FUEL Velu Subramani  Monday, March 28, 2011 

144 - Identification of catalytic active oxygen species on alumina-supported silver nanoparticles with in situ Raman spectroscopy and DFT calculations

Tao Chen, Jih-Mirn Jehng, Amrita Pal, Simon G. Podkolzin, Israel E. Wachs Department of Chemical Engineering and Materials Science, Stevens Institute of Technology, Hoboken, New Jersey, United States; 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

The nature of catalytic active oxygen species in ethylene epoxidation was studied using a series of supported Ag/Al2O3 catalysts. In situ Raman spectra were collected as a function of temperature and oxygen exposure and found to exhibit bands in three regions: (1) below 500, (2) 700-900 and (3) above 900 cm-1. DFT calculations with vibrational analyses using metallic Ag, Ag2O and Ag surfaces with a variable extent of oxidation were performed for the first time in order to elucidate the assignment of the vibrational bands. The low wavenumber region is assigned to chemisorbed atomic oxygen. The highest wavenumber region is assigned to chemisorbed molecular O2. The intermediate wavenumber region, which is associated with catalytic active oxygen, is for the first time shown to be inconsistent with the traditional assignment of atomic oxygen bound to Ag. Our spectroscopic and computational results suggest that atomic oxygen binds to the lattice oxygen of oxidized Ag, forming "hybrid" O-O (adsorbed O - lattice O) surface species. The in situ Raman studies also revealed that the “hybrid” O-O surface species are preferentially consumed during selective oxidation of ethylene to ethylene oxide.




Monday, March 28, 2011 03:45 PM
Spectroscopic Techniques to Elucidate Reaction Mechanisms and Structure-Activity Relationships in Fuel Science (01:30 PM - 05:25 PM)
Location: Anaheim Marriott
Room: Grand Blrm C

 

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