Neutrons optimize highly efficient catalyst for a more environmentally friendly approach to biofuel synthesis

Researchers at the University of Manchester have developed a catalyst that converts biomass into fuel with remarkably high efficiency and offers new opportunities for the production of advanced renewable raw materials.

Neutron scattering experiments at the Department of Energy’s Oak Ridge National Laboratory played a key role in determining the chemical and behavioral dynamics of a zeolite catalyst - zeolite is a common porous material used in commercial catalysis - to provide information to maximize its performance.

The optimized catalyst, called NbAlS-1, converts biomass-derived raw materials into light olefins - a class of petrochemicals such as ethene, propene and butene that are used to make plastics and liquid fuels. The new catalyst has an impressive yield of more than 99%, but requires significantly less energy than its predecessors. The team's research is published in the journal Nature Materials.

"The industry relies heavily on the use of light olefins from crude oil, but their manufacture can have a negative environmental impact," said senior author Longfei Lin of Manchester University. "Previous catalysts, which produced butene from purified oxygen-containing compounds, required a lot of energy or extremely high temperatures. This new catalyst converts raw oxygen-containing compounds directly under milder conditions and with significantly less energy and is more environmentally friendly."

Biomass is an organic substance that can be converted and used as a fuel and raw material. It is typically obtained from residual agricultural waste such as wood, grass and straw, which is decomposed and fed into a catalyst that converts it to butene - an energy-rich gas used by the chemical and petroleum industries to manufacture plastics, polymers and raw materials becomes liquid fuels that are otherwise made from oil.

Typically, a chemical reaction requires an enormous amount of energy to break the strong bonds formed from elements such as carbon, oxygen and hydrogen. Some bindings may need to be heated to more than 1,800 ° F before the bonds break.

The team doped the catalyst for a more environmentally friendly design by replacing the silicon atoms of the zeolite with niobium and aluminum. The substitution creates a chemically unbalanced state, which promotes the separation of the bonds and radically reduces the need for high degrees of heat treatment.

"The chemistry that runs on the surface of a catalyst can be extremely complicated. If you don't control pressure, temperature and concentration exactly, you will produce very little butene," said Yongqiang Cheng, a researcher at ORNL. "To get a high yield you have to optimize the process and to optimize the process you have to understand how the process works."

Due to their deep penetrating properties and their acute sensitivity to light elements such as hydrogen, neutrons are well suited to investigate chemical reactions of this kind. Using the VISION spectrometer at the ORNL spallation neutron source, the researchers were able to use the vibration signatures of the bonds to determine exactly which chemical bonds were present and how they behave. This information allowed them to reconstruct the chemical sequence required to optimize catalyst performance.

"There has been a lot of trial and error associated with developing such a high-performance catalyst as we developed," said Sihai Yang, author of the University of Manchester. "The better we understand how catalysts work, the better we can control the design process of next-generation materials."

Synchrotron X-ray diffraction measurements at the British Diamond Light Source were used to determine the atomic structure of the catalyst, and complementary neutron scattering measurements were taken at the Rutherford Appleton Laboratory's ISIS Neutron and Muon Source.

Journal Reference:

Longfei Lin, Alena M. Sheveleva, Ivan da Silva, Christopher M. A. Parlett, Zhimou Tang, Yueming Liu, Mengtian Fan, Xue Han, Joseph H. Carter, Floriana Tuna, Eric J. L. McInnes, Yongqiang Cheng, Luke L. Daemen, Svemir Rudić, Anibal J. Ramirez-Cuesta, Chiu C. Tang, Sihai Yang. Quantitative production of butenes from biomass-derived γ-valerolactone catalysed by hetero-atomic MFI zeolite. Nature Materials, 2019; DOI: 10.1038/s41563-019-0562-6