Template-ion Exchange Research Articles

Effectiveness of the template-ion exchange method for appearance of catalytic activity of Ni–MCM-41 for the ethene to propene reaction

Abstract The template-ion exchange (TIE) method, an equilibrium adsorption (EA) of nickel ammine complex, and a conventional impregnation (IMP) method were applied to prepare nickel ion-loaded mesoporous silica MCM-41 and silica gel and their catalytic activity was examined for the newly developed ethene to propene (ETP) reaction. When we employed TIE as the preparation method and MCM-41 as the support, the most active and stable catalyst could be prepared. The local structures of the nickel species supported on the TIE and EA samples were very similar to that of layered nickel silicate, while those on the IMP-catalysts were the same as that of NiO particles.

The influence of the preparation methods and pretreatment conditions on the properties of Ag-MCM-41 catalysts

Silver doped mesoporous silica materials MCM-41 were prepared by the direct hydrothermal (DHT) and template ion exchange (TIE) methods. The properties of materials were investigated by the adsorption/desorption of nitrogen, X-ray diffraction (XRD), and photoacoustic infrared spectroscopy (FT-IR/PAS). Redox properties were studied by the temperature programmed reduction method and temperature programmed CO oxidation test reaction. It was found that the introduction of small amounts of silver caused structural changes of the silica materials. Silver species in the catalysts obtained by the TIE method were strongly dispersed on the silica support. XRD and TPR studies of the catalysts prepared by the DHT method indicated co-existence of the large crystallites and isolated silver ions in the silica material. Studies revealed the strong influence of the pretreatment and reaction conditions on the performance of catalysts in the oxidation of CO. Reduction of catalysts was necessary to obtain high activity at low temperatures. Complex deactivation processes were recorded above 300 °C.

Fe-MCM-41 for N2O Decomposition and Reduction with Methane

Abstract The catalytic activities for N2O decomposition and selective reduction with methane were studied on Fe-MCM-41 prepared by direct hydrothermal synthesis (DHT) and template ion exchange (TIE) methods. Fe-MCM-41-DHT showed higher activity than those prepared by TIE and impregnation methods. The high activity of Fe-MCM-41-DHT is caused by the formation of highly isolated and tetrahedrally coordinated iron-oxo species.

Liquid phase catalytic hydrodechlorination of aryl chlorides over Pd–Al-MCM-41 catalyst

Supported Pd catalysts were prepared by direct hydrothermal (DHT) or template-ion exchange (TIE) method on Al-substituted MCM-41 as the support and tested in the hydrodechlorination of aryl chlorides such as 4-chloroanisole in liquid phase, together with impregnated Pd catalysts as references. When Pd was loaded on Al-MCM-41 with the Si/Al ratio of 150 by the TIE method, the catalyst showed the highest activity among the Pd catalysts prepared. PdO originally formed on the catalyst surface was in situ reduced to Pd metal during the reaction as the active form for the dechlorination. The activities of the supported Pd catalysts well correlated with the Pd dispersion on the TIE or impregnated Pd catalysts, whereas the DHT catalysts showed relatively high activities independently on the Pd dispersions. It was confirmed that the dechlorination proceeded by a heterogeneous mechanism catalyzed by Pd metal particles sized less than 10nm on the surface of the catalyst. Al substitution for Si on MCM-41 was effective for the loading of Pd metal with the high dispersion, none the less Pd was located on the surface of the TIE catalyst particles and no significant effect of mesoporous structure on the reaction was observed. Methanol was the most profitable as the solvent among the various solvents tested. Various types of arylchlorides bearing hydroxy, methoxy, methyl, nitro and phenylcarbonyl group at the p-position were efficiently dechlorinated over Pd–Al-MCM-41 catalyst at 40°C. Electrophilic attack of arylchloride was proposed as the rate determining step, where ionic mechanism positively worked and electron-releasing substituents increased the catalytic activity.

