CTAB-templated mesoporous TS-1 zeolites as active catalysts in a desulfurization process: the decreased hydrophobicity is more favourable in thiophene oxidation

Abstract

Mesoporous TS-1 zeolites (MTS-1) were prepared through direct hydrothermal treatment by using CTAB as the mesoporogen under the assistance of ethanol, and they demonstrated much higher catalytic activity and better recyclability in thiophene oxidation, due to the decreased hydrophobicity and mesoporous structure.New regulations for ultra clean oils with a sulfur content lower than 15 or 10 ppm have been mandated in United States and European countries for environmental protection, respectively. Similarly this year, China has implemented the Euro 5 (10 ppm) standard in some big cities like Beijing. Thus, the production of ultra clean oils is an urgent mission for oil industries. However, the cost to reduce the sulfur content from 500 ppm to 15 ppm is much higher than that needed in desulfurizing crude oils to 500 ppm, by using present technologies like hydrodesulfurization (HDS) process. 1,2 The presence of ''inactive sulfur'' like thiophene and its derivates (benzothiophenes and dibenzothiophenes) are refractory and always need treating in fuels under high pressure of hydrogen at elevated temperatures in the HDS process. 2,3 Hence, oxidative desulfurization (ODS), biodesulfurization, ultrasoundassisted technique and solvent extraction have been proposed to meet the stringent regulations. 1,3-5 Among them, oxidative desulfurization which has been developed for about 10 years, combined with solvent extraction, are one of the most promising techniques to obtain ultra-clean oils or even ''zero-sulfur'' oils, and have gained great interest in the past few years. 1,3,6 Benzothiophene (BT), dibenzothiophene (DBT) and their corresponding alkyl-substitutes with high electron density of sulfur atoms, could be oxidized into corresponding sulfones through various reaction systems, such as organic peracids, 7,8 H 2 O 2 / tungsten salts, 9 t-butylhydroperoxide/transition metaloxides, 10 H 2 O 2 /solid redox catalysts, 11-13 and H 2 O 2 /tungsten/ionic liquids complexes. 14,15 However, thiophene, another major source of sulfur compounds in oils, is highly stable and difficult to be oxidized due to the delocalization effect of its electrons. 4,16 The electron density of the sulfur atom in thiophene is as low as 5.696, which cannot meet the lowest standard between 5.716 and 5.739 for sulfoxidation by using hydrogen peroxide as oxidants. 8 Thus, the oxidation of thiophene is much more difficult than either BT or DBT, or their derivates. A large number of literatures have demonstrated that Ti-containing molecular sieves (Ti-Beta and Ti-HMS) combined with H 2 O 2 are active and environmental friendly in the oxidation of BTs and DBTs. 11,[17][18][19] Among them, titanium silicalite-1 (TS-1) zeolites, because of its superior hydrophobicity and intrinsically higher catalytic activity than Ti-Beta, is on the top of a few highly active catalysts in thiophene oxidation. [20][21][22][23][24][25] With the incorporation of Ti into a MFI framework, TS-1 zeolites are crystalline with an extensive microporosity of about 0.55 nm in pore diameter...

Deep oxidative desulfurization of dibenzothiophene using low-temperature-mediated titanium dioxide catalyst in ionic liquids

“…To achieve ultra-low sulfur fuels, http severe processing conditions such as elevated temperature and high hydrogen pressure were required in the HDS process [7,8]. Then, as a complementary technology of HDS, oxidative desulfurization (ODS) has been extensively researched [9][10][11][12][13]. No hydrogen was consumed in the ODS system, where could achieve the purpose of deep desulfurization under mild reaction conditions [14].…”

Synthesis and Characterisation of Hierarchically Structured Titanium Silicalite‐1 Zeolites with Large Intracrystalline Macropores

“…[8] The resulting hierarchically structured zeolites combine the stabilitya nd shape selectivity of the micropores with the improved mass transport properties of meso-o rm acropores.H ierarchically structuredT S-1 zeolites have already demonstrated superior catalytic performance in differentr eactions, such as hydroxylation of phenol, [9] epoxidation of 1-octene, [10] epoxidation of cyclohexene [11] and oxidation of thiophene. [12] The preparationo fh ierarchically structured zeolites has been subject to research for many years and can be divided into top-down and bottom-up processes.…”

“…[9,13] Soft templating typically utilises surfactants or organosilanes during the synthesis of the titanium-containing zeolite to generate mesopores. [12,14] Nanosized TS-1 crystalsh ave also been used for the preparation of hierarchical materials by self-assembly. [15] Another synthesis approach is the use of silanised proto-zeolitic units for the synthesis of hierarchical TS-1 zeolitesd eveloped by Serrano et al [16] The top-down preparation routes for hierarchically structured TS-1 consist mostly of post-synthetic demetallation treatment in alkaline or fluoride mediat og enerate mesopores by extraction of framework atoms.…”

Development of an Analytical Method for Evaluating the Catalytic Active Sites of Titanium Silicalite Zeolite

“…Titanium silicalite-1 (TS-1) was first reported by Taramasso in 1983 [1], which belonged to the MFI structure group. TS-1 possesses interesting catalytic properties, especially in reaction involving the use of H 2 O 2 as the oxidant, such as the hydroxylation of phenol [2]- [5], thiophene oxidation [6], epoxidation of cyclohexene [7], epoxidation of styrene [8], cyclohexane oxidation [9], epoxidation of propene [10] [11], ammoximation of cyclohexanone [12] [13]. Many studies have focused on the catalytic performance of TS-1, however, only a few works have tried to investigate the nature and the properties of the active species formed in TS-1 upon interaction with H 2 O 2 [14]- [16], and not all the framework titanium can contact with substrates quickly, due to the diffusion limitation by the size of the channels (0.56 nm × 0.53 nm).…”