Polynuclear metal oxide photocatalysts in mesoporous silica for CO2 reduction and H2O oxidation

INOR 566

Heinz M. Frei, HMFrei@lbl.gov, Physical Biosciences Division, Lawrence Berkeley National Laboratory, 1 Cyclotron Road, Berkeley, CA 94720
Conversion of CO2 to a liquid fuel like a low alcohol or hydrocarbon using H2O as electron source and visible light as energy source is an attractive goal of solar to fuel conversion. Inert nanoporous oxides such as silica offer opportunities for assembling and coupling well-defined polynuclear photocatalytic components for CO2 reduction and H2O oxidation. Moreover, these high surface area supports afford the high density of photocatalytic sites that is needed for the photosynthesis to keep up with the solar flux, and possess the nanostructured features required for separating the reducing from oxidizing sites. Photocatalytic units consisting of a surface-embedded single CrVI center that serves as visible light electron pump coupled to an Ir oxide nanocluster were assembled inside MCM-41 pores. The units evolve oxygen from aqueous solution under visible light. We have developed methods for assembling and anchoring oxo-bridged binuclear units on the silica pore surface featuring visible metal-to-metal charge-transfer (MMCT) absorptions. Examples include Ti-O-CoII, Ti-O-CuI, Ti-O-SnII and corresponding units featuring Zr centers. For the Zr-O-CuI sites, carbon dioxide reduction to CO was demonstrated upon excitation of the MMCT absorption. Two-electron reduction of CO2 is an essential first step towards development of photocatalytic systems that afford six-electron reduction to methanol. Progress towards the assembly of MMCT units consisting of first row metals that may afford coupling of the oxygen-evolving site to a CO2 reducing MMCT unit in the nanoporous solid will be discussed.

Catalysis Relevant to Energy and Sustainability
8:30 AM-12:15 PM, Tuesday, March 27, 2007 McCormick Place East -- Room E270, Level 2, Oral

Division of Inorganic Chemistry

The 233rd ACS National Meeting, Chicago, IL, March 25-29, 2007