Novel Heterogeneous W-Doped MCM-41 Catalyst for Highly Selective Oxidation of Cyclopentene to Glutaraldehyde by Aqueous H2O2

W-doped MCM-41 (W-MCM-41) has been reported as a novel heterogeneous catalyst for the selective oxidation of cyclopentene to prepare glutaraldehyde with environmentally benign aqueous hydrogen peroxide. It is found that tungsten species could stably exist in the silica-based matrix of MCM-41 up to a Si/W molar ratio of 40 by means of X-ray diffraction, laser Raman spectroscopy, scanning electron microscopy, etc. Proper content of tungsten species, high specific surface area and large mean pore size of the W-MCM-41 account mainly for its high catalytic activity in comparison with other W-containing heterogeneous catalysts. Complete conversion of cyclopentene and very high yield of glutaraldehyde (72%) are obtained over the W-MCM-41 catalyst with an Si/W molar ratio of 40. Furthermore, almost no tungsten species are leached into the reaction solution, enabling the catalyst to be employed for many reaction cycles without obvious degeneration. The correlation of the catalytic behavior with the special structural characteristics of the W-MCM-41 catalyst is also discussed through various characterization methods.     

V-MCM-41催化环己烯环氧化性能

采用水热法合成了V-MCM-41,并用ICP-AES、FTIR、DRS-UV-Vis、XRD、BET等技术对其进行了表征,发现只有部分V进入分子筛,所合成的V-MCM-41具有较高的结晶度,并且其结晶度随晶化液中V/Si摩尔比的增大而升高。V-MCM-41催化环己烯/H₂O₂氧化反应结果表明,当V-MCM-41中V含量大于1.10%（摩尔分数）时,骨架V-O-V物种在催化环己烯氧化反应的同时,也可加速H₂O₂的分解;乙腈是该反应体系的最佳溶剂,最佳反应温度为70℃。最佳反应结果表明,环己烯的单程转化率和H₂O₂有效利用率可分别达到23.91%和95.4%。     

Synthesis, characterization of high Ti-containing Ti-MCM-41 catalysts and their activity evaluation in oxidation of cyclohexene and epoxidation of higher olefins

A series of titanium rich isomorphous substituted Ti MCM-41 and HMS materials have been synthesized with different Si/Ti ratios. The highest amount of Ti incorporated in synthesis gel is in TiMCM-41 (Si/Ti = 10). Whereas for TiHMS catalysts, Ti is incorporated up to Si/Ti = 50 successfully without forming any extra framework TiO₂. Cyclohexene epoxidation reaction with dry tert-butyl hydroperoxide (TBHP) as an oxidant has been studied to evaluate the catalytic properties of Ti substituted mesoporous catalysts. The effect of molar ratio of substrate:oxidant in this reaction has been studied and high conversion, high selectivity were achieved at 2: 1 molar ratio with TiMCM-41 (Si/Ti =25). Dry TBHP (in dichloromethane) and chloroform were found as good oxidant and solvent system for this reaction. Pure siliceous mesoporous silica and low `Ti' substituted mesoporous silicas were found to be efficient catalysts for oxidation of cyclohexene. An interesting variation of the selectivity from allylic oxidation to epoxidation during oxidation of cyclohexene was observed with an increase in the Ti amount in the mesoporous framework. The allylic oxidation of cyclohexene has been carried out using molecular oxygen as an oxidant and in the presence of a small amount of TBHP as initiator. Siliceous HMS materials gave better conversion compared to MCM-41 type of materials and other conventional silicas like silica gel, fumed silica etc. in allylic oxidation of cyclohexene. Epoxidation of higher cyclic olefins like cyclooctene, cyclododecene, cis-cyclododecene and linear olefins 1-Heptene, cis-2-hexene, 1-undecene was carried out over TiMCM-41 (Si/Ti = 25). Ti substituted mesoporous catalysts were characterized by elemental analysis, XRD, FTIR, UVDRS, ²⁹SiMASNMR, BET surface area and pore size distribution techniques.     

