X-rayed catalyst: Bio-mimetic zeolite

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Ezine

  • Published: Jul 15, 2015
  • Author: David Bradley
  • Channels: X-ray Spectrometry
thumbnail image: X-rayed catalyst: Bio-mimetic zeolite

Gas-to-liquid

Scientists in Germany and Netherlands have taken inspiration from nature to build a novel zeolite catalyst that could be used to convert natural gas to liquid fuels. X-ray absorption spectroscopy and other techniques were key to their success. (Photo: Andreas Battenberg/TUM)

Scientists in Germany and Netherlands have taken inspiration from nature to synthesise a novel zeolite catalyst that could be used to convert natural gas to liquid fuels. X-ray absorption spectroscopy and other techniques were key to their success.

Researchers from Technische Universität München (TUM), Germany, Eindhoven University of Technology and University of Amsterdam, The Netherlands, suggest that their gas to liquid catalyst might also be useful for the production of starting materials for commodity chemicals by the industry. They have homed in on the mechanism of the selective oxidation of methane to methanol with an active copper-oxo cluster held within the micropores of the zeolite.

The right source

As mineral oil resources become increasingly scarce, natural gas, methane, looks set to become an increasingly relevant material for fuel and chemical industries despite the logistical and safety problems inherent in transportation and storage of gases. Perhaps the obvious solution is to apply gas to liquid technologies that generate synthesis gas from which methanol and hydrocarbons might be produced in liquid form for shipping to chemical plants and fuel companies across the globe. With today's technology gas to liquid is only viable on the large scale, what is needed is a way for the infrastructure to cope economically and technically with smaller sources at remote locations. As such, there is a great deal of time and effort being invested in the chemistry of methane conversion.

Moniek Tromp (UvA/HIMS), Evgeny Pidko and Emiel Hensen (Eindhoven), Maricruz Sanches-Sanches (TUM), and Johannes Lercher (TUM and Pacific Northwest National Laboratory) realised that of all the promising smaller scale processes for the direct conversion of methane, it is the partial oxidation to methanol that is perhaps the most tenable as it has lower, more efficient, and safer, operating temperatures. As such, the team has focused on a modified zeolite, developed by Lercher's research group in Munich. Their copper-exchanged zeolite with the mordenite structure interestingly mimics the activity of the enzyme methane monooxygenase (MMO), which is known to oxidize methane to methanol efficiently and selectively. The team offers an unprecedented and detailed molecular insight into just how alike the reaction at the active centre in the enzyme and the modified zeolite are. Their XAS measurements were carried out with the support of the Diamond Light Source, in Oxfordshire, UK.

Micropores

The team has demonstrated that the micropores of their zeolite provide a perfect confined environment for the highly selective stabilization of an intermediate copper-containing trimer molecule. This assertion emerges from their combination of kinetic studies in Munich, advanced spectroscopic analysis in Amsterdam and theoretical modelling in Eindhoven. Indeed, they used these tools to home in on trinuclear copper-oxo clusters that have high activity towards the carbon-hydrogen bonds in methane and can thus convert the molecule to methanol.

"The developed zeolite is one of the few examples of a catalyst with well-defined active sites evenly distributed in the zeolite framework - a truly single-site heterogeneous catalyst," explains Lercher. "This allows for much higher efficiencies in conversion of methane to methanol than with zeolite catalysts previously reported." In addition, their results show an obvious correlation between the structure of the active sites and catalytic activity. This, the team suggests, makes the zeolite a more than promising material for achieving catalytic activity that is on a par with the MMO enzyme systems. "The similarity with the enzymatic systems is also implied from the similarity of the reversible rearrangements of the trinuclear clusters occurring during the selective transformations of methane along the reaction path towards methanol, in both the enzyme system and copper-exchanged mordenite," they say in their paper in the journal Nature Communications.

Related Links

Nature Commun 2015, 6, #7546: "Single-site trinuclear copper oxygen clusters in mordenite for selective conversion of methane to methanol"

Article by David Bradley

The views represented in this article are solely those of the author and do not necessarily represent those of John Wiley and Sons, Ltd.

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