Hierarchical CHAbazite core-shell catalysts for Reduction of NOx and N2O – CHARO

Hierarchical CHA-based zeolite catalysts were synthetized, characterized and tested for NH3-SCR of NOx. Different synthesis conditions such as preparation method, aging time and secondary organic structure direct agent amounts were evaluated. In order to probe hydrothermal stability, the developed hierarchical CHA-based catalyst was further treated in air with 10% H2O at 750°C for 16h.

- Pure and crystalline hierarchical materials and Cu-based hierarchical catalysts were successfully developed, characterized and tested for NH3-SCR of NOx;
- The original zeolite structure is maintained after the introduction of the mesoporous template;
- A significantly increased external surface area and mesoporous volume was observed for hierarchical materials, comparing to the microporous zeolite;
- BET specific surface area similar to that of microporous zeolite;
- The existence of intracrystalline mesoporosity was corroborated;
- The zeolite crystalline structure is maintained after hydrothermal treatment and no collapse of the crystalline structure or leaching of Cu was observed.
- The hydrothermal treatment favored the Cu migration to the active sites within chabazite structure, which could significantly improve NOx reduction performances at low temperature ;
- However, the hydrothermal treatment had a strong influence on textural properties.

The formation of a hierarchical zeolite-zeolite core-shell structure is in progress. We anticipate that such structures will prevent the collapse of the mesoporous zeolite structure, maintaining the crystallinity and morphology of the zeolite core.

A publication of scientific article is in progress. These results were presented in French Conference on Catalysis (FCCAT 2019), Frejus, France, 3-7 June 2019 – Oral presentation entitled “Development of Hierarchical chabazite for low-temperature NOx reduction”. Moreover, the results associated to the “Hydrothermal durability of developed catalysts” is accepted as a short oral presentation in French Conference, Gecat-2020, 3-6 November 2020, Hendaye, France.

The reduction of atmospheric pollution from stationary and mobile engines is a serious challenge associated with stringent environmental regulations. In this respect, revisiting after-treatment systems under the prism of disruptive concepts may significantly improve their eco- and health-friendliness. This is the standpoint of this project, which ambitions to develop novel catalysts combining several functionalities in extended ranges of operating conditions. The project will address some of the main pollutants produced by stationary and mobile sources, such as nitrogen oxides (NOx) and nitrous oxide (N2O). Their abatement will be explored via the ubiquitous selective catalytic reduction reaction using ammonia (NH3-SCR) as a selected model reaction. The primary (not exclusive though) application of the project will be the treatment of exhaust gases from automotive lean engines operating with diesel and gasoline direct injection.

For this propose, we propose to use small pore sizes zeolites, so-called chabazites known to be highly efficient and hydrothermally stable molecular sieves, but so far authorizing only limited gas diffusion in operation conditions typical of modern engine exhaust system. To reach high performance, selectivity and stability, the project targets hierarchical materials allowing efficient gas diffusion through mesopores, and synergy at the nanoscale between copper and iron sites in core-shell structures. This is, to our knowledge, a unique architecture, more advanced compared to the one, recently developed at Beijing University for the SCR reaction, that comprises only an active core (T. Zhang et al., Appl. Catal. B 195 (2016) 48). First, this combination is expected to enlarge the temperature window of efficient activity, from 150 to 800°C. This will make the catalytic system compatible with both low-temperature operation such as needed in cold-start systems and high temperature hydrothermal stability such as needed for regeneration of particulate filter. Second, this combination offers a synergetic abatement of both NOx and N2O, with the copper and iron phase being specifically selective to each of these gases. This latter feature is especially valuable in view of foreseeable Euro 7 regulations planned in 2022 that will concern NOx and N2O emissions.

Four scientific work-packages are proposed to reach the objectives. They are interconnected and will drive us step-by-step to the preparation of the unique and advanced core-shell hierarchical architectures and to the quantitative assessment catalytic performances, hopefully to qualify them for industrial applications. A complementary in-situ characterization of the novel catalysts will be also performed, using Environmental tomographic Transmission Electron Microscopy (Et-TEM), a powerful in-situ method available at IRCELYON, and Diffuse Reflectance Infrared Fourier-Transform Spectroscopy (DRIFTS), to understand the dynamical properties of the catalyst at the smallest scales, and to unveil the mechanistic of the catalytic processes.

The young researcher and coordinator was appointed at IRCELYON in 2014 as an assistant professor. She is willing to devote 75% of her time on the project. The project will allow her to initiate an original line of research at IRCELYON focalized on the development of hierarchical based-zeolites and sophisticated core-shell structures for automotive catalytic post-treatment but also for new reactions of interest such as the N2O decomposition/reduction, mild oxidation (CH4 to CH3OH) and CO2 hydrogenation. The project will besides put her at the center of a focused collaboration network with industrial actors and academic research groups in France, Spain and Italy. This first national-scale funding will mark the starting point of her carrier as an independent researcher, which will be supported by a unique combination of techniques available at IRCELYON and the complementary competences of the scientific team.