Characterizing Zeolite Acidity by Spectroscopic and Catalytic Means:  A Comparison

Abstract

Adsorption of H 2 , N 2 , and CO on four different protonated zeolitessH-ZSM-5, H-β, H-Y, and dealuminated H-Ysat low temperatures was studied by transmission Fourier transform infrared spectroscopy. The introduction of the basic probe molecules caused a red-shift of the IR stretching bands of the zeolitic acidic OH groups. This perturbation, which is commonly interpreted as a hydrogen bonding between the acidic OH group and the adsorbate and often taken as a measure of the acidic strength, was then compared with intrinsic activities for the acid-catalyzed cracking of n-hexane previously published for the same zeolite samples. Catalytic and spectroscopic characterization of the acidity is consistent only within the same class of zeolites, e.g. comparison of differently pretreated faujasites. Spectroscopic and catalytic observations for different types of zeolites do not match perfectly, because additional effects, such as interactions of larger molecules with pore walls and the stabilization of transition states and intermediates, can influence the course of an acid-catalyzed reaction.

Revealing Shape Selectivity and Catalytic Activity Trends Within the Pores of H‐ZSM‐5 Crystals by Time‐ and Space‐Resolved Optical and Fluorescence Microspectroscopy

“…More specifically, IR spectroscopy of probe molecules adsorbed on powdered H-ZSM-5 samples has been used to relate Brønst-ed acid-base properties with activity in hydrocarbon cracking. [4] Taking the channel accessibility into consideration, the tapered element oscillating microbalance (TEOM) technique has been utilized to determine the uptake of different hydrocarbons into the pore system of H-ZSM-5, revealing fundamental insight into their diffusion properties. [5,6] However, as those methods are bulk techniques, they provide averaged information over the entire catalyst sample.…”

Zeolite Nanocrystals Inside Mesoporous TUD‐1: A High‐Performance Catalytic Composite

“…This suggests that the presence of hydrogen-bonded silanols is more relevant in these materials. Beside isolated and vicinal silanols, two types of Brønsted acid sites are found in the composites: 1) hydroxyl groups linked to partially extra-framework aluminum ions (structure B) that absorb at 3660-3670 cm À1 ; [21,22] 2) bridged hydroxyl groups (structure C) [21][22][23][24] at around 3620-3580 cm…”

Formation of Reinforcing Inorganic Network in Polymer via Hydrogen Bonding Self-Assembly Process

“…[47][48][49][50][51] Typically, the formation of hydrogen bond would cause red or blue shift of the absorptions for the groups neighboring the hydrogen bonds. [47][48][49][50][51] In order to eliminate the disturbance of PP molecules in the FTIR investigation, the ATR-FTIR of the HNTs and HNTs/MEL mixtures were performed and the results are presented in Figure 8. The peaks between 1000 cm À1 and 1150 cm À1 are assigned to the absorption of Si-O stretching vibrations.…”