Coordination and activation of nitrous oxide by iron zeolites

Iron-containing zeolites are heterogeneous catalysts that exhibit remarkable activity in the selective oxidation of inert hydrocarbons and catalytic decomposition of nitrous oxide (N2O). The reduction of N2O is critical to both these functions, but experimental data tracking the iron active sites during N2O binding and activation are limited. Here, the N2O-ligated Fe(ii) active site in iron-exchanged zeolite beta is isolated and characterized by variable-temperature Mossbauer, diffuse reflectance UV-vis-NIR and Fourier transform infrared spectroscopy. N2O binds through the terminal nitrogen atom with substantial backbonding from the Fe(ii) centre at low temperature. At higher temperatures, the Fe-N2O interaction is weakened, facilitating isomerization to the O-bound form, which is competent in O-atom transfer. Density functional theory calculations show the geometric and electronic structure requirements for N2O binding and activation. A geometric distortion imposed by the zeolite lattice plays an important role in activating N2O. This highlights a mechanism for structural control over function in Fe-zeolite catalysts. Nitrous-oxide-mediated oxidation reactions can be effectively promoted by iron-containing zeolites, although structural information on the interaction between oxidant and metal centre is limited. Here, the authors report the characterization of the N2O-ligated Fe(ii) active site in iron-exchanged zeolite beta.

Automated summary

This study isolated and characterized the N2O-ligated Fe(ii) active site in iron-exchanged zeolite beta using various spectroscopic techniques. The results showed that N2O binds through the terminal nitrogen atom with substantial backbonding from the Fe(ii) center at low temperatures, and weakens at higher temperatures, facilitating isomerization to the O-bound form which is competent in O-atom transfer. Density functional theory calculations provided insights into the geometric and electronic structure requirements for N2O binding and activation, highlighting the role of the zeolite lattice in activating N2O.