Efficient Hydrogen Production from Ammonia Using Ru Nanoparticles on Ce-Based Metal–Organic Framework (MOF)-Derived CeO2 with Oxygen Vacancies

Ammonia is a promising hydrogen storage material because it is easy to store and decompose into CO_X-free hydrogen. A Ru-based catalyst exhibits good catalytic performance in ammonia decomposition, and enhancing the interaction between the Ru atoms and the support is an important way to further improve its catalytic activity. In this study, CeO₂ was prepared by calcination using a cerium-based metal-organic framework (MOF) as the precursor, and the number of oxygen vacancies on the surface of CeO₂ was regulated by hydrogen reduction. The XPS and Raman results showed that abundant oxygen vacancies were formed on the surface of these CeO₂, and their number increased with an increase in the reduction time. The Ru/CeO₂-4 h catalyst, using CeO₂ reduced for 4 h as the support, exhibited good catalytic activity in ammonia decomposition, reaching 98.9% ammonia conversion and 39.74 mmol g_cat^-1 min^-1 hydrogen yield under the condition of GHSV = 36,000 mL g_cat^-1 h^-1 at 500 °C. The XAFS results demonstrated that Ru was stably anchored with oxygen vacancies on the surface of CeO₂ via Ru-O-Ce bonds. Density functional theory calculations further showed that these bondings lower the reaction energy barrier for N-H bond cleavage, thereby significantly enhancing the catalytic activity.