A computational study on N₂adsorption in Cu-ZSM-5

Abstract

The present computational study investigates the adsorption of N(2) by Cu-ZSM-5, with particular regard to the interaction with pairs of Cu(+) ions, employing simple cluster models in the calculations. It shows that several interaction patterns between N(2) and couples of Cu(+) sites are possible within the Cu-ZSM-5 structure. In particular, when pairs of Cu(+) ions are located at opposite sides of ten-membered rings, in the region where linear and sinusoidal channels intersect each other, a quasi-linear Cu-N-N-Cu adsorption occurs. Although lattice restraints cause small deviations from linearity, such interaction turned out to be more favourable than other adsorption patterns within the Cu-ZSM-5 structure. The linearity of the Cu-N-N-Cu fragment and the relatively low concentration of the related sites cause a low extinction coefficient for the N-N IR stretching mode, which is usually detected with very low intensity or not detected at all. The results of the present calculations may explain the experimental evidence for a nearly IR-silent fraction of nitrogen strongly adsorbed in the Cu-ZSM-5 catalyst which, as shown in a previous work, is linearly related to the number of active sites for NO decomposition.

Cation-exchanged SAPO-34 for adsorption-based hydrocarbon separations: predictions from dispersion-corrected DFT calculations

“…Evidence for Cu 2 2+ dimers has been obtained in previous experimental and theoretical studies, especially for Cu-ZSM-5, where they are believed to play an important role in nitric oxide decomposition: here, previous DFT investigations predicted similarly short Cu + -Cu + distances of about 2.5 Å for some cases. 56,57 The detailed computational study of Cu-chabazite by Go ¨ltl et al also revealed a preference of Cu + (and Cu 2+ , in line with experimental results 58,59 ) for the SII site. 60 However, the aspect of dimer formation was not investigated in that work, which considered a smaller number of cations per cell.…”

Probing Gas Adsorption in Zeolites by Variable-Temperature IR Spectroscopy: An Overview of Current Research

“…It is remarkable that ongoing research carried out by several research groups (see, for instance, [ 68 , 69 , 70 , 71 ]) has shown that several copper-exchange zeolites can convert methane into methanol at a relatively mild temperature (150–200 °C), and there is evidence that in Cu-ZSM-5, the catalytic center involves a μ-oxo dicopper complex [ 72 , 73 ]; however, the mechanistic details are yet to be elucidated. Finally, we wish to mention earlier work by several authors [ 74 , 75 , 76 ] showing that Cu-ZSM-5 adsorbs dinitrogen-forming bridged Cu + ···N-N···Cu + complexes on dual Cu + sites. Moreover, the same dual sites were found to be catalytically active in the decomposition of nitrogen oxides.…”

Organocatalyzed Cascade Reaction in Carbohydrate Chemistry

“…The observed yields in association with the configuration of the corresponding pentoses clearly indicate a correlation with the existence of acyclic structures of the pentoses during the course of the reaction [68,69]. To overcome the problem of low yields of Knoevenagel addition products we tested 2-hydroxypyridine as an additional catalyst, which is known to have a large effect on the anomerization equilibration of carbohydrates by formation of hydrogen bonds [70][71][72][73][74][75][76][77][78]. By increasing the equilibrium constant, a higher amount of active acyclic form is available per defined time-unit.…”