Studies on the acidity of mordenite and ZSM 5. 1. Determination of Broensted acid site concentrations in mordenite and ZSM 5 by conductometric titration

Abstract

The Bronsted acidity of H-mordenite and H-ZSM-5 samples of varying proton concentration has been studied using aqueous conductometric titration, IR spectroscopy, and aqueous potentiometrictitration. Good agreement is observed between Bronsted acid site concentrations determined by conductometric titration and IR measurements, while indirect potentiometric titration affords acid site concentrations consistently lower than those measured using the conductometric technique. This finding is rationalized on the basis that, in a conductometric titration, all the accessible Bronsted acid sites are directly titrated, whereas in the potentiometric procedure utilized, only those protons which can be ion-exchanged out of the zeolite are titrated. After allowing for the presence of extraframework aluminum in the zeolites (determined by27Al NMR), the measured acidity for H-mordenite is found to increase linearly with increasing Al content within the range 0-1.5 mmol Al/g but appears to reach a limiting value at higher Al concentrations. For H-ZSM-5, the experimentally determined number of Bronsted acid sites is also found to be linearly dependent on the Al molar fraction within the range measured (0-1.20 mmol Al/g). For both series of zeolite samples, the measured acidity is generally found to be less than the theoretical maximum calculated on the basis of an H+/Al ratio of 1.

Exploring the Regeneration of Mordenite Catalyst in Dimethyl Ether Carbonylation Reaction

“…As it can be seen, these values range from 2.09 to 2.29 mmol/g, which confirm that DME adsorption capacity of the catalyst remained almost intact. It has been reported that conductometric titration is a reliable method for determination of BAS concentration in acidic zeolites like ZSM5 and mordenite (Crocker et al, 1993). Furthermore, it was confirmed that the strong base utilized in this analysis does not neutralize extra-framework Al species in mordenite (Mohammadi and Zanjanchi, 2001), so a straightforward quantification of total BAS (i.e.…”

Fast energy delocalization upon vibrational relaxation of a deuterated zeolite surface hydroxyl

“…8 Recently, the acidity of the zeolite Mordenite has been the subject of much research. [9][10][11][12][13][14] In order to gain better insight into the dynamics of vibrational relaxation and the properties of this surface hydroxyl, we performed a time-resolved vibrational study of deuterated hydroxyls.…”

Carbon Dots as Nano-Organocatalysts for Synthetic Applications

“…2,46,66 Conversely, the carboxyl and hydroxyl groups can be recognized by infrared spectroscopy (FT-IR) and quantified by acid-base or conductometric titrations. 40,[67][68][69] Furthermore, the surface group density and the pyrolytic behavior of CDs at high temperatures may be roughly valued by thermogravimetric analysis (TGA), correlating the mass loss at a certain temperature to the uniformity of functionalities on the CDs surface. 70,71 With all of these pieces of information in hand, it becomes feasible to figure out the range of catalytic use of the considered CDs, and ultimately to estimate the catalytic loading with respect to the referred functional groups.…”

“…Aiming at a systematic development of all of these chemical processes, it is imperative to identify the typology and the amount of catalytically active functionalities on the CD surface. Therefore, as an example, amino groups can be detected by X-ray photoelectron spectroscopy (XPS) and quantified by Kaiser test (KT) or by nuclear magnetic resonance (NMR) upon the formation of covalent adducts (e.g., imines). ,, Conversely, the carboxyl and hydroxyl groups can be recognized by Fourier transform infrared spectroscopy (FT-IR) and quantified by acid–base or conductometric titrations. ,− Furthermore, the surface group density and the pyrolytic behavior of CDs at high temperatures may be roughly valued by thermogravimetric analysis (TGA), correlating the mass loss at a certain temperature to the uniformity of functionalities on the surface of CDs. , With all of these pieces of information in hand, it becomes feasible to figure out the range of catalytic use of the considered CDs and ultimately to estimate the catalytic loading with respect to the referred functional groups.…”