What Nanoporous Supports Do We Need for Solar Light-Driven Fuel Synthesis Direct Solar to Fuel by Solid Photocatalysts Principle:

Direct Solar to Fuel by Solid Photocatalysts Kudo, J. Am. Chem. Soc. 2003, 125, Q.Y. = 56%, > 400 hours ● Direct solar to fuel works with UV light Where we are: UV light-driven Water Splitting: mixed metal oxide nanoparticles

Direct Solar to Fuel by Solid Photocatalysts ● Direct Solar to Fuel Works with UV Light Where we are:UV light-driven CO 2 reduction by H 2 O: Isolated Ti centers in nanoporous silicate Anpo, Catal. Today 1998, 44, 327 Frei, J. Phys. Chem. B 2004, 108, 18269

Direct Solar to Fuel by Solid Photocatalysts Where we are: Visible light-driven H 2 O → H 2 + O 2 Water splitting with visible light observed, but very low efficiency. Single Component mixed metal oxide NiInTaO 3 Two-component mixed metal oxide with shuttle (Z-scheme) Q.Y.= 0.3% at 420 nm Arakawa, Science 2001, 414, 625 Q.Y.= 0.3% at 500 nm Kudo, Chem. Commun. 2001, 2416

Direct Solar to Fuel by Solid Photocatalysts Where we are: Visible light-driven CO 2 Splitting Binuclear photocatalytic sites on inert mesoporous oxide support Frei, J. Am. Chem. Soc. 2005, 127, 1610

What we need Fact: Numerous small bandgap semiconductor photocatalysts work efficiently under visible light (λ>600 nm, q.y.>50%), but require sacrificial reagents Lesson: no defects or ill-defined structures can be involved in energy transduction, charge migration, or catalytic transformation because they will invariably lead to loss of stored energy, charge, or chemical selectivity How can we avoid sacrificial reagents: Active moieties (light harvesting, charge separation, catalytic sites) of molecular makeup Need 3-D high surface area ‘spectator’ support for the molecular functionalities with precisely arranged (Angstrom) anchoring sites and structural elements for physical separation on the nanometer scale. Need to remove promptly the redox products from the reactive surface  exploit gas-solid interface

What Active Molecular Components are Available: Some Examples Ru(bpy) 3 2+ sensitizer/ Ni(cyclam) catalyst (CO 2 to CO, H 2 O reduction) Inorganic: IrO x Clusters (H 2 O oxidation) MMCT units (CO 2 splitting) Organometallic:

Organic/Metal Oxide Hybrid Functionalities on Mesoporous Supports Challenge: Incorporation of organic and polynuclear transition metal units at preselected sites and defined orientation inside silica wall top view side view

Mixed Oxide Functionalities on Mesoporous Silica Supports Challenge: Ir oxide patches of defined composition and structure covalently linked to Co-O-Ti units inside mesoporous silica wall

Solar to Fuel by Solid Photocatalysts: What needs to be done Develop methods that afford imprinting of molecular components and well- defined metal oxide clusters into walls of mesoporous nonreducible oxide supports at predetermined locations and with defined orientation New types of templates Methods for creating channel patterns with oxidizing/reducing sites Mesoporous membranes Defect-free active component/silica interface Design new catalytic components for coupled H 2 O oxidation/CO 2 reduction