Quantum Mechanical Screening of Metal-N₄-Functionalized Graphenes for Electrochemical Anodic Oxidation of Light Alkanes to Oxygenates

Abstract

Developing processes that allow partial oxidation of light alkanes (C 1 −C 4 ) to more valuable oxygenates is important from both industrial and academic perspectives. In this study, quantum mechanics combined with a constant potential model were employed to evaluate the ability of metal-N 4 -functionalized graphene (gMN 4 ) to catalyze anodic partial oxidation of light alkanes to oxygenates via electrochemical means while considering both reactivity and selectivity. During the reaction, reactive oxo (*O) is generated through water electrochemical oxidation. This reactive oxo is used to oxidize light alkanes (represented by methane and propane). On the basis of investigating the systems with different Ms (Cr, Mn, Fe, Co, Ru, Rh, Os, and Ir) in a wide range of electrode potentials (U, 0.0− 2.5 V SHE ) and pH values (0.0−14.0), only gIrN 4 and gFeN 4 were capable of catalyzing this oxidation with acceptable reaction rates. The other catalysts were unable to form *O or inert to C−H bonds. Both alkanes can be oxidized but the rate for methane is slower. gIrN 4 oxidizes methane to formaldehyde under proper Us. For propane, this catalyst generates iso-propanol at low Us and acetone at high Us. gFeN 4 only oxidizes propane to acetone. Our theoretical investigation along with known experimental results suggest a high probability for experimental realization of this anodic partial oxidation, which would allow for utilization of natural gas discovered in remote oil fields.

Advances and Fundamental Understanding of Electrocatalytic Methane Oxidation

“…Typically, metals electrocatalysts enhance power generation with total methane oxidation into CO 2 , according to Equation 5, while oxo‐included ones boost partial oxidation of methane via Equation 6. Interestingly, in work by Luo et al., the free energy of methane activation steps is provided for M−N 4 −G as oxo‐included electrocatalysts in agreement with proposed activation elementary steps over metal oxides by Arnarson et al., which follow Equation 6 [75–76] . A schematic representation of reaction pathways towards different C1 products with two possible activation conditions is shown in Figure 10.…”

“…Luo et al. has investigated the pH effect toward EMO on M‐N 4 ‐G catalysts using Pourbaix diagrams [76] . Among all, the IrN 4 G catalyst with appropriate pH and potential control was predicted to catalyze the EMO toward formaldehyde selectivity but with a slow rate.…”

First‐Principles Evaluation of One‐Dimensional Metal‐Organic Frameworks for Electrocatalytic C−H Activation of Natural Gas

“…To obtain more accurate Pourbaix diagrams for the remaining five cases, we performed Const‐ U DFT calculations at U =0.0, 0.5, 1.0, and 1.5 V SHE and used the procedure that we detailed in our previous work to construct the Pourbaix diagrams (Figure 3). [8a] In comparison to the Pourbaix diagrams calculated at Const‐ Q 0 , we find that P *O is much smaller. For Co − NH , Co − O , Co − cisNH/O , and Co − transNH/O , the diagrams calculated at Const‐ U indicate P *O s of only 0.0, 0.5, 0.4, and 0.1%, respectively.…”

Evaluating Potential Catalytic Active Sites on Nitrogen-Doped Graphene for the Oxygen Reduction Reaction: An Approach Based on Constant Electrode Potential Density Functional Theory Calculations

“…The constant electrode potential method applied in this work leads to different numbers of electrons for each stationary point along the reaction coordinate, and therefore, the calculated G needs to be corrected based on the following equation: where N e, U and N e,0 are the number of electrons in the system under the target U and zero charge, respectively, and μ e ( U ) is the chemical potential of the electrons under U and equal to the Fermi energy. Recently, we applied this approach to study the adsorption of N-heterocyclic carbenes on Au(111), CO 2 electrochemical reduction catalyzed by Cu(111), NDGs, Ag–Cu tandem catalysts, N 2 electrochemical reduction on Ru(0001), and alkane electrochemical hydroxylation catalyzed by metal-N 4 -functionalized graphenes . Additionally, this approach has been used by others to study a variety of electrochemical systems. , …”