Storing energy by sequestration in chemical bonds is an essential component of a renewable energy economy. Two storage formats of major importance are hydrogen and biomass-derived hydrocarbon fuels. In both cases, nanoporous materials may be enabling solutions for stubborn technical problems. For hydrogen storage, solid-state materials that can meet all DOE and manufacturer requirements remain elusive; bond energies in metal hydrides are too strong, whereas H2 adsorption energies are too weak. For biofuels, the economics remain unattractive, but could be improved if lignin, a major waste product of fuel production, could be converted to value-added chemicals. Here, we discuss the use of Metal-Organic Frameworks (MOFs) and porous carbons as hosts for reactive metal ions or nanoparticles that impart unique catalytic properties for hydrogen storage and catalytic bond breaking. The catalytic advantages of these two classes of nanoporous materials are well known, but much of the research to date has been focused on their intrinsic ability to accelerate reactions. However, the nanopores themselves offer an additional design element for creating high-performing catalysts. The new materials described here are derived from our earlier discovery that titanium-doped MOFs can activate H2, allowing metal hydride nanoparticles to be repeatedly cycled. We find that both Ti and Ni-doped MOFs can also catalyze the hydrogenolysis of aryl-ether bonds, a component lignin structural motif. A synergistic interplay between pore size, framework metal ion, and dopant metal is revealed, suggesting design principles useful for optimizing performance of nanoporous catalysts. We are extending these concepts to create catalysts for oxidative bond cleavage. Moreover, the insights gained are suggesting new strategies for hydrogen storage. In particular, materials in which economical porous carbons are doped with alkali metals lead to improved H2 desorption kinetics. Together, our results suggest that this strategy is a powerful route to achieving emergent catalytic properties across a broad range of porous hosts.

Catalytically functionalized nanoporous frameworks and carbons for chemical energy storage

254th National Meeting (2017)

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