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Nitrous oxide in oxidation chemistry and catalysis: application and production

“…An initial binuclear iron complex (I) may form via both a Fe atom migration from tetrahedral positions of the zeolite lattice or an ''external'' Fe insertion from FeCl 3 (e.g., at a solid ion exchange, sublimation, CVD, etc.). The existence of such complexes inside Fe-containing zeolites of various structure including FeZSM-5, Fe-silicalite and Fe-b was suggested and well documented by many authors [61,[71][72][73][74][75][76][77][78][79][80][81]. Upon oxygen desorption at elevated temperatures, complex (I) may transform into a reduced complex (II) (step 1).…”

“…For the a-site formation to occur, the reduced Fe 2+ atoms should convert into a new stable state, in which they lose their ability to react with O 2 and thus make the step (1) irreversible. The process of the Fe 2+ stabilization appeared to depend on the chemical composition of the matrix and is strongly facilitated by the presence of water vapor [20,26,30,71,78]. Presumably, the stabilization can occur in the form of complex (III), in which Fe 2þ 2 entities are strongly incorporated into a silicate fragment of the zeolite matrix and have a more distant position as compared to complex (II), thus making impossible their reoxidation into the latter complex.…”

New frontiers in X-ray spectroscopy in heterogeneous catalysis: Using Fe/ZSM-5 as test-system

“…The next nearest-neighbour atoms are silicon (or aluminium) atoms. The characterization techniques that display typical spectral features for Fe F (Fe III in T d symmetry) and which are most widely used to prove its presence are EPR [17][18][19], Mössbauer [20][21][22] and XAFS [23,24].…”

Characterization of structure of Fe-species in Fe-ferrierite using Mössbauer spectroscopy

“…Panov and co-workers focus on identification of active iron placed in α-sites [3,4,5]. Overweg et al [6] showed that Fe(III) in Fe-ZSM 5 catalyst is reduced to Fe(II) state during thermal treatment at 623 K in N 2 or Ar. Under these conditions, iron ions in isolated extra framework positions and in small oxo-iron clusters were reduced to Fe(II).…”

“…Under these conditions, iron ions in isolated extra framework positions and in small oxo-iron clusters were reduced to Fe(II). The oxidation back to Fe(III) was achieved by a treatment with N 2 O at 623 K. They noticed a remarkable affinity of these iron ions to molecular nitrogen, leading to a reduction of a fraction of Fe(III) ions produced by oxidation in N 2 O after exposure to N 2 [6]. Some Mössbauer studies have been focused on iron analogue of beta zeolite.…”