Image: Iowa State chemical and bioengineers Yue Wu, professor, right, Xiaopeng Liu, PhD student, left, and Fan Yang, postdoc, center, are part of the team that developed a catalyst that converts a greenhouse gas into used chemicals Manufacture plastics and other materials.
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Photo credit: Photo by Christopher Gannon / Iowa State University
AMES, Iowa – Methane, which is more warming than other greenhouse gases and the subject of newly announced US emissions restrictions, is difficult to break down and keep out of the atmosphere.
It is not that the main component of natural gas is chemically complex. A methane molecule consists of only one carbon atom and four hydrogen atoms.
But these carbon-hydrogen bonds are difficult to break.
Typically this involves high temperatures and mixing the combustible gas with oxygen to produce synthesis gas to make methanol and hydrogen to make ammonia. It’s expensive and potentially explosive.
Other conversion reactions are not very efficient and also produce the most common greenhouse gas, carbon dioxide.
So is there any other way to use methane and keep it out of the atmosphere? One that is safe and efficient? One that returns value? One that will help fight climate change?
Yue Wu and his research group at Iowa State University spent several years of experimental failure and discovery searching for ways to do all of this. Now she and a group of coworkers have found and tested a catalyst technology that appears to be an answer.
“The results offered a potential solution to this long-standing challenge and represented the best stability, conversion rate and selectivity for converting methane into ethane or ethylene, two main precursors for the modern petrochemical industry,” according to a project summary by Wu, the Herbert-L. – Styles Professor of Chemical Engineering in the state of Iowa.
A research report recently published in the journal Nature Catalysis reports on the discovery. Wu and Yang Xiao, chief research engineer at the Davidson School of Chemical Engineering at Purdue University in Indiana, are corresponding authors. Zhe Li, who received her PhD from Iowa State in 2019 and is now a postdoc at Johns Hopkins University in Maryland, is the lead author. (See the sidebar for more co-authors.)
Iowa State University’s Office of Innovation Commercialization is seeking a patent for the technology.
Failure leads to success
The catalyst consists of one or two layers of platinum, each only one atom thick, deposited on two-dimensional metal carbide structures, the so-called “MXenes”. In this case the structures consist of carbon, molybdenum and titanium.
Wu said his research group discovered that the thin layers essentially allow any platinum atom to be used as a catalyst, preventing the formation of residues that cover and deactivate the platinum. This means that less platinum is needed to make the catalyst.
Wu said his group began studying carbides – combinations of carbon and metals – about five years ago, with the help of the Office of Naval Research. The original work was to identify the electrical and thermal properties of various carbides. But the work did not go as expected – the thermal conductivity of the material was much lower than predicted.
“Think of it as a failure,” said Wu.
However, the researchers found that the MXene surfaces are very active and can accommodate many molecules. And so, with the support of Wu’s Stiles Professorship and the Iowa State College of Engineering, Wu’s research group began investigating these MXenes as potential catalysts.
“We had never seen carbide so active,” said Wu. “It’s usually very sluggish. It is used, for example, for high-speed drills – the surface is hard and inert. “
They started using the technology to remove hydrogen from shale gas, the natural gas found in shale rock formations. This work was created to investigate other reactions with natural gas.
“Nobody has tried to use these carbides for these large-volume reactions before,” said Wu.
The key to converting methane to ethane / ethylene is getting the carbides pure enough and making the surfaces clean enough to support the reactions, Wu said. Get it right, and these reactions show a methane conversion of about 7% with a selectivity of about 95% for ethane / ethylene in a continuous fixed bed reactor. The products can be processed into plastics and resins, such as the common and ubiquitous polyethylene plastic.
“Notably, these novel catalysts run 72 hours of continuous operation with no sign of deactivation, suggesting a promising start towards technologies suitable for industrial scale use,” Wu wrote.
This is all very good news, he said.
After all, methane emissions are so contributing to climate change that world leaders took steps to limit them during COP26, the most recent United Nations summit on climate change in Glasgow, Scotland. President Joe Biden announced that the US will take steps to limit methane emissions from existing oil and gas operations. More than 100 countries have also signed a Global Methane Pledge to reduce methane emissions by 30% over the next nine years.
The researchers’ new catalyst technology could fuel these efforts to keep methane out of the atmosphere. Wu calls the technology “revolutionary” and says that it “opens the door to reducing the emission of methane and its combustion product CO2 in the future”.
Read the document
“Direct methane activation through atomically thin platinum nano-layers on two-dimensional metal carbides”, Nature Catalysis, Volume 4, October 2021
The research team
In addition to Yue Wu from the state of Iowa, Zhe Li from Johns Hopkins (formerly from the state of Iowa) and Yang Xiao from Purdue, the research team includes:
- from State of Iowa, Bearing He
- Of the Department of Energy’s Ames Laboratory, Tao Ma, Dapeng Jing, Lin Zhou
- from Purdue, Prabudhya Roy Chowdhury, Zhenwei Wu, Johnny Zhu Chen, Pratik J. Potdar, Zhenhua Zeng, Xiulin Ruan, Jeffrey T. Miller, Jeffrey P. Greeley, the late Arvind Varma
- Of the US Department of Energy SLAC National Accelerator Laboratory in California, Gang Wan
- from National University of Chonam in South Korea, Tae-Hoon Kim (formerly Ames Laboratory)
Research method
Experimental study
Research subject
Inapplicable
Article heading
Direct methane activation through atomically thin platinum nano-layers on two-dimensional metal carbides
Publication date of the article
October 20, 2021
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