Coordinatively Unsaturated Metal–Organic Frameworks M₃(btc)₂ (M = Cr, Fe, Co, Ni, Cu, and Zn) Catalyzing the Oxidation of CO by N₂O: Insight from DFT Calculations

Abstract

The oxidation of CO by NO over metal-organic framework (MOF) M(btc) (M = Fe, Cr, Co, Ni, Cu, and Zn) catalysts that contain coordinatively unsaturated sites has been investigated by means of density functional theory calculations. The reaction proceeds in two steps. First, the N-O bond of NO is broken to form a metal oxo intermediate. Second, a CO molecule reacts with the oxygen atom of the metal oxo site, forming one C-O bond of CO. The first step is a rate-determining step for both Cu(btc) and Fe(btc), where it requires the highest activation energy (67.3 and 19.6 kcal/mol, respectively). The lower value for the iron compound compared to the copper one can be explained by the larger amount of electron density transferred from the catalytic site to the antibonding of NO molecules. This, in turn, is due to the smaller gap between the highest occupied molecular orbital (HOMO) of the MOF and the lowest unoccupied molecular orbital (LUMO) of NO for Fe(btc) compared to Cu(btc). The results indicate the important role of charge transfer for the N-O bond breaking in NO. We computationally screened other MOF M(btc) (M = Cr, Fe, Co, Ni, Cu, and Zn) compounds in this respect and show some relationships between the activation energy and orbital properties like HOMO energies and the spin densities of the metals at the active sites of the MOFs.

Computational Approach to Molecular Catalysis by 3d Transition Metals: Challenges and Opportunities

“…On the basis of the work of Ye and Liu, 515 Ketret et al. 516 performed a DFT mechanistic study on M 3 (btc) 2 MOFs (btc = benzene-1,3,5-tricarboxylate, M = Cr, Fe, Co, Ni, Cu, and Zn) to evaluate their suitability to oxidize CO with NO 2 . This study was based on the efficient CO oxidation catalyzed by several MOFs, including Cu 3 (btc) 2 .…”

A more effective catalysis of the CO2 fixation with aziridines: computational screening of metal-substituted HKUST-1

“…1. According to the available research experiences, considering the calculation cost, the models could be cut from the periodic structure and saturated with protons so that the overall charge remains zero in the whole process of mechanistic exploration [48][49][50][51][52][53]. The effectiveness of the Cu 2 (HCOO) 4 model A has been validated in our group by two different models (see B and C in Fig.…”

DFT Study of N2O Adsorption onto the Surface of M-Decorated Graphene Oxide (M = Mg, Cu or Ag)

“…It is found that these materials can be served as promising catalysts for N 2 O decomposing to N 2 and a dissociated oxygen atom. Sombat et al [19] explored the catalytic effects of metal organic structure (MOF) M 3 (BTC) 2 (M = Fe, Cr, Co, Ni, Cu and Zn) on the oxidation of CO by N 2 O, and found that the order of the catalytic reaction rate is: Cr 3 (BTC) 2 > Fe 3 (BTC) 2 > Co 3 (BTC) 2 > Ni 3 (BTC) 2 > Cu 3 (BTC) 2 < Zn 3 (BTC) 2 . The theoretical and experimental study of the decomposition of N 2 O on the bimetallic catalyst Rh-M (M = Co, Ni, Cu) had been carried by Hao Chen et al [20], and it showed that the catalytic activity trend of the Rh–M catalyst is determined as Rh 7 Co 1 /SBA-15 > Rh/SBA-15 > Rh 7 Ni 1 /SBA-15 > Rh 7 Cu 1 /SBA-15.…”