Characterization of the acidity of new ZSM-5 zeolites

by complementary spectroscopic and catalytic methods

• Context

Zeolites – a vast family of microporous crystals – are nowadays undergoing a strong resurgence of research (synthesis pathways, properties) in order to extend their performances and industrial applications. Thus zeolites found applications in the fields of ion exchange, adsorption, catalysis, separation and molecular sieves (gases and liquids filtration) The use of organic structure directing agents (OSDA) such as quats (tetraalkylammoniums, see scheme) during the syntheses makes it possible to extend the range of zeolites’ properties. Noticeably, these syntheses can modify the overall acidity but also the strength of the acid sites present in the porosity of these structures. These acidic properties play a key role in many catalytic reactions. More precisely, protonic H-ZSM-5 zeolites are employed in a large number of industrial catalytic applications (fluid catalytic cracking (FCC), methanol to hydrocarbons (MTH) or to olefins (MTO), bioethanol transformation, etc.) but also, modified by a transition metal, for nitrogen oxides abatment from diesel exhaust gases or smokes from combustion processes. For all these processes, the number and the Al site location strongly influences zeolite activity and stability of the catalyst. For example, t he spatial proximity of two or more active sites have a strong impact in acid-catalyzed reactions. Based on this, catalyst performance can be improved by fine control of ZSM-5 synthesis.

The proposed Master II internship is part of the ANR ZEOORG project, the objective of which is to precisely study the nanometric organization of complex zeolites in order to highlight the role of structuring agents and to adjust the final properties accordingly (diagram opposite). To do this, the project brings together experts in the synthesis and characterization of zeolites, solid-state NMR, theoretical calculations and heterogeneous catalysis.

• Master internship

The internship is part of this ANR project and will focus on the characterization of the acid properties of zeolites of MFI topology (ZSM-5), resulting from different syntheses. More concretely, the student will be involved in two main scientific tasks:

1. Characterization of acidic properties by adsorption-desorption of probe molecules (NH3, CD3CN, R3PO) followed by infrared spectroscopy (and NMR in internal collaboration) or katharometric analysis

2. Measurement of catalytic activity in acid-catalyzed reactions such as the reduction of an NO/NO2 mixture by NH3 and the catalytic cracking of n-hexane and 3-methylpentane

This main objective will be completed by other characterizations of these zeolites (XRD, SEM, TGA).

This internship will interest students who want to deepen their knowledge and skills on the synthesis of nanostructured materials and wishing to train in a set of acidity characterization and catalytic reactivity techniques. The active participation of the student in the research and his autonomy in the work will be gradually encouraged.

• Useful information

The internship (syntheses and characterization) will take place at the Institut Charles Gerhardt of Montpellier (France) under the direction of G. Delahay and Hugo Petitjean in close collaboration with Claudia Cammarano and Bruno Alonso.

Contacts: [email protected] / [email protected]https://www.icgm.fr