Plasmon Assisted Control of Heterogeneous Catalysis

David Boyd, California Institute of Technology

Friday, February 27, 2009

Spanos Auditorium

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This seminar is part of the Jones Seminars on Science, Technology, and Society series

This presentation will introduce a new method for controlling heterogeneous catalysis, which is of critical importance in a variety of chemical, agricultural, and energy conversion processes. For example, the Haber-Bosch process, which transforms nitrogen in air to ammonia, is considered to be one of the most important discoveries of the 20th century, and for nearly 100 years it has provided inorganic fertilizers that have allowed the world's population to grow to its current levels. However, Haber-Bosch is a highly energy intensive and inefficient exothermic process that is estimated to consume between 1 and 2 percent of the world's annual energy supply. Improvements in this process as well as the development of new catalytic systems involving earth abundant materials for solving difficult problems such as photocatalytic splitting of water could have enormous impact on global energy consumption and open new avenues for sustainable energy sources.

Although nanoscale catalysts have been used for some time, there is still "plenty of room at the bottom" for developing new catalytic pathways, especially in light of recent advances in materials science and chemistry that allow the facile creation of nanoscale architectures. At the nanoscale, materials can possess properties that are fundamentally distinct from their bulk counterparts. Noble metal nanoparticles, for example, strongly absorb and scatter visible light even though the characteristic lengths of the particles are much smaller than the wavelength of the excitation light. This "plasmon resonance" is lossy, and the absorbed energy is quickly converted into heat. In addition, if the particles are supported by a solid, heat transfer from the particles does not necessary obey classical heat conduction. Taken together, these two effects can allow significant photothermal heating of nanoparticles with surprisingly small amounts of optical energy and without significant heating of the supporting structure.

The technique we present makes use of this phothermal heating in nanoscale metal structures to drive temperature-dependent catalysis in a local fashion, allowing for unprecedented spatio-temporal control. We demonstrate the technique, which we refer to as plasmon-assisted catalysis, by ethanol reforming in an opto- micro fluidic channel incorporating a self-assembled array of gold nanoparticles. The reaction products, H2, CO, and CO2, are consistent with catalytic ethanol steam reforming. We find that the process allows very precise amounts of gas to be generated in a controlled manner.

About the Speaker

David Boyd is a Sr. Research Fellow at Caltech in Engineering and Applied Science. His active research projects include advanced solid oxide fuel cells based on nano and micron scale architectures, compositionally graded thin-film heterostructures by MOCVD, plasmonics as it pertains to heat transfer from nanostructures, and micro-opto fluidics. David has a strong interest in science education for children, and serves on the board of trustees of the Caltech Children's Center and scientific advisory board for the PBS children's television science program, "Sid the Science Kid". David has been involved in a number of entrepreneurial activities; he has founded three technology companies and actively advises investors regarding emerging technologies.