Ultrasound-assisted catalytic valorization of nitric acid waste to ammonia using hydrogen nanobubbles

초록

The sustainable conversion of nitric acid waste into ammonia offers a dual benefit of wastewater remediation and green ammonia synthesis. Here we report an ultrasound-assisted catalytic process that efficiently converts nitric acid waste into ammonia through the synergistic coupling of ultrasonic irradiation, hydrogen nanobubbles (H-2 NBs), and a hydrogen-bearing ruthenium oxide (HxRuO2) catalyst. Ultrasonic irradiation (2.4 MHz) generates stable H-2 NBs that act as in situ hydrogen reservoirs, promoting nitrate reduction under mild conditions. The coupled H-2 NB-HxRuO2 system achieves over 90% nitrate-to-ammonia conversion at 60 degrees C within 4 hours using pressurized H-2 gas. The process exhibits high ammonia selectivity (approximately 85%) and excellent catalyst recyclability across multiple cycles. Mechanistic analysis reveals that acoustic cavitation enhances catalyst dispersion and interfacial hydrogen transfer between H-2 NBs and HxRuO2, accelerating nitrate hydrogenation. This ultrasound-assisted approach exemplifies the integration of sonochemistry and heterogeneous catalysis for environmentally benign nitrogen recycling and sustainable ammonia production.

키워드