A chemical reaction can transform two harmful greenhouse gases into useful components for cleaner fuels and feedstocks, but the high temperatures needed for the reaction tend to deactivate the catalyst.
A research team led by the Oak Ridge National Laboratory of the Department of Energy has discovered a method to prevent this deactivation. This approach may have broader applications for various catalysts.
By enhancing the dry reforming of methane process, this pioneering research converts methane and carbon dioxide into syngas—a highly sought-after blend of hydrogen and carbon monoxide essential for oil and chemical companies around the world. The team is actively pursuing a patent for this revolutionary invention, which aims to significantly reduce catalytic deactivation and pave the way for a more sustainable future.
“Syngas is important because it’s a platform for the production of a lot of chemicals of mass consumption,” said ORNL’s Felipe Polo-Garzon, who, with ORNL’s Junyan Zhang, led the study.
Enhancing the catalyst that accelerates syngas production holds tremendous potential for bolstering global energy security and advancing cleaner fuels and chemical feedstocks. In nations without oil reserves, syngas derived from coal or natural gas are vital for manufacturing diesel and gasoline. Furthermore, the components of syngas serve as building blocks for a variety of essential chemicals.
For instance, hydrogen can serve as a clean energy source or as a feedstock for producing ammonia for fertilizers. Methanol, an alcohol derived from syngas, provides ingredients for the creation of plastics, synthetic textiles, and pharmaceuticals. Furthermore, methanol acts as an effective carrier for hydrogen, which is typically difficult to pressurize and poses transportation risks.
As the most basic alcohol, methanol has the highest hydrogen-to-carbon ratio, making it safe for transport and easy to convert back to hydrogen upon reaching its destination.
“This [dry reforming of methane] reaction sounds attractive because you are converting two greenhouse gases into a valuable mixture,” Polo-Garzon said. “However, the issue for decades has been that the catalysts required to carry out this reaction deactivate quickly under reaction conditions, making this reaction nonviable on an industrial scale.”
To achieve substantial conversion of reactants, the reaction needs to be carried out at temperatures exceeding 650 degrees Celsius or 1,200 degrees Fahrenheit.
“At this high temperature, the catalysts undergo two deactivation processes,” Polo-Garzon said. “One is sintering, in which you lose surface sites that undertake the reaction. The other is the formation of coke — basically solid carbon that blocks the catalyst from contacting the reactants.”
Catalysts enhance reactions by offering a larger surface area. Metal atoms such as nickel possess electronic characteristics that allow them to temporarily attach to reactants, facilitating the breaking and formation of chemical bonds. Sintering leads to the aggregation of nickel particles, which diminishes the surface area available for chemical reactions. Similarly, coking obstructs a catalyst.
“During the reaction on the catalyst surface, methane will lose its hydrogen atoms one by one until only its one carbon atom is left,” Zhang said. “If no oxygen bonds to it, leftover carbon will aggregate on the catalyst’s nickel surface, covering its active face. This coking deposition causes deactivation. It is extremely common in thermal catalysis for hydrocarbon conversion.”
Currently, the majority of commercial syngas are produced through the steam reforming of methane, a method that necessitates significant amounts of water and heat while also generating carbon dioxide. In contrast, the dry reforming of methane eliminates the need for water and instead uses both carbon dioxide and methane.
By optimizing the interactions between metal active sites and the support during catalyst development, researchers have successfully minimized coke formation and metal sintering. This innovative catalyst demonstrates exceptional efficacy for dry reforming of methane, exhibiting remarkably slow rates of deactivation.
The new catalyst is made up of a crystalline substance known as zeolite, which consists of silicon, aluminum, oxygen, and nickel. The zeolite framework acts as a stabilizing support for the metal active sites, enhancing overall performance.
“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 create the zeolite catalyst, the researchers replaced certain aluminum atoms 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.”
Zhang utilized infrared spectroscopy, demonstrating that nickel was predominantly isolated and connected by two silicon atoms within the zeolite structure.
At DOE’s Brookhaven National Laboratory and SLAC National Accelerator Laboratory, ORNL’s Yuanyuan Li conducted X-ray absorption spectroscopy investigations that elucidated the electronic and bonding characteristics of nickel in the catalyst. At ORNL, Polo-Garzon and Zhang employed a method known as steady-state isotopic transient kinetic analysis to evaluate the efficiency of the catalyst — specifically, the frequency at which a single active site transforms a reactant into a product.
X-ray diffraction and scanning transmission electron microscopy were used to analyze 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 conducted computational analyses indicating that eliminating water from the zeolite enhances its bonding with nickel.
Next, the researchers will develop other catalyst formulations for the dry reforming of the methane process that maintain stability across various 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.”
Journal reference:
- Junyan Zhang, Yuanyuan Li, Haohong Song, Lihua Zhang, Yiqing Wu, Yang He, Lu Ma, Jiyun Hong, Akhil Tayal, Nebojsa Marinkovic, De-en Jiang, Zhenglong Li, Zili Wu & Felipe Polo-Garzon. Tuning metal-support interactions in nickel–zeolite catalysts leads to enhanced stability during dry reforming of methane. Nature Communications, 2024; DOI: 10.1038/s41467-024-50729-8