A DFT periodic study on the interaction between O₂and cation exchanged chabazite MCHA (M = H+, Na+ or Cu+): effects in the triplet–singlet energy gap

Abstract

O(2) adsorption in proton, sodium and copper exchanged chabazite has been studied using periodic and cluster approaches by means of density functional theory. The Grimme's correction has been used to include the dispersion contribution to B3LYP. Two cation locations have been considered: one with the cation at the six-membered ring (MCHA(I)) and the other with the cation at the 8-membered ring (MCHA(IV)). The O(2)-HCHA and O(2)-NaCHA adsorption complexes present a eta(1)-O(2) bent coordination. The adsorption energies, which are due to dispersion, are between -15 and -19 kJ mol(-1), in agreement with the experimental values. On the other hand, the O(2) coordination to CuCHA is through a eta(2)-side-on mode with a square planar coordination around the metal center. This structure favors the Cu d -->pi* O(2) charge transfer which becomes the predominant stabilizing factor. The adsorption of singlet states of O(2) in HCHA and NaCHA, modeled with an ONIOM M12T:48T, is of the same nature as that of the ground state, and only the highest in energy (1)Sigma is significantly more stabilized in MCHA than the triplet state by 14 to 24 kJ mol(-1). The adsorption of singlet O(2) in Cu exchanged zeolites presents a higher electron transfer from Cu(+) to O(2) than that calculated for the triplet species and thus both singlet states are stabilized with respect to the ground state O(2). Generally, singlet oxygen appears more attractive to active zeolite models than those calculated with triplet oxygen, indicating a source of oxidative efficiency for designed structures.

Modeling Ammonia and Water Co-Adsorption in CuI-SSZ-13 Zeolite Using DFT Calculations

“…Geometry optimisation of Cu I -SSZ-13 led to three structures, A, B and C with Cu I located in three different positions in the largest cage ( Figure 2). In agreement with previous DFT results, [45][46] the most stable structure A has a Cu I at site I while the less stable structure C has a Cu at site IV'. [33][34] The intermediate structure B has a Cu at site IV (Table 1).…”

“…with Cu I in site IV, and c) structure B with Cu I in site IV'. Red balls are O, yellow ball are Si, orange ball is Al, and exchange site positions are blue balls.These three geometries exhibit strong similarities with previously calculated structures [45][46]. The relative energy between structure A and structure B (43 kJ.mol-1) is very similar to the value of 40.5 kJ.mol-1 previously calculated with a periodic B3LYP method, including a posteriori correction of the long range dispersion.46 Structure C containing CuI at site IV' has a O2-Al-O4 angle of 100° and O4-Si-O1 angle of 104° in B that decrease to O2-Al-O4 angle of 98° and increases to O4-Si-O1 of 106° in C. These changes in the copper interaction with the SSZ-13 framework in B and C, in comparison with A, are most probably responsible for the stability decrease.…”

Molecular orbital model of the influence of interaction between O2 and aluminosilicate sites on the triplet–singlet energy gap and reactivity

“…This result indicates a stabilization of singlet oxygen in this system [32]. O 2 adsorption in proton, sodium and copper exchanged chabazite has been studied using periodic and cluster approaches by us, in a recent publication [33]. In our paper, O 2 -HCHA adsorption complexes present an O 2 bent coordination and the adsorption energies are due to dispersion.…”

1H and 23Na MAS NMR spectroscopy of cationic species in CO2 selective alkaline earth metal porous silicoaluminophosphates prepared via liquid and solid state ion exchange

“…Another approach that has been proven to be powerful in the determination of cations location and distribution is the use of molecular simulation such as Monte Carlo simulation in faujasite materials [17][18][19] and density functional theory. Examples include description of Na þ mobility upon adsorption of chloroform in Faujasite [20], prediction of extraframework cations site location preference in chabazite materials [21] and evaluation of the adsorption of O 2 in cation exchanged materials [22], just to mention a few. Still, the assumption of a rigid and unique framework structure and allowing non-framework cations to move during the course of the simulation also limits its applicability to a wide variety of ion exchanged zeolitic materials.…”