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Helping to make chemicals greener
RESEARCH NEWS
Converting solar energy into chemical fuel ENERGY
A group of scientists are developing a type of “artificial leaf” that mimics a real leaf’s chemical transformation through photosynthesis, by converting sunlight and water into liquid fuels such as methanol that can be used in cars and trucks. The study on how to mimic photosynthesis using synthetic materials, such as the “artificial leaf”, was a central theme of a recent major symposium on the progress and challenges of solar energy. As part of a drive towards reducing the dependence on fossil fuels as a non-sustainable resource, solar power is seen as one of the most promising alternatives, although part of the problem is making any option affordable for large-scale use. The researchers, including Kazunari Domen of the University of Tokyo, Etsuko Fujita of Brookhaven National Laboratory, New York and Koji Tanaka of the Institute of Molecular Science in Okazaki, Japan, described the development of catalysts for both hydrogen and oxygen production, and how
to build an “artificial leaf” through coupling water splitting and CO2 reduction artificial photosynthesis. The goal of artificial photosynthesis is to produce a liquid fuel, such as methanol, or “wood alcohol,” which would create an “artificial leaf” that not only splits water but uses the reaction products to create a more usable fuel, similar to what leaves do when they capture and convert sunlight into chemical fuel through photosynthesis, a process that involves the conversion of water and carbon dioxide into sugars as well as oxygen and hydrogen. Researchers have already found ways of mimicking this artificial photosynthesis and fuel-making process, but are now looking at the challenges of making solar a viable alternative to fossil fuels on a commercial basis. One of the presenters, Kazunari Domen, whose work has been published in a number of publications (including Wang et al., Nature Mater (2008) doi: 10.1038/NMAT2317),
discussed his research on the development of more efficient and affordable catalysts for producing hydrogen using a new water-splitting technology, entitled “photocatalytic overall water splitting.” This technology uses lightactivated nanoparticles to convert water into hydrogen. The 1st Annual Chemical Sciences and Society Symposium, as reported in Chemical & Engineering News, consisted of 30 top chemists from China, Germany, Japan, the UK and the US, and was organized through a joint effort of the science and technology funding agencies and chemical societies of each country. As well as looking at ways of transforming solar energy into chemical fuel, it also explored ways of employing biomass to convert sunlight into usable energy, creating innovative photovoltaics, and storing solar energy in batteries and as fuel, was part of a new effort to initiate international cooperation and innovative thinking on the global energy challenge. Laurie Donaldson
Helping to make chemicals greener CHARACTERIZATION There is an increasing impetus to find a replacement for traditional liquid-acid catalysts for producing chemicals, as they are environmentally unacceptable due to corrosion, spilling and their tendency to cause acid rain upon evaporation. The focus has shifted to solid-acid catalysts, which are cleaner and can be safely disposed of. A new study by researchers from Lehigh University and Rice University (Zhou et al., Nature Chemistry (2009) doi: 10.1038/NCHEM.433), has examined ways of improving the catalytic processes involved in the production of many chemicals and fuels, using a new approach to the electron microscopy imaging study of a tungstated-zirconia solid acid catalyst. The breakthrough, by the team of Wu Zhou, Elizabeth Ross-Medgaarden, William Knowles, Michael Wong, Israel Wachs and Christopher Kiely, used imaging and spectroscopy techniques to make an active catalytic site, and deposit it on a catalyst with low activity, which gave a 100-fold improvement in catalytic activity.
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By molecularly engineering the catalyst, this research could have applications in the petroleum industry, in the improvement of the octane content of gasoline through isomerization, where a straight chain alkane molecule is converted into a branched chain molecule. Being able to see individual tungsten atoms allowed the researchers to identify the active catalytic sites in these solid acid catalysts. From a set of samples of varying catalytic activity, they compared their nanostructures and found isolated monomers and linked chains of polymeric tungstate species, which turn out to have little catalytic activity. It was only in the samples with high catalytic activity that they found 3-D mixed zirconium-tungsten oxide clusters less than 1 nm in size, which are the active catalytic sites in these solid-acid catalysts. As Christopher Kiely points out, “From a materials characterization standpoint, the highly dispersed tungsten oxide species on the zirconia support were effectively invisible in conventional TEM lattice images, so we needed to adopt an alternative approach.” They
VOLUME 12 – ELECTRON MICROSCOPY SPECIAL ISSUE
applied the HAADF-STEM imaging technique to the analysis of supported metal oxide catalysts, allowing them to understand the structure and size of the catalytic species for the first time. This research is significant because it is the first time this imaging has been successfully employed to image-supported metal-on-oxide catalysts to a supported oxide-on-oxide catalyst system. It also resolves arguments about the nature of the active site in this solid-acid catalyst system, and demonstrates that if the active species in a heterogeneous catalyst system can be positively identified, then appropriate modifications to the catalyst preparation route can be made to increase the number density of these desirable species, improving the overall activity of the catalyst. As their approach is also applicable to other solidacid catalyst systems, the team now intend to further develop solid-acid catalysts with enhanced performance.
