Titanium Silicalite-1 Catalyst Research Articles

Deactivation and regeneration of titanium silicalite catalyst for epoxidation of propylene

Continuous epoxidation of propylene with 30-wt% hydrogen peroxide in isopropyl alcohol solvent over titanium silicalite (TS-1) zeolite was carried out and the good selectivity to propylene oxide and stability of TS-1 were obtained. After the reaction of 263 h, the deactivation of the TS-1 catalyst occurred. The spent catalysts were regenerated by calcinations at 550 °C for 5 h, washing with isopropyl alcohol solvent or washing with dilute hydrogen peroxide, and the activity evaluation of the regenerated catalysts were studied. The deactivated and regenerated catalysts were characterized by scanning electron microscopy, X-ray diffraction, Fourier-transform infrared spectroscopy, 29Si magic angle spinning nuclear magnetic resonance, thermogravimetric analysis and Brunauer–Emmett–Teller method. The compositions deposited on the surface of the catalysts were collected by solvent extraction and were analyzed by gas chromatography–mass spectrometry (GC–MS). The results showed that calcination and washing with dilute hydrogen peroxide were highly effective regeneration methods and the catalytic activity of TS-1 catalysts can be mostly recovered after these treatments. Washing with isopropyl alcohol had a subtle effect in recovering the catalytic activity of the TS-1 catalyst. The major cause of the deactivation of the TS-1 catalyst for epoxidation is blocking micropores induced by bulky organic by-products formed by consecutive reactions of target reaction, such as dimerization or oligomerization of propylene oxide, etherification of propylene oxide with isopropyl alcohol. In addition, leaching of framework titanium also contributes to the deactivation of the catalyst.

Epoxidation of 2-buten-1-ol over Ti-MCM-41 and Ti-MCM-48 titanium silicalite catalysts

Epoxidation of 2-buten-1-ol over Ti-MCM-41 and Ti-MCM-48 titanium silicalite catalysts The results of the epoxidation of 2-buten-1-ol with 30 wt% hydrogen peroxide have been presented. As a solvent methanol was used. The process was carried out over the titanium silicalite catalysts: Ti-MCM-41 and Ti-MCM-48. The influence of temperature (20 - 120°C), the molar ratio of CRA/H2O2 (5:1 - 5:1), methanol concentration (5 - 90 wt%), catalyst concentration (0.1 - 5.0 wt%) and the reaction time (30 - 300 min) was investigated. The obtained results were used for the determination of optimum conditions of running the epoxidation process of 2-buten-1-ol.

The new method of 1,2-epoxy-3-butanol production over titanium silicalite catalysts

The new method of 1,2-epoxy-3-butanol production over titanium silicalite catalysts The results of 1-butene-3-ol (1B3O) epoxidation over the titanium silicalite catalysts: TS-1, Ti-Beta, Ti-MCM-41 has been presented. The optimal parameters obtained for the individual catalyst were compared. The main functions describing the process were: the selectivity of transformation to 1,2-epoxy-3-butanol (1,2E3B) in relation to 1B3O consumed, the conversions of 1B3O and hydrogen peroxide and the selectivity of the transformation to organic compounds in relation to the H2O2 consumed. The main product of the epoxidation process was 1,2-epoksy-3-butanol, the chemical compounds having a lot of applications.

Coke deposition and characterization on titanium silicalite-1 catalyst in cyclohexanone ammoximation

In this work, the changes of catalytic activity, as well as the main deactivation mode were investigated on a commercial titanium silicalite-1 (TS-1) catalyst under simulated industrial conditions in continuous tank slurry reactor. The conclusions about deactivation behavior have been achieved based on the changes of activity, conversion and selectivity. XRD and FTIR analyses indicate the MFI framework structure of zeolite cannot be changed evidently during the reaction. It is found by comparative experiments that the main reason for catalyst deactivation is coke formation on the surface of TS-1. Results from TGA-DTA, N 2 adsorption and pyridine TPD analyses of used catalysts demonstrate there are two types of coke deposited mainly on micropores. Soft coke is located near Ti sites and can be removed by oxidation under 350 °C, while refractory coke can be oxidized by air until 700 °C. Analysis results of GC–MS for soluble coke and NMR, FTIR spectra for insoluble coke indicate that N-containing polycyclic aromatic and/or polyalkene species are the main components of coke deposits.

Epoxidation of methallyl alcohol with hydrogen peroxide over TS-1 catalyst

The influence of the technological parameters on the course of the epoxidation of methallyl alcohol with 30 wt.% hydrogen peroxide over titanium silicalite catalyst TS-1 has been investigated. The effect of different parameters such as temperature, molar ratio of methallyl alcohol to hydrogen peroxide, methanol concentration, catalyst content (in reaction mixture) and the reaction time was determined. The course of the process was described by the following functions: the selectivity of transformation to 2-methylglycidol in relation to consumed methallyl alcohol, conversion of methallyl alcohol and the selectivity of transformation to organic compounds in relation to consumed hydrogen peroxide.

