Plasma-Assisted Synthesis of High-Efficiency Catalysts for Low-Temperature NH3 Cracking to H2

Hydrogen (H2) production from ammonia (NH3) decomposition is gaining interest as a promising green energy source, owing to its high hydrogen storage density and COx-free nature. However, extracting hydrogen through the NH3 decomposition reaction requires high temperatures to achieve high efficiency via catalytic processes. A combination of Ruthenium (Ru) with Ceria (Ce) as a catalyst is an efficient approach for low-temperature NH3 decomposition. Here, Ru-Ce/γ-Al2O3 catalysts were prepared by incipient wetness impregnation combined with DBD plasma-assisted treatment during the catalyst preparation steps. For comparison, a Ru-Ce/γ-Al2O3 catalyst with the same nominal composition was prepared using the corresponding conventional thermal treatment route. The results indicated that the catalyst prepared by plasma-assisted reduction exhibited higher NH3 decomposition activity than the conventionally reduced catalyst. Specifically, the Ru-Ce/γ-Al2O3 catalyst prepared by plasma-assisted reduction achieved near-complete NH3 conversion at 520 °C under a WHSV of 5,000 mL·gcat-1·h-1 (used as the comparative condition before evaluating the optimized catalyst at higher WHSV), with the residual NH3 concentration below the detectable level of the GC system, whereas the conventionally reduced catalyst required 540 °C to reach a comparable conversion level. In the temperature range of 350-500 °C, the NH3 conversion over the catalyst prepared by plasma-assisted reduction was at least 12% higher than that over the conventionally reduced catalyst. The improved activity was associated with plasma-induced changes in Ru dispersion and the surface redox properties of the Ce-containing support, as supported by TEM/STEM–EDS and XPS analyses. In addition, the optimized plasma-reduced catalyst maintained stable NH3 conversion for 93.5 h at 470 °C and WHSV = 30,000 mL·gcat-1·h-1, demonstrating good long-term durability.