CO oxidation on MXene(Mo_(2)CS_(2)) supported single-atom catalyst: A termolecular Eley-Rideal mechanism

Finding transition metal catalysts for effective catalytic conversion of CO to CO_(2)has attracted much attention.MXene as a new 2D layered material of early transition metal carbides,nitrides,and carbo-nitrides is a robust support for achoring metal atoms.In this study,the electronic structure,geometries,thermodynamic stability,and catalytic activity of MXene (Mo_(2)CS_(2)) supported single noble metal atoms (NM=Ru,Rh,Pd,Ir,Pt and Au) have been systematically examined using first-principles calculations and ab initio molecular dynamic (AIMD) simulations.First,AIMD simulations and phonon spectra demonstrate the dynamic and thermal stabilities of Mo_(2)CS_(2)monolayer.Three likely reaction pathways,LangmuirHinshelwood (LH),Eley-Rideal (ER),and Termolecular Eley–Rideal (TER) for CO oxidation on the Ru1-and Ir_(1)@Mo_(2)CS_(2)SACs,have been studied in detail.It is found that CO oxidation mainly proceeds via the TER mechanism under mild reaction conditions.The corresponding rate-determining steps are the dissociation of the intermediate (OCO-Ru_(1)-OCO) and formation of OCO-Ir_(1)-OCO intermediate.The downshift d-band center of Ru1-and Ir_(1)@Mo_(2)CS_(2)help to enhance activity and improve catalytst stability.Moreover,a microkinetic study predicts a maximum CO oxidation rate of 4.01×10^(2)s^(-1)and 4.15×10^(3)s^(-1)(298.15K) following the TER pathway for the Ru_(1)-and Ir_(1)@Mo_(2)CS_(2)catalysts,respectively.This work provides guideline for fabricating and designing highly efficient SACs with superb catalyts using MXene materials.

Theoretical studies of MXene-supported single-atom catalysts:Os_(1)/Ti_(2)CS_(2) for low-temperature CO oxidation

We report herein a new sulfur-functionalized MXene Ti_(2)C(Ti_(2)CS_(2))-supported osmium-metal single-atom catalyst(SAC) Os_(1)/Ti_(2)CS_(2)with high low-temperature catalytic activity for CO oxidation. Using periodic density functional theory calculations, the most stable SAC, Os_(1)/Ti_(2)CS_(2), has been screened from a series of group 8–11 transition metal SACs M_(1)/Ti_(2)CS_(2)(M = Fe, Co, Ni, Cu;Ru, Rh, Pd, Ag;Os, Ir,Pt, Au). The calculations show that it is favorable for O;and CO to be coadsorbed on the Os;single atom(SA) of Os_(1)/Ti_(2)CS_(2)and the adsorption energy of the first O_(2) molecule is slightly higher than that of CO. Moreover, the termolecular co-adsorption of O_(2)+ 2CO on Os_(1) SA is also possible, which is favorable for CO oxidation on Os_(1) SA through a novel threemolecule reaction mechanism. Accordingly, four different catalytic mechanisms, the Langmuir–Hinshelwood(L–H),Eley–Rideal(E–R), termolecular Langmuir–Hinshelwood-A(TLH-A) and termolecular Langmuir–Hinshelwood-B(TLHB), are systematically studied for CO oxidation by O_(2) on Os_(1)/Ti_(2)CS_(2). The theoretical studies indicate that the TLH-B mechanism is the most feasible for CO oxidation with the reaction barrier energy of only 0.74 e V, which is far lower than for L–H, E–R and TLH-A with barrier energies of 1.06, 1.09 and1.47 e V, respectively. The results provide fundamental understanding to the surface chemistry of MXene and designing new sulfur-functionalized two-dimensional MXene catalytic nanomaterials.