The influence of preparation method on the structure and redox properties of mesoporous Mn-MCM-41 materials

Mesoporous silica materials modified by manganese have been prepared using surfactants containing different numbers of carbon atoms. Manganese has been introduced by the direct hydrothermal (HT), template ion-exchange (TIE) and impregnation methods. Structural properties have been investigated by the nitrogen adsorption–desorption, X-ray diffraction (XRD) and FT-IR studies. Redox properties have been investigated by the temperature-programmed reduction method (TPR) and transient CO oxidation reaction. It has been found that structural properties are strongly related to the type of surfactant used, the amounts and the way of Mn introduction. Large distortion effects are observed for samples prepared by the TIE method. Reducibility of the samples containing different pore dimensions and Mn loadings, prepared by TIE method, are very similar. Manganese oxide species in the catalysts of narrow pores and containing small amounts of manganese obtained by the HT and impregnation methods show low reducibility. During CO oxidation reaction some deactivation processes are observed for catalysts prepared by different methods and containing small amounts of Mn. A slight increase in activity for catalysts containing larger amounts of manganese is observed after high temperature treatment. Such changes are attributed to the interaction of manganese with silica and changes of oxidation state during thermal treatment.

Iron-catalyzed propylene epoxidation by nitrous oxide: Toward understanding the nature of active iron sites with modified Fe-MFI and Fe-MCM-41 catalysts

Alkali metal salt (KCl)-modified Fe-MFI and Fe-MCM-41 containing iron species in different locations have been studied for the epoxidation of propylene with nitrous oxide. In the allylic oxidation of propylene without modification, the samples with iron species in the framework positions showed slightly higher activity for the formation of acrolein and allyl alcohol. After modification with KCl, propylene oxide (PO) became the main product. Significant differences in PO formation activity were observed between the samples containing iron in different locations. For the Fe-MFI and the Fe-MCM-41 prepared by the direct hydrothermal (DHT) method, in which iron was located mainly in the framework position, much lower activity was obtained after KCl modification. In contrast, the Fe-MFI after steam treatment and the Fe-MCM-41 prepared by template ion-exchange (TIE) and conventional impregnation methods, which contained extra-framework iron species (e.g., FeO x clusters), exhibited higher PO formation activity after modification. A PO selectivity of 80% could be achieved at a propylene conversion of 3.3% over the KCl-modified Fe-MCM-41 prepared by the TIE or the impregnation method at 598 K (time on stream, 70 min). The modification with KCl increased the dispersion of the extra-framework iron species. Consequently, highly dispersed extra-framework iron species, probably in tetrahedral coordination, are proposed for the epoxidation of propylene with nitrous oxide.

Ammonia decomposition over Ru and Ni catalysts supported on fumed SiO 2, MCM-41, and SBA-15

The effects of using fumed SiO 2, MCM-41, and SBA-15 as supports for Ru and Ni catalysts on ammonia decomposition were investigated. It was found that the supported catalysts on these siliceous materials are more active than those supported on ordinary silica. In general, the supported Ru catalysts are more active than the Ni catalysts, and MCM-41 is the best support material for Ru and Ni. Significant enhancement in activity was observed when the supported Ru catalysts were modified by KOH, but such effect was minimal in the cases of supported Ni catalysts. The results of N 2 adsorption and transmission electron microscopy studies revealed that the Ni particles of Ni/MCM-41(TIE) prepared by template-ion exchange (TIE) method are largely located inside the pores of MCM-41. Compared with the Ni/MCM-41(IMP) catalyst prepared by impregnation method, the Ni/MCM-41(TIE) catalyst exhibited appropriate Ni dispersion and weaker Ni/support interaction, and consequently higher catalytic activity. In terms of the remarkable changes in turnover frequency (TOF) with Ni dispersion on different catalysts, it was demonstrated that NH 3 decomposition over Ni is significantly structure sensitive. Some unique metal clusters similar to B5 active sites should be responsible for the catalytic activities. Preparation methodology has a substantial influence on metal dispersion. For the supported Ni catalysts prepared by the TIE method, the generated metal particles are very small and the constitution of unique active sites becomes unfavorable, which accounts for the apparently lower TOF values.

Iron-containing MCM-41 catalysts for Baeyer–Villiger oxidation of ketones using molecular oxygen and benzaldehyde

Iron(III)-containing mesoporous silica (MCM-41) with Fe contents up to 1.8 wt% have been prepared by direct hydrothermal synthesis (DHT) and template ion exchange (TIE) methods. Characterizations of these catalysts have been done by XRD, XPS, diffuse reflectance UV–vis, ESR, Mössbauer, and XAFS spectroscopies. Fe species in MCM-41 materials are tetrahedrally coordinated for the DHT method with Fe contents up to 1.1 wt% while those are mainly octahedrally coordinated for the TIE method. Among these catalysts, ferrisilicate and Fe 2O 3/Cab-O-Sil as references, Fe-MCM-41-DHT exhibited the highest catalytic activity for Baeyer–Villiger (B–V) oxidation of ketones using molecular oxygen and benzaldehyde. The prominent performance of the Fe-MCM-41-DHT could be ascribed to both tetrahedrally coordinated Fe 3+ incorporated inside the framework of MCM-41 and its uniform nano-order mesopores allowing the access of bulky compounds to the active sites. Furthermore, this heterogeneous Fe catalyst was reusable without any appreciable loss in activity and selectivity. It has been confirmed by IR spectroscopy that the Fe-MCM-41-DHT-catalyzed B–V reaction proceeded via coordination of carbonyl groups of ketone to Fe 3+.