杂原子MCM-41分子筛对过氧化氢液相氧化环己烷的研究

分别考察了反应温度、过氧化氢用量及加入方式等因素对Cr、Fe和Ce改性后的杂原子MCM-41分子筛催化剂液相催化氧化环己烷制取环己酮反应的影响。研究结果表明，Cr-MCM-41〖JP〗催化剂具有较好的催化活性。选择适当的反应温度、过氧化氢用量和加入方式可以有效提高环己烷转化率和过氧化氢利用率。在70 ℃和n(C₆ H₁₂)∶n(H₂O₂)=1∶2条件下，采用两次加入过氧化氢的方式，环己烷转化率为33.7％，酮醇总选择性97.2％，n(环己酮)∶n(环己醇）＝1.99，过氧化氢利用率37.1%。     

Partial oxidation of ethane by in situ generated H2O2

Selective partial oxidation of ethane to ethanol and acetaldehyde by in situ generated H₂O₂ has been achieved under cathodic current passing through a carbon supported Nafion-H catalytic membrane. A correlation between H₂O₂ generation rate and reaction rate has been found.     

The role of niobium in MCM-41 supported with Pt and Au—A comparative study of physicochemical and catalytic properties

This paper reviews a series of results, partly published recently, on niobosilicate mesoporous molecular sieves of MCM-41 type modified with noble metals (Pt, Au). Platinum is introduced to MCM-41 by impregnation technique, whereas gold is incorporated by two methods: during the synthesis by co-precipitation (COP) and by impregnation (IMP). Three fundamental features of the prepared materials have been considered: (i) texture/structure, (ii) noble metal state and dispersion, and (iii) catalytic activity. The latter has been tested in selective reduction of NO by propene, methanol oxidation and WGS process. The role of niobium, as well as the effect of the nature of noble metals and the preparation method on the physicochemical and catalytic properties of the final materials based on NbMCM-41 (in comparison with siliceous MCM-41) is demonstrated.     

Cobalt oxide nanoparticles on mesoporous MCM-41 and Al-MCM-41 by supercritical CO2 deposition

CoO and Co₃O₄ nanoparticles were uniformly dispersed inside mesoporous MCM-41 and Al-MCM-41 supports using supercritical CO₂ reactive deposition. This method represents a one-pot reproducible procedure that allows the dissolution of the organocobalt precursor and supports impregnation in supercritical CO₂ at 70 °C and 110 bar, followed by the precursor thermal decomposition into cobalt species at 200 °C and 160 bar. By the relative concentration of the cobalt precursor [cobalt (II) bis (η⁵-ciclopentadienil)], the load of cobalt nanoparticles was controlled and then determined by Inductively Coupled Plasma (ICP-OES). The synthesis of CoO and Co₃O₄ species inside the MCM-41 and Al-MCM-41 substrates was confirmed by X-ray Photoelectron (XPS) and Laser Raman Spectroscopies (LRS). By N₂ adsorption and Small Angle X-ray Scattering (SAXS), it was determined that the hexagonal arrangement as well as the surface area and pore size of the substrates changed after the addition of cobalt. By means of X-ray mapping from SEM images, a homogeneous distribution of cobalt nanoparticles was observed inside the mesopores when the cobalt loading was 1 wt.%. In addition, spherical cobalt nanoparticles of average diameter close to 20 nm were detected on the outer surface of MCM-41 and Al-MCM-41 supports when the cobalt content was higher. On the other hand, by Transmission Electron Microscopy (TEM), it was possible to measure the interplanar distance of the crystalline plane of the outer nanoparticles, which was later compared with the theoretical distance values which allowed identifying the CoO and Co₃O₄ phases.     

FTIR study of NO, C3H6 and O2 adsorption and interaction on gold modified MCM-41 materials

