CeO2-conjugated CoFe layered double oxides as efficient non-noble metal catalysts for NH3-decomposition enabling carbon-free hydrogen production
Su‐Un Lee, Thien An Le, Youngmin Kim, You‐Jin Lee, Jeong‐Rang Kim, Tae‐Wan Kim, Kwang-Eun Jeong, Ho‐Jeong Chae
Abstract
• The effects of Ce incorporation and LDH-derived CoFe LDOs on NH 3 decomposition. • Ce 0.2 -Co 1.5 Fe 1.5 LDOs exhibited superior NH 3 conversion at low reaction temperature. • Rational regulation of Ce/(Co + Fe) molar ratio boosts recombinative N 2 desorption by altering metal-N binding. • Good stability with excellent NH 3 conversion was maintained under high WHSV conditions. CeO 2 -conjugated Co 1.5 Fe 1.5 LDOs were synthesized through a one-pot co-precipitation method of Ce-introduced Co 1.5 Fe 1.5 LDHs and their thermal treatment. By manipulating the stoichiometric molar ratio of Ce/(Co + Fe), a series of Ce x -Co 1.5 Fe 1.5 LDOs (x = 0.05, 0.1. 0.2, 0.5, and 1, corresponding to the molar ratio for the sum of Co and Fe) was comprehensively characterized to investigate the intricate interplay among factors such as spinel mixed metal oxides, LDH-derived LDOs, and the introduced Ce to achieve high catalytic performance in NH 3 decomposition. Notably, Ce 0.2 -Co 1.5 Fe 1.5 LDOs exhibited remarkable activity, achieving an NH 3 conversion of 81.9 % at 450 °C and a WHSV of 6,000 mL NH3 g cat -1 h −1 , and maintained excellent NH 3 -conversion with a negligible decrease over 80 h of continuous operation at 550 °C and high WHSV of 30,000 mL NH3 g cat -1 h −1 . The synergistic interaction between the incorporated CeO 2 and Co 1.5 Fe 1.5 LDOs induced modifications of structural properties including the distribution of Co and Fe within the spinel crystal structure, as well as affecting the lattice parameters and electronic properties. These modifications play a pivotal role in ultimately altering metal-N binding energy, which facilitates the efficient activation of absorbed NH 3 at the lowest temperature and minimizes the delay in recombinative N 2 -desorption. Hence, this study aims to highlight a new concept and demonstrate its feasibility for fabricating cost-effective and high-performing catalysts at mild temperatures to meet the growing demand for NH 3 as a hydrogen carrier.