Highly active oxygen capable to selectively oxidize methane to methanol at low temperature can be prepared in transition-metal cation exchanged zeolites. Here we show that the αoxygen stabilized by the negative charges of two framework aluminum atoms can be prepared by the dissociation of nitrous oxide over distant binuclear cation structures (M(II)…M (II), M = cobalt, nickel, and iron) accommodated in two adjacent 6-rings forming cationic sites in the ferrierite zeolite. This α-oxygen species is analogous to that known only for iron exchanged zeolites. In contrast to divalent iron cations, only binuclear divalent cobalt cationic structures and not isolated divalent cobalt cations are active. Created methoxy moieties are easily protonated to yield methanol, formaldehyde, and formic acid which are desorbed to the gas phase without the aid of water vapor while previous studies showed that highly stable methoxy groups were formed on isolated iron cations in iron exchanged ZSM-5 zeolites.

Activation of dioxygen is of extreme importance due to its potential for transformation of methane to valuable products and applications in other selective oxidation reactions. Distant binuclear cationic Fe(II) centers in Fe-ferrierite were shown to split dioxygen at room temperature to form a pair of very active oxygen species (i.e., αoxygens) and subsequently oxidize methane to methanol at room temperature as well. Our study reveals that the activity in splitting dioxygen represents a general property of the distant binuclear cationic Fe(II) centers stabilized in the aluminosilicate matrix. Computational models of the ferrierite, beta, A, and mordenite zeolites with various Al sitings in the rings forming the cationic sites were investigated by periodic DFT calculations including molecular dynamics simulations. The results reveal that the Fe(II) sites stabilized in various zeolite matrices can split dioxygen if the two cationic sites forming the distant binuclear Fe(II) centers (i) face each other, (ii) are parallel, and (iii) are axial, and (iv) the Fe•••Fe distance lies in a narrow range from ca. 7 to ca. 8 Å (ca. 7−ca. 10 Å for the distance between the two rings (forming the corresponding cationic sites) in empty zeolites since this distance is equal to or larger than the Fe•••Fe distances). Our study opens the possibility of developing Fe-zeolite-based systems for the dioxygen activation employed for direct oxidations using various zeolite matrices.

Here we demonstrate for the first time the splitting of dioxygen at RT over distant binuclear transition metal (M = Ni, Mn, and Co) centers stabilized in ferrierite zeolite. Cleaved...