Laurie Donaldson
Converting solar energy into chemical fuel ENERGY
A group of scientists are developing a type of “artificial leaf” that mimics a real leaf’s chemical transformation through photosynthesis, by converting sunlight and water into liquid fuels such as methanol that can be used in cars and trucks. The study on how to mimic photosynthesis using synthetic materials, such as the “artificial leaf”, was a central theme of a recent major symposium on the progress and challenges of solar energy. As part of a drive towards reducing the dependence on fossil fuels as a non-sustainable resource, solar power is seen as one of the most promising alternatives, although part of the problem is making any option affordable for large-scale use. The researchers, including Kazunari Domen of the University of Tokyo, Etsuko Fujita of Brookhaven National Laboratory, New York and Koji Tanaka of the Institute of Molecular Science in Okazaki, Japan, described the development of catalysts for both hydrogen and oxygen production, and how
to build an “artificial leaf” through coupling water splitting and CO2 reduction artificial photosynthesis. The goal of artificial photosynthesis is to produce a liquid fuel, such as methanol, or “wood alcohol,” which would create an “artificial leaf” that not only splits water but uses the reaction products to create a more usable fuel, similar to what leaves do when they capture and convert sunlight into chemical fuel through photosynthesis, a process that involves the conversion of water and carbon dioxide into sugars as well as oxygen and hydrogen. Researchers have already found ways of mimicking this artificial photosynthesis and fuel-making process, but are now looking at the challenges of making solar a viable alternative to fossil fuels on a commercial basis. One of the presenters, Kazunari Domen, whose work has been published in a number of publications (including Wang et al., Nature Mater (2008) doi: 10.1038/NMAT2317),
discussed his research on the development of more efficient and affordable catalysts for producing hydrogen using a new water-splitting technology, entitled “photocatalytic overall water splitting.” This technology uses lightactivated nanoparticles to convert water into hydrogen. The 1st Annual Chemical Sciences and Society Symposium, as reported in Chemical & Engineering News, consisted of 30 top chemists from China, Germany, Japan, the UK and the US, and was organized through a joint effort of the science and technology funding agencies and chemical societies of each country. As well as looking at ways of transforming solar energy into chemical fuel, it also explored ways of employing biomass to convert sunlight into usable energy, creating innovative photovoltaics, and storing solar energy in batteries and as fuel, was part of a new effort to initiate international cooperation and innovative thinking on the global energy challenge. Laurie Donaldson
Helping to make chemicals greener CHARACTERIZATION There is an increasing impetus to find a replacement for traditional liquid-acid catalysts for producing chemicals, as they are environmentally unacceptable due to corrosion, spilling and their tendency to cause acid rain upon evaporation. The focus has shifted to solid-acid catalysts, which are cleaner and can be safely disposed of. A new study by researchers from Lehigh University and Rice University (Zhou et al., Nature Chemistry (2009) doi: 10.1038/NCHEM.433), has examined ways of improving the catalytic processes involved in the production of many chemicals and fuels, using a new approach to the electron microscopy imaging study of a tungstated-zirconia solid acid catalyst. The breakthrough, by the team of Wu Zhou, Elizabeth Ross-Medgaarden, William Knowles, Michael Wong, Israel Wachs and Christopher Kiely, used imaging and spectroscopy techniques to make an active catalytic site, and deposit it on a catalyst with low activity, which gave a 100-fold improvement in catalytic activity.
8
By molecularly engineering the catalyst, this research could have applications in the petroleum industry, in the improvement of the octane content of gasoline through isomerization, where a straight chain alkane molecule is converted into a branched chain molecule. Being able to see individual tungsten atoms allowed the researchers to identify the active catalytic sites in these solid acid catalysts. From a set of samples of varying catalytic activity, they compared their nanostructures and found isolated monomers and linked chains of polymeric tungstate species, which turn out to have little catalytic activity. It was only in the samples with high catalytic activity that they found 3-D mixed zirconium-tungsten oxide clusters less than 1 nm in size, which are the active catalytic sites in these solid-acid catalysts. As Christopher Kiely points out, “From a materials characterization standpoint, the highly dispersed tungsten oxide species on the zirconia support were effectively invisible in conventional TEM lattice images, so we needed to adopt an alternative approach.” They
VOLUME 12 – ELECTRON MICROSCOPY SPECIAL ISSUE
applied the HAADF-STEM imaging technique to the analysis of supported metal oxide catalysts, allowing them to understand the structure and size of the catalytic species for the first time. This research is significant because it is the first time this imaging has been successfully employed to image-supported metal-on-oxide catalysts to a supported oxide-on-oxide catalyst system. It also resolves arguments about the nature of the active site in this solid-acid catalyst system, and demonstrates that if the active species in a heterogeneous catalyst system can be positively identified, then appropriate modifications to the catalyst preparation route can be made to increase the number density of these desirable species, improving the overall activity of the catalyst. As their approach is also applicable to other solidacid catalyst systems, the team now intend to further develop solid-acid catalysts with enhanced performance.
Laurie Donaldson