Ammoximation of cyclohexanone in acetic acid using titanium silicalite-1 catalyst: Activity and reaction pathway

The activity of titanium silicalite (TS-1) and the reaction pathway for the ammoximation of cyclohexanone to produce cyclohexanone oxime were studied using acetic acid as a solvent at 60 °C. The effect of solvent, sources of nitrogen, water content and the active site stability were also evaluated. It was found that, in the reaction using acetic acid as a solvent, the ammoximation of cyclohexanone proceeded mainly via the oxidation of imine, which was primarily formed in situ by the condensation of ketone with ammonia. In addition, the ammonium salts of weak acids, such as acetate, citrate and carbonate, can be used as nitrogen sources for the ammoximation in acetic acid. Water was shown to inhibit the formation of imine, and also prevent the side reactions. Moreover, TS-1 possessed an excellent stability, and can be reused without significant loss of activity.

Liquid phase epoxidation of allylic compounds with hydrogen peroxide over titanium silicalite catalysts

The experimental results of the process of epoxidation of allylic compounds (allyl alcohol, methallyl alcohol and methallyl chloride) to corresponding epoxides with hydrogen peroxide over titanium silicalite: TS-1, TS-2, Ti-beta and Ti-MCM-41 have been presented. The epoxidation was carried out with a 30% hydrogen peroxide in methanol as solvent in an autoclave. The applied epoxidation system allowed to obtain glycidol, β-methylglycidol and β-methylepichlorohydrin with a good selectivity and conversion of allylic compounds in most cases. The major applications of glycidol, β-methylglycidol and β-methylepichlorohydrin have been also presented.

Regeneration of Lamina TS-1 Catalyst in the Epoxidation of Propylene with Hydrogen Peroxide

The deactivation and regeneration of the lamina titanium silicalite (TS-1) catalyst for the epoxidation of propylene with dilute H2O2was investigated in a fixed-bed reactor. In the scale-up experiment, the dosage of the lamina TS-1 catalyst is 2. 5 kg, after 1000 h reaction the catalyst still exhibits good performance and further increases the reaction time, the conversion of H2O2begins to decrease. TG and BET analyses of the deactivated catalysts show that the main species occluded within the zeolite pore are propylene oxide oligomers, and these species occupying the active Ti site and blocking the pores of the lamina TS-1 are the main reason for the deactivation of catalyst. The deactivated catalyst can be regenerated by different regeneration methods. The activity of deactivated catalysts regenerated by dilute H2O2or heat treatment by using air or nitrogen as a calcination media can be fully recovered, but a decline in propylene oxide (PO) selectivity of the regenerated catalyst has been observed during the first hours of reaction. However, water vapor treatment of the deactivated catalyst can improve the PO selectivity with the same activity as that of the fresh lamina TS-1 catalyst.

Impregnation treatments of TS-1 catalysts and their relevance in alkene epoxidation with hydrogen peroxide

Ti-containing MFI (TS-1) samples were synthesized and then modified with small amounts (0.3–1.7 wt.%) of alkali, alkaline-earth and lanthanide ions. UV-Vis reflectance spectra for all the samples revealed absorption at 215 nm, due to the O 2−→Ti 4+ charge transfer transition of tetrahedrally coordinated titanium incorporated into the silicalite framework. Similarly, the binding energy of the Ti 2p 3/2 core-level for all the M/TS-1 samples appeared at ca. 460.0 eV, which is also indicative of Ti(IV) coordinated to oxide anions in a tetrahedral symmetry. The catalysts were tested in the epoxidation reaction of 1-octene, using aqueous hydrogen peroxide as an oxidant agent at 353 K. The conversion of hydrogen peroxide was slightly lower for the M/TS-1 samples than for the titanium-silicalite-1 (TS-1) reference and selectivity to epoxide was higher when the metal cation (M n+ ) was added. A good correlation between the formation of secondary reaction products in the 1-octene epoxidation and Brønsted acid sites (measured by the infrared spectra of adsorbed deuterated acetonitrile) was found. This finding is explained as being due to the neutralization of the surface acidity of the TS-1 zeolite by the metal oxide (MO) incorporated, with the subsequent inhibition of the solvolysis reactions of the epoxide on the acid sites.

