| AVS 65th International Symposium & Exhibition | |
| Fundamental Discoveries in Heterogeneous Catalysis Focus Topic | Thursday Sessions |
| Session HC-ThP |
| Session: | Fundamental Discoveries in Heterogeneous Catalysis Focus Topic Poster Session |
| Presenter: | Alba Cabrera-Codony, University of Girona, Spain |
| Authors: | A. Cabrera-Codony, University of Girona, Spain E. Santos-Clotas, University of Girona J. Martin, University of Girona |
| Correspondent: | Click to Email |
Different types of both natural and synthetic zeolites, covering a wide range of physical and chemical properties, were evaluated as adsorbents/catalyst for siloxane removal in lab-scale gas phase adsorption tests of octamethylcyclotetrasiloxane (D4). After bed exhaustion, wet oxidation processes were used for the regeneration of the spent zeolite samples, including ozonation and Fenton-like treatment of the Fe-amended zeolites using hydrogen peroxide. New adsorption tests were performed after theses AOP-driven regeneration processes.
The results on the uptake of gaseous D4 by various zeolites led to the conclusion that BEA type materials presented the highest catalytic activity for the siloxane ring-opening and formation of α -ω -silanediols due to the high content of Bronsted and Lewis acidic sites. Those silanediols formed on the BEA surface were detached from the catalytic acidic sites when water was available, and were narrow enough to diffuse into the channels, hence enhancing the removal efficiency for D4.
The water soluble α -ω -silanediols formed by the catalytic activity of the iron exchanged Fe-BEA type zeolites during D4 adsorption were easily removed by wet regeneration treatment with water, however, the regeneration was incomplete, i.e. the adsorption capacity was partially recovered. Adding H2O2 in a heterogeneous Fenton-like regeneration treatment led to a complete recovery of the adsorption capacity of the Fe-zeolites samples.
However, on successive adsorption/regeneration cycles, the recyclability of the Fe-zeolites catalysts was hampered by the accumulation of carbonaceous materials on the material surface, which caused a loss of the catalytic activity, affecting both the adsorption and the regeneration stages.
Bronsted acidic sites (BAS) and Lewis acidic sites (LAS) promoted the D4 transformation into silanediols, as shown in Figure 1, which was the fundamental step that ruled the D4 uptake on the gas adsorption process. At the same time, the iron exchanged in Fe-BEA type zeolites promoted the catalytic activity towards Fenton-like reactions for the regeneration of the exhausted materials.