This paper is devoted to the detailed FTIR study of the adsorption, co-adsorption, and interaction of all the reagents used in NO HC-SCR process addressed to lean-burn engines with the surface of new gold catalysts based on ordered mesoporous materials. Gold was introduced into silicate and niobiosilicate matrices by the impregnation (Au/MCM-41 and Au/NbMCM-41, respectively) and via co-precipitation with siliceous and niobium sources (AuNbMCM-41). The in situ FTIR study allowed the estimation of the possible chemisorption of the reagents and their interaction towards intermediates, depending on the chemical composition of the catalyst and the way of gold introduction. It has been found that propene is chemisorbed, but not, NO, on gold species at room temperature. Chemisorbed C₃H₆ interacts with NO only in the presence of oxygen excess. Oxygen oxidizes NO to NO₂, the latter interacts with chemisorbed propene towards carboxylates (1570 cm⁻¹) and NO₂ is reduced to N₂O. At higher temperatures carboxylates interact with gaseous NO to carbonate, N₂O, CO and CO₂. The presence of niobium in the NbMCM-41 matrix enhances the oxidative properties of the catalysts and as a consequence the interaction between intermediates in NO reduction with propene in the oxygen excess. The co-precipitated AuNbMCM-41 exhibits higher NOx storage properties than the impregnated one.     

Gold supported CeO2/Al2O3 catalysts for CO oxidation: influence of the ceria phase

A series of low loading gold supported ceria/alumina catalysts have been prepared by the deposition–precipitation method, varying the pH of the synthesis. The catalysts were characterised by means of XRD, TEM, S_BET, XRF and UV–Vis techniques, and their catalytic activity towards CO oxidation in the absence and in presence of water in the stream, were tested. It has been found that in this low loading gold catalysts, where the metallic particles are far away one from another and the oxygen transportation is not the limiting step of the reaction, the electronic properties of the ceria phase and the structure of the metal-support perimeter more than the diameter of the gold nanoparticles is the determinant factor in the catalytic performances of the solid.     

UV/H2O2氧化联合Ca(OH)2吸收同时脱硫脱硝

在小型紫外光-鼓泡床反应器中,对UV/H₂O₂氧化联合Ca(OH)₂吸收同时脱除燃煤烟气中NO与SO₂的主要影响因素[H₂O₂浓度、紫外光辐射强度、Ca(OH)₂浓度、NO浓度、溶液温度、烟气流量以及SO₂浓度]进行了考察。采用烟气分析仪和离子色谱仪分别对尾气中的NO₂和液相阴离子作了检测分析。结果显示:在本文所有实验条件下,SO₂均能实现完全脱除。随着H₂O₂浓度、紫外光辐射强度和Ca(OH)₂浓度的增加,NO的脱除效率均呈现先大幅度增加后轻微变化的趋势。NO脱除效率随烟气流量和NO浓度的增加均有大幅度下降。随着溶液温度和SO₂浓度的增加,NO脱除效率仅有微小的下降。离子色谱分析表明,反应产物主要是SO₄^2-和NO₃^-,同时有少量的NO₂^-产生。尾气中未能检测到有害气体NO₂。     

Reduction of lean NOx by ethanol over Ag/Al2O3 catalysts in the presence of H2O and SO2

The reduction of lean NOx using ethanol in simulated diesel engine exhaust was carried out over Ag/Al₂O₃ catalysts in the presence of H₂O and SO₂. The Ag/Al₂O₃ catalysts are highly active for the reduction of lean NOx by ethanol but the reaction is accompanied by side reactions to form CH₃CHO, CO along with small amounts of hydrocarbons (C₃H₆, C₂H₄, C₂H₂ and CH₄) and nitrogen compounds such as NH₃ and N₂O. The presence of H₂O enhances the NOx reduction while SO₂ suppresses the reduction. The presence of SO₂ along with H₂O suppresses the formation of acetaldehyde and NH₃. By infrared spectroscopy, it was revealed that the reactivity of NCO species formed in the course of the reaction was greatly enhanced in the presence of H₂O. The NCO species readily reacts with NO in the presence of O₂ and H₂O at room temperature, being converted to N₂ and CO₂ (CO). Addition of SO₂ suppresses the formation of NCO species and lowers the reactivity of the NCO species. However, the reduction of NOx is still kept at high conversion levels in the presence of H₂O and SO₂ over the present catalysts. About 80% of NOx in the simulated diesel engine exhaust was removed at 743 K. This revised version was published online in July 2006 with corrections to the Cover Date.     

