Stretching zeolitic hydroxy groups

Figure 22.4 IR spectrum of and H2 0 adsorbed on H-ZSM-5 (adapted from Fig. 2 in Ref [37]). Shown is the assignment based on frequency calculations for models of the neutral adsorption complex [34]. The overtone of the in-plane SiOH bending ( zqh) hilh ooto the red-shifted OH stretching frequency of the bridging hydroxy group of the zeolite, vOH. ...

Hydroxy Groups of Zeolites Characterized by IR Fundamental Stretching Bands... 

Fig. 28. The normal modes (v stretching, 6 in-plane, and y out-of-plane bending modes) of a bridging hydroxy group of a zeolite structure...

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. 

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