The on-purpose dehydrogenation of propane (PDH) is a profitable approach to produce propylene, a chemical building block for the production of polymers, oxygenates, and daily use commodities. The discovery of active and selective dehydrogenation catalysts plays a critical role in the success of PDH processes. Wurtzite group-IIIA metal nitrides are potential dehydrogenation catalysts with high chemical and thermal stability. In addition, they exhibit Lewis acid (metal) and base (nitrogen) centers that can activate paraffinic C−H bonds. Herein, we investigate the catalytic behavior of undoped and gallium-doped AlN surfaces for PDH using combined density functional theory calculations, metadynamics simulations, and microkinetic modeling. Our results reveal that the concerted mechanism (simultaneous activation of two C-H bonds) is kinetically preferred over the stepwise mechanism (sequential activation of two C-H bonds). Interestingly, we demonstrated that doping AlN with gallium substantially (i) decreases the rate-limiting C-H activation barrier of the concerted mechanism and (ii) increases the overall apparent turnover frequencies. To understand moisture effects, we studied PDH in the presence of water on the surface of the catalyst. We revealed that although surface water dissociates and blocks strong Lewis acid-base pairs, its presence can boost the dehydrogenation activity of neighboring unblocked active sites. Microkinetic modeling revealed that Ga-doped AlN exhibits the highest dehydrogenation activity, followed by AlN systems. Finally, our metadynamics simulations demonstrated that H<sub>2</sub> formation (energy demanding step on strong Lewis acid-base pairs) on Ga-doped AlN is accessible at typical dehydrogenation temperatures of 873.15 K. Taken together, we reveal that doping of AlN results in an efficient dehydrogenation catalyst of light alkanes into valuable olefins.

Aluminum nitride as propane dehydrogenation catalysts: Effects from gallium doping and presence of water

ACS Spring 2022

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