Reduction of Biocide-Polluted Wastewater Using O3 and H2O2/O3 Oxidation Processes

The objective of the presented study was to test various oxidation processes with the aim being to reduce the concentration and toxicity of biocide wastewater from a Slovenian phytopharmaceutical factory. Laboratory-scale experiments employing two AOP processes – ozonation (O₃) and peroxone (H₂O₂/O₃) – were applied to reduce the concentration of the active components involved, i.e., methylisothiazolone (MI), chloromethylisothiazolone (CMI) and dichloromethylisothiazolone (DCMI). The reduction of the biocide wastewater load for the performed oxidation processes was evaluated using ecological parameters. The H₂O₂/O₃ oxidation procedure using an O₃ flow rate of 1g/L h, at a pH value of 10 and with the addition of 5 ml of H₂O₂ (0.3 M) proved to be the most effective treatment. The toxicity of the biocide-load wastewater with an initial EC₅₀ = 0.38%, decreased to EC₅₀ (24h) >100% and EC₅₀ (48h) = 76%.     

Sulfated and Persulfated TiO2/MCM-41 Prepared by Grafting Method and their Acid-catalytic Activities for Cyclization of Pseudoionone

Solid acid catalysts of SO₄²⁻/TiO₂/MCM-41 and S₂O₈²⁻/TiO₂/MCM-41 were prepared via grafting method and sulfate/persulfate promotion. The catalysts exhibited desirable activity and better selectivity for cyclization reaction of pseudoionone compared to traditional SO₄²⁻/TiO₂. A combination of XRD, N₂ adsorption–desorption and FTIR spectroscopy indicated that the catalysts possess well-ordered mesostructure, and the grafted TiO₂ are in highly dispersed amorphous form rather than crystalline phase. For S₂O₈²⁻/TiO₂/MCM-41 higher S content and more Br?nsted acid sites can be achieved by persulfation, which is favorable for the protons participated cyclization reaction. The similar Si–O–Ti–O–S=O structure of all acid sites on pore surface of the catalysts is attributed to the improvement of selectivity in comparison with SO₄²⁻/TiO₂.     

Silica Gel- and MCM-41-Supported MoS2 Catalysts for HDS Reactions

MCM-41- and silica gel-supported MoS₂ catalysts were prepared. MCM-41 was synthesized and impregnated with precursor, then activated to obtain the active phase. The sol–gel method was used for providing the SiO₂ support as well as for including the catalyst precursors in one single step of preparation. Such catalysts have applications particularly in hydrodesulfurization (HDS) and hydrodenitrogenation (HDN) processes. A comparison of the activities of the catalysts was made. The catalytic activity results showed the method of preparation used in this study was successful in producing very efficient catalysts for the HDS of dibenzothiophene (DBT).A higher selectivity for direct C–S bond cleavage was observed for the MoS₂ catalyst supported on SiO₂ by the sol–gel method. X-ray diffraction studies showed that the catalysts were poorly crystallized with a very weak intensity of the (002) line of 2H-MoS₂.     

A designed Mn2O3/MCM-41 nanoporous composite for methylene blue and rhodamine B removal with high efficiency

The authors report a facile chemical precipitation method for the fabrication of a highly ordered mesoporous Mn₂O₃/MCM-41 composite. Examination of the acquired samples using X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS), and nitrogen adsorption–desorption measurement has provided fundamental insight into the structure and properties of the Mn₂O₃/MCM-41 composite. It is found that the as-prepared Mn₂O₃/MCM-41 composite has a highly ordered mesoporous structure with a specific surface area of 793 m² g⁻¹. The performance of Mn₂O₃/MCM-41 composite as a remover was further demonstrated in the removal of azo dyes of methyl orange (MO), Congo red (CR), methylene blue (MB), and rhodamine B (RB) with/without visible light irradiation at room temperature. The results show that the Mn₂O₃/MCM-41 composite has an excellent removal performance for MB and RB, making it a promising candidate for wastewater treatment.     

Selective oxidation of methane to methanol and formaldehyde over V2O5/SiO2 catalysts. Role of NO in the gas phase

The role of nitric oxide incorporation into the reaction feed for the partial oxidation of methane to C₂-hydrocarbons and C₂-oxygenates is evaluated. The addition of NO increases the conversion of methane under all the experimental conditions studied and has a strong effect on the product distribution. At low NO concentration the catalysts yield mainly C₂H_n hydrocarbons, but at higher NO concentrations, carbon oxides dominate. Amongst the C₁-oxygenates produced, methanol is the major compound observed and its proportion increases with increasing NO concentration. The highest C₁-oxygenates yield was 7% at atmospheric pressure. This revised version was published online in July 2006 with corrections to the Cover Date.     

