XAS investigation of silica aerogel supported cobalt rhenium catalysts for ammonia decomposition

• Published in: Physical chemistry chemical physics : PCCP 2020-09, Vol.22 (34), p.18932-18949
• Main Authors: Kirste, Karsten G, Laassiri, Said, Hu, Zhigang, Stoian, Dragos, Torrente-Murciano, Laura, Hargreaves, Justin S. J, Mathisen, Karina
• Format: Article
• Language: English
• Subjects: Ammonia; Bimetals; Catalysts; Catalytic activity; Chemical Sciences; Cobalt; Decomposition; Hydrogen production; Low temperature; Reduction (metal working); Rhenium; Ruthenium; Silica aerogels; Silicon dioxide; Synergistic effect
• ISSN: 1463-9076; 1463-9084
• DOI: 10.1039/d0cp00558d

The implementation of ammonia as a hydrogen vector relies on the development of active catalysts to release hydrogen on-demand at low temperatures. As an alternative to ruthenium-based catalysts, herein we report the high activity of silica aerogel supported cobalt rhenium catalysts. XANES/EXAFS studies undertaken at reaction conditions in the presence of the ammonia feed reveal that the cobalt and rhenium components of the catalyst which had been pre-reduced are initially re-oxidised prior to their subsequent reduction to metallic and bimetallic species before catalytic activity is observed. A synergistic effect is apparent in which this re-reduction step occurs at considerably lower temperatures than for the corresponding monometallic counterpart materials. The rate of hydrogen production via ammonia decomposition was determined to be 0.007 mol H 2 g cat −1 h −1 at 450 °C. The current study indicates that reduced Co species are crucial for the development of catalytic activity. In situ XAS applied to a silica supported CoRe catalyst for ammonia decomposition shows the importance of the reduced bimetallic phase.