114 - Investigation of methane conversion to benzene over Mo/ZSM-5 catalysts with operando molecular spectroscopy and DFT calculations
Jih-Mirn Jehng, Jie Gao, Simon G. Podkolzin, Israel E. Wachs Operando Molecular Spectroscopy & Catalysis Laboratory, Department of Chemical Engineering, Lehigh University, Bethlehem, Pennsylvania, United States; Department of Chemical Engineering, National Chung Hsing University, Taichung 402, Taiwan, Taiwan Republic of China; Department of Chemical Engineering and Materials Science, Stevens Institute of Technology, Hoboken, New Jersey, United States
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.
Thursday, March 31, 2011 09:00 AM
Chemistry of Petroleum and Emerging Technologies (08:30 AM - 11:20 AM)
Location: Anaheim Marriott
Room: Grand Blrm G