Enhanced Ammonia Decomposition Performance of K-Promoted Ru/γ-Al2O3 Catalysts: A Study on the Impact of Potassium Content and Calcination Temperature

Enhanced Ammonia Decomposition Performance of K-Promoted Ru/γ-Al2O3 Catalysts: A Study on the Impact of Potassium Content and Calcination Temperature

The Ru/γ-Al2O3 catalyst was prepared using the incipient wetness impregnation method. The γ-Al2O3 support (214 m2/g) was obtained by calcining pseudo-boehmite at 450 °C. To prepare the catalyst, 0.28 g of RuCl3 (purchased from Shaanxi Kaida Chemical Co., Ltd) was dissolved in deionized water with a volume equivalent to the pore volume of the support. The resulting solution was then added dropwise onto 2 g of the support while continuously stirring. The mixture was dried at 120 °C for 4 hours and calcined at different temperatures for 2 hours under an air atmosphere, or without calcination. The resulting samples were labeled as Ru/γ-Al2O3-ORx or Ru/γ-Al2O3-Rx, where x denotes the pretreatment temperature (200, 300, 400, 500, 600, 700, and 800 °C).

The Ru/γ-Al2O3 catalyst was washed with a 10 wt% ammonia aqueous solution and labeled as Ru/γ-Al2O3-RW. Subsequently, different concentrations of KNO3 solutions (2%, 4%, 6%, 8%, 10%, 12%, and 14%) were added to the dechlorinated catalyst powder, stirred evenly, soaked overnight, and dried at 120 °C for 4 hours. These catalysts were labeled as x K-Ru/γ-Al2O3-RW, where x represents the concentration of KNO3 solution. The Ru loading amount for all samples was fixed at 5.0 wt%.

The catalytic activity of the catalyst for ammonia decomposition was tested in a fixed-bed quartz reactor under a flow of pure NH3 at atmospheric pressure. A total of 100 mg of catalyst (20-40 mesh) was loaded into a quartz tube reactor, and then subjected to reduction in 8% H2/Ar (30 mL/min) at the desired temperature with a ramp rate of 10 °C/min for 1 hour. The reactor was then purged with Ar (10 mL/min) and cooled down to room temperature. Subsequently, the gas flow was switched to 100 vol% NH3 (30 mL/min), corresponding to a gas hourly space velocity (GHSV) of 18,000 mL/gcat/h. The reaction was carried out in a temperature range of 200-600 °C with a step of 50 °C. The concentrations of outlet gases were analyzed using an online gas chromatograph (GC 9790Plus).