FeCHA is capable of performing Methane Oxidation
- and the active site likely a Fe2+ isolated on a 6MR!
A collaboration between the Dusselier, Sels, Pierloot and Solomon group has yielded a new entry in the world of methane oxidation and C-H activation at low temperature, with Fe2+.
With samples made in our lab (Julien), Max, Dieter, Profs. Sels and Schoonheydt performed DRUVVIS and methane oxidation with N2O. Prof. Pierloot and Simon confirmed the spectroscopy computationally, while the Stanford team measured, among other, Mossbauer spectroscopy.
Spectroscopic Identification of the α-Fe / α-O Active Site in Fe-CHA Zeolite for the Low-Temperature Activation of the Methane C-H bond
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 N2O 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 on-line 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 aluminium 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 Fe2O3 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.