Transition Metal Atoms Embedded in Graphene: How Nitrogen Doping Increases CO Oxidation Activity

Abstract

We study 14 transition metals on pristine and N-doped graphene using density functional theory. For double vacancies, nitrogen doping increases the binding strength of harder transition metals to the support and reduces their oxygen affinity. Inversely, the oxygen affinity of softer metals increases. Since O2 binding energies are correlated with the CO oxidation barrier in a volcano-like trend, doping also affects the activity of the single-atom catalyst. Among these systems, Fe atoms embedded in N-doped graphene are the most active CO oxidation catalysts. These insights can be used to guide the synthesis of highly active oxidation catalysts from nonprecious metals.

Identification of Active Sites for CO2 Reduction on Graphene‐Supported Single‐Atom Catalysts

“…We focus on the ZnÀ NÀ G catalyst that outperforms other MÀ NÀ G catalysts and assume that single Zn atoms are embedded at divacancy sites of graphene, binding to four neighboring N or C atoms, as suggested by previous experiments (Figure 1). [14,18,20,[26][27][28] Our calculations predict that *OCHO is a favorable initial intermediate of CO 2 R on the Zn site, indicating that CO cannot be produced on this site. Instead, we find that the C atom that is a chemically-bonded nearest neighbor of the Zn atom (C NN ) is highly active for CO 2 reduction to CO, and Zn plays a role as an enhancer of the catalytic activity of the C NN .…”

Confined Transformation of Organometal‐Encapsulated MOFs into Spinel CoFe2O4/C Nanocubes for Low‐Temperature Catalytic Oxidation

“…Although spinel transition metallic oxides can exhibit competitive catalytic activity compared to noble metal catalysts, the water poisoning problem is always existed in catalytic oxidation systems by using transition metal oxides as active sites, thus greatly limits the practical application of low‐temperature CO oxidation 54,55. In this work, the catalytic CO performance of prepared CoFe 2 O 4 /C nanocubes was tested with the ∼2% water vapor in order to examine the water‐resisting property of MOFs‐derived spinel bimetallic oxides.…”

“…[52,53] Although spinel transition metallic oxides can exhibit competitive catalytic activity compared to noble metal catalysts, the water poisoning problem is always existed in catalytic oxidation systems by using transition metal oxides as active sites, thus greatly limits the practical application of low-temperature CO oxidation. [54,55] In this work, the catalytic CO performance of prepared CoFe 2 O 4 /C nanocubes was tested with the ∼2% water vapor in order to examine the water-resisting property of MOFsderived spinel bimetallic oxides. As illustrated in Figure 7e, the existence of H 2 O in feed gas reduced the conversion of CO, but CoFe 2 O 4 /C nanocubes still reached a total conversion at 145 °C and presented high value of TOFs (2.59 × 10 −4 s −1 ) at 100 °C under the moisture rich conditions, which remains a challenge for recent MOFs-derived catalyst development.…”

Influence of Magnetic Moment on Single Atom Catalytic Activation Energy Barriers

“…Pristine graphene is not analyzed, as both our previous work [17] and many examples in the literature have demonstrated that pristine graphene has unsuitably low adsorption and diffusion barrier energies to support single molecules or atoms [45,52,53]. Previous work on N defect moieties supported on graphene surfaces has associated enhanced catalytic activity due to the N dopants altering O 2 binding energies with values approaching that of O 2 on Pt surfaces [29,54,55]. However, the underlying mechanisms of this shift in binding energy is not completely understood.…”