Aerobic photochemical oxidation in mesoporous Ti-MCM-41: epoxidation of alkenes and oxidation of sulfides

Irradiation with visible light of a secondary alcohol, benzhydrol, in the presence of molecular oxygen within a titanium-substituted mesoporous molecular sieve, Ti-MCM-41, led to the formation of the α-hydroperoxoalcohol and then hydrogen peroxide. The peroxide species reacted in situ with alkenes and sulfides and led to the titanium center catalyzed selective formation of epoxides from alkenes and sulfoxides from sulfides. The cascade of reactions represents a new method for the photoactivation of oxygen in the presence of alcohols. This revised version was published online in July 2006 with corrections to the Cover Date.     

Ti-containing MCM-41 catalysts for liquid phase oxidation of cyclohexene with aqueous H2O2 and tert-butyl hydroperoxide

Framework Ti-substituted and Ti-grafted MCM-41 mesoporous material has been prepared by direct hydrothermal synthesis and a post-synthesis grafting method. The materials have been tested as catalysts for cyclohexene oxidation with aqueous H₂O₂ and tert-butyl hydroperoxide (TBHP). With aqueous H₂O₂ in methanol, the major products were cyclohexene diol and its methyl ethers. No cyclohexene oxide was produced. Titanium leaching was a serious problem, and the catalyst lost its activity irreversibly after only one cycle of reaction. With TBHP, the selectivity for cyclohexene oxide was near 100%, titanium leaching was negligible, and the catalyst could be repeatedly used after regeneration without suffering significant activity loss. However, the reaction rate was lower than when H₂O₂ was used. Framework substituted material and catalysts prepared by Ti-grafting onto a MCM-41 support behaved similar, but the Ti-grafted MCM-41 is somewhat more active. The turnover frequency (TOF) per mole of Ti decreases with an increase of Ti content in the catalyst. This is caused by a reduced Ti dispersion within the silica matrix. This revised version was published online in July 2006 with corrections to the Cover Date.     

Ti-MCM-41分子筛催化剂的合成、表征及催化性能

以正硅酸四甲酯为硅源,钛酸四异丙酯为钛源,在异丙醇和水的混合溶液中室温下合成了Ti-MCM-41介孔分子筛,采用TEM、N 2吸附-脱附、XRD、UV-Vis和Raman等研究了分子筛的结构特性。并以过氧化氢异丙苯为氧化剂,考察了硅烷化处理后的Ti-MCM-41分子筛催化剂在丙烯环氧化反应中的催化性能。结果表明,与骨架外六配位钛物种相比,骨架内四配位钛物种活化有机过氧化物的能力更强,速率更快;四配位钛物种是环氧丙烷生成的活性物种,而六配位钛物种的存在则会导致反应副产物的生成。合成时添加适量的异丁醇可有效促进钛物种进入分子筛骨架中,并增大比表面积和孔体积,进而改善Ti-MCM-41催化剂的丙烯环氧化催化性能。性能最佳的催化剂上过氧化氢异丙苯转化率可达94.7%,环氧丙烷选择性可达95.8%。     

Synthesis, structural characterization and photocatalytic activity of Ti-MCM-41 mesoporous molecular sieves

This paper reports the applicability of hydrothermal synthesis in alkaline medium for preparation of Ti-containing mesoporous MCM-41 materials. The influence of different parameters was investigated, such as the Ti source, the molar ratio between Si and Ti and also the synthesis temperature. Structural analysis shows that the high specific surface area, large pore size and well ordered mesostructure, are partially retained in the titania containing materials. Modifying synthesis temperature, it was shown that MCM-41 isotherms are different for temperatures above or under 140°C. UV-VisDR spectroscopy was used to investigate the local environment of Ti sites. The obtained materials were evaluated for the photocatalytic degradation of Rhodamine 6G in aqueous medium. The best photocatalytic activity was found for the sample prepared at higher ageing temperature of 160°C, at which anatase particles were formed.     

