Heather Abbott-Lyon - Relating methanol oxidation to the structure of ceria-supported vanadia monolayer catalysts

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  H.L. Abbott, A. Uhl, M. Baron, Y. Lei, R.J.   Meyer, D.J. Stacchiola, O. Bondarchuk, S. Shaikhutdinov, and   H.-J. Freund, Journal of Catalysis 272, 82 (2010).


  Vanadia ‘‘monolayer”-type catalysts supported on reducible oxides   such as ceria previously have shown high activity for the   selective oxidation of alcohols. Here, a model system consisting   of vanadia particles deposited on well-ordered CeO2(1 1 1) thin   films has been employed. Scanning tunneling microscopy (STM),   photoelectron spectroscopy (PES), and infrared reflection   absorption spectroscopy (IRAS) were used to characterize the   VOx/CeO2 surface as a function of vanadia loading. The formation   of isolated monomeric species as well as two-dimensional vanadia   islands that wet the ceria support was directly observed by STM.   The vanadia species exhibit V in a +5 oxidation state and expose   vanadyl (V=O) groups with stretching vibrations that blue-shift   from ~1005 cm-1 to ~1040 cm-1 with increasing coverage.   Temperature programmed desorption (TPD) of methanol revealed   three peaks for formaldehyde production. One is correlated with   reactivity on the ceria support (565–590 K). Another is   correlated with reactivity on large vanadia particles (475–505 K)   similar to that previously observed on vanadia/silica and   vanadia/alumina model systems. A low temperature reaction pathway   (~370 K) is observed at low coverage, which is assigned to the   reactivity of isolated vanadia species surrounded by a reduced   ceria surface. It is concluded that strong support effects   reported in the literature for the real catalysts are likely   related to the stabilization of small vanadia clusters by   reducible oxide supports.

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