Exploring the Tunability of Trimetallic MOF Nodes for Partial Oxidation of Methane to Methanol

Abstract

Density functional theory is used to study the tunability of trigonal prismatic SBUs found in metal–organic frameworks (MOFs) such as MIL-100, MIL-101, and PCN-250/MIL-127 of chemical composition M3+ 2M2+(μ3-O)­(RCOO)6 for the partial oxidation of methane to methanol. We performed a combinatorial screening by varying the composition of the trimetallic node (M1 3+)2(M2 2+) (where M1 and M2 = V, Cr, Mn, Fe, Co, and Ni) and calculated the reaction pathway on both M1 and M2 sites. The systematic replacement of metals in the trimetallic cluster allowed us to study the influence of spectator atoms on the catalytic activity of a specific metal site in the cluster toward the N2O activation and C–H bond activation steps of the reaction. In the screening, we identified the top-performing node compositions with predicted barriers lower than those already reported for experimentally tested MOFs with trigonal prismatic SBUs. This work demonstrates the opportunity to tune the catalytic activity of MOFs for redox reactions by changing their metal node composition.

Low‐Temperature, Ambient Pressure Oxidation of Methane to Methanol Over Every Tri‐Iron Node in a Metal–Organic Framework Material

“…Although several Fe‐based MOFs have either been proposed or evaluated as light alkane oxidation catalysts, [26–30] the use of a MOF material to convert methane near‐exclusively to methanol at mild temperatures and ambient pressures has not yet been realized. DFT studies have suggested the potential for Fe 2+ sites on MIL‐100(Fe) nodes to catalyze the conversion of methane to methanol using N 2 O as an oxidant [31–33] . Experimental evidence of MIL‐100(Fe) nodes activating methane in the presence of N 2 O, however, is still lacking.…”

“…[22][23][24] Although several Fe-based MOFs have either been proposed or evaluated as light alkane oxidation catalysts, [26][27][28][29][30] the use of aM OF materialt oc onvert methane near-exclusively to methanol at mild temperatures and ambient pressures has not yet been realized.D FT studies have suggested the potential for Fe 2 + sites on MIL-100(Fe) nodes to catalyzet he conversion of methane to methanol using N 2 Oa sa no xidant. [31][32][33] Experimental evidenceo fM IL-100(Fe) nodes activating methane in the presence of N 2 O, however,i ss till lacking. We demonstrate herein not only the potential of MIL-100(Fe) in converting methanet om ethanol under mild conditions (low temperatures and pressures) but also specifically the use of the hydroxyl variant of MIL-100(Fe) in enabling the participation of every potential tri-iron node towards methane to methanol conversion.…”

Unveiling the catalytic potential of the Fe(iv)oxo species for the oxidation of hydrocarbons in the solid state

“…[22][23][24] So far, the vast majority of the Fe(IV)O systems have been studied in the gas phase or in solution, while little is known about the catalytic activity of the Fe(IV)O species in the solid state. Although some theoretical studies have been published very recently on the oxidation of ethane 10,[25][26][27][28][29] in metal-organic frameworks (MOFs) and methane in zeolites 30 , and of methane storage in MOF-74 31 , the shortage of experimental work is surprising given that several crystalline systems can be synthesised relatively straightforward with structures and coordination properties mimicking those observed in highly reactive Fe(IV)O molecular systems. Noticing this enormous knowledge gap and that the family of MOF-74 has been identified as a potential candidate to catalyse the methane activation, 32 we have recently used densityfunctional theory (DFT) calculations to assess the ability of MOFs to act as suitable guests for Fe(IV)O catalytic centres and their reaction substrates.…”

“…Furthermore only the first step of the hydroxylation of methane, the abstraction of an H atom from the substrate, has been studied in detail. 29,[34][35][36][37] The goal of this work is therefore to model the whole oxidation process of methane into methanol in a MOF-74 cavity in the presence of Fe(IV)O sites. This process is modelled as three consecutive steps that are illustrated in Figure 1, as in the classical rebound mechanism proposed by Groves 38,39 , starting with the abstraction of an H atom from methane by a reactive Fe(IV)O group, followed by a rebound step in which the CH 3 • radical binds to the newly formed Fe(IV)OH group to form a methanol molecule, and finally the detachment of CH 3 OH from the catalytic centre.…”

Role of Metal Identity and Speciation in the Low-Temperature Oxidation of Methane over Tri-Metal Oxo Clusters

“…39 Specifically, MIL-100 (MIL =Materials of Institut Lavoisier ) is a MOF that exhibits interesting properties in the partial oxidation of light alkanes. 35,[39][40][41] First discovered by Gérard Férey and coworkers, MIL-100 is comprised of trimetallic clusters [(M(III) 3 (μ 3 -O)] coordinated by trimesate linkers to form a porous structure featuring an MTN (Mobile Thirty Nine) topology (Scheme 1a). 42 Removal of terminal ligands (H 2 O or X -) through thermal activation under inert or vacuum at temperatures below 523 K (Scheme 1b) creates unsaturated open-metal sites over mixed valence nodes [(M(II)M(III) 2 (μ 3 -O)].…”