环己烯分子氧氧化多相催化剂研究进展

根据催化剂主组分的不同,综述了国内外环己烯分子氧氧化多相催化剂的研究进展;主要介绍了钴系、锰系、铁系及镍系催化剂在环己烯分子氧氧化中的应用及其优缺点.指出负载型纳米金催化剂与传统的钴、锰催化剂相结合制备双活性中心催化剂在环己烯分子氧氧化中有较好的应用前景.     

ZrO2/Ti-MCM-41的制备、表征及催化裂解聚丙烯反应的性能

采用水热合成法制备了中孔分子筛ZrO2/Ti-MCM-41,通过XRD、N2吸附-脱附、FT-IR、UV-Vis对其进行表征,表明其具有中孔结构,并且随着ZrO2含量的增加,ZrO2/Ti-MCM-41孔道的长程有序性和结晶度有所减弱,直至失去中孔结构。将其应用于聚丙烯(PP)的催化裂解反应,通过考察硅钛比、负载量、反应温度、催化剂用量和反应时间,对ZrO2/Ti-MCM-41催化裂解PP反应的规律进行了研究。结果表明,n(Si):n(Ti)=40,ZrO2负载质量分数为18%的ZrO2/Ti-MCM-41,在反应温度400℃,m(ZrO2/Ti-MCM-41):m(PP)=0.02,反应时间30 min的条件下,PP的转化率可达91.2%,液体产物的收率为83.6%,该结果优于热裂解及传统的HZSM-5小孔分子筛催化剂的催化裂解结果。     

Synthesis, characterization and cyclohexene hydrogenation activity of high surface area molybdenum disulfide catalysts

An ammonium tetrathiomolybdate (ATTM) catalyst precursor is synthesized and then thermally decomposed at different temperatures in N₂ or H₂ atmosphere. Characterization of the resulting compounds by powder X-ray diffraction (XRD) and surface area analysis indicates the formation of MoS₂–2H with a surface area of 5–9 m²/g. When ATTM is treated with cetyltrimethylammonium chloride and then decomposed in N₂ at 723 K, the resulting material has a surface area nearing 200 m²/g. If treatment also includes hydrazine, the surface area of the resulting MoS₂–2H reaches 215 m²/g. Analysis by XRD and electron microscopy shows a noticeable dispersion in the layers of the resulting MoS₂. The catalytic activity of the materials is tested in a batch reactor for cyclohexene hydrogenation, where the highest activity sulfides are those obtained by thermal decomposition of the chemically treated precursors in N₂.     

钛源浓度对合成Ti - MCM -41及其催化性能的影响

在敞开体系中,以工业用水玻璃为硅源,以TiCl3为钛源,以三甲基十六烷基溴化铵(CTMAB)为模板剂,用H2SO4调节浆料的pH值,在浆料混和物物质的量比组成为n(SiO2)∶n(Na2O)∶n(CTMAB)∶n(TiCl3)∶n(H2O)=7∶2.08∶ 1.4∶(0.07、0.14、0.28)∶530的范围内,37...     

Preparation and characterization of Pd/Si-MCM-41 with high hydrogenation activity

The pure silica mesoporous molecular sieve MCM-41 was synthesized under hydrothermal conditions. Pd/Si-MCM-41 was prepared by the incipient wetness impregnation of pure silica MCM-41 with PdCl₂ as precursor. The samples were characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM), nitrogen adsorption–desorption isotherms at 77 K, inductively coupled plasma (ICP) spectroscopy measurements. The formation of Pd particles reduced the crystalline character of Si-MCM-41, but the structure of Si-MCM-41 framework was retained. The designed Pd/Si-MCM-41 mesoporous material was used as catalysts for hydrogenation of rosin, and showed excellent catalytic performance. Such outstanding catalytic performance should be attributed to the proper size of Pd particles and its high dispersion.     

