Scientists at the U.S. Department of Energy's (DOE) Argonne National Laboratory and Ames National Laboratory have developed a faster, more energy-efficient version of the traditional dehydrogenation reaction to manufacture propylene from propane.
The scientists wanted to understand how a nontraditional metal catalyst on a nontraditional type of support compares with traditionally used materials during the catalytic conversion of propane (Figure 1). Catalyst support materials typically have high surface areas and help to distribute catalysts. As this research shows, they can also play an important role in promoting catalysis.
The scientists focused on the reactivity of zirconium on silicon nitride (Si3N4), the hypothesis being that the nitride might enable facile heterolytic C–H bond activation along the Zr–N bond.
Si3N4 doped with tetrabenzyl zirconium (ZrBn4) was found to be highly active, producing 1.53 mol propene/mol Zr/hr at 450°C (842°F), with 99% conversion to propylene. This temperature is slightly lower than the 550°C (1022°F) typically required for catalysis using traditional materials.
To better understand how the supported organic metallic species achieves this, it was characterized by several advanced techniques, including Dynamic Nuclear Polarization-enhanced Solid State Nuclear Magnetic Resonance (DNP-SSNMR) and X-ray Absorption Spectroscopy (XAS).
These, together with other studies described in a recent Journal of the American Chemical Society (2024; 146 (21): 14404 DOI: 10.1021/jacs.4c02776), indicate that high-surface-area amorphous Si3N4 is suitable for chemisorption of organometallic precursors, and the nitride surface is indeed capable of significantly enhancing catalytic activity, very probably by improved heterolytic C-H bond cleavage.
Additionally, this research gives a glimpse into the reactivity achievable with other low-cost metals in the catalytic conversion of propane into propylene.
This discovery also offers proof that this concept can be generalized to other important reactions. According to Argonne chemist Max Delferro, the team is currently using DNP-SSNMR with other spectroscopic techniques to better understand the structure of the pre-catalysts and the active species.
It is also investigating other non-precious, earth-abundant metal catalysts, such as iron and vanadium, supported on silica nitride and the nitrides of niobium and aluminum.
Meanwhile, Argonne has patented the catalyst composition and applications, and according to Delferro, his team is keen to work with the private sector in a potential research partnership for scale-up and pilot plan demonstrations of the reaction.