Metal oxide catalysts for DME steam reforming: Ga2O3 and Ga2O3–Al2O3 catalysts

The steam reforming of dimethyl ether (DME) was performed on Ga₂O₃–Al₂O₃ mixed oxides prepared by sol–gel method. Ga₂O₃ significantly affects the catalytic performance with respect to the DME conversion and H₂ yield. The catalytic activity increases with the Ga concentration in Ga₂O₃–Al₂O₃ mixed oxides. It is very interesting that without the aid of an additional transition metal component, Ga₂O₃ and Ga₂O₃ containing Al₂O₃ mixed oxide system exhibit good activity in the reforming reaction. To the best of our knowledge, this is the first report that reveals the reforming ability of Ga₂O₃ for the production of H₂ from DME and/or methanol.     

Activation of a Au/TiO2 Catalyst by Loading a Large Amount of Fe–Oxide: Oxidation of CO Enhanced by H2 and H2O

Catalytic activity of a 1 wt% Au/TiO₂ catalyst is markedly improved by loading a large amount of FeO_x, on which the oxidation of CO in excess H₂ is selectively promoted at temperature lower than 60 °C. Oxidation of CO with O₂ on the FeO_x/Au/TiO₂ catalyst is markedly enhanced by H₂, and H₂O moisture also enhances the oxidation of CO but its effect is not so large as the promotion by H₂. We deduced that activation of Au/TiO₂ catalyst by loading FeO_x is not caused by the size effect of Au particles but a new reaction path via hydroxyl carbonyl intermediate is responsible for the superior activity of the FeO_x/Au/TiO₂ catalyst.     

Preferential CO oxidation over Pt–SnO2/Al2O3 in hydrogen rich streams containing CO2 and H2O (CO removal from H2 with PROX)

The effects of reaction gases including CO₂ and H₂O and temperature on the selective low-temperature oxidation of CO were studied in hydrogen rich streams using a flow micro-reactor packed with a Pt–SnO₂/Al₂O₃ sol–gel catalyst that was initially designed and optimized for operation in the absence of CO₂ and H₂O. 100% CO conversion was achieved over the 1 wt% Pt–3 wt% SnO₂/Al₂O₃ catalyst at 110 °C using a feed composition of 1.0% CO, 1.5% O₂, 25% CO₂, 10% H₂O, 58% H₂ and He as balance at a space velocity of 24,000 cm³/(g h). CO₂ in the feed was found to decrease CO conversion significantly while the presence of H₂O in the feed increased CO conversion, balancing the effect of CO₂.     

Significant enhancement of the oxidation of CO by H2 and/or H2O on a FeO x /Pt/TiO2 catalyst

Oxidation of CO on the FeO _x /Pt/TiO₂ catalyst is markedly enhanced by H₂ and/or H₂O at 60 °C, but no such enhancement is observed on the Pt/TiO₂ catalyst, but shift reaction (CO + H₂O → H₂ + CO₂) does not occur on the FeO _x /Pt/TiO₂ catalyst at 60 °C. DRIFT-IR spectroscopy reveals that the fraction of bridge bonded CO increases while that of linearly bonded CO decreases on the FeO _x loaded Pt/TiO₂ catalyst. The in-situ DRIFT IR spectra proved that the bridged CO is more reactive than the linearly bonded CO with respect to O₂, and the reaction of the bridge-bonded CO with O₂ as well as of the linearly bonded CO is markedly enhanced by adding H₂ to a flow of CO + O₂. From these results, we deduced that the promoting effect of H₂ and/or H₂O is responsible for the preferential oxidation (PROX) reaction of CO on the FeO _x /Pt/TiO₂ catalyst, and a following new mechanism via the hydroxyl carbonyl or bicarbonate intermediate is proposed for the oxidation of CO in the presence of H₂O.