Tuning the molecular and electronic structures of catalytic active sites with oxide support nanoligands

CATL 1

Israel E. Wachs, iew0@lehigh.edu1, Elizabeth I. Ross, eir2@lehigh.edu2, William V. Knowles, wvk@rice.edu3, Andrew Burrows4, Christopher J. Kiely4, and MS. Wong, mswong@rice.edu5. (1) Department of Chemical Engineering, Operando Molecular Spectroscopy & Catalysis Laboratory, Lehigh University, 7 Asa Drive, Sinclair 117, Bethlehem, PA 18015, (2) Operando Molecular Spectroscopy and Catalysis Laboratory, Department of Chemical Engineering, Lehigh University, 7 Asa Drive, Bethlehem, PA 18015, (3) Department of Chemical Engineering, Rice University, 6100 Main St., MS-362, Houston, TX 77251-1892, (4) Department of Materials Science and Engineering, Lehigh University, Bethlehem, PA 18015, (5) Departments of Biological & Chemical Engineering and Chemistry, Rice University, Departments of Biological & Chemical Engineering and Chemistry, Rice University, Houston, TX 77251
A titania impregnated SiO2 material was used as the support material to synthesize ~1-10 nm titanium oxide nanodomains on the relatively inert and amorphous SiO2 matrix by varying the titania content. Catalytically active surface redox vanadium oxide and acidic tungsten oxide sites were synthesized by impregnation onto the supported TiO2/SiO2 substrates. Raman spectroscopy established that crystalline V2O5 and WO3 nanoparticles were not formed and that only surface vanadia and tungsten oxide species were present. Furthermore, these catalytic active sites were found to preferentially self-assemble on the titania nanoligands as surface VOx/WOx species. The reactivity of the supported surface VOx and surface WOx catalytic active sites was significantly influenced by the domain size of the titania nanoligand. Whereas, surface redox sites experience enhanced catalytic activity with increasing domain size, the inverse occurs with surface acid sites. Thus, different types of catalytic active sites and reaction mechanisms have different requirements in the nanodomain range.

These model studies with titania nanoligands in a SiO2 matrix have demonstrated for the first time how oxide support nanoligands can tune the catalytic activity of surface redox and surface acidic catalytic active sites. These new insights can assist in the molecular engineering of novel supported metal oxide catalysts by tuning the redox/acidic surface functionalities.

 

Nanotechnology in Catalysis V
9:00 AM-12:10 PM, Sunday, August 19, 2007 BCEC -- 261, Oral

Catalysis & Surface Science Secretariat

The 234th ACS National Meeting, Boston, MA, August 19-23, 2007