No abstract

Activation of dioxygen attracts enormous attention due to its potential for utilization of methane and applications in other selective oxidation reactions. We report a cleavage of dioxygen at room temperature over distant binuclear Fe(II) species stabilized in an aluminosilicate matrix. A pair of formed distant α-oxygen species [i.e., (Fe(IV)═O)2+] exhibits unique oxidation properties reflected in an outstanding activity in the oxidation of methane to methanol at room temperature. Designing a man-made system that mimicks the enzyme functionality in the dioxygen activation using both a different mechanism and structure of the active site represents a breakthrough in catalysis. Our system has an enormous practical importance as a potential industrial catalyst for methane utilization because (i) the Fe(II)/Fe(IV) cycle is reversible, (ii) the active Fe centers are stable under the reaction conditions, and (iii) methanol can be released to gas phase without the necessity of water or water-organic medium extraction.

Figure 1. Schematic depiction of some types of active sitesrelatedt oone and two Al atoms. a) Twoc lose protonic sites, b) isolated protonic site, c) bare M 2 + cations in different rings, d) monovalent [M 3 + ÀO 2À ] + oxo-species, ande)Cu 2 + ÀOÀCu 2 + bridging structure. 557 Reviews Figure 2. Schematic depiction of the types of Al distances in zeolites. a) Distance by the SiAl sequence, b) geometrical distance, and c) visible distance.

No abstract

SSZ-13 is a Si-rich (Si/Al > 5) small pore zeolite (chabazite topology) important for both acid and redox catalysis. Using a sample with Si/Al = 12, a new procedure involving 27Al (3Q) MAS NMR spectroscopy and extensive periodic DFT calculations with molecular dynamics, in addition to the standard methods based on bare Co­(II) cations as probes monitored by FTIR spectroscopy and UV–vis spectroscopy, was employed. The placement of the Al–O–(Si–O)2–Al and Al–O–(Si–O)3–Al sequences in the zeolite framework was determined (Al–O–Si–O–Al sequences are absent). 54% of the framework Al atoms correspond to Al–O–(Si–O)3–Al sequences which cannot form cationic sites for bare divalent cations but are able to accommodate divalent Co­(II) hexaaqua complexes. The corresponding Al–O–(Si–O)3–Al sequence is located in two double 6-ring cages with one Al located in the 4-ring connecting two double 6-ring units. Our study also reveals that 35% of the framework Al atoms can accommodate neither divalent Co­(II) hexaaqua complexes nor bare divalent cations. Furthermore, the siting of the Al atoms of the Al–O–(Si–O)2–Al and Al–O–(Si–O)3–Al sequences forming four cationic sites for divalent cations located in the 6-ring (Al–O–(Si–O)2–Al), 8-ring (Al–O–(Si–O)2–Al and Al–O–(Si–O)3–Al), and double 6-ring (Al–O–(Si–O)2–Al) was determined. These Al atoms correspond to a minority of the Al framework atoms.