Photocatalytic decomposition of 4-nitrophenol over titanium silicalite (TS-1) catalysts

Titanium silicalite zeolites (TS-1) having Si/Ti ratios of 3.3, 13.7, and 26.3 were synthesized and used as photocatalysts for decomposition of 4-nitrophenol (4-NP) in aqueous solution. In the dark, the adsorption of 4-NP on TS-1 changed greatly depending on the Si/Ti ratio in TS-1 and the pH of the solution. The amount of 4-NP adsorbed on TS-1 increased with increasing Si/Ti ratio and decreasing pH of solution. The photocatalytic activities of TS-1 zeolites for the decomposition of 4-NP were found to be greatly affected by H 2O 2. In the absence of H 2O 2, the TS-1 having lower Si/Ti ratio, and consequently containing a larger amount of extra framework titanium, exhibited higher photocatalytic activity. In contrast, in the presence of H 2O 2, the TS-1 with higher Si/Ti ratio, in which the titanium content is lower while the fraction of framework titanium is higher, showed a higher increase in photocatalytic activity. Especially in acid conditions, the addition of H 2O 2 to the reaction solution results in a remarkable enhancement of the photocatalytic activity of TS-1; the apparent rate constant increased with increasing Si/Ti ratio. Such results suggest that, upon UV illumination, OH radicals can be formed easily from the titanium-hydroperoxide species that are formed by the interaction of framework titanium in TS-1 with H 2O 2. The enhancement of photocatalytic activity of TS-1 for the decomposition of 4-NP by the addition of H 2O 2 can be attributed to both the efficient formation of OH radicals and the close proximity of OH radicals to the reactant molecules.

Epoxidation of propylene using supported titanium silicalite catalysts

The propylene epoxidation using supported titanium silicalite TS-1 catalyst was systematically investigated in a fixed bed reactor. Different supports such as SiO 2 and Al 2O 3 were used and two molding methods were adopted to prepare the catalyst. Strip TS-1 catalyst of 1 mm×2 mm dimensions is obtained by the extruding method. Use of SiO 2 as the support rather than Al 2O 3 is better because the latter has strong acidity that promotes the side reaction of propylene oxide (PO) with the solvent. With the decrease of the amount of TS-1 in TS-1/SiO 2, the PO selectivity increases. The lamina TS-1 catalyst, the core of which is an inert ball used as the support and the shell of which is a TS-1 lamina of 0.1–0.2 mm, exhibits better performance than the strip TS-1 catalyst owing to its shorter diffusion path for reaction heat, raw material and product. The lamina TS-1 catalyst was used in the fixed bed reactor for about 200 h. The results indicate that it is a promising catalyst in propylene epoxidation. The effect of aluminum impurity was also investigated. It has been shown acid sites originating from framework aluminum can catalyze the side reaction and a small amount of base can inhibit it. In conclusion, diffusion and the concentration of acid sites are the two main factors influencing the performance of titanium silicalite catalyst in propylene epoxidation.

Effect of sodium ions on propylene epoxidation catalyzed by titanium silicalite

Propylene epoxidation catalyzed by titanium silicalite is easily influenced by acidic or basic impurities. The effect of sodium ions on the reaction was systematically investigated. It has been shown that a proper amount of sodium salt additive can inhibit the further reaction of propylene oxide (PO) with the solvent and can increase the selectivity of PO. But a slightly excessive amount of sodium salt can be a poison to the titanium silicalite catalyst. The sodium salt additive can accumulate on the catalyst in repeated runs of propylene epoxidation in an autoclave, so the catalyst may be poisoned if an equal amount of sodium salt is added in each run. The excessive sodium ions on titanium silicalite can deactivate the catalyst in calcination, while acid treating can restore the activity of titanium silicalite. If the propylene epoxidation is carried out in a fixed bed, the sodium ions on titanium silicalite can gradually come loose and the PO selectivity decreases with time on-stream. A small amount of supplement of sodium salt in the raw material can make the PO selectivity stable for a longer period.

Selective oxidations with hydrogen peroxide and titanium silicalite catalyst

Titanium silicalite (TS-1) samples with increasing amount of titanium incorporated into the silicalite framework (from 1 to 3.45 wt.% TiO 2) have been synthesized and characterized by UV-DRS spectroscopy. The samples have been tested on propylene epoxidation, cyclohexanone ammoximation and ammonia oxidation reactions. It has been found that the yield obtained with TS-1, expressed as turnover number, increases with the Ti content. The trend is common for all the reactions investigated.

