibits the highest specific surface area, thermal stability, and oxygen vacancy concentration, and smallest crystallite size. The catalytic activity of doped-CeO2 materials is explored for hydrogen-iodide decomposition. The order of catalytic activity is as follows: CeO2 < CeO2-N (N = Nd) < CeO2-P (P = Pr) < CeO2-L (L = La). CeO2-L shows higher catalytic activity and stability in comparison to the pure CeO2 material. It also showed an excellent time-on-stream stability for 35 h. The apparent activation energy of CeO2-L, CeO2-P, and CeO2-N was found to be 48.9, 54.8, and 61.4 kJ mol(-1), respectively. The effect of iodine on hydrogen iodide conversion was also studied over a CeO2-L catalyst. Thus, RE-doped CeO2 catalysts show a lot of potential of generating hydrogen from hydrogen iodide in the SI cycle. (C) 2018 Hydrogen Energy Publications LLC. Published by Elsevier Ltd. All rights reserved.