Stéphane Walspurger

Quantitative Determination of Brönsted Acid Sites on Zeolites: A New Approach Towards the Chemical Composition of Zeolites

An original quantitative method based on H/D exchange between H2O/D2O molecules and the OH groups of different zeolites has been developed for the titration of the Brönsted acid sites present on the solid surface. The measured Brönsted acid sites density appears to be in good agreement with the theoretical amount estimated by the Si/Al ratio. In contrary to classical methods, this non-destructive anhydride method titrates the whole quantity of Brönsted acid sites of zeolites.

Room-Temperature Alkane Reactivity in Zeolites: An H/D Exchange Study

As evidenced by H/D exchange with acidic zeolites, isoalkanes react readily at room temperature whereas linear alkanes do not. The observed regioselectivity of the exchange process demonstrates that the main factor controlling the reaction is not the accessibility to the acid sites, but the intrinsic reactivity of the alkane. The mechanism is best rationalized by classic organic chemistry involving carbocationic intermediates including the Markovnikov rule.

Innovative tool for determining the number of brönsted acid sites in solid acids: towards the chemical compos ion of zeolites

An original quantitative method based on H/D exchange between H 2 O/D 2 O molecules and the OH groups of different zeolites has been developed for the titration of the Bronsted acid sites present on the solid surface. The measured Bronsted acid sites density appears to be in good agreement with the theoretical amount estimated by the Si/Al ratio. Therefore, from the decrease in the total number of Bronsted acid sites, we have found an innovative approach to determine both the amount and the localisation of Mo atoms inside the ZSM-5 zeolite framework. A dependeance was found between the decrease of acidic OH groups and the Mo content. Depending on the Si/Al ratio of the zeolite, i.e., the proximity between two Bronsted acid sites, the Mo-atoms substitute a different number of OH groups.