The novel catalyst consists of a crystalline material called a zeolite that contains silicon, aluminum, oxygen and nickel. The zeolite’s supportive framework stabilizes the metal active sites.
“Zeolite is like sand in composition,” Zhang said. “But unlike sand, it has a sponge-like structure filled with tiny pores, each around 0.6 nanometers in diameter. If you could completely open a zeolite to expose the surface area, 1 gram of sample would contain an area around 500 square meters, which is a tremendous amount of exposed surface.”
To synthesize the zeolite catalyst, the researchers remove some atoms of aluminum and replace them with nickel. “We’re effectively creating a strong bond between the nickel and the zeolite host,” Polo-Garzon said. “This strong bond makes our catalyst resistant to degradation at high temperatures.”
The high-performance catalyst was synthesized at ORNL’s Center for Nanophase Materials Sciences. Zili Wu, leader of ORNL’s Surface Chemistry and Catalysis group, served as a strategy advisor for the project.
Zhang performed infrared spectroscopy, revealing that nickel was typically isolated and bound by two silicon atoms in the zeolite framework.
At DOE’s Brookhaven National Laboratory and SLAC National Accelerator Laboratory, ORNL’s Yuanyuan Li led X-ray absorption spectroscopy studies detailing the electronic and bonding structures of nickel in the catalyst. At ORNL, Polo-Garzon and Zhang used a technique called steady-state isotopic transient kinetic analysis to measure catalyst efficiency — the number of times a single active site converts a reactant into a product.
X-ray diffraction and scanning transmission electron microscopy characterized the structure and composition of materials at the nanoscale.
“In the synthesis method, we found that the reason the method works is because we’re able to get rid of water, which is a byproduct of the catalyst synthesis,” Polo-Garzon said. “We asked colleagues to use density functional theory to look into why water matters when it comes to the stability of nickel.”
At Vanderbilt University, Haohong Song and De-en Jiang performed computational calculations showing that removing water from the zeolite strengthens its interactions with nickel.
Next, the researchers will develop other catalyst formulations for the dry reforming of methane reaction that are stable under a broad range of conditions. “We’re looking for alternative ways to excite the reactant molecules to break thermodynamic constraints,” Polo-Garzon said.
“We relied on rational design, not trial and error, to make the catalyst better,” Polo-Garzon added. “We’re not just developing one catalyst. We are developing design principles to stabilize catalysts for a broad range of industrial processes. It requires a fundamental understanding of the implications of synthesis protocols. For industry, that’s important because rather than presenting a dead-end road in which you try something, see how it performs, and then decide where to go from there, we’re providing an avenue to move forward.”
The DOE Office of Science funded the research. The work relied on several DOE Office of Science user facilities: the CNMS at ORNL; the Center for Functional Nanomaterials and the National Synchrotron Light Source II, both at Brookhaven; the Stanford Synchrotron Radiation Lightsource at SLAC and the National Energy Research Scientific Computing Center at Lawrence Berkeley National Laboratory.
UT-Battelle manages ORNL for DOE’s Office of Science. The single largest supporter of basic research in the physical sciences in the United States, the Office of Science is working to address some of the most pressing challenges of our time. For more information, please visit energy.gov/science. — Dawn Levy
This Oak Ridge National Laboratory news article "Improved catalyst turns harmful greenhouse gases into cleaner fuels, chemical feedstocks" was originally found on https://www.ornl.gov/news