Autothermal hydrogen production via oxidative decomposition of ammonia over vacancy-engineered Ru/CeO₂ prepared by...

Ammonia is a promising hydrogen carrier owing to its high volumetric hydrogen density. Oxidative decomposition of ammonia (ODA) enables autothermal hydrogen production by using the heat released from partial ammonia combustion. However, because this heat is supplied by combusting part of the feed, thermal self-sufficiency and hydrogen yield are intrinsically coupled: at NH₃/O₂ = 4 the oxidized fraction caps the attainable H₂ yield at 66.7%. The central catalytic challenge is therefore to maximize decomposition activity at a fixed combustion fraction. Here we activate Ru/CeO₂ by sodium borohydride (NaBH₄)-mediated liquid-phase reduction instead of conventional high-temperature H₂ reduction, thereby decoupling oxygen-vacancy formation from Ru sintering. The liquid-phase-reduced catalyst (LPR) retained a Ru particle size comparable to that of the mildly reduced catalyst (LT) while exhibiting a markedly higher vacancy concentration by XPS and Ce M_4,5-edge EELS. N₂-TPD shows that LPR releases nitrogen at the lowest temperature (370 °C versus 430 °C for LT), consistent with weakened Ru-N binding at the rate-limiting recombinative desorption step, and H₂-TPD with CO/H₂ pulse chemisorption indicates enhanced hydrogen spillover to the support. Thermochemical analysis shows that ODA becomes thermally neutral when about 12.7% of the ammonia feed is oxidized (O₂/NH₃ = 0.095). At O₂/NH₃ = 0.25, LPR delivered a 26.4% H₂ yield versus 20.6% for LT, corresponding to 39.6% and 30.9% of the 66.7% theoretical ceiling. A concept-level techno-economic analysis gives a levelized hydrogen cost of $9.6 kg^-1-H₂ at the experimental yield, dominated by the ammonia feedstock.