Key Descriptors of Single-Atom Catalysts Supported on MXenes (Mo<sub>2</sub>C, Ti<sub>2</sub>C) Determining CO<sub>2</sub> Activation
Anna Vidal-López, Judith Mahringer, Aleix Comas‐Vives
Abstract
High Resolution Image Download MS PowerPoint Slide CO 2 activation is crucial to its upgrade to fuels and chemicals. In this work, we systematically studied CO 2 cleavage on single-atom catalysts (SACs) based on metals M = (Fe, Ru, Co, Rh, Ni, Pd, Pt, Cu, Ag, Au) supported on Mo 2 CO x (6/9 O ML) and Ti 2 CO x (7/9 O ML) MXenes via Density Functional Theory (DFT) calculations and Bader charge analysis to provide insights into the charge redistribution among the metal, MXene, interface, and CO 2 during the process. CO 2 activation involves a two-step mechanism, adsorbing at the M–MXene interface where it bends and acquires a highly anionic character and then breaks, forming CO* and O*. The energy barriers analyzed for the CO 2 activation on M/Mo 2 CO x and M/Ti 2 CO x surfaces show that Cu, Ni, Rh, and Pt on Mo 2 CO x and Cu, Ru, and Rh on Ti 2 CO x presented the lowest energy barriers. Comparing the two MXenes, the electrophilic nature of Mo atoms facilitates CO 2 cleavage, while the Ti atoms distribute charge differently, hindering the CO 2 activation process. The energy barriers toward CO 2 activation on M/Mo 2 CO x and M/Ti 2 CO x surfaces show that Cu, Ni, Rh, and Pt on Mo 2 CO x and Cu, Ru, and Rh on Ti 2 CO x presented the lowest energy barriers. Mo 2 CO x systems presented geometrical structures of the transition states that were more product-like aligning with the Hammond’s principle, implying exoenergetic processes and lower energy barriers in contrast to Ti 2 CO x . Moreover, the CO 2 activation on M/2D-Mo 2 C follows a Brønsted–Evans–Polanyi (BEP) relationship while M/2D-Ti 2 C breaks it, a crucial factor to identify better catalytic materials. The ExtraTreesRegressor machine learning algorithm effectively predicts adsorption and transition-state energies using a small set of descriptors. The findings underscore the importance of transition metal electronic states, charge transfer, and support structure effects for SACs on MXenes, providing valuable insights for the design of catalytic materials. This detailed analysis provides a deeper understanding of the mechanistic aspects of CO 2 activation, highlighting the role of single-atom metals and their interaction with metal-carbide surfaces.