Ti-MWW Catalyst Research Articles

Optimization of a Ti-MWW Catalysed Phenol Hydroxylation Process

AbstractsAs a result of phenol hydroxylation, two useful products can be received: hydroquinone and pyrocatechol. In this work the hydroxylation of phenol with hydrogen peroxide over the Ti-MWW catalyst has been studied. Optimization studies were performed by application of a statistical experimental design method utilizing a rotatable-uniform design. The influence of five parameters on the course of this process was examined: temperature (120-150°C), molar ratio of phenol/hydrogen peroxide (0.5-1.5), acetonitrile - solvent content (20- 50 wt%), catalyst - Ti-MWW content (8-18 wt%) and reaction time (60-120 min). The process description was based on four response functions: the conversion of phenol to organic compounds, the yield of pyrocatechol, the yield of hydroquinone and the conversion of phenol to tars. The most favourable parameters for the process of phenol hydroxylation were as follows: temperature 147-150°C, molar ratio of phenol/hydrogen peroxide 0.5-0.6, acetonitrile content 21-24 wt%, Ti-MWW content 10.3-10.6, reaction time 221-236 min. In summary, these the most favourable parameters allow one to obtain pyrocatechol with the yield of 18 mol%, hydroquinone with the yield of 20 mol%, at the conversion of phenol to organic compounds 38 mol% in relatively mild and safe conditions. These results also showed that Ti-MWWcatalyst can be a good substitute for TS-1 catalyst.

Selective liquid-phase oxidation of allyl alcohol to glycidol over MWW type titanosilicalite

The results of the epoxidation of allyl alcohol with 30% hydrogen peroxide over the Ti-MWW catalyst have been presented. The studies were carried out under atmospheric pressure and in the presence of methanol as a solvent. The influence of the following technological parameters on the course of epoxidation was examined: temperature (20–60 °C), the molar ratio of AA/H2O2 (1:1–5:1), methanol concentration (5–90 wt%), catalyst content (0–5.0 wt%), reaction time (5–300 min) and intensity of stirring (0–500 rpm).

Hydroxylation of Phenol with Hydrogen Peroxide over the Ti-MWW Catalyst in the Presence of Acetonitrile

AbstractThis work presents the results of phenol hydroxylation with hydrogen peroxide over the Ti-MWW catalyst. The studies were carried out under autogenic pressure and in the presence of acetonitrile as a solvent. The influence of the following technological parameters on the course of hydroxylation was examined: the temperature in the range of 100-150 °C, the molar ratio of phenol/H

Catalytic Epoxidation of Allyl Alcohol with Hydrogen Peroxide under Autogenic Pressure over Ti-MWW Catalyst

AbstractThe influence of the technological parameters (temperature (20-100 °C), the molar ratio of allyl alcohol/H

An investigation into cyclohexanone ammoximation over Ti-MWW in a continuous slurry reactor

In the present study, the liquid-phase ammoximation of cyclohexanone with ammonia and hydrogen peroxide was studied using a MWW-type titanosilicate (Ti-MWW) catalyst in a continuous slurry reactor to develop a clean process for producing cyclohexanone oxime. The reaction parameters, which governed the cyclohexanone conversion, oxime selectivity and catalyst deactivation, were investigated by simulating the operating conditions of an industrial process. Under optimized reaction conditions, Ti-MWW produced a cyclohexanone conversion and oxime selectivity over 96% and 99%, respectively. Moreover, Ti-MWW was extremely robust and showed a longer lifetime than the conventional titanium silicalite-1 catalyst. The causes of deactivation were elucidated to be the coke deposition and partial dissolution of the zeolite framework of Ti-MWW during ammoximation. The deactivated Ti-MWW catalyst was regenerated effectively by a combination of acid treatment and cyclic amine-assisted structural rearrangement.

Selective oxidation of pyridine to pyridine- N-oxide with hydrogen peroxide over Ti-MWW catalyst

The oxidation of pyridine to pyridine- N-oxide (PNO) with hydrogen peroxide has been investigated on various titanosilicate catalysts. Superior to other titanosilicates like TS-1, Ti-Beta and Ti-MOR, Ti-MWW showed a higher catalytic activity and product selectivity. The reaction parameters such as solvent, temperature, hydrogen peroxide/substrate ratio, the amount of catalyst and Ti content were optimized to maximize the PNO yield. Ti-MWW was capable of giving pyridine conversion and PNO selectivity both over 99% under optimum reaction conditions. Ti-MWW was a highly active, selective, and reusable catalyst for the synthesis of PNO. The mechanism for the oxidation of pyridine over titanosilicates has also been considered. Ti-MWW was further structurally modified to posses open reaction spaces by interlayer expansion, which reduced the diffusion limitations in the oxidation of pyridine derivatives with bulkier molecular dimensions.

