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Biofuels are renewable and clean alternatives to fossil fuels, but they can be difficult to produce because their source, biomass, contains a fair amount of oxygen. That makes them less stable, too viscous and less efficient than the fuels they're meant to replace.
Using iron as a catalyst to remove the oxygen is inexpensive, but the water in organic biomass can rust the iron, canceling its effectiveness. Another metal, palladium, is rust resistant, but it's not as efficient as iron in removing the oxygen, and it's far more expensive than plentiful iron.
So researchers at Washington State University (WSU) and the U.S. Department of Energy's Pacific Northwest National Laboratory (PNNL) decided to combine the two.
Evoking images of Julia Child in a lab coat and goggles, they added just a pinch of palladium to iron, a recipe that efficiently removes oxygen from biomass without the rust. A meal fit for a gourmet, as it were, at the cost of a cheeseburger.
The paper on their work was chosen as the cover story in the October issue of the scientific journal ACS Catalysis. In it, the researchers said they discovered that combining iron with very small amounts of palladium helped to cover the catalyst's surface with hydrogen, which accelerates the process of turning biomass into biofuel.
"With biofuels, you need to remove as much oxygen as possible to gain energy density," Yong Wang, who led the research, told the WSU news department. "Of course, in the process, you want to minimize the costs of oxygen removal."
Kitchen metaphors aside, Wang's team didn't limit themselves to skillets, knives and can openers, but relied instead on high-resolution transmission electron microscopy, X-ray photoelectron spectroscopy and extended X-ray absorption fine structure spectroscopy. In other words, very sophisticated gear.
These tools led them to understand how the atoms on the surface of the two different catalysts – one made solely of iron, the other made solely of palladium – react with the biomass lignin, the woody material found in most plants. Wang said this led to the idea of combining the two metals.
"The synergy between the palladium and the iron is incredible," said Wang, who holds a joint appointment with Pacific Northwest National Laboratory and WSU. "When combined, the catalyst is far better than the metals alone in terms of activity, stability and selectivity."
The goal of the research is to create what are known as "drop-in biofuels" – direct substitutes for gasoline, diesel fuel and jet fuel that can be used interchangeably with fossil fuels in today's vehicles. So far, that effort has failed because today's biofuels have too much oxygen and are thus less efficient than fossil fuels and can even damage systems built for fossil fuels.
To date, Wang's team has converted biomass into biofuel only in a laboratory. Now, he said, he'd like to expand his work and move it to an environment that's more like a biofuel production plant.
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