Resulting from their unique catalytic, magnetic, and thermochemical properties, first row transition metals and their oxides find applications in various new technologies that aim to address grand challenges ranging from water purification to efficient drug delivery. As a potentially viable approach for efficient carbonaceous fuel conversion and carbon dioxide capture, the so-called chemical looping strategy utilizes redox properties of transition metal oxides to avoid energy intensive separation operations in conventional energy conversion processes. In a typical chemical looping process, carbonaceous feedstock is oxidized into products such as CO2 or syngas by active lattice oxygen (O2-) in the transition metal oxide, a.k.a. oxygen carrier. In a subsequent step, the O2--deprived oxygen carrier is replenished by a gaseous oxidant, generating hydrogen or heat. The cyclic redox operation is shown to significantly reduce the exergy loss in conventional energy conversion processes. While a number of supported metal oxides have demonstrated excellent potential in up to 1 MWth pilot plants, further improvements of the redox activity and stability of these oxygen carriers are of critical importance for successful deployment of this novel technology. We present a rationalized strategy for oxygen carrier optimization: to arrive at oxygen carriers with superior activity, the rate limiting step for iron oxide redox reaction is first identified. Mixed ionic-electronic conductive support that de-bottlenecks such a rate limiting step is then used to improve the iron oxide activity by an order of magnitude. Investigation of deactivation mechanisms of commonly used oxygen carriers further sheds light for designing oxygen carriers with both high activity and extended lifetime. Functional oxygen carriers with tailored nano-structures for chemical looping combustion, methane partial oxidation, solar-based water-splitting, and oxidative dehydrogenation are also exemplified.

Tailored transition metal oxides for carbonaceous fuel conversion

249th National Meeting (2015)

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