Water: A promoter of ammonia selective catalytic reduction over copper-exchanged LTA zeolites

Dealumination of the H-BEA Zeolite via the SN2 Mechanism: A Theoretical Investigation

“…In principle, the dealumination process of the zeolite occurs through a sequence of hydrolysis reactions for four Al–O Al –Si bonds at the BAS . With the help of density functional theory (DFT) calculations, , ab initio molecular dynamics (AIMD) simulations, and enhanced sampling technology, a series of states and processes have been identified and quantified in the dealumination process. For example, Silaghi et al found that the vicinal disilanol defect is an important intermediate state in the first hydrolysis step.…”

Review of the application of Cu-containing SSZ-13 in NH3-SCR-DeNOx and NH3-SCO

“…When NH 3 is present in the feed, solvation of Z 2 Cu with NH 3 is preferred rather than with H 2 O, 158–160 leading to the formation of Cu–amine coordination complexes, i.e. , the principal active sites in the redox cycle.…”

In situ spectroscopic studies of the effect of water on the redox cycle of Cu ions in Cu-SSZ-13 during selective catalytic reduction of NOx

“…[11][12][13] Nonetheless, it has been recently suggested that water can influence the NH 3 -SCR activity of Cu-zeolite catalysts because water can change the coordination chemistry of Cu ions in the zeolite cage. [15][16][17] In our previous report, we have suggested that this change in coordination chemistry enhances the mobility and proximity of Cu ions, which is closely related to the formation of dimeric Cu intermediates ([Cu I (NH 3 ) 2 ] + -O 2 -[Cu I (NH 3 ) 2 ] + ). 3,4,17 In this study, we investigated the effect of water on the NH 3 -SCR redox cycle of Cu ions.…”

“…The water molecules have been proposed to solvate the Cu ions and liberate them from the zeolite framework by weakening the cation-zeolite interaction. 15,17,20 The ionic Cu species with a higher mobility in the CHA cage provides enhanced proximity between two Cu ions, which can promote the formation of dimeric Cu intermediates ([Cu I (NH 3 ) 2 ] + -O 2 -[Cu I (NH 3 ) 2 ] + ) proposed as an active species in the redox cycle of the NH 3 -SCR reaction. Therefore, although the addition of water increases the apparent activation energy, which negatively influences the reaction kinetics, the promoted formation of reaction intermediates can result in a much larger entropic advantage illustrated by the pre-exponential factor in the Arrhenius plots (Fig.…”

“…3,15,17,21 Consequently, the solvation effect by water promotes the redox cycle of the NH 3 -SCR reaction, improving the overall reactivity of the Cu-SSZ-13 catalyst. 15,22 We used in situ diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS) to observe the catalyst surface during reaction at 250 1C (Fig. S5, ESI †) and to interrogate the effect of water on the NH 3 -SCR reaction over Cu-SSZ-13.…”