Portland, Ore. - Using the National Synchrotron Light Source at Brookhaven National Laboratory, researchers have characterized cerium oxide (ceria) nanoparticles to reveal how the particles might more efficiently clean emissions from fossil-fuel exhaust as well as efficiently produce hydrogen for use as a zero-emission fuel.
The experiments at the Department of Energy facility in Upton, N.Y., could yield better catalytic converters in the near term as well as advance the envisioned hydrogen fuel economy.
"Hydrogen is one of the leading energy sources we have been asked to investigate using the synchrotron," said lead researcher Jose Rodriguez. "With it we are learning about the fundamental conditions necessary for optimal operation of catalysts. We used X-rays at the synchrotron on ceria nanoparticles to determine their composition, structure and reactivity."
In normal catalytic converters, bulk ceria acts as a buffer. It absorbs or releasing oxygen, depending on the conditions of the engine, to maintain the optimum operating conditions for converting such harmful emissions as carbon monoxide and nitrogen oxide to carbon dioxide and nitrogen gas. Using nanoparticles of ceria instead of bulk ceria can yield a more efficient catalytic converter, according to Rodriguez' group, which included fellow Brookhaven researchers Xianqin Wang and Jonathan Hanson.
For the synchrotron studies, the group impregnated the ceria nanoparticles with gold and then separately doped them with zirconium to characterize the various facets of catalyst operation. The gold-impregnated nanoparticles permitted the ultrashort bursts of X-ray energy from the synchrotron to map out the catalyst's active phase in the conversion of water and carbon monoxide to hydrogen gas and carbon dioxide. Detailed knowledge of this water-gas shift reaction is key to the efficient generation of hydrogen fuel from sources such as natural gas, the researchers said.
After the ceria nanoparticles were doped with zirconium, the synchrotron generated bursts of high-intensity X-rays to reveal how the nanoparticle version of the catalyst could more efficiently store and release oxygen. The researchers found that zirconium increases the number of vacancies on the nanoparticles in which oxygen can be uptaken or released during the catalytic converter's normal operations. "The doped ceria nanoparticles had much higher chemical reactivity than the bulk form of ceria currently used in catalytic converters," Rodriguez said.
The National Synchrotron Light Source is the brightest source of electromagnetic radiation available to U.S. researchers-more than 10,000 times brighter than conventional beams generated in most laboratories. Its intensity results from forcing electrons to move around the curved synchrotron ring at just under the speed of light. Two separate synchrotrons at the facility generate beams of light in 80 experimental beam lines, which collectively cover the spectrum from infrared to ultraviolet to X-ray. The smaller synchrotron ring-for infrared and ultraviolet-stores electrons at 800 million volts. (For comparison, the electron gun in a cathode-ray tube generates only about 30,000 volts). The larger synchrotron ring, for X-rays, stores electrons at 2.8 billion volts.
The National Synchrotron Light Source at Brookhaven performs tens of thousands of experiments annually for more than 2,400 researchers from over 400 U.S. research institutions.
The Rodriguez group's research was funded by the DOE's Office of Basic Energy Sciences.