Oxidative regeneration of toluene-saturated natural zeolite by gaseous ozone: The influence of zeolite chemical surface characteristics

Abstract

In this study, the effect of zeolite chemical surface characteristics on the oxidative regeneration of toluene saturated-zeolite samples is investigated. A Chilean natural zeolite (53% clinoptilolite, 40% mordenite and 7% quartz) was chemically modified by acid treatment with hydrochloric acid and by ion-exchange with ammonium sulphate. Thermal pre-treatments at 623 and 823K were applied and six zeolite samples with different chemical surface characteristics were generated. Chemical modification of natural zeolite followed by thermal out-gassing allows distinguishing the role of acidic surface sites on the regeneration of exhausted zeolites. An increase in Brønsted acid sites on zeolite surface is observed as a result of ammonium-exchange treatment followed by thermal treatment at 623K, thus increasing the adsorption capacity toward toluene. High ozone consumption could be associated to a high content of Lewis acid sites, since these could decompose ozone into atomic active oxygen species. Then, surface oxidation reactions could take part among adsorbed toluene at Brønsted acid sites and surface atomic oxygen species, reducing the amount of adsorbed toluene after the regenerative oxidation with ozone. Experimental results show that the presence of adsorbed oxidation by-products has a negative impact on the recovery of zeolite adsorption capacity.

Simultaneous phosphate and ammonium removal from aqueous solution by a hydrated aluminum oxide modified natural zeolite

“…The small differences in the spectra for Z-N ( Figure S3a) and Z-Na ( Figure S3b) are consistent with the ion exchange reactions between cations of the same valence [35]. Contrary, after the modification with a trivalent cation (Al (III)) important changes in the zeolite structure are observed on the Z-Al spectra ( Figure S3c), with new peaks at 1396 cm -1 , 1455 cm -1 and 1541 cm -1 associated with the presence of the surface hydroxide groups (≅AlOH) [36][37][38]. The shift of the band at ~3396 cm -1 in the Z-N spectra and the new band at 3616 cm -1 on Z-Al spectra are attributed to hydroxyl groups associated with tetrahedral framework aluminum and octahedral non-framework aluminum oxide species [39,40].…”

Influence of Chemical Surface Characteristics of Ammonium-Modified Chilean Zeolite on Oak Catalytic Pyrolysis

“…Then, generated species from biomass pyrolysis can reach Brønsted acid sites without difficulty, resulting in new species after an absorbate-site interaction. The contribution of a lower composition of compensation cations to a higher diffusion into Chilean natural zeolites pores was reported elsewhere [41]. However, a higher composition of phenols was observed in obtained bio-oil, using NHZ sample, which is probably due to the lower Brønsted acid site density of this sample and a channel blockade as a result of applied chemical treatment.…”

Gaseous ozone decomposition over high silica zeolitic frameworks

“…Concerning Brønsted acid sites, both kinds of ZSM‐5 samples have a lower concentration than H‐FAU and H‐MOR zeolites. However, it has already been reported that these sites are not active for ozone decomposition …”

“…The concentration of Lewis acid sites and Bronsted acid sites were calculated by evaluating the amount of remaining pyridine after the applied thermal desorption procedure by the integration of the IR bands at 1444–1454 cm −1 and 1545 cm −1 , using 1.28 cm · mol −1 and 1.13 cm · mol −1 as molar absorption coefficients, respectively . Detailed information on the procedures and calculations can be found elsewhere …”