Zeolite OH groups

The reaction scheme can be divided into primary reaction, involving accessible zeolitic OH-groups ... 

Cumene interacts more strongly than benzene with zeolite OH groups. At higher temperatures cumene decomposition is revealed by the formation of surface species similar to those found for propene. 

The reactivity of the positively charged protonating agents is substantially higher than that of the neutral zeolite OH groups [60]. 

The strength of the interaction of a guest molecules (probe, reactant, product, adsorbate) with a Bronsted acid site is mainly determined by the acidity of the OH group and its accessibility. The acidity of zeolite OH groups can be affected by various factors, most of them studied both experimentally and computationally [126,127] (i) the aluminum content of the zeolite framework ... 

Zeolite OH groups (mmol/g) metal cation (wt.%) conversion (%) p-ET coke amount selectivity (mg/g) (wt.%) ... 

A large reservoir of benzene precursors is also present in the zeolite under steady-state conditions, also strongly interacting with the zeolite OH groups. From the sequence observed during the start-up period, benzene appears as a secondary product formed from ethylene on the acid sites of the zeolite. 

An in-situ DRIFTS study of a Fe-ZSM-5 catalyst during the selective catalytic reduction of NO by isobutane is reported. The catalyst was prepared by vapour-phase exchange of H-ZSM-5 with FeCb- Catalytic data from in a micro-catalytic flow reactor have been in principle reproduced by using the DRIFTS cell as a flow reactor. Adsorbates, transient intermediates, and interactions of zeolite OH groups have been monitored at 873-523 K, with concomitant NO conversion measurement. It has been found that the spectra of deposits formed on H-ZSM-5 and Fe-ZSM-5 are identical at 523 K. In formation about the deposits obtained at 523 K was not representative for the temperature of peak NO conversion... 

The interpretation of the above IR results of the H20/zeolite system was supported by inelastic neutron scattering (INS) studies by Jobic et al. [658] of H2O adsorbed on hydrogen mordenite. These experiments were carried out in the range below 2000 cm. Activated and water-free H-mordenite gave INS bands at 320 and 1060 cm. On the basis of quantum mechanical calculations, these were assigned to the out-of-plane (yoh) and in-plane (6oh) deformation vibrations of the zeolitic OH groups, since these were predicted at 322 and 1047 cm". On... 

Jacobs et al. [724] introduced the FTIR measurement of the shift of the OH stretching band upon benzene adsorption as a measure of the acid strength of the hydroxy groups. Jacobs [725] also provided a theoretical reasoning for this effect. Similarly, O Malley [794] developed an electrostatic model for predicting the shift of typical IR bands upon adsorption of aromatics on the respective zeolitic OH groups. 

Adsorption of CD3CN on zeolites allows detection of the y(OH) modes of the zeolitic OH groups because they are shifted to higher frequencies and move out of the region of strong framework absorption (366). The intensity of these vibrations decreases with the increase of the strength of the H-bond formed. 

The same mechanism was later on adopted for NO interaction with other zeolitic OH groups, including those in BEA (488), PER (489,490), MOR (491,492), and SSZ-13 (493). It was also reported that the N—O stretching frequency depends on the basicity of the oxygen to which the NO cation is bound, and it was proposed that l>(NO) could be used to estimate surface basicity (494). 

Ballivet-Tkatchenko et al. [51] observed similar infrared evidence for hydrogen bonding interactions between zeolite OH groups and dusters believed to be [H2Fe3(CO)ii], formed from [Fe3(CO)i2] in the HY zeolite by heating to 60 °C. 

Stack plot of the MAS NMR spectra at 558 K of methane-kinetic curves (right) for H/D exchange of methane-d, with zeolite OH groups. The first spectrum (bottom) was recorded 5 min after the temperature was raised and equilibrated at 558 K and the last spectrum (top) after 4110 min of the reaction duration. The time between subsequent spectra... 

Number of Cu cations related to the original number of the zeolite OH groups (0.91 mmol per gram dry zeolite) m, cation valency. 

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