| Autor: |
Bols ML; Department of Microbial and Molecular Systems, Centre for Surface Chemistry and Catalysis , KU Leuven , Celestijnenlaan 200F , B-3001 Leuven , Belgium., Hallaert SD; Department of Chemistry , KU Leuven , Celestijnenlaan 200F , B-3001 Leuven , Belgium., Snyder BER; Department of Chemistry , Stanford University , Stanford , California 94305 , United States., Devos J; Department of Microbial and Molecular Systems, Centre for Surface Chemistry and Catalysis , KU Leuven , Celestijnenlaan 200F , B-3001 Leuven , Belgium., Plessers D; Department of Microbial and Molecular Systems, Centre for Surface Chemistry and Catalysis , KU Leuven , Celestijnenlaan 200F , B-3001 Leuven , Belgium., Rhoda HM; Department of Chemistry , Stanford University , Stanford , California 94305 , United States., Dusselier M; Department of Microbial and Molecular Systems, Centre for Surface Chemistry and Catalysis , KU Leuven , Celestijnenlaan 200F , B-3001 Leuven , Belgium., Schoonheydt RA; Department of Microbial and Molecular Systems, Centre for Surface Chemistry and Catalysis , KU Leuven , Celestijnenlaan 200F , B-3001 Leuven , Belgium., Pierloot K; Department of Chemistry , KU Leuven , Celestijnenlaan 200F , B-3001 Leuven , Belgium., Solomon EI; Department of Chemistry , Stanford University , Stanford , California 94305 , United States.; Photon Science, SLAC National Accelerator Laboratory , 2575 Sand Hill Road , Menlo Park , California 94025 , United States., Sels BF; Department of Microbial and Molecular Systems, Centre for Surface Chemistry and Catalysis , KU Leuven , Celestijnenlaan 200F , B-3001 Leuven , Belgium. |
| Abstrakt: |
The formation of single-site α-Fe in the CHA zeolite topology is demonstrated. The site is shown to be active in oxygen atom abstraction from N 2 O to form a highly reactive α-O, capable of methane activation at room temperature to form methanol. The methanol product can subsequently be desorbed by online steaming at 200 °C. For the intermediate steps of the reaction cycle, the evolution of the Fe active site is monitored by UV-vis-NIR and Mössbauer spectroscopy. A B3LYP-DFT model of the α-Fe site in CHA is constructed, and the ligand field transitions are calculated by CASPT2. The model is experimentally substantiated by the preferential formation of α-Fe over other Fe species, the requirement of paired framework aluminum and a MeOH/Fe ratio indicating a mononuclear active site. The simple CHA topology is shown to mitigate the heterogeneity of iron speciation found on other Fe-zeolites, with Fe 2 O 3 being the only identifiable phase other than α-Fe formed in Fe-CHA. The α-Fe site is formed in the d6r composite building unit, which occurs frequently across synthetic and natural zeolites. Finally, through a comparison between α-Fe in Fe-CHA and Fe-*BEA, the topology's 6MR geometry is found to influence the structure, the ligand field, and consequently the spectroscopy of the α-Fe site in a predictable manner. Variations in zeolite topology can thus be used to rationally tune the active site properties. |