Propylene epoxidation with hydrogen peroxide over palladium containing titanium silicalite

The epoxidation of propylene to propylene oxide with H 2O 2 was studied over palladium impregnated and reduced titanium silicalite (TS-1), over merely impregnated titanium tilicalite and over untreated titanium silicalite. The use of such catalytic systems in the epoxidation of proplyene with a H 2–O 2 mixture motivated us to assess the influence of operating conditions and the effect of the Pd loading on the epoxidation capability of the titanium silicalite catalyst. Concerning the operating conditions TS-1 was found to be very active even at temperatures as low as 10°C. Lowering the H 2O 2 concentrations to only 2 wt.% of H 2O 2 caused the PO yield to increase slightly over TS-1 and 1% Pd/TS-1. TS-1 catalysts that were merely impregnated with [Pd(NH 3) 4]Cl 2 were less active than the catalysts that were reduced after impregnation, though the latter is more active in the decomposition of H 2O 2. The deactivation of TS-1 after impregnation with [Pd(NH 3) 4]Cl 2 was probably caused by the blocking of the Ti sites by ammonia, since the impregnation with PdCl 2 did not cause any decrease in activity. Reducing the catalyst removes the ammonia and improves the catalytic performance of the Pd loaded catalyst.

Characterization and catalytic properties of titanium silicalite-1 catalyst

Titanium silicalite 1 (TS-1) catalyst was prepared by three different hydrothermal synthesis methods. XRD, elemental analysis, SEM, IR,29Si MAS NMR, UV-vis DRS, physical adsorption of nitrogen, and EXAFS analysis were then performed to evaluate its physical properties. For a test of catalytic activity, liquid phase 2-butanol oxidation and 1-hexene epoxidation using hydrogen peroxide as an oxidant were conducted. The crystal size of the TS-1 catalyst was shown to have a considerable effect on the 1-hexene epoxidation, and smaller crystals resulted in higher activity.

Propylene epoxidation with hydrogen peroxide and titanium silicalite catalyst: Activity, deactivation and regeneration of the catalyst

The epoxidation of propene with hydrogen peroxide and a titanium silicalite catalyst with MFI structure was investigated in detail. The relationship between catalytic activity and propylene oxide selectivity can be explained by the acidification of water coordinated to the active titanium site and its reversible deprotonation to an ate complex, which inhibits the formation of the active species for epoxidation. Pretreatment of the catalyst with neutral or acidic salts improves the propylene oxide selectivity without affecting the catalytic activity. Catalyst deactivation occurs by blocking of the zeolite micropores with propylene oxide oligomers. The deactivated catalyst can be regenerated by refluxing with dilute hydrogen peroxide.

A study of the organic by-products in the cyclohexanone ammoximation

The heterogeneous catalyzed ammoximation of cyclohexanone on titanium silicalite catalyst has been studied. Cyclohexanone oxime is formed by reaction of cyclohexanone with ammonia and hydrogen peroxide. The organic by-products formed in the reaction have been studied and the following products were identified: nitrocyclohexane, cyclohexenylcyclohexanone, cyclohexenone oxime and cyclohexanone azine. The effect of some reaction parameters on by-products formation have been investigated. Experiments have been performed to verify if these by-products are due to side or consecutive reactions and derive from non-catalyzed or catalyzed reactions.

Ammoximation of ketones on titanium silicalite. A study of the reaction byproducts

In the new EniChem process cyclohexanone oxime is directly synthesized by ammoximation of cyclohexanone with ammonia and hydrogen peroxide on titanium silicalite catalyst. The ammoximation reaction is suitable for the synthesis of several oximes by reaction of the corresponding ketones with ammonia and hydrogen peroxide on titanium silicalite. New results on ketones ammoximation and on reaction byproducts are reported. The effect of some reaction parameters on the oxime yield and on byproducts formation is discussed.

Catalytic hydroxylation of phenol over a vanadium silicate molecular sieve with MEL structure

Abstract Vanadium silicate molecular sieves with MEL structure (VS-2 ) are found to be active in the hydroxylation of phenol with hydrogen peroxide, a reaction which is commercially practiced over titanium silicalite (TS-1 and TS-2) catalysts. Among various reaction parameters, the influence of the solvent on the conversion and product selectivity appears to be different from that reported on titanium silicalites. In methanol, for example, no hydroxylation takes place. In water, the phenol conversion as well as the H 2 O 2 selectivity follows the order, TS-1 > TS-2 > VS-2. Only those vanadium ions which are in the lattice positions appear to catalyse this reaction.

Synthesis of propylene oxide from propylene and hydrogen peroxide catalyzed by titanium silicalite

The epoxidation of propylene with hydrogen peroxide in the liquid phase, in the presence of titanium silicalite catalyst (TS-1), is described. The best solvents are methanol and methanol/ water mixtures. The temperature is normally between room temperature and 60°C. Under these conditions, reaction rates are fast, yields on H 2O 2 are quantitative, and selectivity to propylene oxide is very high. Propylene glycol and its monomethyl ethers and trace amounts of formaldehyde are the only by-products formed. Selectivity is further improved and the hydrolysis of the epoxide is almost suppressed when the residual acidity of the catalyst is completely neutralized. The activity of spent catalyst is recovered by calcining at 550°C or, more simply, by washing with solvents. Complete activity recovery shows that Ti is not removed from the crystalline framework during the epoxidation reactions.