CO interaction with Cu(I)-MCM-22 zeolite: density functional theory investigation

Ho Thang Viet,Petr Nachtigall

doi:10.32508/stdj.v17i3.1367

Abstract

MCM-22 zeolite has been widely used in many applications for catalysis and adsorption. Especially, this material exchanged with Cu+ cation (Cu(I)-MCM-22) is an active catalyst in green chemical reaction, such as decomposition of NO and N2O. The local geometry of Cu+ in vicinity of Al (III) replacement in six different Si (IV) sites and CO interaction with the most stable Cu+ in each Al site were explored using periodic density functional theory (DFT) method. The CO stretching frequencies were computed applying the ω/r scaling method in which frequencies were determined at high quantum level (couple cluster) and CO bond length calculated at DFT level. The results showed that Cu+ cation located in the channel wall position and intersection position coordinated with 3 or 2 framework oxygen atoms, respectively, before CO adsorption and Cu+ cation coordinated with 2 framework oxygen atoms after CO adsorption. The interaction energies between CO and Cu+ cation were in range - 148 to -195 kJ.mol-1 and CO frequencies exhibit two peaks at 2151 and 2159 cm-1 in good agreement with experimental data. This investigation brought us to understand the Cu+ location in MCM-22 and CO adsorption in Cu(I)-MCM-22 zeolite.

Highlights

MCM-22 (MWW topology structure in IZA code) has shown interesting structure with large and medium pore size including 12-MR large supercage (7.1 x 7.1 x 18.2Å) connected with 10MR crossing window (4.0 x 5.4Å) and 10-MR sinusoidal channels (4.0 x 5.9Å) located in the intralayer space of MCM-22 [1]
Cu+ cation location and its interaction with CO were computationally investigated in various zeolite structures (Cu(I)-ZSM-5, Cu(I)MFI, Cu(I)-FER) by mean of combined QM-pot and periodic DFT [14,15,16,17,18]. These results showed that two type of Cu+ position were found: (i) type I, Cu+ cation located on the wall channel surface coordinated with 3 or 4 framework oxygen atoms; (ii) type II, Cu+ cation located on the intersection site formed between the main and the zig zag channel
The Cu+ cation position located in MCM-22 either on the top of channel wall ring (5 or 6-membered ring) and coordinated with 3 framework oxygen atoms or on the intersection forming between supercage (12membered ring) and crossing window cage (10membered ring) or edge of sinusoidal channel and coordinated with only two framework oxygen atoms

Summary

INTRODUCTION

MCM-22 (MWW topology structure in IZA code) has shown interesting structure with large and medium pore size including 12-MR large supercage (7.1 x 7.1 x 18.2Å) connected with 10MR crossing window (4.0 x 5.4Å) and 10-MR sinusoidal channels (4.0 x 5.9Å) located in the intralayer space of MCM-22 [1]. Cu+ cation location and its interaction with CO were computationally investigated in various zeolite structures (Cu(I)-ZSM-5, Cu(I)MFI, Cu(I)-FER) by mean of combined QM-pot and periodic DFT [14,15,16,17,18] These results showed that two type of Cu+ position were found: (i) type I, Cu+ cation located on the wall channel surface coordinated with 3 or 4 framework oxygen atoms; (ii) type II, Cu+ cation located on the intersection site formed between the main and the zig zag channel. The linear relationship between stretching frequencies at CCSD(T) level and rCO at DFT level accompanying with the correction of harmonic and aharmonic frequencies interpolated exactly with frequencies of CO from CO adsorption complexes with Cu(I)-MCM-22 at DFT level

RESULTS

DISCUSSION

CONCLUSION