November 28, 2008 | 6 Comments
It seems to be a breakout month for catalysts. We just looked a few days ago at a method to see them working and now Rice University has announced and Michael Wong’s team has published their research in seeing catalysts work in the Journal of the American Chemical Society.
This new technique relies on nanoparticles consisting of gold and silica called nanoshells, invented 10 years ago at Rice by nanophotonics pioneer Naomi Halas. Nanoshells, about 20 times smaller than a red blood cell, can amplify light waves and focus them so tightly that scientists can use them to detect just a few molecules of a target chemical. So by building catalysts directly on the surface of the nanoparticles allows researchers to use the nanosensing capabilities of nanoshells to directly follow chemical reactions on the catalyst using light. The method lets the Rice team watch molecules break down on the surface of a catalyst as individual chemical bonds are formed and broken.
Wong said, “We can see the vibrations of the bonds between the atoms of our molecules. By watching the way these vibrations change frequency and intensity with time, we can watch how molecules transform into other molecules step-by-step.”
The original driver for the research is a hunt for a better way to clean up a stubborn water pollutant, TCE or trichloroethene, a common solvent. A carcinogen, TCE is found at 60 percent of the contaminated waste sites on the Environmental Protection Agency’s Superfund National Priorities List, and the Pentagon has estimated the cost of cleaning up TCE contamination at U.S. military bases to be in the billions. Lots of motivation here.
Wong’s research group developed a new palladium-gold catalyst several years ago that helps break TCE into nontoxic components. Early tests showed that the new catalyst worked remarkably quickly. In fact, it was more efficient than predicted, based on the best available theories. “The gold was definitely playing a role that we didn’t fully understand,” Wong said.
So Wong approached Naomi Halas the Stanley C. Moore Professor in Electrical and Computer Engineering, professor of chemistry and director of Rice’s Laboratory for Nanophotonics and Rice theoretical chemist Gustavo Scuseria. Wong’s four-nanometer particles have a gold center covered by palladium atoms, he and graduate student Kimberly Heck wondered if they could cover Halas’ much larger gold nanoshells with palladium atoms and then use the nanoshells to detect the elusive TCE chemical reaction. “We also didn’t know how the TCE molecules decomposed on the catalyst surface,” Wong said.
It took about a year and half to develop the technology and work out the experimental kinks, but Wong said the results were worth waiting for. The method uses surface-enhanced Raman spectroscopy to reveal the structure and makeup of molecules sitting on the palladium-covered gold nanoshell surface. Scuseria, Rice’s Welch Professor of Chemistry, and postdoc Ben Janesko provided sophisticated theoretical calculations that helped match the vibrations with the type of chemical bonds.
“We think we parsed it out pretty well,” Wong said of the hydrodechlorination reaction. “Millions of surface-bound molecules are reacting simultaneously, but with a lot of work we’ve uncovered at least seven chemical steps.”
The irony is the reaction the team set out to analyze — the breakdown of TCE into the nontoxic hydrocarbon ethane gas and chloride salts — happens “way too fast” to be observed by the method. So, the team slowed down the reaction by using a similar molecule called DCE or 1,1-dichloroethene. In fact, DCE is what TCE can become after the catalyst breaks off the first chlorine atom, so by studying the DCE reaction, they are getting a good look at much of what happens with the TCE breakdown.
The clincher is Wong and Halas each think their new method will be especially useful in providing a new level of detail for how molecules are transformed in chemical reactions that take place on catalytic surfaces.
Now add to that Boston College and MIT have a team of scientists opening up a new platform in catalyst research with an announcement of a new class of “exceptionally effective” catalysts that promote the powerful olefin metathesis reaction.
The discovery from a team led by Boston College Prof. Amir H. Hoveyda and MIT Prof. and Nobel laureate Richard Schrock, who shared the 2005 prize in Chemistry for early discoveries of catalytic olefin metathesis, is new class of catalysts that can be easily prepared and possess unique features never before utilized by chemists.
This is exciting because catalytic olefin metathesis transforms simple molecules into complex ones, an important tool if the economical path for biomass to fuel yields simple molecules while markets need the more complex ones. The critical challenge has been developing catalysts for these organic chemical reactions that are practical and offer exceptional selectivity for a significantly broader range of reactions.
Schrock said the unprecedented level of control the new class of catalysts provides will advance research across multiple fields. “We expect this highly flexible palette of catalysts to be useful for a wide variety of catalytic reactions that are catalyzed by a high oxidation state alkylidene species, and to be able to design catalytic metathesis reactions with a control that has rarely if ever been observed before.”
This is a remarkable development with profound implications across biology from pharmaceuticals to fuels and on to materials production. For a deeper sense and explanation, here is the link to the press release pdf. The paper is available at the online edition of Nature.
More Nobels I suspect.
That makes for a big moth for catalysts. The most interesting this is just a few days separate two ways to examine catalysts at work. The implications of for the future of energy and fuels will be huge. And these are just the first breakthrough steps!
I am very impressed, how about you?