Characteristics of Ti-MCM-41 and its Catalytic Properties in Oxidation of Benzene

A series of mesoporous titanosilicate Ti-MCM-41 molecular sieves with various Si/Ti ratios have been hydrothermally synthesized using hexadecyl-trimethylammonium bromide as the organic surfactant. These materials were characterized with powder X-ray diffraction (XRD), framework FTIR, diffuse reflectance UV-visible spectroscopy, nitrogen sorption measurements, differential thermal analysis (DTA), and transmission electron microscopy (TEM). The crystallinity of Ti-MCM-41 after calcination was almost two-fold higher than that of the as-synthesized one. The crystallinity and surface area of Ti-MCM-41 both decrease with an increase of titanium content. The results of XRD and FTIR show that the solid products have the MCM-41 structure and contained only atomically dispersed titanium, consistent with framework titanium in Ti-MCM-41. All of the materials had a uniform pore size distribution with pore size of around 3.0 nm. The hexagonal array structure of uniform pore size was observed by TEM. It proved that the pores were highly aligned. The catalytic activities of Ti-MCM-41 were tested in the partial oxidation of benzene by diluted hydrogen peroxide in a batch reactor. Ti-MCM-41 had a higher activity than TiO₂ and Ti/NaY. The activity of Ti-MCM-41 increased with titanium content. The activity of Ti-MCM-41 prepared with hydrothermal synthesis was higher than that of the sample prepared with impregnation. The high activity in Ti-MCM-41 can be attributed to its hydrohobicity and large pore size. Phenol was the only liquid phase product on all of the samples.     

Gold/hydroxyapatite catalysts: Synthesis, characterization and catalytic activity to CO oxidation

This work reports the synthesis, characterization and catalytic activity for CO oxidation of gold catalysts supported on calcium hydroxyapatite. On both, the hydroxyapatite support and the gold-supported hydroxyapatite catalyst, the CO conversion shows a peak near 100% of conversion at room temperature. The generation of structural vacancies by interaction of CO with the solid provokes the formation of peroxide species in the presence of gaseous oxygen, which seems to be responsible of this high conversion of CO at room temperature. Moreover, the influence of the pre-treatment temperature on the activity has been observed and related with the elimination of carbonate species and the generation of structural defects in the apatite structure, which are able to modify the gold oxidation state.     

Effect of physical mixing of CsCl with Au/Ti-MCM-41 on the gas-phase epoxidation of propene using H2 and O2:: Drastic depression of H2 consumption

Vapor-phase epoxidation of propene using H₂ and O₂ over Au/Ti-MCM-41 with or without a promoter has been investigated at various temperatures and at a space velocity of 4000 h^−1. ml/g (cat). As a promoter, CsCl was impregnated and/or physically (simple mixing) or mechanically (crushed in a mortar) mixed at various concentrations. The support, Ti-MCM-41 (Ti/Si = 3/100), was characterized by XRD, UV-Vis, FT-IR, and specific surface area measurement, whereas Au/Ti-MCM-41 with or without a promoter was characterized by TEM, XPS and ICP techniques before and/or after the catalytic tests. Au/Ti-MCM-41 as such gives propene and H₂ conversions of 3.1 and 47%, respectively, with a PO selectivity of 92% at the reaction temperature of 100°C after 60 min of reaction. Physical mixing of CsCl with Au supported on Ti-MCM-41 reduces H₂ consumption by about 90% and improves propene oxide (PO) selectivity up to 97% at a propene conversion of 1.7%. One constraint is that agglomeration of gold particles is caused by Cl⁻ anions; the mean diameter of Au particles, 2.2 nm, in Au/Ti-MCM-41 increases to about 10–20 nm and some clusters are even larger than 50 nm in size due to direct contact between chloride and Au particles.     

Synthesis,characterization and sulfide oxidation activity of vanadyl Schiff base complexes anchored on MCM-41

Vanadyl Schiff base complexes covalently attached on the surface of MCM-41 have been synthesized by anchoring Schiff base and subsequent reaction with VO(acac)₂. XRD, nitrogen adsorption and desorption, UV-visible spectroscopy and FT-IR show that vanadyl Schiff base complexes were successfully anchored on the surface of MCM-41 and the mesopore ordering decreased after the anchoring. The so-prepared heterogeneous catalysts have showed high activity for sulfide oxidation.     

