Precious-Metal-Free\nMo-MXene Catalyst Enabling Facile\nAmmonia Synthesis Via Dual Sites Bridged by H‑Spillover

To date, NH<sub>3</sub> synthesis under mild conditions\nis largely\nconfined to precious Ru catalysts, while nonprecious metal (NPM) catalysts\nare confronted with the challenge of low catalytic activity due to\nthe inverse relationship between the N<sub>2</sub> dissociation barrier\nand NH<sub><i>x</i></sub> (<i>x</i> = 1–3)\ndesorption energy. Herein, we demonstrate NPM (Co, Ni, and Re)-mediated\nMo<sub>2</sub>CT<sub><i>x</i></sub> MXene (where T<sub><i>x</i></sub> denotes the OH group) to achieve efficient NH<sub>3</sub> synthesis under mild conditions. In particular, the NH<sub>3</sub> synthesis rate over Re/Mo<sub>2</sub>CT<sub><i>x</i></sub> and Ni/Mo<sub>2</sub>CT<sub><i>x</i></sub> can reach\n22.4 and 21.5 mmol g<sup>–1</sup> h<sup>–1</sup> at\n400 °C and 1 MPa, respectively, higher than that of NPM-based\ncatalysts and Cs–Ru/MgO ever reported. Experimental and theoretical\nstudies reveal that Mo<sup>4+</sup> over Mo<sub>2</sub>CT<sub><i>x</i></sub> has a strong ability for N<sub>2</sub> activation;\nthus, the rate-determining step is shifted from conventional N<sub>2</sub> dissociation to NH<sub>2</sub>* formation. NPM is mainly\nresponsible for H<sub>2</sub> activation, and the high reactivity\nof spillover hydrogen and electron transfer from NPM to the N-rich\nMo<sub>2</sub>CT<sub><i>x</i></sub> surface can efficiently\nfacilitate nitrogen hydrogenation and the subsequent desorption of\nNH<sub>3</sub>. With the synergistic effect of the dual active sites\nbridged by H-spillover, the NPM-mediated Mo<sub>2</sub>CT<sub><i>x</i></sub> catalysts circumvent the major obstacle, making\nNH<sub>3</sub> synthesis under mild conditions efficient.