The transformation of cheap and abundant light alkanes could have far-reaching implications on the chemical and energy sectors, yet remains a formidable challenge due to the C-H inertness. Light alkanes can be upgraded into olefins, aromatics, and oxygenates through well-known catalytic processes, namely dehydrogenation, aromatization, and partial oxidation, as well as noncatalytic steam cracking. However, these existing processes still facing challenges of inadequate activity, selectivity and/or catalyst stability. To mitigate these challenges, H2, H2O, and CO2 have been frequently employed as auxiliary reactants during dehydrogenation and aromatization. Based on our recent attempt to use NH3 as an auxiliary reactant during the ethane aromatization, we proposed a unique catalytic system through the direct reaction between light alkanes and the basic NH3 over the acidic metal/HZSM-5 catalyst. Upon careful optimization of the metal/acid functions, the reaction between light alkanes and ammonia can be tuned for selective C-H cleavage through dehydrogenation and C-N linkage through amination. For example, the Pt/HZSM-5 catalyzes the dehydrogenation of ammonia and ethane at temperatures as low as 350oC and atmospheric pressure. The specific rate of CH3CN is 60 μmol/g/min, and the selectivity is up to 99%. We suggest that the production of CH3CN was realized through cascade/tandem mechanism, where the initial ethane dehydrogenation over the Pt sites was followed by direct amination (between ethylene and ammonia) on the Brønsted acids of the zeolites and further ethylamine dehydrogenation again on the Pt sites. We anticipate that the proposed catalytic systems through co-processing light alkanes with ammonia could be important alternatives to the current processes for ethane transformation and acetonitrile production.

Ammonia assisted ethane conversion through dehydrogenation

ACS Fall 2021

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