Catalytic Epoxidation Of Propylene Research Articles

Decomposition of hydrogen peroxide during catalytic epoxidation of propylene

Decomposition of hydrogen peroxide during catalytic epoxidation of propylene

Catalytic epoxidation of propylene over a Schiff-base molybdenum complex supported on a silanized mesostructured cellular foam

A Schiff-base molybdenum complex (MoO2–salen) supported on mesostructured cellular foam (MCF) was initially prepared by an in situ synthesis method under acidic conditions. Following silanization modification, a MoO2–salen@MCF-S sample with improved surface hydrophobicity was obtained. The ligand environment of molybdenum within the samples has been analyzed by Fourier-transform infrared spectroscopy, ultraviolet/visible spectroscopy, and X-ray photoelectron spectroscopy. Furthermore, the textural and structural properties of the corresponding materials have been characterized by nitrogen adsorption–desorption isotherms and transmission electron microscopy. Despite of the presence of fewer MoO2 species, the results showed that MoO2–salen@MCF-S has more active Mo centers than MoO2–salen and MoO2–salen@MCF on the basis of maintaining the mesoporous structure. The catalytic performances of the synthesized samples were assessed in the epoxidation of propylene with tert-butyl hydroperoxide (TBHP) as an oxidant, and the mechanism of propylene epoxidation under MoO2–salen@MCF was given. The prepared MoO2–salen@MCF-S material showed the best epoxidation performance with 1,2-dichloroethane as a solvent and a molar ratio of propylene to TBHP of 10:1 at 120 °C, giving a TBHP conversion of up to 100% after 1 h, with selectivities for propylene oxide and tert-butyl alcohol reaching 94.7% and 84.6%, respectively.

Conditions of deposition of TiCl4 used in preparing the silylated Ti-HMS and their effect on catalytic epoxidation of propylene

Silylated Ti catalysts based on hexagonal mesoporous silica (Ti-HMS) were prepared by chemical vapor deposition of TiCl4 on HMS silica modified by vapor silylation. The influence of TiCl4 deposition conditions on surface properties and catalytic performance of the catalysts were investigated. Among the methods used to characterize the catalysts were N2-adsorption, Inductively coupled plasma-atomic emission spectrometry (ICP-AES), Ultraviolet-visible spectroscopy (UV-Vis), Raman spectroscopy. Catalytic activity was evaluated in the epoxidation of propylene using cumene hydroperoxide (CHP) as oxidant. Most of Ti ions in HMS mesoporous silica occupy tetrahedral sites and these sites are responsible for the efficient epoxidation activity. The Ti content incorporated in silica decreases with increasing calcination temperature. The experiments indicated 400°C as an appropriate deposition temperature since higher deposition temperatures favor the formation of low active Ti species. A deposition time of 2 h is a sufficient time interval for incorporating Ti into HMS mesoporous silica. A suitable calcination temperature can be estimated as 700°C while higher calcination temperatures promote the formation of low active Ti species. Propylene oxide in high yields (> 95%) can be obtained in the epoxidation of propylene over the catalysts described in the work. The mechanism proposed for the deposition reaction suggests that the incorporation of Ti into HMS is due to silica interaction of Si-OH with TiCl4, chlorination removes Cl-containing Ti species and in this way decreases the Ti content of catalysts at high deposition temperatures.

Catalytic epoxidation of propylene with CO/O2 over Au/TiO2

Gold nanoparticles supported on TiO2 are known to catalyze vapor-phase epoxidation of propylene with molecular oxygen in the presence of H2 as the necessary reducing co reagent. Here, we report that carbon monoxide can be employed instead of hydrogen to accomplish similar reaction. The reaction of propylene, CO and O2 can be carried out in a flow reactor over Au/TiO2 at a temperature of 40–90°C. The propylene oxide selectivity attains 80–97% at propylene conversion of 1.7–3.7%. The propylene oxide yield goes through the maximum as a function of reaction time, the maximal value being twice higher compared to yield of propylene oxide achieved by “traditional” reaction with H2/O2 mixture. Utilization efficiency of CO reaches 25%, which is comparable to that of H2 in the analogous reaction of propylene, H2 and O2. Proposed mechanism for the reaction involves the formation of specific oxygen species arising from O2 on catalytic sites reduced with CO. This is in line with generation of highly reactive oxygen species (detectable by oxygen isotopic exchange) on Au/TiO2 surface treated preliminarily with CO.

