Decomposition studies of NH3 and ND3 in presence of H2 and D2 with Pt/Al2O3 and Ru/Al2O3 catalysts. (8th April 2022)

• Record Type: Journal Article
• Authors: Antunes, Rodrigo; Steiner, Roland; Marot, Laurent; Meyer, Ernst
• Is Part Of: International journal of hydrogen energy. Volume 47:Number 30(2022)
• Page Start: 14130
• Page End: 14140
• Publication Date: 2022-04-08
• Subjects: Ammonia -- Isotope -- Decomposition -- Platinum -- Ruthenium; Hydrogen as fuel -- Periodicals; Hydrogène (Combustible) -- Périodiques; Hydrogen as fuel; Periodicals; 665.81
• DOI: 10.1016/j.ijhydene.2022.02.155
• Languages: English
• ISSNs: 0360-3199

Abstract

Abstract: In the fusion reactor ITER, ammonia will be produced as a result of the interaction between the hydrogen isotopes used as fuel and nitrogen used to spread the power loads of a larger area. As part of the fuel management in ITER, NQ3 (NQ3, Q = H, D, T) will have to be decomposed using a palladium membrane reactor. The decomposition of pure NH3 and ND3 was studied in this work using commercial platinum (Pt) and ruthenium (Ru) catalysts on alumina (0.5 wt% loading), in a conventional reactor configuration (i.e., without a palladium membrane). With Pt/Al2 O3, decomposition fractions larger than 90% were achieved with NH3 above 800 K using the lowest flow-to-mass ratio ( F NH 3 /g-cat) of 0.015 sccm g −1 . However, with the increase of F NH 3 /g-cat to 0.220 sccm g −1, similar decompositions were achieved only at ≈ 1000 K. In contrast, with Ru/Al2 O3 decomposition fractions above 90% were attained already below 700 K, regardless of F NH 3 /g-cat. With both catalysts the decomposition of NH3 was found to be more efficient than that of ND3 at a wide range of temperatures, thus evidencing the existence of isotopic effect. A strong inhibition of both NH3 and ND3 in presence of, respectively, H2 and D2 with Pt/Al2 O3 was observed. This effect was stronger at lower temperatures and larger hydrogen partial pressures. The inhibition effect with Ru/Al2 O3 was less pronounced and it was suppressed at 629 K. Isotopic exchange reactions with equimolar mixtures of NH3 -D2 and ND3 -H2 revealed that the most and least abundant isotopologue are, respectively, NH2 D and ND3 . At the relevant temperature window in which the PMR will be operated (673–823 K), the Ru-based catalyst exhibits superior performances in terms of decomposition rates, negligible isotopic and inhibition effects. A slight reduction of the performances with this catalyst was observed with 0.200 sccm g −1 . This work suggests that 0.5 wt% Ru/Al2 O3 is the most suitable catalyst to be used during ITER operation. Highlights: Decomposition efficiencies above 90% were obtained with NH3 and ND3 using Ru/Al2 O3 . The inhibition effect of H2 and D2 with Pt/Al2 O3 was stronger than with Ru/Al2 O3 . NH2 D is the most important isotopologue in NH3 -D2 and ND3 -H2 mixtures. Ru/Al2 O3 is the most suitable to be employed in the ITER Tokamak Exhaust Process.