Researchers from Stanford University and the University of Leuven in Belgium adopted a “tantalizing” principle from nature to convert harmful methane into methanol under room temperature.
The research findings have been published in the journal Science and could be a significant step towards a methanol fuel economy with copious methane as the feedstock, which is an advancement that could change the use of natural gas globally. The simplest alcohol, methanol, is used in the manufacture of varied products, such as plastics and paints, and also as an additive to gasoline.
Methanol is rich in hydrogen and could be the driving force for new-generation fuel cells that might provide substantial environmental benefits.
If methane, the primary component of natural gas, can be converted to methanol, the resulting liquid fuel can be effortlessly stored and shipped compared to natural gas and pure hydrogen. This will also considerably reduce methane emissions from pipelines and natural gas processing plants.
Currently, escaped methane gas — a greenhouse gas more harmful than carbon dioxide — almost nullifies the environmental benefits of natural gas over coal or oil. The new research undertaken by the team is to promote a low-energy means to generate methanol from methane.
This process uses common crystals known as iron zeolites that are known to convert natural gas to methanol at room temperature. But this is extremely challenging chemistry to achieve on a practical level, as methane is stubbornly chemically inert.
Benjamin Snyder, Postdoctoral Fellow, Department of Chemistry, Stanford University
Snyder obtained his doctorate at Stanford, analyzing catalysts to tackle key aspects of this challenge.
Methane infused into porous iron zeolites generates methanol rapidly at room temperature without the requirement of additional energy or heat. In comparison, the traditional industrial process for producing methane involves temperatures of around 1000 °C (1832 °F) along with very high pressures.
That’s an economically tantalizing process, but it’s not that easy. Significant barriers prevent scaling up this process to industrial levels.
Edward Solomon, Study Senior Author and Professor, Chemistry and Photon Science, SLAC National Accelerator Laboratory, Stanford University
Keeping the Zeolites on
A majority of the iron zeolites deactivate rapidly, resulting in the inability to process large amounts of methane. The researchers were on the lookout for means to enhance iron zeolite performance. Hannah Rhoda, study co-author and a Stanford doctoral candidate in inorganic chemistry, employed sophisticated spectroscopy to analyze the physical structure of the most potential zeolites for methane-to-methanol conversion.
A key question here is how to get the methanol out without destroying the catalyst.
Hannah Rhoda, Study Co-Author and Doctoral Candidate, Inorganic Chemistry, Stanford University
The researchers chose two attractive iron zeolites and analyzed the physical structure of the lattices around the iron. They found that the reactivity varied drastically based on the size of the pores in the surrounding crystal structure. The researchers termed it the “cage effect” because the encapsulating lattice is similar to a cage.
Large pores in the cages lead to the deactivation of active sites after one reaction cycle, and they do not reactivate again. However, smaller pore apertures coordinate a precise molecular dance within the reactants and the iron active sites — one that produces methanol and regenerates the active site straightaway.
By taking advantage of the “cage effect,” the researchers reactivated 40% deactivated sites continually, which was a major conceptual advance into a commercial-scale catalytic process.
Snyder adds, “Catalytic cycling — the continual reactivation of regenerated sites — could someday lead to continual, economical methanol production from natural gas.” Snyder carries out his research under the guidance of Jeffrey R. Long.
This essential step in basic science would elucidate chemical engineers and chemists on the process of methanol production using iron zeolites below room temperature. However, a great deal of work needs to be done before industrialization.
Snyder intends to achieve the process not only at room temperature but also with ambient air instead of other sources of oxygen, like nitrous oxide in the study. However, as a highly oxidizing agent and generally hard to control in chemical reactions, oxygen poses a challenge along the path.
Currently, Snyder is both amazed and pleased by the illustrative powers of the advanced spectroscopic instrumentation in the Solomon labs that were leveraged for this research. They were beneficial for his understanding of the chemistry and the chemical structures involved in the methane-to-methanol process.
“It’s cool how you can get some very powerful atomic-level insight, like the cage effect, from these tools that weren’t available to previous generations of chemists,” Snyder concluded.
Snyder, B. E. R., et al. (2021) Cage effects control the mechanism of methane hydroxylation in zeolites. Science. doi.org/10.1126/science.abd5803.