A Density Functional Theory Study of Molecular and Dissociative Adsorption of H2 on Active Sites in Mordenite

In situ FTIR spectroscopy to unravel the bifunctional nature of aromatics hydrogenation synergy on zeolite/metal catalysts

The hydrogenation of pyridine adsorbed on zeolite is dependent on the distance between acid and metal sites. Hydrogen species produced in the metal diffuse into pyridine and promote hydrogenation, suggesting a bifunctional mechanism is occurring.

A comparative computational study on hydrogen adsorption on the Ag(+), Cu(+), Mg(2+), Cd(2+), and Zn(2+) cationic sites in zeolites

In this article the interaction between H2 and Ag(+), Cu(+), Mg(2+), Cd(2+), and Zn(2+) cations in cluster models of several sizes has been studied computationally. Depending on the changes imposed by the adsorption process on the H2 molecule the activation can vary in a wide range - from only slight weakening of the H-H bond to complete dissociation of the H2 molecule. The NOCV (Natural Orbitals for Chemical Valence) analysis allowed for decomposition of the electron density distortion into contributions easier for interpretation. Three essential factors have been identified (i-iii). In the case of bare cations the main contribution is a donation from σH2 to the cation (i). When a zeolite framework surrounding the cation is introduced, it hinders σ-donation and enhances π-backdonation from the cation to the antibonding orbital of the molecule (ii). For Cu(i) and Ag(i) sites π-backdonation becomes dominant, while for Mg(ii), Cd(ii), and Zn(ii) cations, the σ-donation, albeit diminished, still remains a dominant contribution. Calculations showed that the localization and coordination of Zn(ii) have crucial influence on its interaction with H2. We identified a Zn(2+) position at which the H2 molecule dissociates - here the interaction between H2 and oxygen framework (iii) plays a crucial role. Based on the calculations the mechanism of H2 transformation has been proposed. Upon heterolytic dissociation of H2 the Zn(0) moiety and two OH groups can be formed. Eventually, in two elementary steps, the H2 molecule can be restored. In this case, the ability of the site to activate/dissociate hydrogen is caused by the low coordination number of the zinc cation and the geometry of the site which allows positively charged H2 to interact with framework oxygen what enhances the formation of OH and Z-O-(ZnH)(+) groups.

Influence of inlet gas composition on dimethyl ether carbonylation and the subsequent hydrogenation of methyl acetate in two-stage ethanol synthesis

A two-stage reactor loaded with HMOR and Cu/SBA-15 separately was used to improve indirect ethanol synthesis.

Impact of the Si/Al ratio on the selective capture of iodine compounds in silver-mordenite: a periodic DFT study

Decreasing the Si/Al ratio in silver exchanged mordenite drastically limits the potential inhibiting effect of H₂O and CO on the adsorption of I₂ and ICH₃, and allows a spontaneous dissociation of I₂ leading to the formation of AgI complexes.

FTIR spectroscopic and computational studies on hydrogen adsorption on the zeolite Li–FER

The interaction, at a low temperature, between molecular hydrogen and the zeolite Li-FER was studied by means of variable temperature infrared spectroscopy and theoretical calculations using a periodic DFT model. The adsorbed dihydrogen molecule becomes infrared active, giving a characteristic IR absorption band (H-H stretching) at 4090 cm(-1). Three different Li(+) site types with respect to H(2) adsorption were found in the zeolite, two of which adsorb H(2). Calculations showed a similar interaction energy for these two sites, which was found to agree with the experimentally determined value of standard adsorption enthalpy of DeltaH(0) = -4.1 (+/-0.8) kJ mol(-1). The results are discussed in the broader context of previously reported data for H(2) adsorption on Na-FER and K-FER.