Hydrogenation of NOx into ammonia under ambient conditions: From mechanistic investigation to multiphase catalysis.

This work proposes a NO x recycling approach through nitrite hydrogenation into ammonia (NH 3 /NH 4 OH), and the screened out Pd0/Pd2+-loaded heterogeneous catalyst achieves excellent ammonia yield. Initially, the DFT calculation of nitrite hydrogenation was conducted to study the determining step for N 2 /ammonia generation and guide the catalyst design. Consequently, the designed Pd2+/0/ Covalent Triazine Framework (CTF) presented 100% nitrite conversion with 100% ammonia selectivity. The XPS and H 2 -TPR results demonstrated the Pd2+/Pd0 ratios and Pd2+ reducibility greatly affected the nitrite conversion and ammonia selectivity. DRIFTs examined the reaction intermediates and the impact of Pd distribution behind ammonia generation. Under ambient conditions, a model test from NO x adsorption to ammonia release has been completed, and it exhibited an overall conversion of 70% NO x into ammonia in a single cycle with TOF of 3.9 h−1, which proposes a direction of NO x recycling and utilization with less energy consumption and free of CO 2 emissions. [Display omitted] • This work proposed a NO x recycling route into ammonia under ambient condition. • Pd2+/0/CTF presented 100% nitrite conversion and 100% ammonia selectivity. • The optimal Pd2+/Pd0 ratios and easily reduced Pd2+ enhanced nitrite conversion. • NO* was the main intermediates and its further hydrogenation into HNO* produce ammonia. [ABSTRACT FROM AUTHOR]