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

To date, NH 3 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 N 2 dissociation barrier and NH x ( x = 1-3) desorption energy. Herein, we demonstrate NPM (Co, Ni, and Re)-mediated Mo 2 CT x MXene (where T x denotes the OH group) to achieve efficient NH 3 synthesis under mild conditions. In particular, the NH 3 synthesis rate over Re/Mo 2 CT x and Ni/Mo 2 CT 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 Mo 4+ over Mo 2 CT x has a strong ability for N 2 activation; thus, the rate-determining step is shifted from conventional N 2 dissociation to NH 2 * formation. NPM is mainly responsible for H 2 activation, and the high reactivity of spillover hydrogen and electron transfer from NPM to the N-rich Mo 2 CT x surface can efficiently facilitate nitrogen hydrogenation and the subsequent desorption of NH 3 . With the synergistic effect of the dual active sites bridged by H-spillover, the NPM-mediated Mo 2 CT x catalysts circumvent the major obstacle, making NH 3 synthesis under mild conditions efficient.