Synthesis,characterization and activity in cyclohexene epoxidation of mesoporous TiO2–SiO2 mixed oxides

A series of porous TiO₂–SiO₂ mixed metal oxides were synthesized via sol–gel route using n-alkyl amine as pore directing templates. The mixed oxides were characterized by nitrogen physisorption for surface area, pore volume and pore size distribution, as well as by FTIR, TGA, SEM, and TEM for the dispersion of titanium. These compounds are good catalysts for liquid phase epoxidation of cyclohexene using hydrogen peroxide as the oxidant. The effects of various factors on catalyst reactivity were also studied. The catalysts performance and selectivity are enhanced in protic solvents when compared to aprotic solvents.     

Nitrogen-incorporated TS-1 zeolite: Synthesis, characterization and application in the epoxidation of propylene

A novel nitrogen-incorporated TS-1 zeolite (N-TS-1) was successfully synthesized by direct calcinating the as-synthesized TS-1 powder in NH₃ flow at high temperature. The samples were characterized by XRD, FTIR, UV-Vis, NH₃-TPD, ICP-AES, CHN, XPS and ²⁹Si MAS NMR techniques. The results showed that nitrogen was incorporated into the framework of TS-1, and N-TS-1 preserved the MFI structure well. The fresh N-TS-1 samples showed low H₂O₂ conversion in the epoxidation of propylene with dilute H₂O₂, which was due to the coverage of the active titanium sites by unstable nitrogen species. By refluxing the fresh N-TS-1 samples with methanol, the unstable nitrogen species were washed out and the conversion of H₂O₂ increased markedly. The stable nitrogen species incorporated into the zeolite framework could effectively decrease the acidity of TS-1 zeolite and inhibit the side reactions, thereby improving the propylene oxide (PO) selectivity. After the 20th run, the N-TS-1-850-5 catalyst gave a H₂O₂ conversion of 91.5%, a H₂O₂ selectivity of 92.0%, and a PO selectivity of 90.9%. Finally, a model for nitridation of the as-synthesized TS-1 powder at high temperature was proposed.     

超微粒介孔分子筛Ti-MC M-41的制备及催化氧化乙苯合成苯乙酮和α-苯乙醇

在强酸性及常温常压下 ,以无水乙醇和异丙醇为混合溶剂 ,合成了n(Si)∶n(Ti)分别为 30∶1、5 0∶1和 70∶1的超微粒介孔分子筛Ti MCM 41。经X衍射光谱、Fourier红外光谱 (FTIR)和扫描电镜表征 ,该分子筛具有规则的晶体结构 ,颗粒直径为 0 0 5～ 0 1μm ,在FTIR的 96 0cm-1处表现出Si—O—Ti的特征吸收峰。同时研究了该分子筛在乙苯液相氧化中的催化行为 ,讨论了催化剂及反应条件的影响。结果表明 ,在Ti MCM 41催化下 ,双氧水可以将乙苯氧化为苯乙酮和α 苯乙醇。当催化剂n(Si)∶n(Ti)由 70∶1降至 30∶1,催化剂加入量由 10 0mg增加到 30 0mg ,n(H2 O2 )∶n(乙苯 )由 1 0∶1 0增至 3 0∶1 0 ,反应时间由 1h延长至 10h ,反应温度由 15℃升高到6 0℃时 ,乙苯的转化率分别提高到 3 3倍、1 4倍、2 6倍、1 7倍和 2 2倍。以氯仿、丙酮和甲醇为溶剂时 ,乙苯的转化率分别为 0 6 4%、1 2 7%和 3 5 5 %。     

Redox behavior and selective oxidation properties of mesoporous titano- and zirconosilicate MCM-41 molecular sieves

