Control of zeolite microenvironment for biomass conversion

The highly selective conversion of biomass-derived 2-methyltetrahydrofuran (2-MTHF) into pentadienes has been achieved over an aluminium and niobium bimetallic atomically doped on MCM-41. The Nb(V) sites enhance the catalytic performance by binding 2-MTHF.

Methyltetrahydrofuran (2-MTHF) can be produced readily from lignocellulose-derived furfural via low-cost, high-yield processes and has been identified as a sustainable resource for making pentadienes via ring-opening, hydrogen transfer and dehydration processes. Leading catalysts for this reaction include amorphous SiO2/Al2O3, and Al or B- zeolites. However, these microporous catalysts often suffer from deactivation due to the formation of cokes. Furthermore, achieving effective selectivity control towards pentadienes in this reaction is still a significant challenge. 

MCM-41 is a mesoporous silica-based material used as a catalyst or catalyst support for a wide range of reactions; emerging niobium-based catalysts have shown exceptional performance for the hydrodeoxygenation of biomass under mild conditions. 

An international team of researchers studied whether MCM-41 materials containing weak acid sites and active niobium sites effectively address the challenges of pentadiene production. The reaction mechanism of conversion of 2-MTHF is complex, involving multiple reaction intermediates and products. The ring-opening of 2-MTHF is the rate-limiting step in this conversion. The research team aimed to determine the full molecular details of the catalytic mechanism through the use of operando X-ray Absorption Spectroscopy (XAS), combined with Diffuse Reflectance Infrared Fourier Transform Spectroscopy (DRIFTS) and in situ high-field solid-state Nuclear Magnetic Resonance spectroscopy. 

On Diamond's I20-EDE beamline, they used the spectroscopy group's recently commissioned high-temperature synchronous gas/vapour phase XAS/DRIFTS set-up coupled to the mass spectrometer and in-house developed gas dosing rig. This combination enabled them to propose a detailed reaction mechanism via temperature programmed spectroscopy. 

This work reported the synthesis of a series of new (Al,Nb)-bimetallic mesoporous silica materials for the first time. AlNb-MCM-41(35/1/0.9) shows excellent catalytic performance for converting biomass-derived 2-MTHF to pentadienes. 

The direct transformation of biomass derivatives to C5 dienes under mild conditions described in this study will have a significant impact on the development of future sustainable chemical processes. In addition, these findings have revealed the nature of Nb(V) sites during the conversion of 2-MTHF, and promoted the understanding of the catalytic role of Nb(V) sites in MCM-41, which will be of interest to those working in the fields of solid-state materials, catalysis and sustainable chemical production. 

The last user experiment of I20-EDE took place in April 2023, and the beamline is now closed to beamtime applications. To learn more about new applications for research, including the SWIFT flagship beamline for the Diamond-II upgrade please contact Science Group Leader Sofia Diaz-Moreno: [email protected]