Epoxidation of styrene with molecular oxygen catalyzed by cobalt(II)-containing molecular sieves

Co-containing molecular sieves, mainly Co–faujasite zeolite and Co-MCM-41, have been studied for the epoxidation of styrene with molecular oxygen. Characterizations with XRD, TEM, laser-Raman, XPS, and H 2-TPR suggest that the cobalt introduced into MCM-41 by a template-ion exchange method resembles that exchanged in the faujasite zeolite and exists in the single-site Co(II) state, whereas the sample prepared by the impregnation method contains a large proportion of Co 3O 4. The Co(II) sites located in the molecular sieves catalyze the epoxidation of styrene by oxygen with higher activity than Co 3O 4 (ca. 2.6 times based on the same cobalt amount). On the other hand, in homogeneous reactions, Co(NO 3) 2 and Co(Ac) 2 are almost inactive for the conversion of styrene with oxygen, whereas CoCl 2 and Co(acac) 3 show some activity, but the selectivity for epoxide is remarkably lower as compared with the Co(II)-containing molecular sieves. Among various oxidants examined, oxygen is found to be the best one for the epoxidation of styrene over the Co(II)-containing molecular sieve catalysts. The solvent plays an important role in epoxidation, and superior catalytic performances have been obtained with an acylamide such as N,N-dimethylformamide (DMF) as the solvent. The oxygen species with a radical nature generated by the activation of molecular oxygen over the solvent-coordinated Co(II) site has been proposed for the epoxidation reactions.

Hydrogen Transfer Activity of Tin-Incorporated Mesoporous Silica

Preparation procedure of tin-incorporated in mesopores of MCM-41 has been studied for reduction of acetophenone to 1-phenylethanol. Tin was incorporated into the mesopores of MCM-41 by a template ion exchange (TIE in the following) method. Almost 20 wt% of tin was loaded in the mesopores and about 70% of template was still remained together. Calcination treatment to remove the residual template ions brought about significant collapse of the periodical hexagonal structure of MCM-41 and decrease of surface area because of heat of combustion of the template in the pores accompanying with sintering of incorporated tin. We have investigated the procedure to remove the template from the MCM-41 by rinsing with HCl before or after the tin incorporation to avoid vigorous exothermic combustion during the calcination. Almost 70–80% of template was liberated by the rinse with HCl. The hexagonal structure and surface area were maintained after tin incorporation. The rinse with HCl aqueous solution before the tin incorporation brought about an enhancement of specific activity, formation rate of 1-phenylethanol from acetophenone per incorporated amount of tin. The rinse of HCl before the incorporation increased the specific activity by a factor of 2–3.

XAFS study on active iron sites in MCM-41 as a catalyst for liquid phase oxidation

Iron-containing mesoporous molecular sieves (Fe-MCM-41) synthesized by both direct hydrothermal (DHT) and template-ion exchange (TIE) methods have been used as catalysts for the liquid phase oxidation of bulky organic compounds, i.e., anthracene and trans-stilbene, with diluted hydrogen peroxide. In the case of Fe-MCM-41-DHT, analysis of Fe K-edge XAFS revealed that isolated and tetrahedrally coordinated Fe species exist in the framework of MCM-41. On the other hand, the Fe-MCM-41-TIE mainly contains small iron oxide clusters, which have octahedrally coordinated Fe species. The tetrahedrally coordinated Fe species in Fe-MCM-41-DHT showed both high activity and efficiency of hydrogen peroxide in the liquid phase oxidations, whereas the iron oxide clusters in the Fe-MCM-41-TIE showed low activity. Moreover, the iron cations incorporated inside the framework of MCM-41 do not leach during the reaction, whereas the small iron oxide clusters leach out into the liquid phase and do not contribute to the catalytic reaction.

