(704g) Catalytically Active Edge Sites of Mxene-Confined Pt Nanolayers for Conversion of Short Alkanes

The activity, selectivity, and stability of a heterogeneous catalyst are three important metrics to consider when assessing its catalytic performance. In a continuous-flow reactor, catalyst stability describes the trend of losing its activity and/or selectivity with time-on-stream (TOS). Poor stability leads to rapid catalyst deactivation, which is a major concern in industrial applications of catalysts. As compared to the other two metrics (activity and selectivity), catalyst stability is less frequently investigated on a fundamental level; although it is a central metric in assessing the viability of a catalyst for industrial practice. Pt-based catalysts have been widely used in industrial applications, however, they typically suffer from severe deactivation due to coke deposit and sintering.

To improve the stability of Pt-based catalysts, atomically thin Pt nanolayers of 2 nm * 2nm * 0.5 nm are synthesized on the surface of Mo₂TiC₂ MXenes and used for the catalytic dehydrogenation of methane, ethane, and propane into ethane, ethylene, and propylene, respectively. The edge sites of the MXene-confined Pt nanolayer catalysts are active for cleaving C-H bonds from alkanes. The Pt nanolayer catalyst showed superior coke-resistance (no deactivation for 72 h), high activity (turnover frequencies (TOFs) of 0.4–1.2 s^−1), and selectivity (>95%) toward ethane, ethylene, and propylene, respectively. It is found that the electronic effect plays a critical role in dehydrogenative product selectivity and catalyst stability. We conclude that low coordination numbers induce the edge sites of confined Pt nanolayers to be active for C-H bond cleavages in alkanes, and spatial confinement effects in the interspace (~0.5 nm) between two MXene layers constrain the growth of coke precursors when the reaction operating conditions are well controlled.