The Ti-MWW catalyst - its characteristic and catalytic properties in the epoxidation of allyl alcohol by hydrogen peroxide

The Ti-MWW catalyst - its characteristic and catalytic properties in the epoxidation of allyl alcohol by hydrogen peroxide Ti-MWW, one of the latest titanium-silicalite catalysts, has been prepared by direct hydrothermal synthesis using hexamethyleneimine as a structure-directing agent. The characteristic of the catalyst was performed by means of the following methods: XRD, SEM, IR, UV-vis and X'Ray microanalysis. The catalytic properties of Ti-MWW have been compared with those of the conventional titanium-silicalites TS-1 and TS-2 in the epoxidation of allyl alcohol with hydrogen peroxide. The process has been described by the following main functions: the selectivity of the transformation to glycidol in relation to allyl alcohol consumed, the conversions of the substrates (allyl alcohol and hydrogen peroxide) and the selectivity of the transformation to organic compounds in relation to hydrogen peroxide consumed.

Epoxidation of crotyl alcohol in the presence of titanium silicalite Ti-MWW catalyst — the new and friendly method of 2,3-epoxybutane-1-ol synthesis

Epoxidation of crotyl alcohol in the presence of titanium silicalite Ti-MWW catalyst — the new and friendly method of 2,3-epoxybutane-1-ol synthesis Epoxidation of crotyl alcohol (CA) with 30 wt% hydrogen peroxide over Ti-MWW catalyst has been studied with methanol as a solvent and at autogenic pressure. The influence of temperature in the range of 20-120°C, the molar ratio of CA/H2O2 1:1-5:1, methanol concentration 5-90 wt%, Ti-MWW catalyst concentration 0.0-5.0 wt% and the reaction time 5-300 min have been studied. The main product of CA epoxidation is 2,3-epoxybutane-1-ol (2,3EB1O), a compound with many applications.

Synthesis and characteristics of titanium silicalite TS-1, Ti-Beta and Ti-MWW catalysts

Synthesis and characteristics of titanium silicalite TS-1, Ti-Beta and Ti-MWW catalysts The synthesis methods of the following titanium-silicalite catalysts: TS-1, Ti-Beta and Ti-MWW were presented. The results of the analyses of the catalysts by XRD, SEM and IR, UV-vis methods were also shown. A brief description of the catalytic performances of these catalysts in the oxidation process of olefins, alkenes, alcohols and aromatic compounds was presented.

Epoxidation of Various Functionalized Olefins by a Ti-MWW/H2O2 Catalytic System

Abstract The catalytic properties of Ti-MWW catalysts for the epoxidation of olefins with different functional groups using hydrogen peroxide as an oxidant were studied. Ti-MWW shows higher olefin conversion and epoxide selectivity than the conventional titanosilicate TS-1. Solvents influence the catalytic activity of Ti-MWW, and water is the best one in the epoxidation of ethyl acrylate and allyl acetate. The functional groups with high electrophilicity and adjacent to the C=C bonds retard the catalytic activity for olefin epoxidation.

Highly selective synthesis of methyl ethyl ketone oxime through ammoximation over Ti-MWW

The liquid-phase ammoximation of methyl ethyl ketone (MEK) with ammonia and hydrogen peroxide was conducted on Ti-MWW, TS-1, Ti-MOR and Ti-Beta catalysts in order to produce methyl ethyl ketone oxime (MEKO) cleanly. Compared with other titanosilicates, Ti-MWW produced MEKO more efficiently and selectively, achieving a conversion and selectivity both over 99% under optimized conditions. Ti-MWW was particularly superior to TS-1 in MEKO selectivity, as TS-1 co-produced easily 2-nitrobutane byproduct as a result of consecutive oxidation of MEKO unless the ammonia/MEK molar ratio was increased to 4. The catalyst deactivated in repeated ammoximation, mainly owing to a partial dissolution of framework silicon in basic reaction media. Efforts were thus made in order to develop practicable regeneration methods. By adding a controlled amount of silica source into the reaction mixture, we could suppress the deactivation of Ti-MWW catalyst and then the lifetime was prolonged effectively.

Epoxidation of 2,5-dihydrofuran to 3,4-epoxytetrahydrofuran over Ti-MWW catalysts

Liquid-phase epoxidation of 2,5-dihydrofuran (DHF, 1-oxa-3-cyclopentene) to 3,4-epoxytetrahydrofuran (ETHF) has been compared among various titanosilicate catalysts like Ti-MWW, TS-1, Ti-Beta and Ti-MOR. The effects of Ti content as well as the reaction conditions such as solvent, catalyst amount, reaction temperature and time have been studied on Ti-MWW in detail. The Ti-MWW catalyst, capable of giving a conversion >95% and an epoxide selectivity >99%, was much more active and selective than the others. The 2,5-DHF epoxidation over Ti-MWW preferred water or acetonitrile as a solvent in which the solvolysis of 3,4-ETHF and the reactions on the allylic positions of 2,5-DHF were limited to an extremely low level. The deactivation of Ti-MWW was essentially due to the deposition of heavy organic species inside pore. It turned to be reusable when subjected to the regeneration by high-temperature calcination.