Incorporation of luminescent lanthanide complex inside the channels of organically modified mesoporous silica via template-ion exchange method

Luminescent lanthanide complex, Eu(phen)2Cl3·2H2O (Euphen, phen = 1,10-phenanthroline) has been incorporated inside the channels of mesoporous silica MCM-41 with its external surface modified by phenyltriethoxysilane (Ph-Si(OEt)3) via a simple template-ion exchange method. The passivation of active groups such as silanols in the external surface ensures that the ion exchange reaction occurs between the surfactant cations and the lanthanide complex ions inside the channels of the modified MCM-41. The passivation result is confirmed by 29Si MAS NMR spectroscopy. FT-IR demonstrates that the cationic surfactants are completely removed. XRD and N2 adsorption–desorption measurements are employed to characterize the mesostructure of Euphen-Ph-MCM-41. Luminescence and stability studies on the materials of Euphen and Euphen-Ph-MCM-41 show that the resultant hybrid material Euphen-Ph-MCM-41 exhibits the characteristic emission of Eu3+ ions under UV irradiation with higher 5D0 luminescence quantum efficiency, longer lifetime and better thermal stability than the corresponding pure complex Euphen. Moreover, the characterization results show that the local symmetry and the first coordination shell of Eu3+ ions are changed after the complex ions become incorporated into the MCM-41 channels and that a more symmetric environment is occupied by the Eu3+ ions in Euphen-Ph-MCM-41 than in Euphen. There is also a more efficient ligand-to-Eu(III) intramolecular energy transfer process in Euphen-Ph-MCM-41.

Coordination structures of vanadium and iron in MCM-41 and the catalytic properties in partial oxidation of methane

The coordination structures of vanadium and iron introduced into MCM-41, a typical mesoporous silica, by both direct hydrothermal synthesis (DHT) and template–ion exchange (TIE) methods have been studied by X-ray absorption spectroscopy (XANES and EXAFS). Vanadium is tetrahedrally coordinated with oxygen in V-MCM-41 prepared by both methods but the location of vanadium is probably different; vanadium is mainly incorporated inside the framework of MCM-41 by the DHT method as the content is lower than approximately 1 wt%, while the vanadyl tetrahedra are probably dispersed on the wall surface of MCM-41 over the samples by the TIE method. In the case of Fe-MCM-41, the DHT method results in iron atoms mainly in tetrahedral coordination and isolated from each other in the framework of MCM-41. However, aggregated iron oxides with iron in octahedral coordination are mainly observed in the TIE samples. The V-MCM-41 by the TIE method shows better catalytic performances than that by the DHT method in the partial oxidation of methane to formaldehyde with oxygen. However, the Fe-MCM-41 by the DHT method exhibits remarkably higher methane conversion and formaldehyde selectivity than that by the TIE method.

Template ion exchange route to nanocrystalline MIn2S4 (M=Mn, Zn)

A template ion exchange method has been established to synthesize ternary sulfides MIn2S4 (M=Mn, Zn) by the reaction of metal chlorides and NaInS2 in absolute ethanol at 140 °C for 12 h. The effects of reactant NaInS2, temperature and reaction time on the template ion exchange reaction were investigated.

Template ion exchange route to nanocrystalline MIn 2S 4 (M=Mn, Zn)

A template ion exchange method has been established to synthesize ternary sulfides MIn 2S 4 (M=Mn, Zn) by the reaction of metal chlorides and NaInS 2 in absolute ethanol at 140 °C for 12 h. The effects of reactant NaInS 2, temperature and reaction time on the template ion exchange reaction were investigated.

Characterizations and catalytic properties of Cr-MCM-41 prepared by direct hydrothermal synthesis and template-ion exchange

Abstract Cr-MCM-41 prepared by direct hydrothermal synthesis (DHT) and template-ion exchange (TIE) has been characterized by X-ray diffraction (XRD), N2 adsorption (77 K), diffuse reflectance UV–vis, X-ray absorption (XANES and EXAFS), and UV-Raman spectroscopic measurements. It is suggested that monochromate species mainly exist on the Cr-MCM-41 by the DHT method while several types of chromate species including both monochromates and polychromates coexist on that by the TIE method. The two kinds of samples exhibit similar catalytic property in the dehydrogenation of propane with carbon dioxide. The selectivity to propylene is higher than 90% and the presence of carbon dioxide enhances propane conversion. The chromate species on both types of samples are reduced to aggregated Cr(III) with octahedral coordination during the dehydrogenation reactions. On the other hand, the selectivity to formaldehyde in the partial oxidation of methane with oxygen is remarkably higher over the sample by the DHT method than that by the TIE method. The structure of the chromate species is kept during the oxidation of methane, and the high dispersion of monochromate species probably accounts for the higher selectivity over the sample by the DHT method.

