NETL researchers envision a day when carbon dioxide (CO2) may transition from a waste gas that contributes to climate change to a high-value feedstock used in the production of fuels, pharmaceuticals, plastics, fertilizers and a range of consumer goods.
In a recent groundbreaking study, researchers reported making important strides in dry reforming, a process that reacts CO2, instead of steam or oxygen, with methane to yield the mixture of hydrogen and carbon monoxide known as synthesis gas or syngas, a chemical building block for many products.
The promising technology driving a greener future for CO2 is microwave-assisted dry reforming of methane (MW-DRM). According to NETL researchers, microwave systems enable the high-temperature reactions required by the process because they can selectively and efficiently heat the catalyst bed in the microwave reactor without needing to heat the entire reactor volume.
“From a functional perspective, the catalyst bed can be kept hundreds of degrees hotter than the surrounding area, and the necessary energy is efficiently directed to where the chemistry occurs,” said Chris Marin, Ph.D., a research scientist on NETL’s Functional Materials Team and lead author of the study “Designing Perovskite Catalysts for Controlled Active-Site Exsolution in the Microwave Dry Reforming of Methane.”
Steam methane reforming has been the dominant method for producing syngas by reacting hydrocarbons with water. “But in recent years, CO2 has come under growing consideration as an oxidizing agent to produce syngas because its use could help reduce greenhouse gas emissions from fossil energy plants,” Marin explained.
“That’s what makes our study so exciting. We’re turning the table on greenhouse gas and putting it to work to produce synthesis gas, which can be used to make fuels for our vehicles and even everyday products for our homes like wax paper,” he added.
The study, which has been submitted for peer review, also pointed out that the MW-DRM process could provide new markets for methane (CH4). Currently, large volumes of CH4 are flared off at gas wells sites, adding to global emissions.
Methane’s lifetime in the atmosphere is much shorter than CO2, but CH4 is a potent greenhouse gas and more efficient at trapping radiation in the atmosphere than CO2. The NETL researchers stated that methane is a growing environmental concern because it makes up a large component of natural gas trapped within shale formations, which are projected to produce significantly more energy in the future.
Commercialization of the dry reforming reaction has been limited due to the high temperatures required to drive the reaction and inability to prevent coking – the formation of carbon deposits on the catalyst. Desirable DRM catalysts must be designed for both chemical selectivity and efficient microwave absorption, an added complexity.
To address those issues, the researchers turned their attention to perovskites, a family of complex metal oxides that can be fine-tuned by adding dopants, or traces of other elements, and testing the materials as both microwave absorbers and catalysts.
Results included the discovery of a strontium doped lanthanum cobaltite (LSC), a perovskite-based MW-DRM catalyst, with a melting point of 1700 degrees Celsius. The study also found that the use of transition metal dopants improves the tendency of chemical compounds to form oxides and maximizes MW-DRM performance.The best performer in the study was a manganese-doped LSC catalyst that showed 80-90% single-pass CO2 and CH4 conversions at 90-watt applied microwave power.
Researchers concluded that further refinement in reactor design and scale-up studies could make MW-DRM an economically viable process for on-demand syngas production from captured CO2 and CH4.
The U.S. Department of Energy’s National Energy Technology Laboratory develops and commercializes advanced technologies that provide reliable and affordable solutions to America's energy challenges. NETL’s work supports DOE’s mission to advance the national, economic, and energy security of the United States.