An international team of researchers, led by scientists from the University of Manchester, has developed a fast and cost-effective method of converting methane, or natural gas, into liquid methanol at room temperature and pressure. The process takes place under continuous flow over a photocatalytic material using visible light to drive the conversion.
To help observe how the process works and its selectivity, the researchers used neutron scattering on the VISION instrument at Oak Ridge National Laboratory’s spallation neutron source.
The process involves a continuous flow of methane/oxygen-saturated water over a new catalyst with an organometallic structure (MOF). MOF is porous and contains different components that each have a role in light absorption, electron transfer, and activation and reunion of methane and oxygen. Liquid methanol is easily extracted from water. Such a process has generally been considered “a holy grail of catalysis” and is an area of research interest supported by the US Department of Energy. Details of the team’s findings, titled “Direct photo-oxidation of methane to methanol at a mono-hydroxy iron site”, are published in Natural materials.
Naturally occurring methane is an abundant and valuable fuel, used for furnaces, boilers, 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 escapes into the atmosphere, where it is a potent greenhouse gas. The main sources of atmospheric methane include the production and use of fossil fuels, the decomposition or combustion of biomass such as forest fires, agricultural waste, landfills and the melting of permafrost.
Excess methane is usually burned or flared to reduce its impact on the environment. However, this combustion process produces carbon dioxide, which is itself a greenhouse gas.
Industry has long sought an economical and efficient way to convert methane into methanol, a highly marketable and versatile feedstock used to make a variety of consumer and industrial products. This would not only help reduce methane emissions, but also provide 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 make thousands of products such as solvents, antifreeze, and acrylic plastics; synthetic fabrics and fibres; adhesives, paint and plywood; and chemical agents used in pharmaceuticals and agrochemicals. Converting methane into a high-value fuel such as methanol is also becoming more attractive as oil reserves dwindle.
Break the link
A major challenge in the conversion of methane (CH4) to methanol (CH3OH) was the difficulty of weakening or breaking the carbon-hydrogen (CH) chemical bond in order to insert an oxygen (O) atom to form a C-OH bond. Conventional methane conversion methods typically involve two steps, steam reforming followed by syngas oxidation, which are energy-intensive, expensive, and inefficient because they require high temperatures and pressures.
The rapid and cost-effective process for converting methane to methanol developed by the research team uses a multicomponent MOF material and visible light to drive the conversion. A stream of CH4 and O2 saturated water is passed through a layer of MOF granules while being exposed to light. The MOF contains various engineered components that are located and held in fixed positions inside the porous superstructure. They work together to absorb light to generate electrons which are passed to oxygen and methane inside the pores to form methanol.
“To greatly simplify the process, when methane gas is exposed to the functional MOF material containing mono-iron-hydroxyl sites, activated oxygen molecules and light energy promote activation of the CH bond in methane. to form methanol,” Sihai said. Yang, Manchester chemistry professor and corresponding author. “The process is 100% selective, which means there are no unwanted by-products, comparable to methane monooxygenase, which is the natural enzyme in this process.”
Experiments have shown that the solid catalyst can be isolated, washed, dried and reused for at least 10 cycles, or approximately 200 hours of reaction time, without any loss in performance.
The new photocatalytic process is analogous 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 vapour.
“This process has been called the ‘holy grail of catalysis’. Instead of burning methane, it is now possible to convert the gas directly into methanol, a valuable chemical that can be used to produce biofuels, solvents, pesticides and fuel additives for vehicles,” said Martin Schröder, Vice President and Dean of Manchester School of Science and Engineering and corresponding author. “This new MOF material may also be able to facilitate other types of chemical reactions by serving as a sort of test tube in which we can combine different substances to see how they react.”
Using neutrons to visualize the process
“The use of neutron scattering to take ‘pictures’ at the VISION instrument initially confirmed the strong interactions between CH4 and mono-iron-hydroxyl sites in the MOF that weaken CH bonds,” said Yongqiang Cheng, instrument scientist at ORNL’s Neutron Science Branch.
“VISION is a high-throughput neutron vibrational spectrometer optimized to provide information on molecular structure, chemical bonds and intermolecular interactions,” said Anibal “Timmy” Ramirez Cuesta, who leads the chemical spectroscopy group at SNS. “Methane molecules produce strong and characteristic neutron scattering signals from their rotation and vibrations, which are also sensitive to the local environment. This allows us to unambiguously reveal the bond weakening interactions between CH4 and MOF with advanced neutron spectroscopy techniques.”
Fast, economical and reusable
By eliminating the need for high temperatures or pressures and using the energy of sunlight to drive the photo-oxidation process, the new conversion method could significantly reduce equipment and operating costs. The higher process speed and its ability to convert methane to methanol without unwanted by-products will facilitate the development of on-line processing that minimizes costs.
Gold-phosphorus nanosheets selectively catalyze natural gas into greener energy
Sihai Yang, Direct photo-oxidation of methane to methanol at a mono-iron hydroxyl site, Natural materials (2022). DOI: 10.1038/s41563-022-01279-1. www.nature.com/articles/s41563-022-01279-1
Provided by Oak Ridge National Laboratory
Quote:Found: The ‘Holy Grail of Catalysis’ – turning methane into methanol under ambient conditions using light (2022, June 30) Retrieved June 30, 2022 from https://phys.org/news/2022-06 -holy-grail-catalysisturning-methane-methanol.html
This document is subject to copyright. Except for fair use for purposes of private study or research, no part may be reproduced without written permission. The content is provided for information only.