UV Raman Spectroscopy for Characterization of Chromium Species on Cr-MCM-41

Abstract UV Raman spectroscopy could distinguish the chromate species on Cr-MCM-41. Only one kind of monochromate species was observed on the Cr-MCM-41 synthesized by a direct hydrothermal synthesis method whereas several types of chromate species possibly including both monochromates and polychromates existed on that synthesized by a template-ion exchange method.

Post-synthesis introduction of transition metals in surfactant-containing MCM-41 materials

V and TiMCM-41 have been prepared by post-synthesis modification of an as-made pure silica material in the liquid phase. Relatively high metal contents can be introduced without affecting the long-range ordering of the parent material. Solids with increasing metal contents have been characterized by X-ray diffraction, UV–VIS, IR and X-ray photoelectron spectroscopies. The results indicate that the metal species are essentially atomically dispersed at low loading (Me/Si<0.02) but that metal oxide particles are formed at higher loading. These particles are probably located mainly on the outer surface of silica, and they do not modify the pore size of MCM-41. Higher dispersions are generally observed when MCM-41 is treated in aqueous solutions. This was explained by a reorganization of the silica network in the presence of surfactant molecules under hydrothermal conditions. V and Ti are not introduced into the mesopores by ionic exchange with template molecules but react in the liquid phase with hydroxyl groups of the silica surface. Template ion exchange is only possible using alcoholic solutions of alkali cations. In this case, the organic molecules can be totally removed from the mesopores without affecting the nature and oxidation state of the anchored metal species. This extraction procedure represents an economically and environmentally interesting step in the preparation of metal-containing mesoporous silicas.

Manganese-containing MCM-41 for epoxidation of styrene and stilbene

Mn-MCM-41 is found to be the most effective heterogeneous catalyst for the epoxidation of styrene with tert-butyl hydroperoxide (TBHP) among several metal ion-containing mesoporous molecular sieves including Mn-, V-, Cr-, Fe-, and Mo-MCM-41. ESR, XANES, diffuse reflectance UV–VIS, UV–Raman and XPS are used to characterize the Mn-MCM-41 synthesized by both direct hydrothermal (DHT) and template ion exchange (TIE) methods. The results suggest that Mn 2+ and Mn 3+ coexist in the Mn-MCM-41 samples synthesized by both methods and a large part of manganese atoms could be incorporated into the framework of MCM-41 obtained by the DHT method. The oxidation of either styrene or stilbene with TBHP as the oxidant over the Mn-MCM-41 produces corresponding epoxide as the main product; the reaction probably proceeds through a radical intermediate. The TIE catalyst shows higher activity, while the DHT catalyst gives higher TBHP efficiency for the epoxidation reactions.

Characterizations of Iron-Containing MCM-41 and Its Catalytic Properties in Epoxidation of Styrene with Hydrogen Peroxide

Iron-containing mesoporous molecular sieves (Fe–MCM-41) synthesized by both direct hydrothermal (DHT) and template-ion exchange (TIE) methods have been characterized and used as catalysts for the liquid-phase epoxidation of styrene with diluted H2O2. The characterizations with XRD, diffuse reflectance UV–vis, ESR, and EXAFS suggest that iron cations are highly dispersed and tetrahedrally coordinated with oxygen in the DHT samples with iron content lower changes as meant? if not, please recast sentence for clarity than ca. 0.9–1.1 wt% (Si/Fe=105–86). This coordination environment is similar to that in a ferrisilicate zeolite with MFI structure and contributes to the increase in relative strong acidic sites, as indicated by NH3-TPD studies. On the other hand, the TIE samples mainly contain small iron oxide clusters. The conversion of styrene over the DHT catalyst increases significantly with increasing iron content up to 1.1 wt%. The selectivity to styrene oxide and the efficiency of H2O2 for the epoxidation can be improved by adding H2O2 slowly to keep the H2O2 concentration low during the reaction. As compared with the DHT catalyst, the TIE catalyst shows a much poorer performance for the epoxidation of styrene. It is suggested that the atomically isolated iron sites account for the epoxidation reaction with hydrogen peroxide. The iron cations incorporated inside the framework of MCM-41 do not leach during the reaction, whereas the small iron oxide clusters leach out into the liquid phase and do not contribute to the catalytic reaction.