Precious-Metal-Free Mo-MXene Catalyst Enabling Facile Ammonia Synthesis Via Dual Sites Bridged by H‑Spillover

To date, NH3 synthesis under mild conditions is largely confined to precious Ru catalysts, while nonprecious metal (NPM) catalysts are confronted with the challenge of low catalytic activity due to the inverse relationship between the N2 dissociation barrier and NH x (x = 1–3) desorption energy. Herein, we demonstrate NPM (Co, Ni, and Re)-mediated Mo2CT x MXene (where T x denotes the OH group) to achieve efficient NH3 synthesis under mild conditions. In particular, the NH3 synthesis rate over Re/Mo2CT x and Ni/Mo2CT x can reach 22.4 and 21.5 mmol g–1 h–1 at 400 °C and 1 MPa, respectively, higher than that of NPM-based catalysts and Cs–Ru/MgO ever reported. Experimental and theoretical studies reveal that Mo4+ over Mo2CT x has a strong ability for N2 activation; thus, the rate-determining step is shifted from conventional N2 dissociation to NH2* formation. NPM is mainly responsible for H2 activation, and the high reactivity of spillover hydrogen and electron transfer from NPM to the N-rich Mo2CT x surface can efficiently facilitate nitrogen hydrogenation and the subsequent desorption of NH3. With the synergistic effect of the dual active sites bridged by H-spillover, the NPM-mediated Mo2CT x catalysts circumvent the major obstacle, making NH3 synthesis under mild conditions efficient.