Structure and reactivity in the selective oxidation of methane to formaldehyde of low-loaded FeOx/SiO2 catalysts

Francesco Arena, Giorgio Gatti, Gianmario Martra, Salvatore Coluccia, Lorenzo Stievano, Lorenzo Spadaro, Pio Famulari, Adolfo Parmaliana

Risultato della ricerca: Contributo su rivistaArticolo in rivistapeer review

Abstract

The structure of low-loaded (0.09-0.73 Fe wt%) FeOx/SiO2 catalysts prepared by adsorption-precipitation of Fe2+ precursor on silica (AP) has been assessed by DR UV-Vis and Mossbauer techniques in comparison with counterpart incipient wetness (IW) systems. Spectroscopic findings indicate the speciation of the active phase into isolated Fe3+ species, oligomeric 2-d FeOx patches, and 3-d Fe2O3 nonoparticles, characterised by decreasing interaction strength with silica carrier. The reduction pattern of the above surface structures has been probed by temperature-programmed reduction (TPR) measurements, and a deconvolution analysis of spectra allowed the concentration of the various surface species to be highlighted. The catalytic activity in the selective oxidation of CH4 to HCHO with oxygen (MPO) has been systematically evaluated by batch (BR) and continuous-flow (CF) measurements in the range of 400-750 degrees C. Direct relationships among Fe dispersion and specific atomic rate of CH4 conversion (Fe-CH4, S-1) and HCHO formation (Fe-HCHO, s(-1)) confirm the superior catalytic performance of AP systems. After a poor reactivity of "isolated species" and the unselective behaviour of 3-d Fe2O3 particles, 2-d oligomeric patches feature the best catalytic pattern, owing to an optimum Fe-O bond strength. Sintering and surface reconstructuring phenomena affect the catalyst stability during the MPO reaction.
Lingua originaleInglese
pagine (da-a)365-380
Numero di pagine16
RivistaJournal of Catalysis
Volume231
Numero di pubblicazione2
DOI
Stato di pubblicazionePubblicato - 25 apr 2005
Pubblicato esternamente

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