KU Leuven: ‘Biocatalyst’ converts residual methane into methanol

Carbon dioxide or CO 2 is not the only culprit that is warming our climate. Methane (better known as natural gas) is also a greenhouse gas. A particularly powerful one, because although it occurs in much smaller concentrations in the atmosphere and its emissions are also much lower than those of CO 2 , the substance is just as responsible for a quarter of the current global warming.

Methane is mainly released as a residual product during the extraction and refining of oil and gas, during waste processing and during agricultural activities. The gas is only collected at a small part of these so-called small-scale methane sources. Often it is then burned (or “flared” in the case of oil and gas installations) through which energy is generated, but in which also again CO 2 is released.

However, methane is an important basic raw material for the chemical industry, from the production of fuels, oils and fats and plastics to pharmaceuticals and pesticides. Often the substance is first converted to methanol, whereby the methane molecules (CH 4) a hydroxyl group is added (OH). This so-called hydroxylation reaction takes place at a high temperature in extensive methanol factories that consume large quantities of primary extracted natural gas. But that is not a good solution for the ‘residual methane’ from small-scale sources, since the gas then first has to be transported over (often large) distances. An equally small-scale, local conversion of residual methane to methanol, at ambient temperature, is therefore preferred. After all, methanol can be easily transported, after which useful substances and materials can be made from it in chemical factories.

Unfortunately, that low-temperature conversion is anything but smooth today. Chemists have therefore been searching for a while for a catalyst that can speed up the reaction and efficiently convert methane to methanol. In that search, researchers at KU Leuven have now made a groundbreaking, fundamental discovery. Their research was published earlier this month in the journal Science .

Leentje neighbor with nature
With zeolites, minerals with microscopic pores that are already used as catalysts in other industrial processes, the Leuven researchers saw how a special molecular effect ensures that the substances also quickly ‘hydroxylate’ methane – as the reaction to methanol is called in chemical jargon. . “In a specific type of zeolite, we locked the iron atoms (the chemically active components) in cages, as it were,” says Max Bols of the Department of Microbial and Molecular Systems. “In this way, we prevented an intermediate reaction product from escaping and thereby deactivating the other iron atoms.” Precisely thanks to this ‘cage effect’, all iron atoms in the zeolite remained active, so that they continued to convert methane to methanol.

For the cage effect, Bols and his colleagues found inspiration in living nature, where biological cells also convert hydrocarbons (such as methane) using iron atoms – and this at ambient temperature. In the cells, the effect prevents very strongly reacting intermediate substances (radicals) from causing damage elsewhere. The Leuven research can therefore be seen as a nice form of biomimicry, in which scientists borrow from nature. In this case, therefore, by equipping a chemical accelerator substance (a specific zeolite) with an existing property of an enzyme (as biological catalysts are called).

The discovery is very fundamental, which means that additional research is needed to arrive at a conversion reaction for methane to methanol that can also be scaled up industrially. But it is precisely because of this fundamental character that the find can also propel research elsewhere in catalyst chemistry. “With the cage effect, we can better control and steer the reaction mechanisms in catalysts in general. This allows us to make chemical reactions more efficient in many industrial and environmental applications,” says Bols.

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