Adsorption of Benzene to Copper in CuHY Zeolite

Abstract

Adsorption of benzene to copper-exchanged Y zeolites has been studied employing Fourier transform infrared spectroscopy and QM/MM calculations. Experimentally, both Cu(I) and Cu(II)-Y zeolites were used as adsorbents. Benzene adsorption was observed on both copper and Brønsted acid sites, but the copper site is preferred. The FTIR spectra show the activation of the ν 13 in-plane ring stretching mode at 1471 and 1479 cm -1 for Cu and Brønsted sites, respectively. With respect to the gas-phase value, Cu sites cause a red shift of 13 cm -1 whereas Brønsted sites show a shift of 5 cm -1 only. Theoretical investigations were performed on complexes of benzene with Cu-exchanged Y zeolites at two different sites, SII and SIII, with different Si/Al ratios. An η 2 -coordination of benzene to copper was observed for all adsorption complexes. After adsorption, the 3-fold coordination of Cu to framework oxygens is reduced to 2-fold at site SII, whereas 2-fold coordination prevails at site SIII. Benzene binds with Cu more strongly at SIII than at SII. The calculated frequency shifts are slightly overestimated compared to experiment. Population analysis reveals that 3dπ back-donation from Cu dominates over pπ donation from benzene. Comparison between experimental and theoretical results allows for the prediction of the preferred benzene-copper adsorption complexes, which may be of importance in the catalytic phenol formation from benzene and dioxygen using copper-containing zeolites.

Interaction of benzene with hydroxyl groups in zeolites: A FTIR study of C6H6 and C6D6 adsorption on H-ZSM-5 and D-ZSM-5

“…However, the 3670 cm À1 OH band in FAU zeolite is shifted by benzene to one band at 3450 (Dm = 220 cm À1 ) [33]. Evidently, in this case the wavenumber of the shifted OH band is too high in order Fermi resonance to occur.…”

Monomer- and polymer radicals of vinyl compounds: EPR and DFT studies of geometric and electronic structures in the adsorbed state

“…zeolites, alumina, aluminosilicalites or higher-order oxides are attractive materials in numerous applications in catalysis. Previous research has shown that those materials play a significant role in the separation and stabilization of various reactive intermediates as atoms, radicals, radical ions, and clusters [1][2][3][4][5][6][7]. Studies of such intermediates are very important for a better understanding of the mechanisms of chemical reactions in polymerization, heterogeneous catalysis, photochemistry, and radiation chemistry and biology.…”

“…The latter spectrum was assigned to the radical CH 3 Ċ α HC 6 an averaging due to the free rotation usually occurring along the >C α -CH 3 bond in this type of radicals [42]. The anisotropy of the methyl coupling was somewhat averaged by the rotation to become axially symmetric.…”

Removal of Toluene over NaX Zeolite Exchanged with Cu2+

“…The difference between samples could be attributed not only to a difference in the copper content, but also to the difference in their textural properties. Archipov et al [34] studied the adsorption of benzene in copper-exchanged Y zeolites, using Fourier transform infrared spectroscopy; the authors found that benzene adsorbed on both copper and brønsted acid sites of the zeolite, but preferentially on copper site. With the assumptions of a similar behavior for the toluene-zeolite system, it can be expected that the copper-exchanged samples exhibit higher capacities of adsorption in comparison to the NaX zeolite.…”