Conversion of Ammonia to Hydrazine Induced by High-Frequency Ultrasound

Hydrazine is a chemical of utmost importance in our society, either for organic synthesis or energy use. The direct conversion of NH3 to hydrazine is highly appealing, but it remains a very difficult task because the degradation of hydrazine is thermodynamically more feasible than the cleavage of the N-H bond of NH3. As a result, any catalyst capable of activating NH3 will thus unavoidably decompose N2H4. Here we show that cavitation bubbles, created by ultrasonic irradiation of aqueous NH3 at a high frequency, act as microreactors to activate and convert NH3 to NH species, without assistance of any catalyst, yielding hydrazine at the bubble-liquid interface. The compartmentation of in-situ-produced hydrazine in the bulk solution, which is maintained close to 30 degrees C, advantageously prevents its thermal degradation, a recurrent problem faced by previous technologies. This work also points towards a path to scavenge (OH)-O-. radicals by adjusting the NH3 concentration.

Automated summary

This study demonstrates that cavitation bubbles created by ultrasonic irradiation of aqueous NH3 at a high frequency can activate and convert NH3 to hydrazine without the need for any catalyst. The in-situ-produced hydrazine is compartmentalized in the bulk solution maintained close to 30 degrees Celsius, preventing its thermal degradation. Additionally, this work suggests a pathway to scavenge (OH)-O-. radicals by adjusting the NH3 concentration.