Catalytic epoxidation of propylene with CO/O2 over Au/TiO2

Catalytic epoxidation of propylene with CO/O2 over Au/TiO2

Direct epoxidation of propylene with molecular oxygen over Ag–MoO 3/ZrO 2 catalyst

Direct gas-phase epoxidation of propylene to propylene oxide (PO) by molecular oxygen was studied over the MoO 3-modified supported-silver catalyst. The effect of promoter and support on the performance of the Ag–MoO 3 catalyst and their role were investigated by XPS, XRD, SEM, BET surface area, NH 3-TPD, CO 2-TPD techniques and so on. As the promoter, MoO 3 plays a great role of electron- and structure-type bi-functional promoter. Of all the supports studied, ZrO 2 is the most suitable one for the Ag–MoO 3 catalyst. The presence of support can regulate the size of the Ag–MoO 3 particles and the pore radii of catalyst, and decrease the loading of MoO 3 from ∼50 wt.% in the unsupported Ag–MoO 3 catalyst to ∼4 wt.% in the Ag–MoO 3/ZrO 2 catalyst. The properly weak Lewis acidic sites, the larger size of the Ag–MoO 3 particles and pore channel on the Ag–MoO 3/ZrO 2 catalyst are beneficial to improve epoxidation performance of the catalyst. The effect of the reaction temperature and space velocity on the catalytic epoxidation of propylene was also investigated. The low temperature or high space velocity can decrease the deep oxidation of propylene oxide to improve the selectivity to PO. Over the 20%Ag–4%MoO 3/ZrO 2 catalyst at 400 °C, 0.1 MPa and space velocity of 7500 h −1, the selectivity to PO of 60.3% was achieved with the O 2 conversion of 4.8%; under the space velocity of 12 000 h −1, the selectivity to PO was 71.5% with 2.5% O 2 conversion.

A GREENER ROUTE TO PROPYLENE OXIDE

A TUNGSTEN CATALYST SYStem developed by a team of researchers in China holds promise for a more economical and environmentally friendly route to production of propylene oxide. The apparent front-runner among several possible processes that have emerged to replace the two industrial methods currently in use is the catalytic epoxidation of propylene with hydrogen peroxide. Researchers at the Chinese Academy of Sciences' Dalian Institute of Chemical Physics have now come up with a novel catalyst system for that process [ Science , 292, 1139 (2001)]. Chemistry professor Xi Zuwei and coworkers Zhou Ning, Sun Yu, and Li Kunlan discovered a tungsten-containing catalyst, {C 5 H 5 NC 16 H 33 } 3 {PO 4 (WO 3 ) 4 }, that initially is insoluble in organic solvents. But under the action of in situ-generated H 2 O 2 it forms a soluble active species that catalyzes propylene epoxidation. As H 2 O 2 is used up, the catalyst becomes insoluble again, simplifying its recovery The only products of the reaction are propylene ...

Propylene epoxidation with hydrogen peroxide catalyzed by molecular sieves containing framework titanium

The catalytic epoxidation of propylene with aqueous hydrogen peroxide over four Ti-containing silicates, namely titanium silicalite (TS-1), a TiO 2–SiO 2 xerogel, Ti-MCM-41, and a TiCl 4-modified HZSM-5 zeolite has been investigated. It was found that only the crystalline molecular sieve TS-1 and the TiCl 4 modified HZSM-5 zeolite were active, whereas the TiO 2–SiO 2 xerogel and the mesoporous Ti-MCM-41 were almost inactive. The structure of these Ti-containing silica materials plays an important role in determining their catalytic performances. Shape-selectivity and the hydrophobic nature of the material are the two most important factors. In the presence of TS-1, propylene oxide was the predominant product, whereas propylene diol and its mono-methyl ethers were formed with a TiCl 4 modified HZSM-5. It is suggested that the acidity of catalyst is a crucial factor in determining product selectivity. Propylene diol and the mono-methyl ethers are produced by further reactions of propylene oxide with H 2O and methanol. The oxirane ring opening reactions are catalyzed on acid sites. The H 2O 2 turnover frequency based on the titanium content increased while the selectivity to propylene oxide decreased with an increase of the Si/Ti ratio in TS-1 catalyst. The influence of CH 3OH/H 2O ratio in the solvent as well as the reaction temperature on the title reaction and the regeneration of deactivated catalyst have also been investigated.

On the mechanism of propylene epoxidation catalyzed by molybdenum naphthenate

The mechanism of the catalytic epoxidation of propylene with α-phenylethyl hydroperoxide has been investigated. The epoxidation step is a molecular interaction between propylene and a complex formed from hydroperoxide and catalyst, while part of side products is formed in free radical reactions. This mechanism is valid for the kinetics of both epoxidation and catalytic decomposition of hydroperoxide.

Catalytic epoxidation of propylene with tert-butyl hydroperoxide in the presence of modified carboxy cation-exchange resin “Amberlite” IRC-50

Catalytic epoxidation of propylene with tert-butyl hydroperoxide in the presence of a modified weakly acidic cation-exchange resin, Amberlite IRC-50, is carried out. The order of reaction with respect to the hydroperoxide and the catalyst is studied, as well as the effect of temperature and the solvent, and an assumption is made for the formation of an intermediate complex between the olefine, the catalyst, and the hydroperoxide.

Catalytic epoxidation of propylene with tert-butyl peroxide in presence of molybdenum complexes on polymer carriers

A polymer catalyst has been synthesized on the basis of Amberlite IRA-45 anion-exchange resin modified with molybdenum hexacarbonyl. Its catalytic activity in the epoxidation of propylene with tert-butyl hydroperoxide is similar to the activity of Mo(CO)6 used under homogeneous conditions.