Abstract
Titanosilicate ferrierite zeolite (FER) and its delaminated form (ITQ-6), with various Si/Ti molar ratios, were synthetized and tested as catalysts for diphenyl sulfide (Ph 2 S) and dimethyl sulfide (DMS) oxidation with H 2 O 2 . The zeolites were characterized with respect to their chemical composition (ICP-OES), structure (XRD, UV–vis DRS) and texture (low-temperature N 2 adsorption-desorption). Titanium in the FER and ITQ-6 samples was present mainly in the zeolite framework with a significant contribution of titanium in the extraframework positions. Titanosilicate zeolites of FER and ITQ-6 series were found to be active catalysts of diphenyl and dimethyl sulfides oxidation by H 2 O 2 to sulfoxides (Ph 2 SO/DMSO) and sulfones (Ph 2 SO 2 /DMSO 2 ). The efficiency of these reactions depends on the porous structure of the zeolite catalysts – conversion of larger molecules of diphenyl sulfide was significantly higher in the presence of delaminated zeolite Ti-ITQ-6 due to the possibility of the interlayer mesopores penetration by reactants. On the other side diphenyl sulfide molecules are too large to be accommodated into micropores of FER zeolite. The efficiency of dimethyl sulfide conversion, due to relatively small size of this molecule, was similar in the presence of Ti-FER and Ti-ITQ-6 zeolites. For all catalysts, the organic sulfide conversion was significantly intensified under UV irradiation. It was suggested that Ti cations in the zeolite framework, as well as in the extraframework, species play a role of the single site photocatalysts active in the formation of hydroxyl radicals, which are known to be effective oxidants of the organic sulfides. ⁃ Ti-FER and Ti-ITQ-6 are active catalysts of Ph 2 S and DMS oxidation with H 2 O 2 . ⁃ Delaminated structure of Ti-ITQ-6 is more effective in oxidation of Ph 2 S molecules. ⁃ UV irradiation increases efficiency of diphenyl and dimethyl sulfides oxidation.
Highlights
Zeolites have been known as very important materials for catalysis since their successful application in petrochemistry in the 60’s of 20th century [1]
Delaminated zeolites are characterized by the total pore volume of about 4–6 times larger and micropore volume significantly reduced compared to the Titanosilicate ferrierite (Ti-FER) samples. These results clearly show the successful delamination of Ti-PREFER resulting in Ti-ITQ-6 zeolites
Conversion of Ph2S was more effective in the presence of delami nated Ti-ITQ-6 catalysts microporous Ti-FER
Summary
Zeolites have been known as very important materials for catalysis since their successful application in petrochemistry in the 60’s of 20th century [1]. The specific layered structure of PREFER gives an opportunity to obtain delaminated zeolitic materials, characterized by the hierarchical microporous and mesoporous structure [3] Such delaminated zeolitic materials, called ITQ-6, and microporous FER are very interesting as catalysts or catalytic supports for various chem ical process [4]. A very important advantage represented by ITQ-6 is its delaminated structure consisting of larger pores located between chaotically arranged zeolite layers and micro pores inside zeolite layers Such hierarchical porous structure was re ported to be effective in the conversion of bulkier molecules due to reduced internal diffusion restrictions of reactants. These studies were extended for titanosiliate zeolites, Ti-FER and Ti-ITQ-6, used as catalysts in the process of dimethyl and diphenyl sulfides oxidation using hydrogen peroxide as an oxidant with and without UV irradiation
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