Brookhaven chemist James Muckerman
works with a team of researchers to design catalysts inspired by photosynthesis,
the natural process by which green plants convert sunlight, water, and carbon
dioxide into oxygen and carbohydrates. The goal is to design a bio-inspired
system that can produce fuels like methanol or hydrogen directly from carbon
dioxide or water, respectively, using renewable solar energy.
To replicate one of the important
steps in natural photosynthesis, Muckerman uses molecular complexes containing
the metal ruthenium as catalysts to drive the conversion of water into oxygen,
protons, and electrons. Specifically, Muckerman's group has set out to determine
the electronic activity of a catalyst recently developed in Japan. Unlike
previous ruthenium catalysts, which have a very short life, this catalyst has
quinone ligands attached to each of its ruthenium centers. These
electron-accepting molecules appear to make the catalyst very active and stable.
The challenge is to determine
exactly how the catalyst works."It was a controversial result," said Muckerman,
who compares the lab results to calculations based on theory. "I believe that
the reaction occurs by ruthenium-mediated electron transfer from water molecules
bound to the metal centers to the quinone ligands. These electron transfers are
initiated by proton transfers from the bound water moieties to the aqueous
solution. The ruthenium atoms maintain the same charge state during the entire
catalytic cycle, indicating that this catalyst works in a totally different way
than the other catalysts.
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