Catalysts are materials that make a chemical transformation quicker, easier, more energy-efficient and often safer. A car's catalytic converter, for example, transforms exhaust gases into innocuous products.
Catalysts that are currently available to burn methane, however, do not do so completely, leaving unburned methane to escape into the atmosphere and contribute to climate change.
"Particularly if you have a natural-gas engine, methane is going to be a major part of that tailpipe exhaust," Gorte said.
In addition, these conventional catalysts can require high temperatures of 600-700 degrees Celsius to encourage reactions to move along. Yet the catalysts themselves often lose their efficiency or deactivate when exposed to the high temperatures generated by methane combustion.
Additional environmental harm can result when methane is used to produce energy in a gas turbine. In this process, methane is typically burned at very high temperatures, in excess of 800 degrees C. When those temperatures rise to around 1,300 degrees C or higher, the reaction can produce harmful byproducts, including nitrogen oxides, sulfur oxides and carbon monoxide.
Conventional catalysts for methane combustion are composed of metal nanoparticles, and in particular palladium (Pd), deposited on oxides such as cerium oxide (CeO2). Tweaking that approach, the researchers instead used a method that relies on self-assembly of nanoparticles. They first built the palladium particles just 1.8 nanometers in diameter and then surrounded them with a protective porous shell made of cerium oxide, creating a collection of spherical structures with metallic cores.
Because small particles such as these tend to clump together when heated and because these clumps can reduce a catalyst's activity,
|Contact: Katherine Unger Baillie|
University of Pennsylvania