Hydrogen generation via ammonia decomposition on highly efficient and stable Ru-free catalysts: approaching complete conversion at 450 °C

Hydrogen (H-2) is a prospective zero-carbon and high-energy-density fuel alternative to fossil fuels for generating power and clean energy. Ammonia (NH3) is a promising H-2 (17.7%) carrier, which can easily overcome the challenges associated with H-2 storage and transportation. Thermocatalytic ammonia decomposition reaction (ADR) is an effective way to produce clean H-2 but it relies on the use of expensive and rare ruthenium (Ru)-based catalysts at elevated temperatures (>500 degrees C), hence is not sustainable and economically feasible. Herein, we report a synergistic strategy to design a heterostructured Ru-free catalyst, consisting of CoNi alloy nanoparticles well-dispersed on a MgO-CeO2-SrO mixed oxide support with potassium promotion. The resulting K-CoNialloy-MgO-CeO2-SrO catalyst presents 97.7% and 87.5% NH3 conversion efficiency at 450 degrees C at gas hourly space velocities (GHSVs) of 6000 and 12 000 mL h(-1) g(cat)(-1), respectively. At 500 degrees C, the H-2 production rate (57.75 mmol g(cat)(-1) min(-1)) becomes comparable to that of most of the reported Ru-based catalysts. The catalyst stability has been successfully demonstrated in both a fixed-bed reactor under high pressure (120 h at 5.0 bar) and a membrane reactor prototype (600 h at 1.5 bar) at 500 degrees C. High-temperature in situ XPS analysis, temperature-programmed desorption/reduction, and density functional theory calculations have been carried out to elucidate the possible active sites and performance enhancement mechanisms. This work highlights the importance of constructing optimal interfaces between active metal nanoparticles and oxide support for boosting the NH3 to H-2 conversion efficiency and long-term stability.