Mesoporous titano- and zirconosilicate molecular sieves, Ti-MCM-41 and Zr-MCM-41, respectively, with Si/M ratios in the range from 11 to 96 (M=Ti or Zr), have been synthesized by the hydrothermal method and characterized by XRD, XRF, N₂ adsorption and diffusive reflectance UV–Vis (DRUV–Vis), FT-IR and electron spin resonance (ESR) spectroscopic techniques. The redox behavior and selective oxidation properties of these materials have been investigated. ESR of samples reduced with LiAlH₄ (298 K) and H₂ (673–873 K) reveals two types of metal ion species: species I^′ located inside the pore walls and species I^′′ located at the pore surface. The reduced species I^′′ are highly reactive towards oxygen and form M(O₂^−·) radicals. The M(O₂^−·) radicals were also observed when the samples were reacted with aqueous H₂O₂ or tert-butylhydroperoxide (TBHP). ESR studies reveal that Ti-MCM-41 is easier to reduce and reoxidize than Zr-MCM-41. The DRUV–Vis spectra are consistent with a monoatomic dispersion of the metal ions. In the samples with high metal loading the presence of a nanocrystalline metal oxide phase cannot be ruled out. Both Ti-MCM-41 and Zr-MCM-41 catalyze the hydroxylation of 1-naphthol with aqueous H₂O₂ and the epoxidation of norbornylene with TBHP.     

有机弱碱体系中介孔分子筛MCM-41的合成与表征

在有机弱碱无水乙二胺为碱介质的条件下(pH≈10) ,以阳离子表面活性剂十六烷基三甲基溴化铵(CTAB)为模板剂,以正硅酸乙酯(TEOS)为硅源,在室温下合成了介孔分子筛MCM-41。与在强碱水热体系中合成的样品相比,室温弱碱体系中合成的样品具有孔道短程有序度高等特点。详细考察了晶化时间、表面活性剂浓度和晶化温度对产物结构的影响。用XRD对所合成的产物进行表征,结果表明,晶化时间越长,所得到产物的有序度越高;随着表面活性剂质量分数的增加,所合成产物的结构和晶型的完整性越高,但并不是表面活性剂的质量分数越大越好,当表面活性剂的质量分数大于6%时,就呈现下降的趋势;随着晶化温度的升高,所得样品的规整性变差,但晶格参数a₀随温度的升高而呈现变大的趋势。     

A new class of highly dispersed VOx catalysts on mesoporous silica: Synthesis, characterization, and catalytic activity in the partial oxidation of ethanol

The morphology of vanadium oxide supported on a titania-modified mesoporous silica (MCM-41), obtained by means of a careful grafting process through atomic layer deposition, was studied using a variety of characterization techniques. The X-ray diffraction (XRD) together with transmission electron microscopy (TEM), ⁵¹V nuclear magnetic resonance (⁵¹V-NMR), Raman, FTIR and DRS-UV/Vis results showed that the vanadia species are extremely well dispersed onto the surface of the mesoporous support; the dispersion being stable upon thermal treatments up to 400 °C. Studies of the catalytic activity of these materials were performed using the partial oxidation of ethanol as a probe reaction. The results indicate an intrinsic relationship between dispersion, the presence of a TiO₂–VO_x phase, and catalytic activity for oxidation and dehydration.     

乙二胺体系铝镧MCM-41介孔分子筛的合成、表征及在乙氧基化反应中的催化性能

以十六烷基三甲基溴化铵(CTAB)为模板剂,正硅酸乙酯(TEOS)为硅源,乙二胺为碱性介质,当n(TEOS)∶n(NaAlO2)(或LaCl3)∶n(CTAB)∶n(H2NCH2CH2NH2)∶n(H2O)=1∶X∶0 12(或0 14)∶3 5(或8 0)∶130,其中X=0 1,0 05,0 033时,水热法合成了硅铝(硅镧)摩尔比为10、20和30的Al MCM 41和La MCM 41介孔分子筛。通过XRD、IR、NH3 TPD吸附脱附、BET及CCl4吸附等方法对分子筛的晶体结构和表面物性进行了研究,结果表明,合成的分子筛具有典型的六方介孔结构特征。将Al MCM 41和La MCM 41分子筛分别用于催化乙氧基化反应,研究结果表明,Al MCM 41的催化活性高于La MCM 41,当Al MCM 41用量为正辛醇质量的3%,反应温度为120℃,反应压力0 2MPa,n(正辛醇)∶n(环氧乙烷)=1∶2时,正辛醇聚氧乙烯醚产品的收率达85%。