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The “holy grail of catalysis” is the conversion of methane to methanol under ambient conditions using light.

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Credit: ORNL/Jill Hemman.

An international team of researchers led by scientists from the University of Manchester has developed a fast and economical method for converting methane or natural gas to liquid methanol at ambient temperature and pressure. The method is carried out with continuous flow through the photocatalyst material using visible light to control the conversion.

To observe how this process works and how selective it is, the researchers used VISION neutron scattering at the Oak Ridge National Laboratory’s spallation neutron source.

The method involves a continuous flow of water saturated with methane/oxygen over a novel metal-organic framework (MOF) catalyst. MOF is porous and contains various components, each of which plays a role in light absorption, electron transport, activation, and combination of methane and oxygen. Liquid methanol is easily extracted from water. Such a process is generally considered the “Holy Grail of catalysis” and is the subject of research supported by the US Department of Energy. Detailed information on the findings of the group entitled “Direct photooxidation of methane to methanol at the hydroxyl site of mono-iron” is published in natural materials.






An international team of researchers led by scientists from the University of Manchester has developed a fast and economical method for converting methane or natural gas to liquid methanol at ambient temperature and pressure. The method is carried out with continuous flow through the photocatalyst material using visible light to control the conversion. Credit: ORNL/Jill Hemman.

Naturally occurring methane is a common and valuable fuel used for furnaces, furnaces, water heaters, furnaces, automobiles, and turbines. However, methane can also be dangerous due to the difficulty of extracting, transporting and storing it.

Methane gas is also harmful to the environment when it is released or seeps into the atmosphere, where it is a potent greenhouse gas. The main sources of atmospheric methane are the production and use of fossil fuels, rotting or burning of biomass, such as forest fires, agricultural waste, landfills, and melting permafrost.

Excess methane is usually burned or flared to reduce its environmental impact. However, combustion produces carbon dioxide, which is itself a greenhouse gas.

The industry has long been looking for an economical and efficient way to convert methane to methanol, a highly profitable and versatile feedstock used to manufacture a variety of consumer and industrial products. This will not only help reduce methane emissions, but also create an economic incentive to do so.

Methanol is a more versatile carbon source than methane and is an easily transportable liquid. It can be used to produce thousands of products such as solvents, antifreezes and acrylic plastics; synthetic fabrics and fibers; glues, paints and plywood; and chemical agents used in pharmaceuticals and agrochemicals. Converting methane to a valuable fuel such as methanol is also becoming more attractive as oil reserves shrink.

Disconnection

The main problem of converting methane (CHfour) to methanol (CH3OH) was the difficulty of weakening or breaking a carbon-hydrogen (CH) chemical bond in order to insert an oxygen atom (O) to form a C-OH bond. Conventional methane conversion methods typically involve two steps, steam reforming followed by syngas oxidation, which are energy intensive, costly, and inefficient because they require high temperatures and pressures.

The fast and economical methane-to-methanol conversion process developed by the research team uses a multi-component MOF material and visible light to control the conversion. CH flowfour and about2 saturated water passes through the layer of MOF beads under the influence of light. The MOF contains various engineered components that are positioned and held in fixed positions within the porous superstructure. They work together to absorb light and generate electrons, which are donated to oxygen and methane inside the pores to form methanol.

“To greatly simplify the process, when methane gas is exposed to a MOF functional material containing mono-iron hydroxyl sites, activated oxygen molecules and light energy contribute to the activation of the CH bond in methane to form methanol,” Sihai said. Jan, professor of chemistry at Manchester and author of the related paper. “This process is 100% selective, meaning there are no unwanted by-products, and can be compared to methane monooxygenase, which is a natural enzyme for this process.”

Experiments have shown that the solid catalyst can be isolated, washed, dried and reused for at least 10 cycles or about 200 hours of reaction without any loss in performance.

The new photocatalytic process is similar to how plants convert light energy into chemical energy during photosynthesis. Plants absorb sunlight and carbon dioxide through their leaves. A photocatalytic process then converts these elements into sugars, oxygen and water vapor.

“This process is called the “Holy Grail of catalysis.” Instead of burning methane, it will now be possible to convert the gas directly into methanol, a valuable chemical that can be used to produce biofuels, solvents, pesticides and vehicle fuel additives,” said Martin Schroeder, Vice President and Dean of the Faculty of Science and Engineering at Manchester and the corresponding author. “This new MOF material could also facilitate other types of chemical reactions by acting as a kind of test tube in which we can combine different substances to see how they react.”

Using neutrons to image the process

“The use of neutron scattering to obtain “photographs” on the VISION instrument initially confirmed the strong interactions between CHfour and mono-iron-hydroxyl sites in MOF that weaken CH bonds,” said Yongqiang Cheng, a researcher at ORNL’s Office of Neutron Sciences.

“VISION is a high performance neutron vibrational spectrometer optimized to provide information on molecular structure, chemical bonds and intermolecular interactions,” said Anibal “Timmy” Ramirez Cuesta, head of the chemical spectroscopy group at SNS. “Methane molecules produce strong and characteristic neutron scattering signals due to their rotation and vibration, which are also sensitive to the local environment. This allows us to unambiguously identify interactions that weaken bonds between CHfour and MOF with advanced neutron spectroscopy techniques.”

Fast, economical and reusable

By eliminating the need for high temperatures or pressures and using sunlight to drive the photo-oxidation process, the new conversion method can significantly reduce equipment and operating costs. The higher speed of the process and its ability to convert methane to methanol without unwanted by-products will facilitate the development of cost-minimizing process production.


Gold-phosphorus nanosheets selectively catalyze natural gas for cleaner energy


Additional Information:
Sihai Yang, Direct photooxidation of methane to methanol at the hydroxyl center of mono-iron, natural materials (2022). DOI: 10.1038/s41563-022-01279-1. www.nature.com/articles/s41563-022-01279-1

Courtesy of Oak Ridge National Laboratory.

Quote: Found: “Holy Grail of Catalysis” – Converting Methane to Methanol Under Ambient Conditions Using Light (June 30, 2022), retrieved July 1, 2022 from https://phys.org/news/2022-06-holy -grail-catalysisturning. -methane-methanol.html

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