TY - JOUR
T1 - Investigation of methane conversion to benzene over Mo/ZSM-5 catalysts with operando molecular spectroscopy and DFT calculations
AU - Jehng, Jih Mirn
AU - Gao, Jie
AU - Podkolzin, Simon G.
AU - Wachs, Israel E.
PY - 2011
Y1 - 2011
N2 - The initial structure of the molybdenum active site in Mo/ZSM-5 was studied by closely integrating experimental operando Raman and UV-vis spectroscopies at reaction conditions with online mass spectrometer analysis of products and density functional theory calculations. The Raman and UV-vis spectra reveal that molybdenum is initially present as isolated MoOx species, with the structure being dependent on the Si/Al ratio, Mo loading and pretreatment temperature. Molybdenum is found to preferentially bind to an Al site inside the ZSM-5 pore and form the dioxo MoO2(O2) structure with two terminal Mo=O bonds and two bridging Mo-O-Al bonds. This MoO2(O2) structure on a single framework Al was observed for all investigated catalysts. For catalysts with a high Al content (Al/Mo > 4), another dioxo MoO2(O2) structure was observed where Mo atom is bound simultaneously to 2 framework Al atoms across a zeolite ring. For catalysts with a low Al content, dioxo MoO4 and mono-oxo MoO5 species were identified on the outer surface of the zeolite. The initial Mo oxide nanostructures transform into Mo carbide species under reaction conditions, but can be fully recovered on catalyst regeneration with gas-phase oxygen.
AB - The initial structure of the molybdenum active site in Mo/ZSM-5 was studied by closely integrating experimental operando Raman and UV-vis spectroscopies at reaction conditions with online mass spectrometer analysis of products and density functional theory calculations. The Raman and UV-vis spectra reveal that molybdenum is initially present as isolated MoOx species, with the structure being dependent on the Si/Al ratio, Mo loading and pretreatment temperature. Molybdenum is found to preferentially bind to an Al site inside the ZSM-5 pore and form the dioxo MoO2(O2) structure with two terminal Mo=O bonds and two bridging Mo-O-Al bonds. This MoO2(O2) structure on a single framework Al was observed for all investigated catalysts. For catalysts with a high Al content (Al/Mo > 4), another dioxo MoO2(O2) structure was observed where Mo atom is bound simultaneously to 2 framework Al atoms across a zeolite ring. For catalysts with a low Al content, dioxo MoO4 and mono-oxo MoO5 species were identified on the outer surface of the zeolite. The initial Mo oxide nanostructures transform into Mo carbide species under reaction conditions, but can be fully recovered on catalyst regeneration with gas-phase oxygen.
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M3 - Conference article
AN - SCOPUS:80051894400
SN - 0065-7727
JO - ACS National Meeting Book of Abstracts
JF - ACS National Meeting Book of Abstracts
T2 - 241st ACS National Meeting and Exposition
Y2 - 27 March 2011 through 31 March 2011
ER -