Highly efficient and selective production of epichlorohydrin through epoxidation of allyl chloride with hydrogen peroxide over Ti-MWW catalysts

The catalytic properties of Ti-MWW in the epoxidation of allyl chloride (ALC) with hydrogen peroxide to epichlorohydrin (ECH) were studied by comparing these properties with those of TS-1, Ti-MOR, and Ti-Beta. Issues concerning the stability and reuse of Ti-MWW were also considered. The investigation on various reaction parameters showed that Ti-MWW is an active and selective catalyst for ALC epoxidation. Ti-MWW prefers aprotic solvents, such as acetonitrile and acetone, over protic alcohols, which is favorable for suppressing the formation of solvolysis byproducts. ALC conversion and ECH selectivity were both as high as 99% on Ti-MWW. 3-Chloro-1,2-propanediol and other heavy byproducts with high boiling points had a negative effect on ALC conversion for both TS-1 and Ti-MWW. A novel secondary synthesis caused a structural rearrangement of the Ti-MWW framework and then improved its stability.

A novel titanosilicate with MWW structure: III. Highly efficient and selective production of glycidol through epoxidation of allyl alcohol with H 2O 2

The catalytic properties of Ti-MWW in the epoxidation of allyl alcohol (AAL) with hydrogen peroxide to glycidol (GLY) have been studied in detail by a comparison with those of TS-1 and pure silica Ti-Beta, and mechanical considerations have been given to the relation between the catalytic performance and the structural, acidic, and hydrophilic/hydrophobic nature of titanosilicates. Ti-MWW catalyzed the AAL epoxidation more actively and selectively than TS-1 and Ti-Beta in the presence of H 2O or MeCN, and exhibited a conversion of 95% for AAL and a selectivity of 99% for GLY when the AAL epoxidation was carried out at 333 K for 30 min and at 12 wt% of catalyst to substrate. Ti-MWW proved to be a reusable and sustainable catalyst as it stood up to Ti leaching and maintained the catalytic activity and the product selectivity in the reaction-regeneration cycles. The acidic character due to the boron framework was very weak, and thus contributed negligibly to the solvolysis of GLY. The AAL epoxidation proceeded mainly within the intralayer sinusoid 10-MR channels which supplied more steric fitness to the substrate molecules than the tunnel-like channels of TS-1 ad Ti-Beta. Ti-MWW was more hydrophilic than TS-1, but much more hydrophobic than Ti-Beta. The hydrophilicity of Ti-MWW was presumed to derive mainly from the defect sites due to the incomplete dehydroxylation between the layers and partially as a result of deboronation. The sinusoidal 10-MR channels serving as the reaction space for the AAL epoxidation were considered to be hydrophobic, thus rendering the Ti-MWW catalyst applicable to the substrates and solvents, both of a polar nature.

A Novel Titanosilicate with MWW Structure: II. Catalytic Properties in the Selective Oxidation of Alkenes

The catalytic properties of Ti–MWW catalysts have been studied for the oxidation of alkenes using hydrogen peroxide or tert-butyl hydroperoxide (TBHP) as an oxidant. Ti–MWW shows superior activity independent of the nature of oxidant when compared to the other Ti-containing catalysts both of microporous TS-1 and Ti-MOR and of mesoporous Ti–MCM-41 in the oxidation of cyclohexene. Compared to large-pore Ti–Beta, Ti–MWW is less active than in the oxidation of cyclohexene using H2O2, but its shows comparable activity in the case of TBHP. Ti–MWW is very stable in both the structure and the states of Ti species in the actual cycle of reaction–regeneration. The framework B species remaining within the Ti–MWW catalysts seem to have little influence on the intrinsic activity of framework Ti species, but they act as Brønsted acid sites contributing to the hydrolysis of the oxide product to form glycols. The turnover number (TON) of Ti–MWW for the cyclohexene conversion decreases sharply with increasing Ti content, while the TON for the 1-hexene conversion shows volcanic behavior when related to the Ti content. It is clarified that the bulky reaction is catalyzed mainly by the Ti species within the supercages and the exterior pockets of the MWW structure, while in addition to these highly accessible Ti species, those within the channels of a 10-membered ring greatly contribute to the oxidation reactions not significantly sizedemanding.