Study of the local structure and oxidation state of iron in complex oxide catalysts for propylene ammoxidation

Abstract

A combination of X-ray absorption, Raman and UV-visible spectroscopy reveals the competing redox reactions during the deactivation of Fe-based complex catalysts.

Structural dynamics of an iron molybdate catalyst under redox cycling conditions studied with in situ multi edge XAS and XRD

“…The features observed for the initial state of Fe at 100 1C show similarity with the Fe 2 (MoO 4 ) 3 spectral features reported earlier. 29 Initially, the Fe K-edge absorption peak maxima was observed at 7131.8 eV, which is similar to the value reported in literature. 29 At higher temperature, the spectra exhibited a gradual shift towards lower energy indicating a change in the average oxidation state of Fe from III to II, mainly corresponding to formation of FeMoO 4 , however the presence of other Fe(II) species cannot be ruled out.…”

“…29 Initially, the Fe K-edge absorption peak maxima was observed at 7131.8 eV, which is similar to the value reported in literature. 29 At higher temperature, the spectra exhibited a gradual shift towards lower energy indicating a change in the average oxidation state of Fe from III to II, mainly corresponding to formation of FeMoO 4 , however the presence of other Fe(II) species cannot be ruled out. In the temperature range 200-300 1C, the presence of iron oxides such as Fe 2 O 3 and FeO were also expected as intermediate phases.…”

Probing the Structural Changes and Redox Behavior of Mixed Molybdate Catalysts under Ammoxidation Conditions: An Operando Raman Spectroscopy Study

“…To probe the structural changes of catalysts under reaction conditions, in situ and, in particular, operando Raman spectroscopy are suitable tools . In the case of metal molybdates, it is possible to identify different molybdate structures by their characteristic spectroscopic features . Thus, we have demonstrated recently by operando Raman spectroscopy of mixed molybdate catalysts under propene oxidation conditions that the formation and changes of molybdate phases induced by exposure to different reaction gas mixtures can be followed by inspecting the intensity changes of their characteristic bands.…”

“…[6][7][8][9][10][11] In the case of metal molybdates,i t is possible to identify different molybdate structures by their characteristic spectroscopic features. [12][13][14][15][16][17][18][19] Thus,w ehave demonstrated recently by operando Raman spectroscopy of mixed molybdate catalysts under propene oxidation conditions [20] that the formation and changes of molybdate phases induced by exposure to different reactiong as mixtures can be followed by inspecting the intensity changes of their characteristic bands. In accordance with the above-mentioned in situ Mçssbauer experiments, [5] Inspiredb yt hese first optimistic results we extended our studies on the ammoxidation of propene to acrylonitrile over mixed molybdate catalysts ystems.…”

Catalisadores Multicomponentes Com Adição De Promotores Para Produção Da Acrilonitrila

“…A produção mundial de acrilonitrila ultrapassa cinco milhões de toneladas por ano, sendo projetado um crescimento anual de 3,7% até 2018, impulsionado principalmente pela demanda das resinas ABS e SAN (CESPI et al, 2014;ZHENG et al, 2015).…”